Acoustic matching material, method of manufacture thereof, and ultrasonic transmitter using acoustic matching material

Information

  • Patent Grant
  • 6545947
  • Patent Number
    6,545,947
  • Date Filed
    Wednesday, October 17, 2001
    23 years ago
  • Date Issued
    Tuesday, April 8, 2003
    21 years ago
Abstract
An acoustic matching member 1 is used, when a sound is propagated from a first object to a second object, for matching an acoustic impedance of the first object and an acoustic impedance of the second object. The acoustic matching member 1 includes a plurality of fine pieces 2, and at least one of the plurality of fine pieces 2 is bonded with at least another of the plurality of fine pieces at a contact portion so as to form a gap in the acoustic matching member 1.
Description




TECHNICAL FIELD




The present invention relates to an acoustic matching member used, when a sound is propagated from one object to another object, for matching acoustic impedances of the two objects, a method for producing the acoustic matching member, and an ultrasonic transmitting and receiving device using the acoustic matching member.




BACKGROUND ART




An acoustic impedance of an object is obtained by (density×sonic speed). The acoustic impedance of air Z


AIR


is about 428 kg/m


2


s, and the acoustic impedance of a piezoelectric vibrator Z


PZT


for generating an ultrasonic wave is about 30×10


6


kg/m


2


s.




When an ultrasonic wave is radiated from the piezoelectric vibrator into the air, sound reflection is generated by the difference between the acoustic impedance of the piezoelectric vibrator Z


PZT


and the acoustic impedance of air Z


AIR


, and thus the radiation efficiency of the sound is reduced.




The acoustic matching member is used to alleviate the reduction in the radiation efficiency of the sound by matching the acoustic impedance of the piezoelectric vibrator Z


PZT


and the acoustic impedance of air Z


AIR


.




An acoustic impedance of an acoustic matching member Z


M


is obtained by expression (1) based on theoretical calculation.






Z


M


={square root over ( )}(Z


PZT


×Z


AIR


)  expression (1)






Here, the value of Z


M


is an ideal value at which there is no sound reflection. Using the above-mentioned values of Z


PZT


and Z


AIR


, the value of Z


M


is about 0.11×10


6


kg/m


2


s.





FIG. 29

is a graph illustrating the relationship between the acoustic impedance of the acoustic matching member and the ratio of the sound energy radiated from the piezoelectric vibrator into the air (transmission ratio). It is appreciated from

FIG. 29

that when the acoustic impedance of the acoustic matching member is about 0.11×10


6


kg/m


2


s, the transmission ratio is 1, at which there is no sound reflection.




In order to obtain an acoustic matching member having such an ideal acoustic impedance, a material having a low density and allowing a low sonic speed needs to be selected for such an acoustic matching member.





FIG. 30

shows an example of a conventional acoustic matching member. The acoustic matching member shown in

FIG. 30

is obtained by mixing glass balloons


121


in a resin material


120


and solidifying the resultant mixture.




The glass balloons are hollow and thus have a feature of being very lightweight. A structure obtained by mixing the glass balloons in the resin material and solidifying the resultant mixture has a lower density than that of a structure obtained by solidifying only the resin material. The size of the glass balloons is set to a value which is sufficiently smaller than the wavelength of the vibration (sound) propagating through the acoustic matching member (about {fraction (1/10)} of the wavelength of the vibration or less). The size of the glass balloons is set to such a value in order to make the propagation of the vibration less liable to the influence of the glass balloons.




When glass balloons having a true density of 0.13 g/cm


3


(“Scotchlight™ Glass Bubbles Filler” available from Sumitomo 3M Ltd.) are mixed in a resin material allowing a sonic speed of about 2300 m/s and having a density of 1.2 g/cm


3


, and the resultant mixture is solidified, a structure having a density of 0.56 g/cm


3


and allowing a sonic speed of 2100 m/s is obtained. An acoustic impedance Z


COM


of the structure thus obtained is 1.18×10


6


kg/m


2


s.




Japanese Laid-Open Publication No. 2-177799 describes that an acoustic matching member is formed using only hollow glass spheres. This acoustic matching member is produced by heating the hollow spheres up to a temperature for softening the hollow glass spheres, compressing the hollow spheres, and binding the plurality of hollow spheres at respective contact points. As the hollow glass spheres, “Scotchlight™ Glass Bubbles Filler” available from Sumitomo 3M Ltd. is used. Japanese Laid-Open Publication No. 2-177799 describes that the acoustic matching member thus produced has characteristics of a sonic speed of 900 m/s and an acoustic impedance Z


BG


of about 0.45×10


6


kg/m


2


s. Since the acoustic impedance of an object is represented by (sonic speed×density), the density of this acoustic matching member is 0.5 g/cm


3


.




As described above, the sonic speed allowed by glass is 5000 to 6000 m/s, but the sonic speed allowed by an acoustic matching member is reduced to 900 m/s by producing the acoustic matching member using hollow glass spheres.




An acoustic matching member can be bonded to a vibrator or a case accommodating the vibrator with an adhesive formed of a resin material such as an epoxy resin. Japanese Laid-Open Publication No. 2-177799 describes an example of heating the plurality of hollow spheres up to a temperature for softening the plurality of hollow spheres and binding the plurality of hollow spheres at respective contact points as well as bonding the acoustic matching member to a vibrator. By such a bonding method, the acoustic matching member is formed only of glass, and thus has superior temperature characteristics to those of an acoustic matching member formed using a resin material. The reason is that the thermal expansion ratio of glass is lower than the thermal expansion ratio of the resin material. When the flow rate of a gas is measured using an ultrasonic transmitting and receiving device, the temperature characteristics of the ultrasonic transmitting and receiving device significantly influences the measurement precision. In order to accurately measure a very small flow rate of gas, the temperature characteristics of the ultrasonic transmitting and receiving device need to be small.




Some types of gases are explosive. A vibrator which needs to provide such a gas with an electric signal is required to be accommodated in a case in order to prevent the vibrator from contacting the gas. Conditions to be satisfied by the material of the case include a high strength against breakage and satisfactory temperature characteristics. For this reason, metal is preferable as a material of the case. The thermal expansion ratio of metal is different from the thermal expansion ratio of glass. Therefore, a metal case and the acoustic matching member come apart from each other and cannot be bonded together at the stage of binding the plurality of hollow spheres at respective contact points after the plurality of hollow spheres are heated to a temperature for softening the plurality of hollow spheres as in the method described in Japanese Laid-Open Publication No. 2-177799.




When the acoustic impedances Z


BG


and Z


COM


of the above-described acoustic matching materials are plotted in the graph of

FIG. 29

, Z


BG


is positioned at A and Z


COM


is positioned at ▪. The transmission ratio is 0.21 for Z


BG


and 0.05 for Z


COM


. Thus, the transmission ratio (i.e., the transmission ratio of sound) for Z


BG


is four times the transmission ratio for Z


COM


. However, in actuality, an output which is four times larger is not obtained, but the outputs are of an equivalent level for Z


BG


and Z


COM


. This is considered to occur since the structure having Z


BG


is more likely to cause the sound to attenuate when the sound is propagated therethrough than the structure having Z


COM


. By contrast, the structure having Z


COM


is less likely to cause the sound to attenuate while the sound is propagated therethrough but allows a higher sonic speed than the structure having Z


BG


. Therefore, the structure having Z


COM


has a larger acoustic impedance and causes the sound radiated into the air to be reflected more than the structure having Z


BG


.




In the end, there is no significant difference in the sound outputs of the both types of acoustic matching members. Therefore, an acoustic matching member providing a large sound output is demanded rather than the acoustic matching member formed of the structure having Z


BG


or Z


COM


One possible reason why the structure having Z


BG


causes the sound to significantly attenuate is that because the hollow spheres bound at only the respective contact points and thus the total number of contact points are relatively small.




As described above, the conventional ultrasonic transmitting and receiving device has the following problems.




First, when the acoustic matching member is formed using a resin material, the measurement precision of the ultrasonic transmitting and receiving device is not satisfactory due to the temperature characteristics of the resin material.




Second, when the acoustic matching member is formed of only hollow glass spheres, sound is significantly attenuates due to a small number of contact points of the hollow spheres.




Third, when the vibrator is accommodated in a metal case so as to prevent the vibrator from contacting the gas, bonding of the acoustic matching member to the metal case with an adhesive formed of a resin material such as an epoxy resin deteriorates the measurement precision of the ultrasonic transmitting and receiving device due to the temperature characteristics of the adhesive.




Fourth, the metal case and the acoustic matching member come apart from each other and cannot be bonded together at the stage of binding the plurality of hollow spheres at respective contact points after the plurality of hollow spheres are heated to a temperature for softening the plurality of hollow spheres, due to the difference in thermal expansion ratio of the metal case and glass, which is the material of the hollow spheres. Even when the metal case and the acoustic matching member are bonded, flexure is generated and thus the vibration of the vibrator is not propagated.




The present invention has been made in order to solve the first through fourth problems.




DISCLOSURE OF THE INVENTION




An acoustic matching member according to the present invention is used, when a sound is propagated from a first object to a second object, for matching an acoustic impedance of the first object and an acoustic impedance of the second object. The acoustic matching member includes a plurality of fine pieces. At least one of the plurality of fine pieces is bonded with at least another of the plurality of fine pieces at a contact portion so as to form a gap in the acoustic matching member.




The plurality of fine pieces may each have an amorphous three-dimensional structure.




The plurality of fine pieces may be located so as to prevent the sound from being linearly propagated through the acoustic matching member.




The plurality of fine pieces may each be formed of a glass or a ceramic material.




A method for producing an acoustic matching member according to the present invention is used, when a sound is propagated from a first object to a second object, for matching an acoustic impedance of the first object and an acoustic impedance of the second object. The method includes the steps of (a) forming a plurality of fine pieces; (b) heating the plurality of fine pieces to a temperature for softening the plurality of fine pieces, thereby bonding at least one of the plurality of fine pieces with at least another of the plurality of fine pieces at a contact portion so as to form a gap in the acoustic matching member.




