Patent Application
20050139013
The present invention relates to an ultrasonic sensor for transmitting or receiving an ultrasonic wave, and more precisely, to an ultrasonic transmitter for transmitting an ultrasonic wave, or an ultrasonic receiver for receiving an ultrasonic wave, or an ultrasonic transmitter-receiver for performing either one or both of them.
In recent years, ultrasonic transmitter-receivers are industrially utilized in a wide variety of fields of distance measurement, object detection, flow measurement, robot control and so on.
As a first ultrasonic transmitter-receiver, there is the ultrasonic transmitter-receiver described in Japanese Examined Patent Publication No. 6-101880. The construction and operation of the conventional ultrasonic transmitter-receiver will be described with reference to
In the construction of
A piezoelectric ceramic is typically used for the ultrasonic transducer 101 that generates ultrasonic vibrations, and its acoustic impedance is, for example, about 30×106 kg·m−2·s−1. When the circumjacent fluid is a gas of air or the like, the acoustic impedance of, for example, air is about 400 kg·m−2·s−1, the acoustic impedance of the acoustic matching layer 102 is set to about 0.11×106 kg·m−2·s−1, and the thickness is preferably set to a quarter of the wavelength at the estimated ultrasonic frequency.
Conventionally, in order to form a matching layer that has an acoustic impedance intermediate between those of the piezoelectric transducer and air, there is used a material obtained by solidifying a material (for example, glass balloons or plastic balloons) of a comparatively small density with resin.
Operation during ultrasonic wave reception will be described next. The ultrasonic wave, which has propagated through the circumjacent fluid and reached the ultrasonic transmitter-receiver 100, is transmitted to the ultrasonic transducer 101 via the acoustic matching layer 102 conversely to ultrasonic wave transmission. The ultrasonic transducer 101 converts the dynamic action of the ultrasonic wave into an electric signal, and the signal is transmitted to an electric processing section (not shown) via the signal wires 104.
During the transmission and reception operations of the ultrasonic transmitter-receiver 100 described above, the transmission and reception of an ultrasonic wave are effected in a direction in which the ultrasonic transducer 101 and the acoustic matching layer 102 are laminated, i.e., in the perpendicular direction of the acoustic matching layer 102.
As a second conventional ultrasonic transmitter-receiver, there is, for example, the ultrasonic transmitter-receiver laid open in the ultrasonic flowmeter described in Japanese Unexamined Patent Publication No. 2000-304581. The construction and operation of the conventional ultrasonic transmitter-receiver will be described below with reference to
Operation of the ultrasonic transmitter-receiver 100 in the construction of
The ultrasonic wave, which has propagated through the second acoustic matching layer 105, is refracted by a difference in acoustic velocity between the second acoustic matching layer 105 and the interface of the circumjacent fluid and radiated to the circumjacent fluid with the direction thereof changed.
During wave reception, the ultrasonic wave, which has propagated through the circumjacent fluid and reached the ultrasonic transmitter-receiver 100 through the process reverse to wave transmission, is refracted at the interface to the second acoustic matching layer 105 to enter the second acoustic matching layer 105 and converted into an electric signal by the ultrasonic transducer 101 via the first acoustic matching layer 104. In this case, the acoustic wave arriving from the direction of wave transmission is selectively received.
The second conventional ultrasonic transmitter-receiver, which can integrate the ultrasonic transmitter-receiver with the wall of the measurement channel when being applied to an ultrasonic flowmeter since the direction of the acoustic wave is changed by utilizing refraction, therefore has an advantage that no disorder of the flow of the fluid to be measured is generated.
However, there has been an issue that a propagation loss has inevitably occurred and the efficiency of wave transmission and reception has been reduced even if a matching layer of a low density like the first conventional ultrasonic transmitter-receiver is used when propagating an ultrasonic wave from an ultrasonic transducer of piezoelectric ceramic or the like into a gas of air or the like. The reason why it is difficult to make an ultrasonic wave efficiently propagate from a solid to a gas is that the acoustic impedance of the gas is extremely smaller than the acoustic impedance of the solid, and a strong reflection of an ultrasonic wave disadvantageously occurs at the interface even if the matching layer is interposed.
Further, the ultrasonic transmitter-receiver of the type that effects deflection of an ultrasonic wave utilizing the refraction exhibited by the second conventional ultrasonic transmitter-receiver has had an issue that it has not substantially been applicable as a consequence of a significant reduction in the wave transmission and reception efficiency when the angle of deflection is increased due to an additionally inflicted loss caused by the angle of deflection.
Accordingly, the present invention is made in view of the aforementioned issues and has the object of providing a highly sensitive ultrasonic sensor that can deflect an ultrasonic wave and has a high efficiency of wave transmission and reception.
In order to achieve the aforementioned object, the present invention is constructed as follows.
According to the present invention, there is provided an ultrasonic sensor for performing transmission or reception of an ultrasonic wave to a circumjacent space stuffed with a fluid, the sensor comprising:
Further, according to the present invention, there is provided an ultrasonic sensor for performing transmission or reception of an ultrasonic wave to a circumjacent space stuffed with a fluid, the sensor comprising:
According to the present invention, there is also provided an ultrasonic sensor for performing transmission or reception of an ultrasonic wave to a: circumjacent space stuffed with a fluid, the sensor comprising:
According to the present invention, there is provided an ultrasonic flowmeter comprising:
According to a 27th aspect of the present invention, there is provided an ultrasonic flowmeter comprising:
According to a 29th aspect of the present invention, there is provided an ultrasonic sensor for performing transmission or reception of an ultrasonic wave to a circumjacent space stuffed with a fluid, the sensor comprising:
These and other aspects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which:
Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings.
Before describing preferred embodiments of the present invention below with reference to the drawings, various aspects of the present invention are described in advance.
According to a first aspect of the present invention, there is provided an ultrasonic sensor for performing transmission or reception of an ultrasonic wave to a circumjacent space stuffed with a fluid, the sensor comprising:
According to a second aspect of the present invention, there is provided an ultrasonic sensor for performing transmission or reception of an ultrasonic wave to a circumjacent space stuffed with a fluid, the sensor comprising:
According to a third aspect of the present invention, there is provided the ultrasonic sensor as defined in the second aspect, wherein the propagation medium portion has a first surface region that faces an ultrasonic vibration surface of the ultrasonic transducer and a second surface region that faces a flow that stuffs the circumjacent space, and the second surface region of the propagation medium portion is inclined with respect to the first surface region.
According to a fourth aspect of the present invention, there is provided an ultrasonic sensor for performing transmission or reception of an ultrasonic wave to a circumjacent space stuffed with a fluid, the sensor comprising:
According to a fifth aspect of the present invention, there is provided the ultrasonic sensor as defined in the fourth aspect, wherein the propagation medium portion has a first surface region that faces an ultrasonic vibration surface of the ultrasonic transducer, a second surface region that faces a flow that stuffs the circumjacent space and at least one third surface region that is arranged between the first surface region and the second surface region in the propagation path of the ultrasonic wave and brought in contact with the reflector, and the second surface region of the propagation medium portion is inclined with respect to at least one of the first surface region and the third surface region.
According to a sixth aspect of the present invention, there is provided the ultrasonic sensor as defined in any one of the first through fifth aspects, wherein a density ρ1 of the propagation medium portion, an incident angle θ1 of an ultrasonic wave to an interface between the propagation medium portion and the fluid that stuffs the circumjacent space, a density ρ2 of the fluid that stuffs the circumjacent space, and an approach angle θ2 of the ultrasonic wave from the interface to the fluid that stuffs the circumjacent space almost satisfy a relation expressed as ρ2/ρ1=cotθ2/cotθ1.
