Patent Application
20140203684
The present invention relates to an ultrasonic generation device, and more specifically, to an ultrasonic generation device that provides a high sound pressure and makes the output sound pressure stable to, for example, temperature change.
Recently, a distance measuring method utilizing ultrasonic waves has been used as an accurate distance measuring method. In the method, ultrasonic waves are emitted from an ultrasonic generation device and are caused to impinge on an object to be measured. The ultrasonic waves reflected by the object are detected by an ultrasonic microphone device, and the distance to the object is calculated from the time elapsed between the emission and the detection.
For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2004-297219) discloses an ultrasonic generation device in which piezoelectric vibrators are attached to a housing. The device in Patent Document 1 is configured as an ultrasonic sensor device in which a single device serves as both an ultrasonic generation device and an ultrasonic microphone device.
To make a measurement result more accurate and to lengthen a measurable distance in the distance measuring method using such an ultrasonic generation device, it is useful to increase an output sound pressure of the ultrasonic generation device.
However, increasing the output sound pressure in the ultrasonic generation device 200 is limited. That is, although increasing the output sound pressure requires that polarization of the piezoelectric vibrator be increased or electric power applied to the piezoelectric vibrator be enlarged, the polarization of the piezoelectric vibrator is limited. Further, if the applied electric power is excessively enlarged, the piezoelectric vibrator exceeds its breakdown limit. Hence, increasing the output sound pressure is limited.
In recent years, there is a strong demand to reduce the sizes of electronic apparatuses and devices. However, if the piezoelectric vibrator is miniaturized to reduce the size of the ultrasonic generation device, a problem arises in that the output sound pressure falls. Therefore, there also is a problem in that size reduction of the ultrasonic generation device is difficult.
Accordingly, the present applicant has addressed the development of an ultrasonic generation device having a high outpour sound pressure, and has succeeded in developing an ultrasonic generation device that has a high output sound pressure with a specific structure. Although a patent application on this ultrasonic generation device has been filed (for example, PCT/JP2011/68095), the application has not been laid open yet at the time of filing the present application.
The ultrasonic generation device 300 includes an ultrasonic generation element 201.
The ultrasonic generation element 201 includes a frame 202, a first piezoelectric vibrator 203, and a second piezoelectric vibrator 204. The frame 202 has a through hole in its center portion. The first piezoelectric vibrator 203 is bonded to a lower principal surface of the frame 202, and the second piezoelectric vibrator 204 is bonded to an upper principal surface of the frame 202.
The first piezoelectric vibrator 203 and the second piezoelectric vibrator 204 are vibrated in mutually opposite phases by applying driving signals with the same frequency thereto. That is, the ultrasonic generation element 201 vibrates in a buckling tuning-fork vibration mode, and ultrasonic waves are generated from each of the first piezoelectric vibrator 203 and the second piezoelectric vibrator 204.
The ultrasonic generation device 300 further includes a housing composed of a substrate 207 and a cover member 208. The ultrasonic generation element 201 is mounted on the substrate 207 with pillow members 209, such as conductive adhesive, so that a gap is formed between the ultrasonic generation element 201 and the substrate 207. Further, the cover member 208 is bonded to the substrate 207. The cover member 208 has ultrasonic emission ports 208b from which the ultrasonic waves generated by the first piezoelectric vibrator 203 and the second piezoelectric vibrator 204 are emitted outside.
An acoustic path R201 is defined by a gap formed between the first piezoelectric vibrator 203 and the substrate 207 and a gap formed between an outer peripheral surface of the ultrasonic generation element 201 and an inner surface of the housing composed of the substrate 207 and the cover member 208. An acoustic path R202 is defined by a gap formed between the second piezoelectric vibrator 204 and the cover member 208. When the ultrasonic generation element 201 is driven, ultrasonic waves generated by the first piezoelectric vibrator 203 and ultrasonic waves generated by the second piezoelectric vibrator 204 reach the ultrasonic emission ports 208b via the acoustic path R201 and the acoustic path R202, respectively, and are combined into ultrasonic waves having a high output sound pressure. The ultrasonic waves are emitted outside from the ultrasonic emission ports 208b.