The step (b) may include the step of heating the plurality of fine pieces while applying a load on the plurality of fine pieces.




The step (a) may include the steps of mixing the plurality of fine pieces and a liquid; and vaporizing the liquid from a mixture of the plurality of fine pieces and the liquid.




A specific gravity of the liquid may be smaller than a specific gravity of the plurality of fine pieces.




The liquid may be vaporized after the plurality of fine pieces are precipitated in the liquid.




The plurality of fine pieces may be formed by pulverizing a plurality of hollow spheres.




A density of the acoustic matching member may be controlled in accordance with a degree to which the plurality of hollow spheres are pulverized.




The degree to which the plurality of hollow spheres is pulverized may be expressed by a ratio between a volume of the plurality of hollow spheres before being pulverized and a volume of the plurality of fine pieces obtained by pulverizing the plurality of hollow spheres.




An ultrasonic transmitting and receiving device according to the present invention includes a vibrator; a metal case for accommodating the vibrator; an acoustic matching member used for matching an acoustic impedance of the vibrator and an acoustic impedance of a fluid flowing outside the metal case; and a bonding member for bonding the acoustic matching member and the metal case. The acoustic matching member includes a plurality of fine pieces, and at least one of the plurality of fine pieces is bonded with at least another of the plurality of fine pieces at a contact portion so as to form a gap in the acoustic matching member. The bonding member has a structure for reducing a difference between a thermal expansion ratio of the metal case and a thermal expansion ratio of the acoustic matching member.




The bonding member may include a first layer formed on the metal case, a second layer formed on the first layer, and a third layer formed on the second layer. The first layer may be formed of silver solder. The second layer may be formed of titanium. The third layer may be formed of silver solder.




The bonding member may further include a fourth layer formed on the third layer and a fifth layer formed on the fourth layer. The fourth layer may be a ceramic plate or a glass plate. The fifth layer may be formed of glass having a melting point lower than a melting point of the material of the fourth layer.




The bonding member may include a first layer formed on the metal case, and the first layer may be formed based on a mixture obtained by mixing silver solder powder and titanium powder.




The bonding member may include a first layer formed on the metal case, and the first layer may be formed based on a mixture obtained by mixing silver solder powder, titanium powder and ceramic powder.




The bonding member may include a first layer formed on the metal case and a second layer formed on the first layer, and a bonding face between the first layer and the second layer may have a convexed and concaved shape.




The first layer may be formed on the metal case intermittently.




The first layer may contain a plurality of particles having a thermal expansion ratio lower than a thermal expansion ratio of the material of the first layer.




The bonding member may include a first layer formed on the metal case and a second layer formed on the first layer. The first layer may be formed by heating a mixture containing a first particle of a first material which is easily oxidized, nitrided or carbided and a second particle of a second material having a specific gravity larger than a specific gravity of the first material and having a melting point lower than a melting point of the first material, the first layer being formed as a layer of the second material. The second layer may be formed on the layer of the second material, the second layer being formed as a layer obtained as a result of oxidizing, nitriding or carbiding the first material.




The first material may have a thermal expansion ratio which is lower than a thermal expansion ratio of the second material.




The mixture may be heated at a temperature which is lower than the melting point of the first material and higher than the melting point of the second material.




The first particle may have a size of 150 μm or less.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a cross-sectional view of an acoustic matching member


1


according to a first example of the present invention.





FIG. 2

is a cross-sectional view of an acoustic matching member


5


according to a second example of the present invention.





FIG. 3

is a cross-sectional view of an acoustic matching member


7


according to a third example of the present invention.





FIG. 4

shows a structure of a measurement device for measuring a sound output of an acoustic matching member.





FIG. 5

shows measurement results obtained when a conventional acoustic matching member having an acoustic impedance Z


COM


is used as an acoustic matching member


11


to be tested.





FIG. 6

shows measurement results obtained when the acoustic matching member


7


having an acoustic impedance Z


DVE


is used as the acoustic matching member


11


to be tested.





FIG. 7

shows an exemplary structure of a production apparatus according to a fourth example of the present invention.





FIG. 8

is a flowchart illustrating a procedure of a method for producing an acoustic matching member using the production apparatus shown in FIG.


7


.





FIG. 9

is a cross-sectional view of an acoustic matching member


30


formed by solidifying an aggregation of fine pieces


21


.





FIG. 10

shows a production method according to a fifth example of the present invention.





FIG. 11

shows a method for forming a plurality of fine pieces according to a sixth example of the present invention.





FIG. 12

shows a method for forming a plurality of fine pieces according to the sixth example of the present invention.





FIG. 13

shows a method for distinguishing unpulverized fine hollow spheres


31


from fine pieces


34


.





FIG. 14A

shows a shape of the fine pieces


34


obtained when h


2


/h


1


=0.5.





FIG. 14B

shows a shape of the fine pieces


34


obtained when h


2


/h


1


=0.33.





FIG. 14C

shows a shape of the fine pieces


34


obtained when h


2


/h


1


=0.2.





FIG. 15

shows the relationship between h


2


/h


1


and the density of the acoustic matching member, and the relationship between h


2


/h


1


and the attenuation ratio of the sound.





FIG. 16

shows a cross-section of an acoustic matching member formed using the plurality of fine pieces


34


obtained when h


2


/h


1


=0.33.





FIG. 17

shows an exemplary structure of an ultrasonic transmitting and receiving device according to a seventh example of the present invention.





FIG. 18

shows an exemplary structure of a bonding member


52


.





FIG. 19

shows another exemplary structure of a bonding member


52


.





FIG. 20

shows still another exemplary structure of a bonding member


52


.





FIG. 21

shows still another exemplary structure of a bonding member


52


.





FIG. 22

shows an exemplary structure of an ultrasonic transmitting and receiving device according to an eighth example of the present invention.





FIG. 23

shows another exemplary structure of an ultrasonic transmitting and receiving device according to the eighth example of the present invention.





FIG. 24

shows still another exemplary structure of an ultrasonic transmitting and receiving device according to the eighth example of the present invention.





FIG. 25

shows still another exemplary structure of an ultrasonic transmitting and receiving device according to the eighth example of the present invention.





FIG. 26

is a flowchart illustrating a procedure of a bonding method according to a ninth example of the present invention.





FIG. 27

shows a cross-section of a main part of an ultrasonic transmitting and receiving device produced by bonding an acoustic matching member


64


and a metal case


62


in accordance with the procedure shown in FIG.


26


.





FIG. 28A

shows an example of a contact state of fine pieces


2


(fine pieces


201


through


203


) for forming a gap in the acoustic matching member


1


.





FIG. 28B

shows an example of a contact state of fine pieces


2


(fine pieces


204


through


207


) for forming a gap in the acoustic matching member


1


.





FIG. 28C

shows an example of a contact state of fine pieces


2


(fine pieces


208


through


212


) for forming a gap in the acoustic matching member


1


.





FIG. 29

is a graph illustrating the relationship between the acoustic impedance of an acoustic matching member and the ratio of sound energy radiated from the air from a piezoelectric vibrator (transmission ratio).





FIG. 30

shows an exemplary structure of a conventional acoustic matching member.











BEST MODE FOR CARRYING OUT THE INVENTION




Hereinafter, example of the present invention will be described with reference to the figures.




EXAMPLE 1





FIG. 1

shows a cross-section of an acoustic matching member


1


according to a first example of the present invention. The acoustic matching member


1


is attached to a vibrator


3


.




The acoustic matching member


1


is used, when a sound is propagated from a first object (for example, the vibrator


3


) to a second object (for example, air), for matching an acoustic impedance of the first object and an acoustic impedance of the second object.




The acoustic matching member


1


includes a plurality of fine pieces


2


. The plurality of fine pieces


2


each have a structure having a planar face. The plurality of fine pieces


2


are each bonded to at least one other fine piece


2


at a contact portion.




The contact can be a point-to-point contact, a line-to-line contact, or a face-to-face contact. What is required is that a gap is formed in the acoustic matching member


1


by bonding the plurality of fine pieces


2


to each other. The gap can be formed in the acoustic matching member


1


by locating the fine pieces


2


irregularly as shown in FIG.


1


.





FIGS. 28A through 28C

each show an example of a contact state of the fine pieces


2


(fine pieces


201


through


212


) for forming a gap in the acoustic matching member


1


.




In the example shown in

FIG. 28A

, the fine pieces


201


and


202


are bonded together in the state where a corner of the fine piece


201


and a planar face of the fine piece


202


contact each other. The fine pieces


201


and


203


are bonded together in the state where another corner of the fine piece


201


and a planar face of the fine piece


203


contact each other. The fine pieces


202


and


203


are bonded together in the state where a planar face of the fine piece


202


having a longer length contacts a planar face of the fine piece


203


having a shorter length. Thus, a gap is formed by bonding the fine pieces


201


through


203


to each other.




In the example shown in

FIG. 28B

, the fine pieces


204


through


207


are bonded to each other in the state where planar faces of the fine pieces


204


through


207


partially contact each other. Thus, a gap is formed by bonding the fine pieces


204


through


207


to each other.




In the example shown in

FIG. 28C

, the fine pieces


208


through


212


are bonded to each other in the state where planar faces of the fine pieces


208


through


212


partially contact each other. Thus, a gap is formed by bonding the fine pieces


208


through


212


to each other.




Even when the fine pieces


2


have a planar shape, a gap can be formed by bonding the plurality of fine pieces


2


to each other. In this case, a gap can be easily formed by locating the fine pieces


2


irregularly and also by forming the fine pieces


2


to have irregular sizes. The contact between the fine pieces


2


can be a point-to-point contact, a line-to-line contact, or a face-to-face contact.




The plurality of fine pieces


2


are located so as not to linearly propagate the vibration (sound) of the vibrator


3


through the acoustic matching member


1


. Therefore, a propagation path


4


is not linear but winding. As a result, the total speed of the sound propagating through the propagation path


4


in the acoustic matching member


1


is lower than the inherent sonic speed allowed by the material of the fine pieces


2


.