According to a seventh aspect of the present invention, there is provided the ultrasonic sensor as defined in any one of the first through fifth aspects, wherein the propagation medium portion is formed of a dry gel of an inorganic oxide or an organic polymer.
According to an eighth aspect of the present invention, there is provided the ultrasonic sensor as defined in the sixth aspect, wherein a solid frame portion of the dry gel is made hydrophobic.
According to a ninth aspect of the present invention, there is provided the ultrasonic sensor as defined in the seventh aspect, wherein a density of the dry gel is not greater than 500 kg/m3, and a mean pore diameter of the dry gel is not greater than 100 nm.
According to a 10th aspect of the present invention, there is provided the ultrasonic sensor as defined in any one of the first through fifth aspects, comprising: an acoustic matching layer that is provided between the ultrasonic transducer and the propagation medium portion, for acoustically matching the ultrasonic transducer with the propagation medium portion.
According to an 11th aspect of the present invention, there is provided The ultrasonic sensor as defined in any one of the first through fifth aspects, wherein the fluid that stuffs the circumjacent space is a gas having a density ρ2 of not greater than 10 kg/m3.
According to a 12th aspect of the present invention, there is provided the ultrasonic sensor as defined in any one of the first through fifth aspects, wherein a direction of transmission or reception of an ultrasonic wave is almost parallel to the second surface region.
The embodiments of the present invention will be described below.
An ultrasonic transmitter-receiver as one example of the ultrasonic sensor according to the first embodiment of the present invention will be described in detail below with reference to the drawings.
The present inventor has discovered the fact that an ultrasonic wave can be propagated from a solid to a fluid (particularly, gas) causing almost no loss at an interface if the ultrasonic wave is appropriately refracted by using a propagation medium portion made of an appropriate material in an ultrasonic transmitter-receiver and then come to consider the present invention.
In the ultrasonic transmitter-receiver according to the first embodiment of the present invention, a propagation medium portion that has a plane (first surface region) parallel to the vibration surface of the ultrasonic transducer and a plane (second surface region) brought in contact with the fluid that stuffs the circumjacent space is arranged between the ultrasonic transducer and the fluid that stuffs the circumjacent space. It is to be noted that the term of “fluid that stuffs the circumjacent space” means a fluid brought in contact with at least the second surface region and does not necessarily mean a fluid that stuffs the whole periphery of the ultrasonic sensor (for example, the ultrasonic transmitter-receiver) but means a fluid that stuffs a part of the periphery within the specification and the scope of the claims of the present application.
First of all, the ultrasonic transmitter-receiver according to the first embodiment of the present invention will be described with reference to
The ultrasonic transmitter-receiver 1 shown in
The propagation medium portion 6 is stuffed in a space that is enclosed by the housing 9 constructed of the terminal plate 9x and the side portion 9y, located outside the transducer casing 4 and other than the acoustic matching layer 3 arranged inside the space, and has a first surface region 7 which faces the acoustic matching layer 3 and the ultrasonic transducer 2 (note that it directly faces the acoustic matching layer 3) and a second surface region 8 which faces the fluid that stuffs the circumjacent space. Further, the second surface region 8 of the propagation medium portion 6 is inclined at a prescribed angle with respect to the first surface region 7 so as not to become parallel to the first surface region 7. In this case, the prescribed angle, as one example, which is an angle greater than 0° and smaller than 90°, preferably substantially smaller than 80°. In the first embodiment, assuming that the density of the propagation medium portion 6 is ρ1, the acoustic velocity of the propagation medium portion 6 is C1, the density of the fluid that stuffs the circumjacent space is ρ2 and the acoustic velocity of the fluid that stuffs the circumjacent space is C2, then the material of the propagation medium portion 6 is selected so as to satisfy the relation expressed by the following expression (1):
(ρ2/ρ1)<(C1/C2)<1 (1)
When the fluid is a gas of air or the like, it is difficult to find a material that satisfies the above-mentioned condition. The reason for the above is that there is few solid materials whose acoustic velocity C1 is smaller than the acoustic velocity C2 of gas. In the first embodiment, in order to provide the propagation medium portion 6 that satisfies the aforementioned condition, the propagation medium portion 6 is formed of a dry gel of an inorganic oxide or an organic polymer. The solid frame portion of the dry gel employed in the first embodiment is made hydrophobic, and the density thereof is not greater than 500 kg/m3. This dry gel is a nano-porous dry gel (nanoporous dry gel) having a mean pore diameter of not greater than 100 nm.
The solid frame portion of the dry gel of the inorganic oxide preferably has an ingredient of at least silicon oxide (silica) or aluminum oxide (alumina). Moreover, the solid frame portion of the dry gel of the organic polymer can be constructed of a general thermosetting resin or a thermoplastic resin. For example, there can be used polyurethane, polyurea, phenol cured resin, polyacrylamide, polymethyl methacrylate, or the like.
In the case where the propagation medium portion 6 is formed of a nanoporous dry gel that has a main ingredient of, for example, silica, if the density ρ1 is 200 kg/m3, then the acoustic velocity C1 can be set within a range of about 100 m/s to 180 m/s. When the fluid that stuffs the circumjacent space is air, since the density ρ2 of air is 1.22 kg/m3 and the acoustic velocity C2 is 340 m/s, it is possible to concurrently satisfy the relations expressed as ρ2<ρ1 and C1<C2 and satisfy the relation expressed as (ρ2/ρ1)<(C1/C2) by adopting the above propagation medium portion 6. When measuring a gas such as natural gas, the propagation medium portion 6 preferably has a density ρ1 ranging from 100 to 300 kg/m3 and an acoustic velocity C1 ranging from 100 to 300 m/s.
The ultrasonic transducer 2 is a piezoelectric element and is able to generate an electric signal by the generation of ultrasonic vibrations and/or the arrival of an ultrasonic wave as a consequence of applying an electric signal. Piezoelectric ceramics are suitably employed as the piezoelectric material. If it is desired to control the resonance characteristic and reduce the mechanical Q-value, an absorber may be peripherally arranged.
The ultrasonic transmitter-receiver 1 of the first embodiment has a function to improve the acoustic matching between the ultrasonic transducer 2 that is the ultrasonic generating source and the propagation medium portion 6 by providing the acoustic matching layer 3 between the propagation medium portion 6 and the ultrasonic transducer 2.
In the case where the propagation medium portion 6 is formed of the nanoporous dry gel (acoustic impedance: 3×104 kg·m−2·s−1) having a main ingredient of silica and the ultrasonic transducer 1 is constructed of a piezoelectric ceramic (acoustic impedance: 30×106 kg·m·m−2·s−1), by adopting an acoustic matching layer 3 produced from a material having an acoustic impedance in the vicinity of 1×106 kg·m−2·s−1, the propagation efficiency of ultrasonic energy can be made almost one or concretely not smaller than 0.95. The above material can be provided by a composite material obtained by solidifying a hollow glass ball with a resin material, or a porous ceramic. The thickness of the acoustic matching layer 3 is preferably set to a quarter wavelength of the ultrasonic wave used.
Furthermore, in the ultrasonic transmitter-receiver 1 of the first embodiment, the ultrasonic transducer 2 is housed in the transducer casing 4, while the ultrasonic transducer 2 is bonded to the inside of the top surface of the transducer casing 4 and the acoustic matching layer 3 is bonded to the outside of the top surface of the transducer casing 4, constituting a laminate structure. The transducer casing 4 is preferably formed of a conductive metallic material of stainless steel or the like, and the acoustic matching between the ultrasonic transducer 2 and the acoustic matching layer 3 can be maintained in a satisfactory state by thickness setting to a thickness of not greater than {fraction (1/10)} or preferably not greater than {fraction (1/20)} of the wavelength of the estimated ultrasonic wave.