However, in the above-described ultrasonic generation device 300 whose patent application has been filed by the present applicant (not laid open), a zone where the output sound pressure becomes minimal exists at a frequency comparatively close to a frequency where the output sound pressure becomes maximal in the frequency-sound pressure characteristics. Hence, there is a problem in that the output sound pressure rapidly may fall according to the assembly accuracy, tolerance of components, or temperature change.
The low-frequency side peak Lp is formed by resonance of air using the vicinity of a vibration surface of the first piezoelectric vibrator 203 as an antinode and each of the ultrasonic emission ports 208b as a node. At this time, ultrasonic waves that are generated in the first piezoelectric vibrator 203 and propagate through the acoustic path R201 and ultrasonic waves that are generated in the second piezoelectric vibrator 204 and propagate through the acoustic path R202 are in phase with each other.
The anacoustic zone Ns is formed when the ultrasonic waves that are generated in the first piezoelectric vibrator 203 and propagate through the acoustic path R201 and the ultrasonic waves that are generated in the second piezoelectric vibrator 204 and propagate through the acoustic path R202 are opposite in phase.
The high-frequency side peak Hp is formed by resonance of air using the vicinity of a vibration surface of the second piezoelectric vibrator 204 as an antinode and the vicinity of each of the pillow members 209 as a node. Although the resonance itself occurs within the ultrasonic generation device 300, since the vicinities of the ultrasonic emission ports 208b are open ends, ultrasonic waves having a comparatively high output sound pressure are emitted from the ultrasonic emission ports 208b. At this time, the ultrasonic waves that are generated in the first piezoelectric vibrator 203 and propagate through the acoustic path R201 and the ultrasonic waves that are generated in the second piezoelectric vibrator 204 and propagate through the acoustic path R202 are opposite in phase.
The ultrasonic generation device 300 most efficiently emits ultrasonic waves when the ultrasonic generation element 201 is driven at the frequency of the low-frequency side peak Lp where the output sound pressure becomes maximal. However, since the frequency of the low-frequency side peak Lp and the frequency of the anacoustic zone Ns are comparatively close to each other, as described above, there is a problem in that the output sound pressure rapidly may fall according to the assembly accuracy, tolerance of components, or temperature change.
The present invention has been made to solve the problem in the ultrasonic generation device whose patent application was filed by the present applicant (not laid open). As its means, an ultrasonic generation device according to the present invention includes an ultrasonic generation element including a frame having at least one of a groove and a through hole in a center portion thereof, a first piezoelectric vibrator shaped like a flat plate and bonded to one principal surface of the frame, and a second piezoelectric vibrator shaped like a flat plate and bonded to the other principal surface of the frame, the ultrasonic generation element emitting ultrasonic waves in a buckling tuning-fork vibration mode in which the first piezoelectric vibrator and the second piezoelectric vibrator vibrate in mutually opposite phases at the same frequency. The ultrasonic generation device further includes a housing that receives the ultrasonic generation element and has one or a plurality of ultrasonic emission ports, a first acoustic path extending from a vicinity of a vibration surface of the first piezoelectric vibrator to a vicinity of the one or the plurality of ultrasonic emission ports and defined by the ultrasonic generation element and an inner surface of the housing, and a second acoustic path extending from a vicinity of a vibration surface of the second piezoelectric vibrator to the vicinity of the one or the plurality of ultrasonic emission ports and defined by the ultrasonic generation element and the inner surface of the housing. Frequency-sound pressure characteristics representing a relationship between a vibration frequency of the first piezoelectric vibrator and the second piezoelectric vibrator and an output sound pressure of the ultrasonic waves emitted from the one or the plurality of ultrasonic emission ports include a low-frequency side peak and a high-frequency side peak. A frequency difference between the low-frequency side peak and the high-frequency side peak is 10 kHz or more.