For example, when the fine pieces


2


are formed of glass, the sonic speed allowed by the acoustic matching member


1


having the structure shown in

FIG. 1

is lower than about 5000 m/s, which is the inherent sonic speed allowed by glass. Since the acoustic matching member


1


has gaps as shown in

FIG. 1

, the density of the acoustic matching member


1


is clearly lower than the density of a body having the same size and formed of the same material as the fine pieces


2


. The acoustic impedance of an object is represented by (density×sonic speed), and thus the acoustic impedance of the acoustic matching member


1


can be smaller.




As the material of the fine pieces


2


, plastic, metal, glass, or ceramic materials, for example, are usable.




Where the vibration frequency of the vibrator


3


is ν and the sonic speed is C, the wavelength λ of the sound is represented by expression (2).






λ=C/ν. . .   expression (2)






Here, the sonic speed C shows the speed of the sound propagating through the acoustic matching member


1


. It is now assumed that the acoustic matching member


1


is formed as a bulk of glass. Since the sonic speed allowed by glass is about 5000 m/s, the wavelength λ of the sound is 10 mm when the vibration frequency v of the vibrator


3


is 500 kHz. When the acoustic matching member


1


is formed as an aggregation of the fine pieces


2


of glass, the sonic speed allowed by the acoustic matching member


1


is lower than about 5000 m/s, which is the sonic speed allowed by glass. For example, where the sonic speed allowed by the acoustic matching member


1


is 1000 m/s, the wavelength λ of the sound is 2 mm when v is 500 kHz.




In order to cause the gap formed in the acoustic matching member


1


to have less influence on the propagation of the sound, the size of the gap needs to be sufficiently small as compared to the wavelength of the sound to be propagated. In order to make the size of the gap equal to or less than 200 μm, which is {fraction (1/10)} of the wavelength of the sound, the length of each fine piece


2


is preferably 200 μm or less. In order to reduce the density of the acoustic matching member


1


, the fine pieces


2


preferably have a smaller thickness, and is preferably formed of, for example, a glass plate having a thickness of about 1 μm.




In the first example, all the fine pieces


2


included in the acoustic matching member


1


do not need to be bonded to another fine piece


2


at a contact portion. Namely, the acoustic matching member


1


can include fine pieces


2


which are not bonded to another fine piece


2


. An effect similar to the above-described effect is provided so long as at least one of the plurality of fine pieces


2


included in the acoustic matching member is bonded to at least one other fine piece


2


at a contact portion.




EXAMPLE 2





FIG. 2

shows a cross-section of an acoustic matching member


5


according to a second example of the present invention.




The acoustic matching member


5


includes a plurality of fine pieces


6


. At least one of the plurality of fine pieces


6


is bonded to at least one other fine piece


6


at a contact portion so as to form a gap in the acoustic matching member


5


.




In the second example, the plurality of fine pieces


6


each have a structure having a plurality of projections. The projections of the fine piece


6


contact another fine piece


6


, and the fine pieces


6


contact each other at the contact portions. Thus, a gap can be formed around the projections. By providing each fine piece


6


with a plurality of projections, two adjacent fine pieces


6


can be in contact with each other at a plurality of contact portions. In this manner, the bonding strength can be increased as compared to the case where the fine pieces


6


are bonded at one contact portion.




The plurality of projections can be provided on a thin plate or on a cube. In these cases also, a gap can be formed around the projections of the fine pieces


6


. As a result, the density of the acoustic matching member


5


can easily be reduced.




The contact between the fine pieces


6


can be a point-to-point contact, a line-to-line contact, or a face-to-face contact.




The operation and function of the acoustic matching member


5


are similar to the operation and function of the acoustic matching member


1


described in the first example. The size of the fine pieces


6


is preferably 200 μm or less as described above.




EXAMPLE 3





FIG. 3

shows a cross-section of an acoustic matching member


7


according to a third example of the present invention. The acoustic matching member


7


includes a plurality of fine pieces


8


. At least one of the plurality of fine pieces


8


is bonded to at least one other fine piece


8


at a contact portion so as to form a gap in the acoustic matching member


7


.




In the third example, the plurality of fine pieces


8


are each a thin plate having an amorphous convexed concaved structure. Thus, the plurality of fine pieces


8


each have an amorphous three-dimensional structure. By contacting a projection or end of a fine piece


8


with another fine piece


8


, a gap can be easily be formed around the contact portion. By providing each fine piece


8


with the convexed portions and concaved portions, two adjacent fine pieces


8


can be in contact with each other at a plurality of contact portions. In this manner, the bonding strength can be increased as compared to the case where the fine pieces


8


are bonded at one contact portion. The number of the convexed portions and concaved portions is not limited to any specific value.




The contact between the fine pieces


8


can be a point-to-point contact, a line-to-line contact, or a face-to-face contact.




The operation and function of the acoustic matching member


7


are similar to the operation and function of the acoustic matching member


1


described in the first example. The size of the convexed portions and the concaved portions of the fine pieces


8


is preferably 200 μm or less as described above. The fine pieces


8


having the convexed and concaved structure are preferably plates having a minimum possible thickness. The thickness of the fine pieces


8


is preferably about 1 μm in order to reduce the density of the acoustic matching member


7


.




For example, when the fine pieces


8


are formed of glass, the plurality of fine pieces


8


can be bound to each other by heating the plurality of fine pieces


8


up to a temperature at which glass is softened.




By heating the fine pieces


8


to a softening point of glass, the convexed and concaved structure of the fine pieces


8


can be prevented from being destroyed. At the contact portions of the fine pieces


8


, the softened glass pieces are bound to each other.




By heating the fine pieces


8


while applying a slight load to the fine pieces


8


, the binding of the fine pieces


8


at the contact portions can be strengthened. The reason is that the fine pieces


8


are softened by heating while being pressurized.




When the load on the fine pieces


8


is increased, the fine pieces


8


are deformed by the pressure while the convexed and concaved structure is not eliminated. In this case, the contact area between the fine pieces


8


is increased and the bonding strength at the contact portions is increased due to the load. Thus, the attenuation of the sound propagating through the contact portions of the fine pieces


8


can be reduced.




As described above, the bonding strength between the fine pieces


8


can be adjusted in accordance with the load applied on the fine pieces


8


. However, when a load is applied on the fine pieces


8


, the density of the acoustic matching member


7


is increased. As a result, an acoustic impedance of the acoustic matching member


7


is increased.




The acoustic matching member


7


shown in

FIG. 3

is a structure formed by applying a load of 415 g/cm


2


at a temperature of 700° C. on an aggregation of the fine pieces


8


having a convexed and concaved structure formed of glass which is softened at about 700° C. The structure has a density of about 0.537 g/cm


3


, allows a sonic speed of about 1224 m/s, and has an acoustic impedance Z


DEV


of 0.657×10


6


kg/m


2


s. The acoustic impedance Z


DVE


is plotted in the graph of

FIG. 29

with &Circlesolid;. The acoustic impedance Z


DVE


is between the acoustic impedances Z


BG


and Z


COM


described in the “Background Art” section. In order to compare the magnitudes of actual sound transmission, a voltage of an ultrasonic sensor at the receiving end was measured using a measurement device shown in FIG.


4


.




As shown in

FIG. 4

, an acoustic matching member


11


to be tested is attached to an ultrasonic transmitting device


10


. A standard acoustic matching member


12


is attached to an ultrasonic receiving device


13


.




The ultrasonic transmitting device


10


transmits an ultrasonic wave in accordance with the voltage output from a signal source


9


. The ultrasonic receiving device


13


receives the ultrasonic wave transmitted from the ultrasonic transmitting device


10


. The ultrasonic wave received by the ultrasonic receiving device


13


is observed by measuring the voltages at both ends of a resistor


14


bound to the ultrasonic receiving device


13


. Here, a distance between the ultrasonic transmitting device


10


and the ultrasonic receiving device


13


is about 10 mm.





FIG. 5

shows measurement results obtained when the conventional acoustic matching member having the acoustic impedance Z


COM


described with reference to

FIG. 30

was used as the acoustic matching member


11


to be tested. In

FIG. 5

, (a) shows a waveform of the voltage from the signal source


9


, and (b) shows a waveform of the voltages at both ends of the resistor


14


(i.e., the output waveform from the ultrasonic receiving device


13


).





FIG. 6

shows measurement results obtained when the acoustic matching member


7


having the acoustic impedance Z


DVE


shown in

FIG. 3

was used as the acoustic matching member


11


to be tested. In

FIG. 6

, (a) shows a waveform of the voltage from the signal source


9


(the same waveform as that in (a) of FIG.


5


), and (b) shows a waveform of the voltages at both ends of the resistor


14


(i.e., the output waveform from the ultrasonic receiving device


13


).




The maximum value of the amplitude of the voltage waveform shown in (b) of

FIG. 5

is 23 mV, and the maximum value of the amplitude of the voltage waveform shown in (b) of

FIG. 6

is 33 mV. From this, it is appreciated that the acoustic matching member


7


having the acoustic impedance Z


DVE


is superior to the conventional acoustic matching member having the acoustic impedance Z


COM


in the output level.




The measurement results obtained when the conventional acoustic matching member having the acoustic impedance Z


BG


was used are substantially the same as the measurement results obtained when the conventional acoustic matching member having the acoustic impedance Z


COM


was used. From this, it is appreciated that the acoustic matching member


7


having the acoustic impedance Z


DVE


is superior to the conventional acoustic matching member having the acoustic impedance Z


BG


in the output level.