The transducer casing 4 is bonded to the terminal plate 9x of the housing 9 by a processing method of electric welding or the like and is able to have a hermetic structure stuffed with an inert gas of dry nitrogen, argon, or the like. With the above-mentioned arrangement, the ultrasonic transducer 2 is physically insulated from the external air environment, allowing the reliability to be improved. In addition, there is provided an electrically shielded structure, and therefore, high safety can be secured even when the fluid that stuffs the circumjacent space is a flammable fluid of natural gas or the like.
Next, the behavior of an ultrasonic wave propagating from the propagation medium portion 6 to the fluid that stuffs the circumjacent space will be described in detail below with reference to
According to the aforementioned relation of arrangement, the ultrasonic wave enters from the normal direction of the first surface region 7 that faces the vibration surface of the ultrasonic transmitter-receiver 1 and is parallel to the vibration surface. Therefore, the ultrasonic wave enters along a direction inclined with respect to the normal direction of the second surface region 8 that is the interface between the propagation medium portion 6 and the fluid that stuffs the circumjacent space. It is assumed that the incident angle of the ultrasonic wave with respect to the normal direction of the second surface region 8 is θ1 (0°<θ1<90°). At this time, the ultrasonic wave is refracted at the second surface region 8 that is the interface between the propagation medium portion 6 and the fluid that stuffs the circumjacent space and enters the fluid to be measured at an angle θ2 (approach angle) with respect to the normal direction (θ1<θ2).
In the first embodiment, the various parameters (ρ1, θ1, and θ2) are set so as to almost satisfy the relation of the following expression (2) when the density ρ2 of the fluid that stuffs the circumjacent space is given.
(ρ2/ρ1)=(cotθ2/cotθ1) (2)
With the above setting, propagation efficiency from the propagation medium portion 6 of ultrasonic energy to the fluid that stuffs the circumjacent space becomes almost one. At this time, the incident angle θ1 satisfies the condition expressed by the following expression (3).
(cotθ1)2=[(c1/c2)2−1]/[(ρ2/ρ1)2−(c1/c2)2] (3)
Therefore, if ρ1 and C1 of the propagation medium portion 6 and ρ2 and C2 of the fluid that stuffs the circumjacent space are determined, then the incident angle θ1 is determined according to the expression (3). Moreover, if the incident angle θ1 is determined, then the approach angle θ2 is also determined according to the expression (2). If the incident angle θ1 and the approach angle θ2 are determined, then the inclination angle and so on of the second surface region 8 of the propagation medium portion 6 can also be determined.
The above-mentioned fact is also applied to the case where the ultrasonic wave, which has propagated through the fluid that stuffs the circumjacent space, is received, and therefore, the ultrasonic wave arriving from the direction of the approach angle θ2 is selectively received.
In the first embodiment, by forming the propagation medium portion 6 of the aforementioned material, the acoustic velocity C1 of the propagation medium portion 6 can be set to 180 m/s, and the density ρ1 can be set to 200 kg/m3. In the case where the circumjacent space is an ordinary space stuffed with air, the density ρ2 of air is 1.22 kg/m3 and the acoustic velocity C2 is 340 m/s. Therefore, according to the relations of the expression (2) and the expression (3), it is proper to set the incident angle θ1 to 32° and set the approach angle θ2 to 89°. Since the approach angle θ2 is close to 90°, the ultrasonic wave transmitted in the air travels almost parallel to the second surface region 8 that is the wave transmission surface. Therefore, the direction of transmitting and receiving an acoustic wave in the first embodiment is directed in the direction of arrow 90 of
According to the first embodiment, almost no propagation loss occurs in the second surface region 8 that is the interface between the propagation medium portion 6 and the fluid that stuffs the circumjacent space, and therefore, it is not required to match their acoustic impedances at this interface with each other. Therefore, the ultrasonic wave emitted from inside the propagation medium portion 6 is refracted at the second surface region 8 that is the interface between the propagation medium portion 6 and the fluid that stuffs the circumjacent space, allowing the ultrasonic wave to deflect in the direction along the plane that includes the second surface region 8. In addition, almost no propagation loss occurs in the second surface region 8, and therefore, a highly sensitive ultrasonic sensor that has high wave transmitting and receiving efficiency can be provided.
It is to be noted that the propagation medium portion 6 is not required to be constructed of a material whose density ρ1 and acoustic velocity C1 are uniform throughout the entire body but allowed to have a laminate structure in which a plurality of kinds of material layers having varied densities ρ1 and acoustic velocities C1 are laminated. When the laminate structure as described above is possessed, it is sometimes the case where the ultrasonic wave does not straightly travel through the propagation medium portion 6, which, however, poses no problem. An important point is that the density ρ1 and the acoustic velocity C1 and the incident angle θ1 of the propagation medium portion 6 are set so as to satisfy the aforementioned expressions in the region in the vicinity of the interface between the propagation medium portion 6 and the fluid to be measured.
Operation of the ultrasonic transmitter-receiver of the first embodiment will be described next.
First of all, when transmitting wave to the fluid that stuffs the circumjacent space, an ac voltage, a pulse voltage, or a burst voltage having a frequency in the vicinity of the resonance frequency (for example, about 100 kHz to 1 MHz) is applied from a transmitter circuit 701 that concurrently serves as a drive circuit shown in
Next, when receiving the ultrasonic wave, which propagates through the fluid that stuffs the circumjacent space and reaches the ultrasonic transmitter-receiver 1, a path reverse to that of wave transmission holds with regard to the ultrasonic wave that have propagated from the wave transmission direction. The ultrasonic wave, which have entered the transmitter-receiver 1, reaches the ultrasonic transducer 2 on the condition of an efficiency of almost one and are converted into electric signals and transmitted to an external electric circuit (for example, a receiver circuit 702) through the signal wires 5.
According to the first embodiment, there is provided the propagation medium portion 6 that exhibits the appropriate density ρ1 and acoustic velocity C1, and the ultrasonic wave is refracted at an appropriate angle. Therefore, the propagation loss at the interface between the substances is made almost zero, allowing the flow measurement to be achieved at a satisfactory signal-to-noise ratio. Then, according to the first embodiment, the transmission and reception of an ultrasonic wave through a gas (for example, hydrogen gas or the like), which has had extreme difficulties in transmitting and receiving an ultrasonic wave in the conventional ultrasonic transmitter-receiver, becomes possible scarcely generating loss at the interface by appropriately refracting the ultrasonic wave by means of the propagation medium portion 6, and therefore, an application to the flow measurement capable of measuring these gases becomes possible.
Furthermore, in the ultrasonic transmitter-receiver 1 of the first embodiment, the ultrasonic wave emitted from the propagation medium portion 6 is refracted at the second surface region 8 that is the interface between the propagation medium portion 6 and the fluid that stuffs the circumjacent space, and the direction in which the ultrasonic wave are transmitted and received is deflected in the direction along the plane that includes the second surface region 8. Therefore, in, for example, a flowmeter, projections and recesses concerning the mounting of the transmitter-receiver in the measurement channel are removed, and a flowmeter free from the disorder of fluid flow can be constructed. Moreover, the flowmeter can also be applied to object detection in the horizontal direction and so on even when the flowmeter is mounted while being aligned with the horizontal plane of a variety of kinds of equipment that has a horizontal portion.