In the ultrasonic generation device of the present invention, the frequency-sound pressure characteristics representing the relationship between the vibration frequency of the first piezoelectric vibrator and the second piezoelectric vibrator and the output sound pressure of the ultrasonic waves emitted from the one or the plurality of ultrasonic emission ports include the low-frequency side peak and the high-frequency side peak, and the frequency difference between the low-frequency side peak and the high-frequency side peak is 10 kHz or more. Hence, for example, even when the temperature of a usage environment changes, the output sound pressure does not rapidly fall, and a stable output sound pressure can be maintained.
In the ultrasonic generation device of the present invention, the ultrasonic generation element includes the first piezoelectric vibrator and the second piezoelectric vibrator, both the vibrators are driven in the buckling tuning-fork vibration mode, and ultrasonic waves emitted from both the vibrators are combined and output. Hence, ultrasonic waves having a high output sound pressure can be emitted.
An embodiment of the present invention will be described below with reference to the drawings.
The ultrasonic generation device 100 includes the ultrasonic generation element 1.
The ultrasonic generation element 1 includes a frame 2, a first bimorph piezoelectric vibrator 3, and a second bimorph piezoelectric vibrator 4. The frame 2 has a through hole 2a in its center portion. The first bimorph piezoelectric vibrator 3 is bonded to a lower principal surface of the frame 2 with an adhesive 5a, and the second bimorph piezoelectric vibrator 4 is bonded to an upper principal surface of the frame 2 with an adhesive 5b. That is, the through hole 2a of the frame 2 is covered with the first bimorph piezoelectric vibrator 3 and the second bimorph piezoelectric vibrator 4. The ultrasonic generation element 1 has a thickness of about 320 μm, for example.
The frame 2 is formed of, for example, a ceramic material (glass epoxy is adopted now), and has a thickness of about 200 μm. The diameter of the through hole 2a is about 2.4 mm, for example. Instead of the through hole 2a, a groove may be provided in the center portion of the frame 2. That is, the frame 2 is not limited to a closed annular structure, but may be an annular structure that is partly open.
The first bimorph piezoelectric vibrator 3 includes piezoelectric ceramics 3a shaped like a rectangular flat plate and formed of, for example, lead zirconate titanate (PZT). An inner electrode 3b is provided within the piezoelectric ceramics 3a, and outer electrodes 3c and 3d are provided on both principal surfaces of the piezoelectric ceramics 3a, respectively. For example, the inner electrode 3b and the outer electrodes 3c and 3d are formed of Ag or Pd. The inner electrode 3b is extended to two adjacent corners of the piezoelectric ceramics 3a. In contrast, each of the outer electrodes 3c and 3d is extended to two adjacent corners of the piezoelectric ceramics 3a where the inner electrode 3b is not extended. The thickness of the first bimorph piezoelectric vibrator 3 is about 60 μm, for example.
Similarly to the first bimorph piezoelectric vibrator 3, the second bimorph piezoelectric vibrator 4 also includes piezoelectric ceramics 4a shaped like a rectangular flat plate and formed of, for example, PZT. An inner electrode 4b is provided within the piezoelectric ceramics 4a, and outer electrodes 4c and 4d are provided on both principal surfaces of the piezoelectric ceramics 4a, respectively. The inner electrode 4b and the outer electrodes 4c and 4d are also formed of Ag or Pd, for example. The inner electrode 4b is extended to two adjacent corners of the piezoelectric ceramics 4a. In contrast, each of the outer electrodes 4c and 4d is extended to two adjacent corners of the piezoelectric ceramics 4a where the inner electrode 4b is not extended. The thickness of the second bimorph piezoelectric vibrator 4 is also about 60 μm, for example.
The piezoelectric ceramics 3a of the first bimorph piezoelectric vibrator 3 and the piezoelectric ceramics 4a of the second bimorph piezoelectric vibrator 4 are each polarized therein. In the piezoelectric ceramics 3a, the direction of polarization is the same between the outer electrode 3c and the inner electrode 3b and between the inner electrode 3b and the outer electrode 3d. Similarly, in the piezoelectric ceramics 4a, the direction of polarization is the same between the outer electrode 4c and the inner electrode 4b and between the inner electrode 4b and the outer electrode 4d. In contrast, the direction of polarization between the outer electrode 3c and the inner electrode 3b and between the inner electrode 3b and the outer electrode 3d in the piezoelectric ceramics 3a is opposite from the direction of polarization between the outer electrode 4c and the inner electrode 4b and between the inner electrode 4b and the outer electrode 4d in the piezoelectric ceramics 4a.