Simply considering only the magnitude of the acoustic impedance, the conventional acoustic matching member having the acoustic impedance Z


BG


should have the highest output level of the two. However, the actual measurement results are different from that. It is considered that this occurs because in the acoustic matching member


7


having the acoustic impedance Z


DVE


, the bonding strength of the aggregation of the fine pieces is stronger and thus the sound attenuation while the sound is propagated is smaller than in the conventional acoustic matching member having the acoustic impedance Z


BG


. The conventional acoustic matching member having the acoustic impedance Z


BG


has a structure in which hollow spheres are assembled in a matrix and bound at the contact point of each of the hollow spheres. In such a structure, the number of the contact points is small and the areas of the contact points are small. Therefore, the binding between the hollow spheres is considered to be weak.




EXAMPLE 4





FIG. 7

shows an exemplary structure of a production apparatus according to a fourth example of the present invention. The production apparatus is used for producing an acoustic matching member described in the first through third examples.




The production apparatus includes a molding case


23


used for mixing a plurality of fine pieces


21


and a liquid


22


and molding the mixture, a bottom lid


24


for opening and closing one of openings of the molding case


23


, and a pressurizing rod


25


for pressurizing the mixture of the plurality of fine pieces


21


and the liquid


22


.




The molding case


23


is formed of, for example, Teflon. Teflon is slippery and thus allows the molded mixture (molded product) to be removed from the molding case


23


without applying an extra force. Thus, the molded product is prevented from being destroyed.




The bottom lid


24


is provided at one of the openings of the molding case


23


. The bottom lid


24


is closed until the molding of the mixture is finished so that the mixture of the fine pieces


21


and the liquid


22


does not leak from the molding case


23


. The bottom lid


24


can be, for example, a Teflon plate or a plate-shaped piece of cellophane tape extended over the opening of the molding case


23


.




The pressurizing rod


25


is movable along an inner wall of the molding case


23


and is used for pressurizing the mixture of the plurality of fine pieces


21


and the liquid


22


. By pressurizing the mixture, the liquid


22


is removed from the mixture. By adjusting the distance by which the mixture is pressurized, the density of the plurality of fine pieces


21


can be set at a desirable density. The pressurizing rod


25


is, for example, stainless steel.




The fine pieces


21


are formed of, for example, glass having a three-dimensional structure. The three-dimensional structure of the fine pieces


21


is not limited to any specific three-dimensional structure. The material for the fine pieces


21


, though, needs to be selected so that the bulk density of the fine pieces


21


is lower than the density of the material of the fine pieces


21


. As the bulk density of the fine pieces


21


is smaller than the density of the material of the fine pieces


21


by a larger difference, more gaps can be formed in the aggregation of the fine pieces


21


. Thus, the density of the acoustic matching member formed of an aggregation of the fine pieces


21


can be reduced.




In the fourth example, the glass fine pieces


21


have a size of 100 μm or less and a thickness of several micrometers. The glass has a density of 2.2 g/cm


3


and allows a sonic speed of about 5000 m/s. However, the fine pieces


21


have a three-dimensional structure, and so the bulk density of the aggregation of the fine pieces


21


is lower than the density of the glass. As the material of the fine pieces


21


, ceramic or metal materials are usable.




The liquid


22


is, for example, distilled water. The specific gravity of water is 1 g/cm


3


. As the liquid


22


, a liquid having a higher viscosity than water such as, for example, a mixture of PVA (polyvinyl alcohol) and water can be used. By using a liquid having a higher viscosity than water, the shape of the molded product can be easily maintained even after the molding of the mixture of the fine pieces


21


and the liquid


22


is finished.





FIG. 8

shows a procedure of a method for producing an acoustic matching member using the production apparatus shown in FIG.


7


.




In step


26


, a mixing process is performed. In the mixing process, for example, the plurality of glass fine pieces


21


and the liquid


22


(for example, distilled water) are fully stirred in a beaker. As a result, a mixture of the plurality of fine pieces


21


and the liquid


22


is produced. By performing the stirring in the beaker fully, the distribution of the plurality of fine pieces


21


in the mixture can be almost uniform. The amount of the liquid


22


can be arbitrarily set. In this example, the amount of the liquid


22


is an amount which allows the mixture to flow into the molding case


23


when the plurality of fine pieces


21


and the liquid


22


are fully mixed.




In step


27


, a molding process is performed. In the molding process, the mixture of the plurality of fine pieces


21


and the liquid


22


is placed in the molding case


23


and pressurized by the pressurizing rod


25


. As a result, an extra portion of the liquid


22


is pressurized out from the molding case


23


. Thus, the density of the aggregation of the fine pieces


21


is adjusted. The adjustment of the density of the aggregation of the fine pieces


21


is performed by setting the total weight and the total volume of the plurality of fine pieces


21


to be placed in the molding case


23


.




In step


28


, a drying process is performed. In the drying process, the molding case


23


is heated at a temperature at which the liquid


22


is not boiled. Thus, the liquid


22


vaporizes.




In step


29


, a molded product removal process is performed. In the molded product removal process, the bottom lid


24


is opened and the aggregation of the plurality of fine pieces


21


is pressurized out by the pressurizing rod


25


. Thus, the aggregation of the plurality of fine pieces


21


is removed from the molding case


23


.




In step


30


, a heating process is performed. In the heating process, the fine pieces


21


are heated up to a temperature at which the fine pieces


21


are softened. Thus, the aggregation of the fine pieces


21


is solidified.





FIG. 9

shows a cross-section of an acoustic matching member


30


formed by solidifying the aggregation of the fine pieces


21


. In

FIG. 9

, the path indicated by the arrow is one of sound propagation paths.




As shown in

FIG. 9

, the length of the sound propagation path in the acoustic matching member


30


is larger than the thickness of the acoustic matching member


30


. Thus, the sonic speed allowed by the acoustic matching member


30


can be reduced. Since the fine pieces


21


have a three-dimensional structure, a gap can be formed and a plurality of contact points can also be provided. Therefore, the number of the contact portions is increased and so the contact area is increased. As a result, the binding between the fine pieces


21


can be strengthened. Since the aggregation of the fine pieces


21


can be molded of the mixture obtained by fully stirring the fine pieces


21


and the liquid


22


, the distribution of the fine pieces


21


can be uniform. As a result, the density nonuniformity dispersion and the sonic speed nonuniformity of the acoustic matching member


30


can be suppressed.




EXAMPLE 5




A production method according to a fifth example of the present invention will be described. This production method is a variation of the production method described in the fourth example with reference to FIG.


8


.




In the molding process shown in step


27


of

FIG. 8

, the liquid


22


can be caused to vaporize after the plurality of fine pieces


21


are precipitated. The density nonuniformity caused by the load can be reduced by precipitating the plurality of fine pieces


21


using gravity without applying any extra load to the plurality of fine pieces


21


.




When the plurality of fine pieces


21


of different weights and different sizes exist, the fine pieces


21


are precipitated in an order from the heaviest fine pieces


21


due to the gravity. Thus, an acoustic matching member including having a plurality of layers having different densities can be produced.





FIG. 10

shows a state in which the plurality of fine pieces


21


having different weights and sizes are precipitated. In

FIG. 10

, identical elements previously discussed with respect to

FIG. 7

bear identical reference numerals and the detailed descriptions thereof will be omitted.




The liquid


22


is, for example, distilled water. The amount of the liquid


22


is set to be sufficiently larger than the total volume of the plurality of fine pieces


21


so that the plurality of fine pieces


21


are easily precipitated. The density of the distilled water is 1 g/cm


3


, which is lower than the density of the glass of 2.2 g/cm


3


. Accordingly, when the glass fine pieces


21


are put into the distilled water, the glass fine pieces


21


are precipitated.




EXAMPLE 6




With reference to

FIGS. 11 and 12

, a method for producing a plurality of fine pieces according to a sixth example of the present invention will be described.




A metal case


32


and a pressurizing rod


33


are formed of, for example, stainless steel. However, the metal case


32


and the pressurizing rod


33


are not limited to such a material.




The pressurizing rod


33


is movable along an inner wall of the metal case


32


, and is used for pressurizing and thus pulverizing fine hollow spheres


31


.





FIG. 11

shows a state where the plurality of fine hollow spheres


31


are accommodated in the metal case


32


(a state where the pressurizing rod


33


is not pushed). In

FIG. 11

, hi shows a height of an aggregation of the fine hollow spheres


31


in the state where the pressurizing rod


33


is not pushed.




The fine hollow spheres


31


are, for example, glass balloons (“Scotchlight™ Glass Bubbles Filler” available from Sumitomo 3M Ltd.). The glass balloons have a true density of 0.13 g/cm


3


, a diameter of about 100 μm, and a thickness of several micrometers.





FIG. 12

shows a state where the pressurizing rod


33


is pushed from the state shown in

FIG. 11

down to a height h


2


. The pressurizing rod


33


is operated using, for example, a hydraulic press.




The fine hollow spheres


31


pressurized by the pressurizing rod


33


are compressed and pulverized. Fragments (fine pieces) of the pulverized fine hollow spheres


31


are a part of the spheres. Thus, fine pieces


34


having a three-dimensional structure can be obtained.




A step of forming the plurality of fine pieces


34


by pulverizing the fine hollow spheres


31


can be inserted, for example, before step


26


(mixing process) of the production method for producing the acoustic matching member shown in FIG.


8


.




All the fine hollow spheres


31


accommodated in the metal case


32


are not pulverized. When there are hollow spheres


31


which have not been pulverized, it is preferable to distinguish the unpulverized hollow spheres


31


from the fine pieces


34


and re-use the unpulverized hollow spheres


31


.





FIG. 13

shows an example of a method for distinguishing the unpulverized hollow spheres


31


from the fine pieces


34


.




A liquid


35


is distilled water. The density of the distilled water (1 g/cm


3


) is between the density of the hollow spheres


31


(0.13 g/cm


3


) and the density of the fine pieces


34


(2.2 g/cm


3


). Accordingly, the hollow spheres


31


, which have a lower density than that of the liquid


35


, float. The fine pieces


34


, which have a higher density than that of the liquid


35


, is precipitated. Thus, the unpulverized hollow spheres


31


can be distinguished from the fine pieces


34


, utilizing the difference in density.