An ultrasonic transmitter-receiver as one example of the ultrasonic sensor according to the second embodiment of the present invention will be described with reference to
Hereinafter, characteristic points of the ultrasonic transmitter-receiver 11 of the second embodiment will be described below, and no description is provided for portions similar to those of the ultrasonic transmitter-receiver 1 of the first embodiment and the aforementioned corresponding portions.
In the ultrasonic transmitter-receiver 11 of the second embodiment, a cylindrical side portion 9z is fixed to a disk-shaped terminal plate 9x constituting the housing 9A, providing a construction symmetrical to the axis around the center shaft 9a fixed to the center of the terminal plate 9x. Therefore, an ultrasonic transducer 12 and an acoustic matching layer 13 arranged on the disk-shaped terminal plate 9x of the housing 9A are constructed in a ring-like shape. Moreover, a disk-shaped protecting section 15, which is part of the housing 9A and of which the center portion is connected to the center shaft 9a, is further provided to protect the second surface region 8. A ring-shaped opening 14 is provided between the housing 9A and the protecting section 15, and an ultrasonic wave is transmitted and received in the direction of arrow 90A through the opening 14. A space, which is located inside the housing 9A and is other than the ultrasonic transducer 12 and the acoustic matching layer 13, is almost stuffed with the propagation medium portion 6A. Then, the propagation medium portion 6A has a first surface region 7 that faces the acoustic matching layer 13 and the ultrasonic transducer 12 (note that the first surface region 7 directly faces the acoustic matching layer 13) and a second surface region 8 that faces the fluid that stuffs the circumjacent space. Further, the second surface region 8 of the propagation medium portion 6A is approximately uniformly inclined at a prescribed angle from the periphery toward the center side with respect to the center shaft 9a so that the second surface region 8 does not become parallel to the first surface region 7.
In the second embodiment, the concrete transmission and reception of an ultrasonic wave are performed with high efficiency similarly to the first embodiment, so that effects similar to those of the first embodiment can be produced. A difference from the first embodiment resides in that omnidirectional wave transmission and reception around the center shaft 9a can be achieved since the ultrasonic transmitter-receiver 11 has the structure symmetrical to the center shaft 9a. When the circumjacent space is stuffed with a gas, the wave transmission and reception become almost horizontal, and an application to omnidirectional object sensing and so on becomes possible.
The segmentation of the electrode sections is allowed to be achieved on at least one surface of the electrode sections 16 formed on the front and rear sides. Moreover, a similar effect can be obtained also by arranging the ultrasonic transducer 12 while segmenting the transducer 12 itself. Although the number of segmentation of the electrode section 6 is four in
An ultrasonic transmitter-receiver as one example of the ultrasonic sensor according to the third embodiment of the present invention will be described with reference to
Hereinafter, characteristic points of the ultrasonic transmitter-receiver 21 and the ultrasonic transmitter-receiver 31 of the third embodiment will be described below, and no description is provided for portions similar to those of the ultrasonic transmitter-receiver 1 of the first embodiment and the ultrasonic transmitter-receiver 11 of the second embodiment and the aforementioned corresponding portions.
In the housing 9B of the ultrasonic transmitter-receiver 21 of the third embodiment, as shown in
On the other hand, as shown in
In the third embodiment, the concrete transmission and reception of an ultrasonic wave are performed with high efficiency similarly to the first embodiment and the second embodiment, and effects similar to those of the first embodiment and the second embodiment can be produced. A difference from the second embodiment resides in that the transmission and reception of an ultrasonic wave are performed in the forward direction (upward direction in
An ultrasonic transmitter-receiver as one example of the ultrasonic sensor according to the fourth embodiment of the present invention will be described with reference to
Hereinafter, characteristic points of the ultrasonic transmitter-receiver 41 and the ultrasonic transmitter-receiver 51 of the fourth embodiment will be described below, and no description is provided for portions similar to those of the ultrasonic transmitter-receiver 1 of the first embodiment and the ultrasonic transmitter-receivers 11 and 21 of the second embodiment and the aforementioned corresponding portions.
In the housing 9D of the ultrasonic transmitter-receiver 41 of the fourth embodiment, as shown in
The reflector 44 is constructed of a metallic material of stainless steel or the like, and, when the propagation medium portion 6 is formed of the nanoporous dry gel that has a main ingredient of, for example, silica, the reflection efficiency in the third surface region 45 becomes almost one. With regard to the reflector 44, an inclination angle is set with respect to the first surface region 7 and the second surface region 8 so that the incident angle of an ultrasonic wave to the second surface region 8 satisfies the expression (3).
The ultrasonic transducer 42 is excited with vibrations in the vicinity of the resonance frequency, and the vibrations are radiated as an ultrasonic wave on the condition of an efficiency of almost one roughly on the center side of the propagation medium portion 6D through the acoustic matching layer 43. The acoustic wave, which have propagated through the propagation medium portion 6D, is reflected on the third surface region 45 that is the interface to the reflector 44 with an efficiency of almost one to propagate with the direction thereof changed roughly toward the second surface region 8 side, then refracted at the second surface region 8 that is the interface between the propagation medium portion 6D and the fluid that stuffs the circumjacent space, and radiated to the fluid that stuffs the circumjacent space with an efficiency of almost one.
Moreover, when receiving the ultrasonic wave, which propagates through the fluid that stuffs the circumjacent space and reach the ultrasonic transmitter-receiver 41, a path reverse to that of wave transmission holds with regard to the ultrasonic wave that has propagated from the direction of wave transmission. The ultrasonic wave, which enters the second surface region 8 of the ultrasonic transmitter-receiver 41 with an efficiency of almost one, propagates through the propagation medium portion 6D and are reflected with an efficiency of almost one on the third surface region 45 that is the interface to the reflector 44 to propagate with the direction thereof changed roughly toward the ultrasonic transducer 42 side and reach the ultrasonic transducer 42 and then converted into electric signals by the ultrasonic transducer 42.
With the above construction, the ultrasonic transmitter-receiver 41 also becomes able to highly efficiently transmit and receive an ultrasonic wave to and from the fluid that stuffs the circumjacent space, and effects similar to those of the first embodiment can be produced.
On the other hand, as shown in
The ultrasonic transducer 52 is excited with vibrations in the vicinity of the resonance frequency, and the vibrations are radiated as an ultrasonic wave roughly to the peripheral side of the propagation medium portion 6E through the acoustic matching layer 53 on the condition of an efficiency of almost one. The ultrasonic wave, which has propagated through the propagation medium portion 6E, is reflected on the third surface region 55 that is the interface to the reflector 54 with an efficiency of almost one to propagate with the direction thereof changed roughly toward the second surface region 8 side, refracted at the second surface region 8 that is the interface between the propagation medium portion 6E and the fluid that stuffs the circumjacent space and then radiated to the fluid that stuffs the circumjacent space with an efficiency of almost one.
Moreover, when receiving the ultrasonic wave, which propagates through the fluid that stuffs the circumjacent space and reaches the ultrasonic transmitter-receiver 51, a path reverse to that of wave transmission holds with regard to the ultrasonic wave that has propagated from the wave transmission direction. The ultrasonic wave, which enters the second surface region 8 of the ultrasonic transmitter-receiver 51 with an efficiency of almost one, propagates through the propagation medium portion 6E and is reflected at the third surface region 55 that is the interface to the reflector 54 with an efficiency of almost one to propagate with the direction thereof changed roughly toward the ultrasonic transducer 52 side and reach the ultrasonic transducer 52, and then converted into electric signals by the ultrasonic transducer 52.