Extended electrodes 6a, 6b, 6c, and 6d are provided at four corners of the ultrasonic generation element 1, respectively. Two adjacent extended electrodes 6a and 6b are electrically connected to the inner electrode 3b of the piezoelectric ceramics 3a and the inner electrode 4b of the piezoelectric ceramics 4a. In contrast, two remaining adjacent extended electrodes 6c and 6d are electrically connected to the outer electrodes 3c and 3d of the piezoelectric ceramics 3a and the outer electrodes 4c and 4d of the piezoelectric ceramics 4a. (While the extended electrodes 6a and 6d are illustrated in
The ultrasonic generation device 100 further includes a housing composed of a substrate 7 and a cover member 8.
The substrate 7 is formed of, for example, glass epoxy, and is shaped like a rectangular flat plate. A plurality of land electrodes (not illustrated) are provided on an upper principal surface of the substrate 7. The ultrasonic generation element 1 is mounted on the substrate 7 by bonding the extended electrodes 6a, 6b, 6c, and 6d of the ultrasonic generation element 1 to the land electrodes with pillow members 9 formed of conductive adhesive. The ultrasonic generation element 1 is mounted on the substrate 7 with a fixed gap being disposed therebetween.
The cover member 8 is formed of, for example, nickel silver, and has an opening 8a that receives the ultrasonic generation element 1. The cover member 8 further has rectangular ultrasonic emission ports 8b in its top surface. While any number of ultrasonic emission ports 8b can be provided, four ultrasonic emission ports 8b are provided in the embodiment. The ultrasonic generation element 1 is received in the opening 8a, a peripheral edge of the opening 8a of the cover member 8 is bonded to the upper principal surface of the substrate 7, for example, with adhesive (not illustrated). The ultrasonic generation element 1 is mounted on the substrate 7 with a fixed gap being disposed between the ultrasonic generation element 1 and the cover member 8.
In the ultrasonic generation device 100, a first acoustic path R1 and a second acoustic path R2 are formed by the gaps provided between the ultrasonic generation element 1 and an inner surface of the housing composed of the substrate 7 and the cover member 8. The first bimorph piezoelectric vibrator 3 has a vibration surface F1 opposed to the inner surface of the housing. The second bimorph piezoelectric vibrator 4 has a vibration surface F2 opposed to the inner surface of the housing. The first acoustic path R1 extends from the vibration surface F1 of the first bimorph piezoelectric vibrator 3 to the ultrasonic emission ports 8b. The second acoustic path R2 extends from the vibration surface F2 of the second bimorph piezoelectric vibrator 4 to the ultrasonic emission ports 8b.
Since the ultrasonic generation element 1 is bonded at four corners to the substrate 7 with the pillow members 9, propagation of ultrasonic waves emitted from the ultrasonic generation element 1 is not hindered.
A description will now be given of a driving state of the ultrasonic generation device 100 of the embodiment (a driving state of the ultrasonic generation element 1).
The first bimorph piezoelectric vibrator 3 and the second bimorph piezoelectric vibrator 4 that constitute the ultrasonic generation element 1 include the inner electrodes 3b and 4b and the outer electrodes 3c, 3d, 4c, and 4d, as described above, and are polarized, as described above. Hence, when the driving signal is applied, the first bimorph piezoelectric vibrator 3 and the second bimorph piezoelectric vibrator 4 vibrate at the same frequency in mutually opposite phases, and repeat the states illustrated in
Ultrasonic waves emitted from the first bimorph piezoelectric vibrator 3 pass through the first acoustic path R1 and propagate to the ultrasonic emission ports 8b. Ultrasonic waves emitted from the second bimorph piezoelectric vibrator 4 pass through the second acoustic path R2, and propagate to the ultrasonic emission ports 8b. These ultrasonic waves are combined near the ultrasonic emission ports 8b to increase the output sound pressure, and are then emitted outside. In this way, the ultrasonic waves emitted from the two piezoelectric vibrators are combined in the ultrasonic generation device of the present invention. Hence, ultrasonic waves having a high output sound pressure can be emitted outside.