FIG. 14A

shows a shape of the fine pieces


34


obtained when h


2


/h


1


=0.5.

FIG. 14B

shows a shape of the fine pieces


34


obtained when h


2


/h


1


=0.33.

FIG. 14C

shows a shape of the fine pieces


34


obtained when h


2


/h


1


=0.2.




Here, h


2


/h


1


(i.e., the ratio between the volume of the plurality of fine hollow spheres


31


before being pulverized and the volume of the plurality of fine pieces


34


obtained by pulverizing the plurality of fine hollow spheres


31


) indicates the degree of the pulverization of the plurality of hollow spheres


31


.




As shown in

FIGS. 14A through 14C

, the size of the fine pieces


34


can be controlled by controlling the degree of the pulverization of the plurality of hollow spheres


31


.





FIG. 15

shows the relationship between h


2


/h


1


and the density of the acoustic matching member, and the relationship between h


2


/h


1


and the attenuation ratio of the sound. Here, it is assumed that the acoustic matching member is formed of the plurality of fine pieces


34


. As the attenuation ratio of the sound is larger, the output of the sound is smaller.




As shown in

FIG. 15

, as h


2


/h


1


is smaller, the density of the acoustic matching member is higher and the attenuation ratio of the sound is lower.




The reason why the density of the acoustic matching member is higher as h


2


/h


1


is smaller is considered to be as follows: as h


2


/h


1


is smaller, the size of the fine pieces


34


is smaller and thus the fine pieces


34


more easily enter even a small gap. The reason why the attenuation ratio of the sound is lower as h


2


/h


1


is smaller is considered to be as follows: since the fine pieces


34


exist with no gap therebetween, the contact area between the fine pieces


34


becomes larger and thus the binding between the fine pieces


34


is strengthened.




Thus, the density of the acoustic matching member and the attenuation ratio of the sound can be controlled by controlling h


2


/h


1


.




The characteristic of the acoustic matching member shown in

FIG. 15

is one example. The characteristic of the acoustic matching member according to the present invention is not limited to this.





FIG. 16

shows a cross-section of an acoustic matching member formed of the plurality of fine pieces


34


obtained when h


2


/h


1


=0.33.




A production method of the acoustic matching member shown in

FIG. 16

is similar to the production method shown in FIG.


8


. This acoustic matching member has a density of 0.55 g/cm


3


, allows a sonic speed of 1400 m/s, and has an acoustic impedance of 0.77×10


6


kg/m


2


s. This acoustic matching member has a larger acoustic impedance but a smaller attenuation ratio of sound than the conventional acoustic matching member formed only of glass balloons described in Japanese Laid-Open Publication No. 2-177799, and therefore, can output a louder sound.




EXAMPLE 7





FIG. 17

shows an exemplary structure of an ultrasonic transmitting and receiving device according to a seventh example of the present invention. The ultrasonic transmitting and receiving device is used for a flow rate measurement device for measuring a flow rate of a fluid, or a distance measurement device for measuring a distance between an object and the distance measurement device, both using an ultrasonic wave.




The ultrasonic transmitting and receiving device includes a vibrator


43


, a metal case


41


for accommodating the vibrator


43


, an acoustic matching member


40


used for matching,an acoustic impedance of the vibrator


43


and an acoustic impedance of a fluid flowing outside the metal case


41


, and a bonding member


52


for bonding the acoustic matching member


40


and the metal case


41


.




The metal case


41


includes a main body


41




a


and a lid


41




b


welded to the main body


41




a.






An electrode


45


is electrically connected to the vibrator


43


via a conductive rubber member


44


. A glass member


49


is sealed between the electrode


45


and the metal case


41


. The electrode


45


is electrically insulated from the lid


41




b


of the metal case


41


by the glass member


49


.




An electrode


46


is electrically connected to the lid


41




b


of the metal case


41


. The electrode


46


is grounded.




The electrodes


45


and


46


are supplied with an AC voltage of about 5 V. The voltage applied to the electrodes


45


and


46


is applied to the vibrator


43


. By applying an AC voltage of 500 kHz to the electrodes


45


and


46


, the vibrator


43


vibrates at 500 kHz. The vibration of the vibrator


43


is propagated to the main body


41




a


of the metal case


41


, thereby vibrating the main body


41




a


of the metal case


41


.




The vibration of the main body


41




a


of the metal case


41


is propagated to the acoustic matching member


40


via the bonding member


52


, thereby vibrating the acoustic matching member


40


.




A role of the acoustic matching member


40


is to efficiently propagate the vibration of the vibrator


43


to a fluid (for example, a gas) flowing outside the metal case


41


.




The conductive rubber member


44


also plays a role of a buffer to vibration for preventing the vibration of the vibrator


43


from propagating to the lid


41




b


of the metal case


41


so as to efficiently propagate an energy of the vibration of the vibrator


43


to the acoustic matching member


40


.




The vibrator


43


and the conductive rubber member


44


are accommodated inside the metal case


41


. By using the metal case


41


and also by sealing the glass member


49


between the electrode


45


and the lid


41




b


of the metal case


41


, permeation of the fluid (for example, a gas) to the inside of the metal case


41


can be inhibited with certainty. As a result, deterioration of the vibrator


43


by the fluid (for example, a gas) can be prevented.




As the acoustic matching member


40


, the acoustic matching members described in the first through third example or the acoustic matching members produced by the product ion methods described in the fourth through sixth examples are usable.




The metal case


41


is formed of, for example, stainless steel. The acoustic matching member


40


is, for example, an aggregation of glass fine pieces. When the thermal expansion ratio of the metal case


41


is significantly different from the thermal expansion ratio of the acoustic matching member


40


as in this case, direct bonding of the metal case


41


and the acoustic matching member


40


with solder results in the acoustic matching member


40


easily coming off from the metal case


41


due to the stress applied to the bonding portion.




The bonding member


52


is provided between the metal case


41


and the acoustic matching member


40


so as to reduce the difference between the thermal expansion ratio of the metal case


41


and the thermal expansion ratio of the acoustic matching member


40


. The bonding member


52


prevents the acoustic matching member


40


from coming off from the metal case


41


.





FIG. 18

shows an exemplary structure of the bonding member


52


.




The bonding member


52


includes a silver solder foil (a first layer)


53


formed on the metal case


41


, a titanium foil (a second layer)


54


formed on the silver solder foil


53


, and a silver solder foil (a third layer)


55


formed on the titanium foil


54


. The acoustic matching member


40


is formed on the silver solder foil (a third layer)


55


.




The thermal expansion ratio at 20° C. is 14.7 K


−1


for stainless steel, 8.6 K


−1


for titanium, and 0.55 to 8 K


−1


for glass. By causing titanium, having an intermediate thermal expansion ratio between those of stainless steel and glass, to be placed between the glass member and the stainless steel member, the stress applied on the bonding face can be reduced. The stainless steel member and the titanium foil are bonded together via the silver solder, and the titanium foil is bound with oxygen contained in glass. Thus, the metal case


41


and the acoustic matching member


40


are bonded together.




The acoustic matching member


40


, which is formed as an aggregation of glass fine pieces, do not have a high mechanical strength. In order to prevent the stress generated by the difference in thermal expansion ratio between stainless steel and glass from being applied on the acoustic matching member


40


, a bonding member


52


shown in

FIG. 19

can be used instead of the bonding member


52


shown in FIG.


18


.





FIG. 19

shows another exemplary structure of the bonding member


52


.




The bonding member


52


shown in

FIG. 19

includes, in addition to the silver solder foil (the first layer)


53


, the titanium foil (the second layer)


54


and the silver solder foil (the third layer)


55


included in the bonding member


52


shown in

FIG. 18

, a ceramic or high melting point glass plate (a fourth layer)


56


formed on the silver solder foil


55


and a low melting point glass plate (a fifth layer)


57


formed on the ceramic or high melting point glass plate


56


. The acoustic matching member


40


is formed on the low melting point glass plate


57


.




As the low melting point glass of the fifth layer


57


, a glass material having a lower melting point than that of the glass of the acoustic matching member


40


is used. As the glass of the fourth layer


56


, a glass material having a higher melting point than that of the low melting point glass of the fifth layer


57


is used.




By forming the fourth layer


56


to be a plate, the mechanical strength of the fourth layer


56


can be higher than that of the acoustic matching member


40


. Since the thermal expansion ratio of the fourth layer


56


and that of the acoustic matching member


40


are substantially equal to each other, almost no stress is applied on the acoustic matching member


40


.





FIG. 20

shows still another exemplary structure of the bonding member


52


.




The bonding member


52


shown in

FIG. 20

includes a powder paste layer (a first layer)


58


formed on the metal case


41


, a ceramic or high melting point glass plate (a second layer)


56


formed on the powder paste layer


58


and a low melting point glass plate (a third layer)


57


formed on the ceramic or high melting point glass plate


56


. The acoustic matching member


40


is formed on the low melting point glass plate


57


.




The second layer


56


and the third layer


57


shown in

FIG. 20

are identical with the fourth layer


56


and the fifth layer


57


shown in FIG.


19


.




The powder paste layer


58


(the first layer) is formed by mixing silver solder powder and titanium powder into a paste and then applying the paste on the metal case


41


.




The ceramic or high melting point glass plate (the second layer)


56


is placed on the powder paste layer


58


, and the layers are heated to be bonded together. Then, the low melting point glass plate (the third layer)


57


is formed on the ceramic or high melting point glass plate (the second layer)


56


. After that, the bonding member


52


is heated. Thus, the metal case


41


and the acoustic matching member


40


are bonded tog ether.




By adjusting the amount of the silver solder powder and the amount of the titanium solder powder, the bonding strength can be adjusted to a certain degree. For example, when the weight ratio between titanium and silver solder is 1:30, the bonding strength can be reduced from that of the structure shown in

FIG. 18

which uses the titanium foil


54


. Thus, the stress generated by the difference in thermal expansion ratio can be reduced. As a result, the distortion of the stainless steel generated in the metal case


41


can be reduced. Therefore, the gap between the vibrator


43


and the metal case


41


can be reduced, and thus the vibration of the vibrator


43


can be efficiently transferred to the metal case


41


.