With the above construction, the ultrasonic transmitter-receiver 51 also becomes able to highly efficiently transmit and receive an ultrasonic wave to and from the fluid that stuffs the circumjacent space, and effects similar to those of the first embodiment can be produced.
It is to be noted that a plurality of reflectors 44 and 54 of the fourth embodiment may be arranged, and in the above case, there is existing a plurality of third surface regions 45 and 55 in terms of construction. Moreover, in this case, a construction in which the first surface region 7 and the second surface region 8 are parallel to each other also holds, and at least one of the plurality of third surface regions 45 and 55 is required to be inclined at a prescribed angle with respect to the second surface region 8.
The ultrasonic transmitter-receiver 41 and the ultrasonic transmitter-receiver 51 have a structure in which wave transmission and reception can be performed omnidirectionally around the central axis similarly to the second embodiment. When the circumjacent space is stuffed with a gas, the wave transmission and reception become almost horizontal, and an application to omnidirectional object sensing and so on becomes possible.
Moreover,
As shown in
The ultrasonic transmitter-receiver as one example of the ultrasonic sensor according to the fifth embodiment of the present invention will be described with reference to
Hereinafter, characteristic points of the ultrasonic transmitter-receiver 61 of the fifth embodiment will be described below, and no description is provided for portions similar to those of the ultrasonic transmitter-receiver 1 of the first embodiment, the ultrasonic transmitter-receivers 11 and 21 of the second embodiment, the ultrasonic transmitter-receiver 31 of the third embodiment, the ultrasonic transmitter-receivers 41 and 51 of the fourth embodiment and the aforementioned corresponding portions.
In the ultrasonic transmitter-receiver 61 of the fifth embodiment, the portion, which are the cylindrical or conical portion of the ultrasonic transmitter-receivers 41 and 51 of the fourth embodiment are made rectangular. A rectangular plate-shaped terminal plate 69x is fixed to the lower end of a rectangular plate-shaped side portion 69g, a triangular prismatic reflector 64 is fixed to the peripheral portions of the side portion 69g and the terminal plate 69x, and a rectangular disk-shaped upper plate 69m is fixed, with protruded like a flange, to the upper end of a rectangular plate-shaped center shaft 69k, providing a symmetrical construction with respect to a center line C. Ultrasonic transducers 62 and acoustic matching layers 63 are rectangular plates and are fixed to the inner surface of the center shaft 69k, and the acoustic matching layers 63 are arranged outside the ultrasonic transducers 62. The propagation medium portions 6F have a first surface region 7 parallel to the vibration surface of the ultrasonic transducer 62 and a second surface region 8 brought in contact with the fluid that stuffs the circumjacent space and is brought in contact with reflectors 64 provided adjacent to the propagation medium portions 6F by third surface regions 65. The reflectors 64 have a material and an inclination angle which are similar to those of the reflector 44.
The fifth embodiment differs from the fourth embodiment in that the transmission and reception of an ultrasonic wave in the ultrasonic transmitter-receiver 61 of the fifth embodiment are performed transversely in
With the above construction, the ultrasonic transmitter-receiver 61 also becomes able to highly efficiently transmit and receive ultrasonic waves to and from the fluid that stuffs the circumjacent space, and effects similar to those of the first embodiment can be produced. Moreover, the ultrasonic transmitter-receiver 61 has a structure such that wave transmission and reception in the transverse direction can be performed, and when the circumjacent space is stuffed with a gas, the transmission and reception waves become almost horizontal, and an application to transverse object sensing and so on becomes possible.
An ultrasonic transmitter-receiver as one example of the ultrasonic sensor according to the sixth embodiment of the present invention will be described with reference to
Hereinafter, characteristic points of the ultrasonic transmitter-receivers 71-1, 71-2, 71-3 and 71-4 of the sixth embodiment will be described below, and no description is provided for portions similar to those of other embodiments and the aforementioned corresponding portions.
The ultrasonic transmitter-receivers 71-1, 71-2, 71-3 and 71-4 of the sixth embodiment have a structure in which the ultrasonic transmitter-receiver 61 of the fifth embodiment is divided along the center line C. Therefore, although the transmission and reception of an ultrasonic wave are limited to one direction, the transmission and reception of an ultrasonic wave are performed with high efficiency similarly to the fifth embodiment, and effects similar to those of the first embodiment can be produced. When the circumjacent space is stuffed with a gas, the wave transmission and reception becomes almost horizontal, and an application to object sensing and so on becomes possible.
Application equipment of an ultrasonic transmitter-receiver as one example of the ultrasonic sensor according to the seventh embodiment of the present invention will be described with reference to
In
Referring to
In
In
An ultrasonic flowmeter for measuring the flow rate of a fluid by an ultrasonic wave, which is one example of the application equipment of the ultrasonic transmitter-receiver as one example of the ultrasonic sensor according to the eighth embodiment of the present invention will be described with reference to
Before describing the ultrasonic flowmeter of the eighth embodiment, reference is made to a conventional ultrasonic flowmeter.
In recent years, an ultrasonic flowmeter, which measures the mobile velocity of a fluid by measuring a time during which an ultrasonic wave is transmitted through a prescribed propagation path and measures a flow rate from the measured value, is being utilized for a gas meter, chemical reaction controlling, and so on.
The principle of measurement of the conventional ultrasonic flowmeter will be described below with reference to
Operation of the ultrasonic flowmeter will be described first in the case where the ultrasonic transmitter-receiver 401 is used as a transmitter of an ultrasonic wave and the ultrasonic transmitter-receiver 402 is used as a receiver of an ultrasonic wave.
If an AC voltage having a frequency in the vicinity of the resonance frequency of the ultrasonic transmitter-receiver 401 is applied to the piezoelectric transducer of the ultrasonic transmitter-receiver 401, then the ultrasonic transmitter-receiver 401 radiates an ultrasonic wave into the fluid in the pipe. This ultrasonic wave propagates along a propagation path L1 and reaches the ultrasonic transmitter-receiver 402. The piezoelectric transducer of the ultrasonic transmitter-receiver 402 receives this ultrasonic wave and outputs a voltage signal.
Subsequently, the ultrasonic transmitter-receiver 402 is operated as a transmitter of an ultrasonic wave. In concrete, by applying an AC voltage having a frequency in the vicinity of the resonance frequency of the ultrasonic transmitter-receiver 402 to the piezoelectric transducer of the ultrasonic transmitter-receiver 402, the ultrasonic transmitter-receiver 402 radiates an ultrasonic wave into the fluid in the pipe. The ultrasonic wave propagates along a propagation path L2 and reaches the ultrasonic transmitter-receiver 401. The piezoelectric transducer of the ultrasonic transmitter-receiver 401 receives this ultrasonic wave and outputs a voltage signal.
As described above, the ultrasonic transmitter-receivers 401 and 402, which are each one ultrasonic transducer, can produce the function of a receiver and the function of a transmitter. According to this ultrasonic flowmeter, ultrasonic waves are continuously radiated from the ultrasonic transmitter-receiver when an ac voltage is continuously applied and it becomes difficult to measure the propagation time. Therefore, a burst voltage signal having a carrier of a pulse signal is normally used as a drive voltage.
If an ultrasonic burst signal is radiated from the ultrasonic transmitter-receiver 401 by applying a drive burst voltage signal to the ultrasonic transmitter-receiver 401, then this ultrasonic wave burst signal propagates through the propagation path L1 of a distance L and reaches the ultrasonic transmitter-receiver 402 after a lapse of time t.
The ultrasonic transmitter-receiver 402 can convert only the ultrasonic wave burst signal that has propagated into an electric burst signal at a high signal-to-noise ratio. An ultrasonic wave burst signal is radiated by using this electric burst signal as a trigger and applying again the drive burst voltage signal to the ultrasonic transmitter-receiver 401.
A device as described above is called the “sing-around device”. Moreover, a time required for an ultrasonic pulse to reach the ultrasonic transmitter-receiver 402 from the ultrasonic transmitter-receiver 401 is called the “sing-around period”, and its reciprocal is called the “sing-around frequency”.
It is assumed that the flow velocity of the fluid flowing in the pipe is V, the velocity of the ultrasonic wave in the fluid is C and the angle between the flow direction of the fluid, and the propagation direction of the ultrasonic pulse is θ in the ultrasonic flowmeter of
f1=1/t1=(C+V cos θ)/L (4)
Conversely, if it is assumed that the sing-around period is t2 and the sing-around frequency is f2 when the ultrasonic transmitter-receiver 402 is used as a transmitter and the ultrasonic transmitter-receiver 401 is used as a receiver, then the relation of following expression (5) holds.
f2=1/t2=(C−V cos θ)/L (5)
A frequency difference Δf between both the sing-around frequencies is expressed by the following expression (6) based on the expression (4) and the expression (5).
Δf=f1−f2=2V cos θ/L (6)
As is apparent from the expression (6), the flow velocity V of the fluid can be obtained from the distance L of the propagation path of the ultrasonic wave and the frequency difference Δf. Then, the flow rate can be determined from the flow velocity V.
In the ultrasonic flowmeter of
Acoustic Impedance=(Density)×(Acoustic Velocity) (7)
The acoustic impedance of the piezoelectric transducer that generates ultrasonic vibrations is, for example, about 30×106 kg·m−2·s−1, and the acoustic impedance of air is about 400 kg·m−2·s−1. When measuring the flow velocity of air, it is preferable to set the acoustic impedance of the matching layer to about 0.11×106 kg·m−2·s−1.
Conventionally, in order to form a matching layer having acoustic impedance intermediate between those of the piezoelectric transducer and air, a material obtained by solidifying a material (for example, glass balloons or plastic balloons) of a comparatively small density with a resin has been used.
However, there has been a problem that, even with the matching layer employed as described above, a propagation loss has inevitably occurred by all means and the measurement sensitivity has been reduced when propagating an ultrasonic wave from the piezoelectric transducer into a gas of air or the like. The reason why it is difficult to efficiently propagate an ultrasonic wave from a solid to a gas is that the acoustic impedance of the gas is significantly smaller than the acoustic impedance of the solid, and a strong reflection of the ultrasonic wave occurs at the interface even if the matching layer is interposed.
Moreover, in the ultrasonic flowmeter of the type shown in
The eighth embodiment of the present invention is made in view of the aforementioned problems and has the object of providing a highly sensitive ultrasonic flowmeter capable of also coping with the flow measurement of a ultrasmall quantity without disordering the flow inside the channel that is the flow measurement section.
The ultrasonic flowmeter of the eighth embodiment of the present invention includes a flow measurement section having an inner wall that defines the channel of the fluid to be measured, at least one ultrasonic transducer that is provided outside the channel space enclosed by the inner wall of the flow measurement section and performs transmission and/or reception of an ultrasonic wave, and an ultrasonic flowmeter that is arranged between the ultrasonic transducer and the channel space and provided with a propagation medium portion that forms the propagation path of the ultrasonic wave. The density ρ1 of the propagation medium portion, the acoustic velocity C1 of the propagation medium portion, the density ρ2 of the fluid to be measured, and the acoustic velocity C2 in the fluid to be measured are constructed so as to satisfy the relation expressed as (ρ2/ρ1)<(C1/C2)<1.
In a preferred embodiment, the number of the ultrasonic transducers is plural, a first ultrasonic transducer among the plurality of ultrasonic transducers is arranged so as to emit an ultrasonic wave to a second ultrasonic transducer among the plurality of ultrasonic transducers, and the second ultrasonic transducer is arranged so as to emit an ultrasonic wave to the first ultrasonic transducer.
In a preferred embodiment, the propagation medium portion has a first surface region that faces the ultrasonic vibration surface of the ultrasonic transducer and a second surface region that faces the channel space, and the second surface region of the propagation medium portion is inclined with respect to the first surface region.
In a preferred embodiment, the first surface region of the propagation medium portion is inclined in the direction of flow velocity of the fluid to be measured in the channel space, and the second surface region is parallel to the direction of flow velocity of the fluid to be measured in the channel space.
In a preferred embodiment, the second surface region of the propagation medium portion forms substantially no difference in level between it and the inner wall of the flow measurement section.
In a preferred embodiment, the density ρ1 of the propagation medium portion, the incident angle θ1 of an ultrasonic wave to the interface between the propagation medium portion and the fluid to be measured, the density ρ2 of the fluid to be measured, and the approach angle θ2 of the ultrasonic wave from the interface to the fluid to be measured are constructed so as to almost satisfy the relation expressed as ρ2/ρ1=cotθ2/cotθ1.
In a preferred embodiment, the fluid to be measured is a gas whose density ρ2 is not greater than 10 kg·m−3.
In a preferred embodiment, the propagation medium portion is formed of a dry gel of an inorganic oxide or an organic polymer.
In a preferred embodiment, the solid frame portion of the dry gel is made hydrophobic.
In a preferred embodiment, the dry gel has a density of not greater than 500 kg/m3, and the dry gel has a mean pore diameter of not greater than 100 nm.
In a preferred embodiment, there is possessed a matching layer, which is provided between the ultrasonic transducer and the propagation medium portion and acoustically matches the ultrasonic transducer with the propagation medium portion.
In a preferred embodiment, the size of the channel space in the flow measurement section, measured in a direction perpendicular to the direction of flow velocity of the fluid to be measured, is not greater than one half of the wavelength at the center frequency of the ultrasonic wave in the fluid to be measured.
In a preferred embodiment, the ultrasonic transducer is constructed so as to form a convergence sound field.
In a preferred embodiment, the first surface region of the propagation medium portion is curved so as to form a lens surface.
The ultrasonic flowmeter of the present invention includes: a flow measurement section having an inner wall that defines a gas channel; a pair of ultrasonic transducers provided outside the channel space enclosed by the inner wall of the flow measurement section, for performing transmission and/or reception of an ultrasonic wave; and a pair of propagation medium portions arranged between each of the one pair of ultrasonic transducers and the channel space, for refracting the propagation path of the ultrasonic wave. The propagation medium portion has a first surface region that faces the ultrasonic vibration surface of the ultrasonic transducer and a second surface region that faces the channel space. The first surface region of the propagation medium portion is inclined with respect to the direction of flow velocity of the gas in the channel space, and the second surface region is almost parallel to the direction of flow velocity of the gas in the channel space.
The present inventors have found the fact that an ultrasonic wave can be propagated from a solid to a fluid (particularly, gas) causing almost no loss at the interface if the ultrasonic wave is appropriately refracted by using a propagation medium portion made of an appropriate material in an ultrasonic transmitter-receiver, and come to consider the present invention.
In the ultrasonic transmitter-receiver according to the eighth embodiment of the present invention, the propagation medium portion, which has the surface (first surface region) inclined in the flow direction of the fluid to be measured and the surface (second surface region) almost parallel to the flow direction of the fluid to be measured, is arranged between the ultrasonic transducer and the fluid to be measured. The second surface region of the propagation medium portion is matched with the plane that defines the channel of the fluid so as not to disorder the flow of the fluid.