FIG. 21

shows still another exemplary structure of the bonding member


52


.




The bonding member


52


shown in

FIG. 21

includes a base layer (a first layer)


59


formed on the metal case


41


and a low melting point glass plate (a second layer)


57


formed on the base layer


59


. The acoustic matching member


40


is formed on the low melting point glass plate (the second layer)


57


.




The second layer


57


shown in

FIG. 21

is identical with the fifth layer


57


shown in FIG.


19


.




The base layer


59


(the first layer) is formed by mixing silver solder powder, titanium powder and ceramic powder into a paste, next applying the paste on the metal case


41


, and then baking the paste.




The low melting point glass plate (the second layer)


57


is placed on the base layer


59


, and then the bonding member


52


is heated. Thus, the metal case


41


and the acoustic matching member


40


are bonded together.




When the ceramic powder and the silver solder powder are mixed and baked, the ceramic powder is covered with the silver solder powder. However, a ceramic portion can be exposed on a surface of the base layer


59


by polishing the surface of the base layer


59


. The ceramic portion and the glass of the second layer


57


are bound to each other by heating, and the glass of the second layer


57


and the acoustic matching member


40


are also bound to each other by heating. Thus, the metal case


41


and the acoustic matching member


40


are bonded together.




EXAMPLE 8





FIG. 22

show an exemplary structure of an ultrasonic transmitting and receiving device according to an eighth example of the present invention.




The ultrasonic transmitting and receiving device includes a vibrator


61


, a metal case


62


for accommodating the vibrator


61


, an acoustic matching member


64


used for matching an acoustic impedance of the vibrator


61


and an acoustic impedance of a fluid flowing outside the metal case


62


, and a bonding member


60


for bonding the acoustic matching member


64


and the metal case


62


.




The vibrator


61


is, for example, a piezoelectric vibrator formed of a ceramic material.




The metal case


62


is preferably formed of a material having a satisfactory resistance against corrosion and a high strength. The metal case


62


is formed of, for example, stainless steel.




The metal case


62


has a thickness of 200 to 300 μm. The thickness of the metal case


62


is made thin for the following reasons. First, when considering the transmission of the sound from the vibrator


61


to the acoustic matching member


64


, an acoustic impedance of the metal case


62


can be ignored. Second, the attenuation of sound energy when the sound is propagated through the metal case


62


can be reduced. When the thickness of the metal case


62


is excessively small, however, the strength of the stainless steel used as a material of the metal case


62


is decreased. The thickness of the metal case


62


is made as small as possible but sufficient to maintain a satisfactory strength of the stainless steel.




The metal case


62


accommodates the vibrator


61


therein in a sealed state as in the seventh example. Thus, a gas or water is prevented from permeating into the vibrator


61


, and thus deterioration or malfunction of the vibrator


61


can be prevented.




The acoustic matching member


64


is, for example, formed as an aggregation of glass fine pieces having a three-dimensional structure shown in FIG.


3


. The acoustic matching member


64


can have a structure having a number of gaps. Here, the acoustic matching member


64


has a density of 0.4 to 0.6 g/cm


3


and allows a sonic speed of 1000 to 1300 m/s. The acoustic matching member


64


has a thickness which is about ¼ of the wavelength of the sound. The wavelength λ of the sound can be obtained by expression (2).




In the eighth example, a sound of 500 kHz is propagated. Therefore, the wavelength of the sound is 2 to 2.6 mm, and ¼ of the wavelength of the sound is 0.5 to 0.65 mm.




The bonding member


60


includes a first layer


65


formed on the metal case


62


, a second layer


66


formed on the first layer, and a third layer


67


formed on the second layer


66


. The acoustic matching member


64


is formed on the third layer


67


.




The first layer


65


is formed of silver solder. One face of the first layer


65


is bonded to the metal case


62


, and the other face of the first layer


65


has a convexed and concaved shape. Hereinafter, the face having the convexed and concaved shape will be referred to as a “convexed and concaved face”. The first layer


65


has a thickness of 20 to 50 μm.




The second layer


66


is formed of titanium oxide. The second layer


66


is formed along the convexed and concaved face of the first layer


65


. The second layer


66


has a thickness of several micrometers.




The third layer


67


is formed of glass having a melting point which is lower than that of the material used for the acoustic matching member


64


. One face of the third layer


67


is bonded to the second layer


66


, and the other face of the third layer


67


is bonded to the acoustic matching member


64


. The third layer


67


has a thickness of 50 to 100 μm.




Electrodes


68


and


69


are used for applying a voltage to the vibrator


61


and removing an output signal from the vibrator


61


. An insulating member


70


electrically insulates the electrode


69


from the metal case


62


. The insulating member


70


is formed of an insulating material such as, for example, glass or a resin.




Hereinafter, the operation and function of the ultrasonic transmitting and receiving device shown in

FIG. 22

will be described.




When an AC voltage of about 500 kHz is applied to the electrodes


68


and


69


, the vibrator


61


vibrates at about 500 kHz.




The vibration of the vibrator


61


is propagated to the acoustic matching member


64


via the metal case


62


and the bonding member


60


(the first layer


65


, the second layer


66


and the third layer


67


).




The metal case


62


has a thickness of 200 to 300 μm, and the bonding member


60


has a thickness of about 100 μm. The thickness of the metal case


62


and the thickness of the bonding member


60


are sufficiently shorter than the wavelength of the sound to be propagated. Accordingly, the influence of the acoustic impedances of the metal case


62


and the bonding member


60


can be ignored. As a result, the vibrator


61


can be considered to be in a state similar to that of being adjacent to the acoustic matching member


64


.




By reducing the thick ness of the metal case


62


and the thickness of the bonding member


60


, the attenuation of sound energy can be reduced.




The vibration of the vibrator


61


is propagated to air via the acoustic matching member


64


. The vibrator


61


has an acoustic impedance of about 30×10


6


kg/m


2


s and the acoustic matching member


64


has an acoustic impedance of about 0.6×10


6


kg/m


2


s. The air has an acoustic impedance of about 428 kg/m


2


s. Accordingly, the sound transmission ratio of the vibrator


61


to the air is about 0.16.




The ultrasonic transmitting and receiving device can transfer the vibration of the air to the vibrator


61


via the acoustic matching member


64


, in which case the vibrator


61


converts the vibration into an electric signal and outputs the electric signal to the electrodes


68


and


69


.




Thus, the ultrasonic transmitting and receiving device converts an electric signal into a mechanical vibration by the vibrator


61


and transfers the vibration to the air or the like, or converts the vibration of the air into an electric signal by the vibrator


61


and receives the electric signal by the electrodes


68


and


69


.




Hereinafter, the function of the ultrasonic transmitting and receiving device shown in

FIG. 22

when an ambient temperature thereof is changed will be described. When the ambient temperature of the ultrasonic transmitting and receiving device is changed, the components of the ultrasonic transmitting and receiving device shown in

FIG. 22

have the shape including the thickness thereof changed based on the thermal expansion ratio of the materials of the components. However, the thermal expansion ratio at 20° C. is 14.7×10


−6


k


−1


for stainless steel, 15 to 16×10


−6


k


−1


for silver solder, 8.6×10


−6


k


−1


for titanium, and 0.55 to 8×10


−6


k


−1


for glass. The components formed of these materials have their shapes changed much less than components formed of resin materials. Especially when the acoustic matching member


64


is formed of glass, the change of the shape in accordance with the temperature is small. Since the thickness of the acoustic matching member


64


can be maintained at ¼ of the wavelength of the sound, the change of the output characteristic in accordance with the temperature can be restricted to be small. The melting point of each of the materials is 400° C. or higher, and therefore the components are not softened unless put under a very high temperature. Thus, the stable quality of the ultrasonic transmitting and receiving device is guaranteed.




The thermal expansion ratio of stainless steel is significantly different from the thermal expansion ratio of glass. Therefore, direct bonding of the metal case


62


formed of stainless steel and the acoustic matching member


64


formed of glass results in an excessive stress. Especially when the metal case


62


is as thin as 200 to 300 μm, the bonding face may be flexed or the acoustic matching member


64


may be destroyed.




According to the present invention, in order to prevent such an inconvenience from occurring, the second layer


66


formed of a titanium material, having an intermediate thermal expansion ratio between stainless steel and glass, is provided between the glass member and the stainless steel member. Thus, the stress applied on the bonding face is reduced. In addition, the bonding face between the first layer


65


and the second layer


66


is formed to be a convexed and concaved face, so as to diversify the direction of the stress applied on the bonding face. Thus, the stress applied on the second layer


66


and the third layer


67


is reduced.




The thermal expansion ratio of stainless steel is about the same as that of the first layer


65


(silver solder). Therefore, the stainless steel member and the first layer


65


(silver solder) tend to contract in a horizontal direction by the same degree. At this point, a stress is generated at a border between the second layer


66


(titanium), having a lower thermal expansion ratio than the stainless steel member and the first layer


65


, and the first layer


65


(silver solder). Concurrently, a stress is generated at a border between the third layer


67


(low melting point glass), having a lower thermal expansion ratio than the second layer


66


(titanium), and the second layer


66


(titanium).




Direction s of the stress generated at the border between the third layer


67


(low melting point glass) and the second layer


66


(titanium) are indicated by thick arrows in FIG.


22


. Vectors of stress can be divided into vectors of force in the upward and downward directions and vectors of force in the leftward and rightward directions, as indicated by thin arrows in FIG.


22


. The vectors in the upward and downward directions counteract each other, and the vectors in the leftward and rightward directions counteract each other. As a result, the overall stress is reduced.




As described above, the metal case


62


and the acoustic matching member


64


are bonded together with the bonding member


60


for reducing the difference between the thermal expansion ratio of the metal case


62


and the thermal expansion ratio of the acoustic matching member


64


. Due to such a structure, the bonding face is prevented from being flexed and the acoustic matching member


64


is prevented from coming off from the metal case


62


. Thus, an ultrasonic transmitting and receiving device whose characteristic is little changed in accordance with the temperature can be provided.