The eighth embodiment of the present invention will be described below with reference to the drawings.
Reference is first made to the ultrasonic flowmeter of the eighth embodiment of the present invention with reference to
The illustrated ultrasonic flowmeter 310 includes: a tubular flow measurement section 304 having an inner wall 340 that defines a channel of the fluid to be measured; a pair of ultrasonic transmitter-receivers (ultrasonic transducers) 301a and 301b provided outside the channel space 309 enclosed by the inner wall 340 of the flow measurement section 304, for performing transmission and/or reception of an ultrasonic wave; and propagation medium portions 303a and 303b arranged between the ultrasonic transmitter-receivers 301a and 301b and the channel space 309, for forming a propagation path of an ultrasonic wave. The fluid to be measured is assumed to flow in the direction of arrow 305 inside the channel space 309 enclosed by the inner wall 340 of the flow measurement section 304. The ultrasonic transmitter-receivers (ultrasonic transducers) 301a and 301b are any of the ultrasonic transmitter-receivers of the first through sixth embodiments. The propagation medium portions 303a and 303b correspond to the propagation medium portions 6, 6A, 6B, 6C, 6D, 6E, 6F, and 6G. It is to be noted that the casing is not shown for the sake of simplicity.
In the eighth embodiment, the ultrasonic wave radiation surface of the ultrasonic transmitter-receiver 301a is inclined in the flow direction 305 of the fluid to be measured, and the ultrasonic wave emitted from the ultrasonic transmitter-receiver 301a is diagonally incident on the inner wall of the flow measurement section 304. Then, the ultrasonic wave is refracted at the interface between the propagation medium portion 303a and the fluid to be measured, and received by one ultrasonic transmitter-receiver 301b through a propagation path 306.
The section (cross section perpendicular to the flow direction 305) of the channel space 309 in the eighth embodiment is rectangular as shown in
The propagation medium portions 303a and 303b have a first surface region 331 that faces the ultrasonic vibration surfaces of the ultrasonic transmitter-receivers 301a and 301b and a second surface region 332 that faces the channel space 309. In the eighth embodiment, assuming that the density of the propagation medium portions 303a and 303b is ρ1, the acoustic velocity of the propagation medium portions 303a and 303b is C1, the density of the fluid to be measured is ρ2, and the acoustic velocity of the fluid to be measured is C2, then the material of the propagation medium portions 303a and 303b is selected so that the relation expressed by the following expression (8) is satisfied.
(ρ2/ρ1)<(Cl/C2)<1 (8)
When measuring the flow rate of a gas, it is difficult to find the material that satisfies the aforementioned condition. The reason is that there are few solid materials whose acoustic velocity C1 is smaller than the acoustic velocity C2 of a gas. In order to provide the propagation medium portions 303a and 303b that satisfy the aforementioned condition in the eighth embodiment, the propagation medium portions 303a and 303b are formed of a dry gel of an inorganic oxide or a dry gel of an organic polymer. The solid frame portion of the dry gel employed in the eighth embodiment is made hydrophobic, and its density is not greater than 500 kg/m3. This dry gel is a nano-porous dry gel (nanoporous dry gel) having a mean pore diameter of not greater than 100 nm.
The solid frame portion of the dry gel of the inorganic oxide preferably has an ingredient of at least silicon oxide (silica) or aluminum oxide (alumina). Moreover, the solid frame portion of the dry gel of the organic polymer can be constructed of a general thermosetting resin or a thermoplastic resin. For example, there can be used polyurethane, polyurea, phenol cured resin, polyacrylamide, polymethyl methacrylate, or the like.
In the case where the propagation medium portions 303a and 303b are formed of a nanoporous dry gel that has a main ingredient of, for example, silica, if the density ρ1 is 200 kg/m3, then the acoustic velocity C1 can be set within a range of about 100 m/s to 180 m/s. When the fluid to be measured is air, since the density ρ2 of air is 1.22 kg/m3 and the acoustic velocity C2 is 340 m/s, it is possible to concurrently satisfy the relations expressed as ρ2<ρ1 and C1<C2 and satisfy the relation expressed as (ρ2/ρ1)<(C1/C2) by adopting the propagation medium portions 303a and 303b. When measuring the flow rate of a gas such as natural gas, the propagation medium portions 303a and 303b preferably has a density ρ1 ranging from 100 to 300 kg/m3 and an acoustic velocity C1 ranging from 100 to 300 m/s.
The ultrasonic transmitter-receivers 301a and 301b have a piezoelectric element that functions as an ultrasonic transducer, and the transmission and/or reception of an ultrasonic wave can be performed. As a piezoelectric element, piezoelectric ceramics are suitably employed.
In the ultrasonic flow measuring unit 310 of the eighth embodiment, a matching layer 302a is provided between the propagation medium portion 303a and the ultrasonic transmitter-receiver 301a, and a matching layer 302b is provided between a propagation medium portion 303b and an ultrasonic transmitter-receiver 301b. The matching layers 302a and 302b have functions to improve the acoustic matching between piezoelectric ceramics (acoustic impedance: 30×106 kg·m−2·s−1) that are the ultrasonic generation sources of the ultrasonic transmitter-receivers 301a and 301b and the propagation medium portions 303a and 303b.
When forming the propagation medium portions 303a and 303b of the nanoporous dry gel (acoustic impedance: 3×104 kg·m−2·s−1) having a main ingredient of silica, by adopting matching layers 302a and 302b produced from a material of an acoustic impedance in the vicinity of 1×106 kg·m−2·s−1, the propagation efficiency of ultrasonic energy can be made to be almost one and more concretely be not smaller than 0.95. The material as described above can be provided by a composite material obtained by solidifying hollow glass balls with a resin material. The thickness of the matching layers 302a and 302b is preferably set to a quarter wavelength of the ultrasonic wave used.
Next, the behavior of an ultrasonic wave propagating from the propagation medium portion 303a to the fluid to be measured will be described in detail below with reference to
According to the aforementioned relation of arrangement, an ultrasonic wave enters an interface S along a direction inclined from the normal direction of the interface S between the propagation medium portion 303a and the fluid to be measured. It is assumed that the incident angle of the ultrasonic wave with respect to the normal direction with the interface is θ1 (0°<θ1<90°). At this time, the ultrasonic wave is refracted at the interface S between the propagation medium portion 303a and the fluid to be measured and enters the fluid to be measured at an angle (approach angle) θ2 with respect to the normal direction of the interface S (θ1<θ2).
In the eighth embodiment, when ρ2 of the fluid to be measured is given, various parameters (ρ1, θ1, and θ2) are set so as to approximately satisfy the relation of the following expression (9).
(ρ2/ρ1)=(cotθ2/cotθ1) (9)
With the above setting, the propagation efficiency of ultrasonic energy from the propagation medium portion 303a to the fluid to be measured becomes almost one. At this time, the incident angle θ1 satisfies the condition expressed by the following expression (10).
(cotθ1)2=[(c1/c2)2−1]/[(ρ2/ρ1)2−(c1/c2)2] (10)
Therefore, if ρ1 and C1 of the propagation medium portion 303a and ρ2 and C2 of the fluid to be measured are determined, then the incident angle θ1 is determined according to the expression (10). Moreover, if the incident angle θ1 is determined, then the approach angle θ2 is determined according to the expression (9).