In the example shown in

FIG. 22

, the first layer


65


is formed of silver solder, the second layer


66


is formed of titanium, and the third layer


67


is formed of glass. The bonding member


60


has a structure which is resistant against corrosion even in a gas containing sulfur or the like. Due to such a structure, an ultrasonic transmitting and receiving device having a long life can be provided.





FIG. 23

shows another exemplary structure of an ultrasonic transmitting and receiving device according to the eighth example of the present invention. The ultrasonic transmitting and receiving device shown in

FIG. 23

has a structure for reducing more stress applied on the bonding member


60


than the ultrasonic transmitting and receiving device shown in FIG.


22


.




The bonding member


60


includes a first layer


71


formed on the metal case


62


, a second layer


72


formed of first layer


71


, an a third layer


73


formed on the second layer


72


.




The first layer


71


is formed on the metal case


62


intermittently. In other words, the first layer


71


is divided into a plurality of partial layers. In the example shown in

FIG. 23

, the first layer


71


is divided into partial layers


71




a


,


71




b


and


71




a


. One face of each of the partial layers


71




a


,


71




b


and


71




c


is bonded to the metal case


62


, and the other face of each of the partial layers


71




a


,


71




b


and


71




c


has a convexed and concaved shape. Hereinafter, the face having the convexed and concaved shape will be referred to as a “convexed and concaved face”.




The second layer


72


is formed on the first layer


71


intermittently. In other words, the second layer


72


is divided into a plurality of partial layers. In the example shown in

FIG. 23

, the second layer


72


is divided into partial layers


72




a


,


72




b


and


72




c


. The partial layer


72




a


is formed along the convexed and concaved face of the partial layer


71




a


. The partial layer


72




b


is formed along the convexed and concaved face of the partial layer


71




b


. The partial layer


72




c


is formed along the convexed and concaved face of the partial layer


71




c.






By forming the first layer


71


and the second layer


72


intermittently as described above, the change of the shape can be restricted to be small even when the thermal expansion ratio is large. Thus, the stress applied on the bonding face of the second layer


72


and the third layer


73


can be reduced. In addition, the changes of the shape of the partial layers existing intermittently can counteract each other, and thus the stress applied on the bonding face of the second layer


72


and the third layer


73


can be reduced.




In the example shown in

FIG. 23

, the first layer


71


and the second layer


72


are formed intermittently. Therefore, the third layer


73


and the metal case


62


contact each other in a part of the metal case


62


. However, the contact area between the third layer


73


and the metal case


62


is very small, and therefore the third layer


73


and the metal case


62


can be bonded together even when the layer


73


and the case


62


are significantly different in thermal expansion ratio. Even when the layer


73


and the case


62


cannot be bonded together, the influence of the non-contact state on the propagation of the vibration (sound) is negligible because the contact area is very small.




The operation and function of the ultrasonic transmitting and receiving device shown in

FIG. 23

are similar to the operation and function of the ultrasonic transmitting and receiving device shown in FIG.


22


and will not be described here.




By forming the first layer


71


intermittently, the stress applied on the bonding member


60


can be reduced. This allows the acoustic matching member


64


to be formed of a material having a smaller thermal expansion ratio than that of glass. As a result, an ultrasonic transmitting and receiving device whose output characteristic is little changed in accordance with the temperature can be provided.





FIG. 24

shows still another exemplary structure of an ultrasonic transmitting and receiving device according to the eighth example of the present invention.




The bonding member


60


includes a first layer


81


formed on the metal case


62


, a second layer


82


formed on the first layer


81


, an a third layer


83


formed on the second layer


82


.




The bonding member


60


shown in

FIG. 24

has the same structure as that of the bonding member


60


shown in

FIG. 22

except that the former includes a plurality of alumina particles


82


.




The alumina particles


82


have a thermal expansion ratio of 6 to 7×10


−6


K


−1


, which is significantly lower than that of the silver solder used for forming the first layer


81


. Therefore, the alumina particles


82


have the shape thereof hardly changed. Thus, the entire change of the shape of the first layer


81


can be reduced.




Use of different sizes of alumina particles


82


has an advantage of facilitating the formation of a convexed and concaved face of the first layer


81


.





FIG. 25

shows another exemplary structure of an ultrasonic transmitting and receiving device according to the eighth example of the present invention. The ultrasonic transmitting and receiving device shown in

FIG. 25

has a structure for reducing more stress applied on the bonding member


60


than the ultrasonic transmitting and receiving device shown in FIG.


24


.




The bonding member


60


includes a first layer


91


formed on the metal case


62


, a second layer


92


formed of first layer


91


, and a third layer


93


formed on the second layer


92


.




The bonding member


60


shown in

FIG. 25

has the same structure as that of the bonding member


60


shown in

FIG. 24

except that the former includes the first layer


91


and the second layer


92


formed intermittently.




By forming the first layer


91


and the second layer


92


intermittently as described above, the change of the shape can be restricted to be small even when the thermal expansion ratio is large. In addition, the changes of the shape of the partial layers existing intermittently can counteract each other.




Accordingly, in the ultrasonic transmitting and receiving device shown in

FIG. 25

, first, the stress applied on the bonding face of the first layer


91


and the second layer


92


can be reduced. Second, the stress applied on the bonding face of the second layer


92


and the third layer


93


can be reduced. As a result, the stress applied on the bonding member


60


shown in

FIG. 25

can be smaller than the stress applied on the bonding member


60


shown in FIG.


24


.




By forming the first layer


91


intermittently, the stress applied on the bonding member


60


can be reduced. This allows the acoustic matching member


64


to be formed of a material having a smaller thermal expansion ratio than that of glass. As a result, an ultrasonic transmitting and receiving device whose characteristic is little changed in accordance with the temperature can be provided.




EXAMPLE 9





FIG. 26

shows a procedure of a bonding method according to a ninth example of the present invention. Following the procedure shown in

FIG. 26

, the acoustic matching member


64


and the metal case


62


of the ultrasonic transmitting and receiving device shown in

FIG. 22

are bonded together via the bonding member


60


.




In step


101


(a mixing process), particles of silver solder used for forming the first layer


65


and particles of titanium used for forming the second layer


66


are mixed at a prescribed ratio, thereby forming a mixture.




In order to cause the distribution of the materials in the mixture to be uniform, it is preferable to add a solidification assisting agent formed of a viscous resin material. For example, a solidification assisting agent having a significantly lower melting point than that of silver, copper or titanium can be used. In this case, the solidification assisting agent is preferably vaporized before the silver solder used for forming the first layer


65


is melted.




In step


102


(a mixture applying process), the mixture is applied to the metal case


62


.




In step


103


(a mixture heating process), the metal case


62


having the mixture applied thereto is placed in a vacuum furnace and heated.




In step


104


(a low melting point glass applying process), the metal case


62


having the first layer


65


and the second layer


66


applied thereto is removed from the vacuum furnace, and low melting point glass used for forming the third layer


67


is applied to the second layer


66


. By mixing the solidification assisting agent formed of a resin material with the low melting point glass, the low melting point glass can be uniformly applied.




In step


105


(a bonding process), the acoustic matching member


64


is placed on the low melting point glass, and heated to about 450° C. in an atmosphere while being supplied with a load of about 30 g. The low melting point glass is melted and thus bonded with the titanium oxide film of the second layer


66


and also bonded with the glass of the acoustic matching member


64


. Since the glass of the acoustic matching member


64


is softened at a temperature of 600° C. or higher, the glass of the acoustic matching member


64


is not melted at 450° C.




Particles of a plurality of materials having different thermal expansion ratios are mixed so as to produce a mixture, and the mixture is melted. In this manner, a bonding member having a plurality of layers having different thermal expansion ratios can be formed.




In the ninth example, titanium is used as a material which is especially easy to oxidize. Silver solder is used as a material having a specific gravity larger than that of titanium. Titanium has a density of 4.54 g/cm


3


, and an alloy of silver and copper has a density of 9 to 10 g/cm


3


. When a mixture of these materials is melted, titanium floats on the silver solder, and thus titanium is oxidized. In this manner, a film of titanium oxide can be formed on the silver solder layer.




In the ninth example, in step


103


(mixture heating process), the mixture is heated at about 800 to 900° C. This heating temperature is sufficiently lower than the melting point of titanium, which is 1650° C., but is higher than the melting point of silver solder. Therefore, titanium can be floated on the liquid of silver solder. The floating titanium reacts with oxygen in the vacuum furnace and thus is melted, and as a result, a film of titanium oxide is formed. In this manner, the second layer


66


is formed.




In the ninth example, the size of particles of titanium, which is easily oxidized, is set to be 150 μm or less. Thus, titanium reacts with oxygen and thus is melted without being heated to the melting point of titanium. As a result, a film of titanium oxide as thin as several micrometers can be formed.




In the ninth example, titanium as a material which is easily oxidized has a thermal expansion ratio at 20° C. of 8.6×10


−6


K


−1


. Silver solder having a larger specific gravity than that of titanium has a thermal expansion ratio at 20° C. of 15 to 17×10


−6


K


−1


. That is, the formation of a titanium film having a small thermal expansion ratio causes the second layer


66


, the first layer


65


and the metal case


62


to have step-wise thermal expansion ratios. Thus, the stress generated by the difference between the thermal expansion ratio of the low melting point glass used for forming the third layer


67


and the thermal expansion ratio of the stainless steel used for forming the metal case


62


can be reduced. Therefore, even when the acoustic matching member


64


is formed of glass, the acoustic matching member


64


and the metal case


62


can be bonded together.





FIG. 27

shows a cross-section of a main part of an ultrasonic transmitting and receiving device produced by bonding the acoustic matching member


64


and the metal case


62


in accordance with the procedure shown in FIG.


26


.




In

FIG. 27

, reference numeral


62


represents a stainless steel metal case. Reference numeral


111


represents a silver solder layer (a first layer), reference numeral


112


represents a titanium oxide layer (a second layer), reference numeral


113


represents alumina particles, and reference numeral


114


represents a low melting point glass layer (a third layer). Reference numeral


64


represents a glass acoustic matching member.




Here, the silver solder layer


111


and the titanium oxide layer


112


are formed to have a convexed and concaved face by scattering the alumina particles


113


in the silver solder layer


111


.




As can be appreciated from

FIG. 27

, the metal case


62


and the silver solder layer


111


are bonded together with no gap. The silver solder layer


111


and the titanium oxide layer


112


are also bonded together with no gap.




When a mixture containing silver solder particles and titanium particles is melted, the silver solder particles and the titanium particles are bonded together in a softened state. As a result, the two layers can be bonded with no gap at the bonding face. By forming the convexed and concaved faces using the alumina particles


113


, the stress applied on the titanium oxide layer


112


and the low melting point glass layer


114


can be reduced.




The alumina particles


113


has a thermal expansion ratio of 6 to 7×10


−6


K


−1


, which is lower than that of silver solder. When the alumina particles


113


are contained in the silver solder layer


111


, the silver solder layer


111


locally has a low thermal expansion ratio. Thus, the thermal expansion ratio of the entire silver solder layer


111


can be reduced. As a result, the stress applied on the low melting point glass layer


114


is reduced.




The convexed and concaved face of the bonding face can diversify the direction of the stress applied on the bonding face. Thus, the stress applied on the low melting point glass layer


114


can be reduced. Since the low melting point glass and the glass of the acoustic matching member


64


have about the same thermal expansion ratio, substantially no stress is applied on the bonding face between the low melting point glass layer


114


and the acoustic matching member


64


.




Due to the above-described structure, the acoustic matching member


64


and the bonding member


60


for bonding the acoustic matching member


64


and the metal case


62


can be formed of a material having a low thermal expansion ratio. Thus, the change of the characteristic of the ultrasonic transmitting and receiving device in accordance with the temperature can be decreased.




In the ninth example, titanium, specifically, can be reacted with nitrogen or carbon so as to form a titanium nitride film or a titanium carbide film as the second layer


66


. In this case, the titanium nitride film or the titanium carbide film have the same effect as the titanium oxide film. The titanium nitride film can be formed by heating a mixture containing titanium particles and silver solder particles in a nitrogen atmosphere. The composition of the film can be set in accordance with the composition of a material with which the film is bonded.




In the above-described examples, a gas is used as an example of a subject of measurement. Alternatively, a liquid can be a subject of measurement.




INDUSTRIAL APPLICABILITY




In an acoustic matching member according to the present invention, at least one of a plurality of fine pieces is bonded with at least another of the plurality of fine pieces at a contact portion, so as to form a gap in the acoustic matching member. By bonding the fine pieces at the contact portion, the contact area between the fine pieces is increased. Thus, the coupling between the fine pieces can be enhanced. This provides an effect of reducing the attenuation of vibration at the coupling point of the fine pieces. Therefore, the vibration of the vibrator can be efficiently transferred to a fluid as a subject of measurement.




In the case where the fine pieces have an amorphous three-dimensional structure, the gap formed in the acoustic matching member can be enlarged. Thus, the density of the acoustic matching member can be lower than the inherent density of the material of the fine pieces. As a result, the acoustic impedance of the acoustic matching member can be reduced. Therefore, the vibration of the vibrator can be efficiently transferred to a fluid as a subject of measurement.




In the case where the fine pieces are located so as not to propagate the sound linearly through the acoustic matching member, the sonic speed allowed by the acoustic matching member can be decreased. As a result, the acoustic impedance of the acoustic matching member can be reduced. Therefore, the vibration of the vibrator can be efficiently transferred to a fluid as a subject of measurement.




In the case where the fine pieces are formed of glass or ceramic materials, an acoustic matching member having a low thermal expansion ratio and a stable temperature characteristic can be provided. Thus, an ultrasonic transmitting and receiving device having a high precision can be realized. The above-obtained acoustic matching member is resistant against corrosion caused by impurities such as, for example, sulfur contained in a gas.




By a method for producing an acoustic matching member according to the present invention, a plurality of fine pieces are bonded together by heating the fine pieces to a temperature for softening the material of the fine pieces. An adhesive formed of an epoxy resin or the like does not need to be used for producing the acoustic matching member. The acoustic matching member can be lighter by the weight of the adhesive. Thus, the acoustic impedance of the acoustic matching member can be reduced. Therefore, the vibration of the vibrator can be efficiently transferred to a fluid as a subject of measurement.




In an ultrasonic transmitting and receiving device according to the present invention, a bonding member for bonding a metal case for accommodating the vibrator and the acoustic matching member has a structure for reducing the difference between the thermal expansion ratio of the metal case and the thermal expansion ratio of the acoustic matching member. Thus, the metal case and the acoustic matching member having different thermal expansion ratios can be bonded stably without using an adhesive based on a resin such as, for example, an epoxy resin.



Claims
  • 1. An acoustic matching member used, when a sound is propagated from a first object to a second object, for matching an acoustic impedance of the first object and an acoustic impedance of the second object, wherein:the acoustic matching member includes a plurality of fine pieces, at least one of the plurality of fine pieces is bonded with at least another of the plurality of fine pieces at a contact portion so as to form a gap in the acoustic matching member, and a size of the gap is sufficiently small as compared to a wavelength of the sound to be propagated.
  • 2. An acoustic matching member according to claim 1, wherein the plurality of fine pieces each have an amorphous three-dimensional structure.
  • 3. An acoustic matching member according to claim 1, wherein the plurality of fine pieces are located so as to prevent the sound from being linearly propagated through the acoustic matching member.
  • 4. An acoustic matching member according to claim 1, wherein the plurality of fine pieces are each formed of a glass or a ceramic material.
  • 5. An ultrasonic transmitting and receiving device, comprising:a vibrator; metal case for accommodating the vibrator; an acoustic matching member used for matching an acoustic impedance of the vibrator and an acoustic impedance of a fluid flowing outside the metal case; and a bonding member for bonding the acoustic matching member and the metal case, wherein: the acoustic matching member includes a plurality of fine pieces, and at least one of the plurality of fine pieces is bonded with at least another of the plurality of fine pieces at a contact portion so as to form a gap in the acoustic matching member, a size of the gap is sufficiently small as compared to a wavelength of the sound to be propagated, and the bonding member has a structure for reducing a difference between a thermal expansion ratio of the metal case and a thermal expansion ration of the acoustic matching member.
  • 6. An ultrasonic transmitting and receiving device according to claim 5, wherein the bonding member includes a first layer formed on the metal case, a second layer formed on the first layer, and a third layer formed on the second layer; the first layer is formed of silver solder; the second layer is formed of titanium; and the third layer is formed of silver solder.
  • 7. An ultrasonic transmitting and receiving device according to claim 6, wherein the bonding member further includes a fourth layer formed on the third layer and a fifth layer formed on the fourth layer; the fourth layer is a ceramic plate or a glass plate; and the fifth layer is formed of glass having a melting point lower than a melting point of the material of the fourth layer.
  • 8. An ultrasonic transmitting and receiving device according to claim 5, wherein the bonding member includes a first layer formed on the metal case, and the first layer is formed based on a mixture obtained by mixing silver solder powder and titanium powder.
  • 9. An ultrasonic transmitting and receiving device according to claim 5, wherein the bonding member includes a first layer formed on the metal case, and the first layer is formed based on a mixture obtained by mixing silver solder powder, titanium powder and ceramic powder.
  • 10. An ultrasonic transmitting and receiving device according to claim 5, wherein the bonding member includes a first layer formed on the metal case and a second layer formed on the first layer, and a bonding face between the first layer and the second layer has a convexed and concaved shape.
  • 11. An ultrasonic transmitting and receiving device according to claim 10, wherein the first layer is formed on the metal case intermittently.
  • 12. An ultrasonic transmitting and receiving device according to claim 10, wherein the first layer contains a plurality of particles having a thermal expansion ratio lower than a thermal expansion ratio of the material of the first layer.
  • 13. An ultrasonic transmitting and receiving device according to claim 5, wherein:the bonding member includes a first layer formed on the metal case and a second layer formed on the first layer, and the first layer is formed by heating a mixture containing a first particle of a first material which is easily oxidized, nitrided or carbided and a second particle of a second material having a specific gravity larger than a specific gravity of the first material and having a melting point lower than a melting point of the first material, the first layer being formed as a layer of the second material; and the second layer is formed on the layer of the second material, the second layer being formed as a layer obtained as a result of oxidizing, nitriding or carbiding the first material.
  • 14. An ultrasonic transmitting and receiving device according to claim 13, wherein the first material has a thermal expansion ratio which is lower than a thermal expansion ratio of the second material.
  • 15. An ultrasonic transmitting and receiving device according to claim 13, wherein the mixture is heated at a temperature which is lower than the melting point of the first material and higher than the melting point of the second material.
  • 16. An ultrasonic transmitting and receiving device according to claim 13, wherein the first particle has a size of 150 μm or less.
Priority Claims (6)
Number Date Country Kind
11-322564 Nov 1999 JP
11-326339 Nov 1999 JP
2000-164276 Jun 2000 JP
2000-303242 Oct 2000 JP
2000-303341 Oct 2000 JP
2000-317451 Oct 2000 JP
PCT Information
Filing Document Filing Date Country Kind
PCT/JP00/07981 WO 00
Publishing Document Publishing Date Country Kind
WO01/37609 5/25/2001 WO A
US Referenced Citations (3)
Number Name Date Kind
5375099 Gill Dec 1994 A
5664456 Eckert Sep 1997 A
5860584 Inazuru Jan 1999 A
Foreign Referenced Citations (2)
Number Date Country
2225426 May 1990 GB
3-295547 Dec 1991 JP