If the incident angle θ1 and the approach angle θ2 are determined, then the inclination angle of the first surface region 331 of the propagation medium portion 303a and the interval between the two ultrasonic transmitter-receivers 301a and 301b and so on can also be determined.
The aforementioned fact is applied as it is when the ultrasonic wave is received.
In the eighth embodiment, by forming the propagation medium portions 303a and 303b of the aforementioned material, the acoustic velocity C1 of the propagation medium portions 303a and 303b can be set to 180 m/s, and the density ρ1 can be set to 200 kg/m3. When measuring the flow rate of air, the density ρ2 of the fluid (air) to be measured is 1.22 kg/m3, and the acoustic velocity C2 is 340 m/s. Therefore, it is proper to set the incident angle θ1 to 32° and set the approach angle θ2 to 89° according to the relations of the expression (9) and the expression (10). The approach angle θ2 is close to 90°, and therefore, the ultrasonic wave in the fluid to be measured is to propagate in a direction almost parallel to the flow direction 305.
A size H (see
According to the eighth embodiment, almost no propagation loss occurs at the interface S between the propagation medium portions 303a and 303b and the fluid to be measured, and therefore, it is not required to match the acoustic impedances of them at this interface S.
The propagation medium portions 303a and 303b are not required to be constructed of a material whose density ρ1 and acoustic velocity C1 are thoroughly uniform but allowed to have a laminate structure in which a plurality of kinds of material layers of varied density ρ1 and acoustic velocity C1 are laminated. When the laminate structure as described above is possessed, although it is sometimes the case where an ultrasonic wave does not travel straightly in the propagation medium portions 303a and 303b, there is no special problem. An important point is that the density ρ1, the acoustic velocity C, and the incident angle θ1 of the propagation medium portions 303a and 303b are set so as to satisfy the aforementioned expressions in the region in the vicinity of the interface between the propagation medium portions 303a and 303b and the fluid to be measured.
Moreover, as shown in
Operation of the ultrasonic flowmeter of the eighth embodiment will be described next.
First of all, an AC voltage having a frequency in the vicinity of the resonance frequency (for example, about 100 kHz to 1 MHz) is applied from the transmitter circuit 701 that concurrently serves as the drive circuit of
The acoustic wave, which has propagated through the medium portion 303a, is refracted at the interface between the propagation medium portion 303a and the channel space 309, radiated in the channel space 309 with an efficiency of almost one, and propagated through the inside of the fluid to be measured. Subsequently, the ultrasonic wave reaches the ultrasonic transmitter-receiver 301b through the propagation medium portion 303b and the matching layer 302b provided on the opposite side. The ultrasonic transmitter-receiver 301b converts the received ultrasonic wave into a voltage to generate a voltage signal (electric signal). The method for measuring the propagation time of the ultrasonic wave by the flow rate calculating section 705 on the basis of this electric signal and converting the flow velocity into the flow rate is similar to that of the prior art. A structural example of the drive circuit is described in Japanese Unexamined Patent Publication No. 2000-298045 and Japanese Unexamined Patent Publication No. 2000-298047.
According to the eighth embodiment, there are provided the propagation medium portions 303a and 303b that exhibit appropriate density ρ1 and acoustic velocity C1, and the ultrasonic wave is refracted at an appropriate angle. Therefore, the propagation loss at the interface of the substances can be made almost zero, and flow measurement can be achieved at a satisfactory signal-to-noise ratio. Then, according to the eighth embodiment, the flow rate of a gas (for example, hydrogen gas), of which the measurement has been extremely difficult by the conventional ultrasonic flowmeter, can easily be measured.
Furthermore, according to the eighth embodiment, there is existing neither large unevenness nor difference in level, which may cause a disorder of flow, inside the channel space 309 of the flow measurement section 304, and extremely stable flow measurement becomes possible. Moreover, since the ultrasonic transmitter-receivers are arranged outside the channel space 309, the size of the channel space 309 can be arbitrarily designed not depending on the sizes of the ultrasonic transmitter-receivers. As a result, the size of the channel space 309 is reduced to allow the flow measurement of an ultrasmall quantity to be performed.
An ultrasonic flowmeter as one example of the ultrasonic sensor according to the ninth embodiment of the present invention will be described with reference to
Hereinafter, characteristic points of the ultrasonic transmitter-receiver 320 of the ninth embodiment will be described below, and no description is provided for portions similar to those of the ultrasonic flowmeter 310 of the eighth embodiment.
In the ultrasonic flowmeter 320 of the ninth embodiment, the ultrasonic transmitter-receivers 301a and 301b are constructed so as to form a convergence sound field. In concrete, the first surface region of propagation medium portions 308a and 308b are curved so as to form a lens surface. With this arrangement, a matching layer 308 has a concave type surface on the measured fluid side. With the above construction, the ultrasonic wave transmitted from an ultrasonic transmitter-receiver 301a is to converge inside a propagation medium portion 308a. This convergence effect enables the transmission and reception of an ultrasonic wave with a larger sound pressure by means of an ultrasonic transducer of same identical capability, and therefore, the signal-to-noise ratio can be further improved.
In each of the eighth and ninth embodiments described above, a first surface region 331 of the propagation medium portion is inclined in the flow velocity direction 305 of the fluid to be measured in the channel space 309, and the second surface region 332 is parallel to the flow velocity direction 305 of the fluid to be measured in the channel space 309. However, the present invention is not limited to the above construction. For example, as shown in
The second surface region 332 of the propagation medium portions 303a and 303b preferably has no substantial difference in level between it and the inner wall 340 of the flow measurement section 304. However, when the disorder of the flow does not pose a major problem, there may exist a difference in level or unevenness as shown in
In each of the aforementioned eighth and ninth embodiments, one pair of ultrasonic transmitter-receivers has a substantially identical construction, and an arrangement rotationally symmetrical at an angle of 180° is adopted. However, the present invention is not limited to the above construction. It is acceptable to apply the construction of the eighth and ninth embodiments to one of the one pair of ultrasonic transmitter-receivers and give a different construction (for example, the construction shown in
According to the eighth and ninth embodiments of the present invention, the loss in propagating an ultrasonic wave into the fluid to be measured can be reduced to almost zero, and therefore, the flow rate of various fluids including a gas can be measured with high sensitivity.
Moreover, according to the eighth and ninth embodiments of the present invention, there is no need to provide a difference in level or unevenness inside the channel, and therefore, the embodiments can also cope with the flow measurement of an extremely small quantity without disordering the flow of the fluid to be measured.
According to the present invention, there are provided the ultrasonic transducer for performing the transmission and/or reception of an ultrasonic wave and the propagation medium portion that forms the propagation path of the ultrasonic wave. By appropriately setting the mutual relation between the density ρ1 and the acoustic velocity C1 of the propagation medium portion and the density ρ2 and the acoustic velocity C2 of the fluid that stuffs the circumjacent space and appropriately refracting the ultrasonic wave at an appropriate angle, the loss in radiating an ultrasonic wave into the fluid that stuffs the circumjacent space can be reduced to almost zero, and/or the loss in receiving the ultrasonic wave entering from the fluid that stuffs the circumjacent space can be reduced to almost zero. Therefore, highly efficient wave transmission and reception become possible for various fluids including a gas. Moreover, when the fluid is a gas, the wave transmission and reception are can be performed almost horizontally (parallel) with respect to the wave transmission and reception surface of the ultrasonic transmitter-receiver, and the present invention can be used for developing a variety of applications.
By properly combining arbitrary embodiments of the aforementioned various embodiments, the effects possessed by them can be produced.
Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP03/05436 | 4/28/2003 | WO |