As shown in
The low-frequency side peak Lp is formed by resonance of air using the vicinity of the vibration surface F1 of the first bimorph piezoelectric vibrator 3 as an antinode and each of the ultrasonic emission ports 8b as a node. At this time, in the ultrasonic generation device 100, the sound pressure near the vibration surface F1 of the first bimorph piezoelectric vibrator 3 becomes the highest, and the sound pressure near the ultrasonic emission ports 8b becomes the lowest. Ultrasonic waves that are generated in the first bimorph piezoelectric vibrator 3 and propagate through the first acoustic path R1 and ultrasonic waves that are generated in the second bimorph piezoelectric vibrator 4 and propagate through the second acoustic path R2 are in phase with each other.
The anacoustic zone Ns is formed when the ultrasonic waves that are generated in the first bimorph piezoelectric vibrator 3 and propagate through the first acoustic path R1 and the ultrasonic waves that are generated in the second bimorph piezoelectric vibrator 4 and propagate through the second acoustic path R2 are opposite in phase.
The high-frequency side peak Hp is formed by resonance of air using the vicinity of the vibration surface F2 of the second bimorph piezoelectric vibrator 4 as an antinode and each of the pillow members 9 as a node. Although the resonance itself occurs within the ultrasonic generation device 100, since the vicinities of the ultrasonic emission ports 8b are open ends, ultrasonic waves having a comparatively high sound pressure are emitted from the ultrasonic emission ports 8b. At this time, in the ultrasonic generation device 100, the sound pressure near the vibration surface F2 of the second bimorph piezoelectric vibrator 4 becomes the highest, and the sound pressure near the pillow members 9 becomes the lowest. The ultrasonic waves that are generated in the first bimorph piezoelectric vibrator 3 and propagate through the first acoustic path R1 and the ultrasonic waves that are generated in the second bimorph piezoelectric vibrator 4 and propagate through the second acoustic path R2 are opposite in phase.
The ultrasonic generation device 100 (ultrasonic generation element 1) most efficiently emits ultrasonic waves when being driven at a frequency near 40 kHz serving as the low-frequency side peak Lp where the output sound pressure becomes maximal.
In the present invention, the frequency difference between the low-frequency side peak Lp and the high-frequency side peak Hp is set at 10 kHz or more. In the embodiment, the frequency difference between the low-frequency side peak Lp and the high-frequency side peak Hp is set at 10.5 kHz. In this case, the frequency of the acoustic zone Ns is sufficiently apart from the frequency of the driving signal for driving the ultrasonic generation device 100 (ultrasonic generation element 1). Hence, the output sound pressure does not rapidly fall, for example, even if the temperature of the usage environment changes.
The reason why the output sound pressure of the ultrasonic generation device changes with a change in temperature of the usage environment is as follows. That is, the output sound pressure of the ultrasonic generation device is greatly influenced by resonance of air occurring in the acoustic paths of the ultrasonic generation device. The frequency at which the resonance occurs changes with acoustic velocity, and the acoustic velocity changes with temperature. That is, since the acoustic velocity (m/s) is expressed by 331.5+0.61 t (t: degrees C.), for example, when the temperature of the usage environment falls, the acoustic velocity decreases, and the frequencies of the low-frequency side peak Lp, the anacoustic zone Ns, and the high-frequency side peak Hp also decrease totally. However, the frequency of the driving signal for driving the ultrasonic generation device 100 (ultrasonic generation element 1), which is initially set at a frequency near the low-frequency side peak Lp, does not change even if the temperature of the usage environment changes. As a result, the frequency of the driving signal approaches the frequency of the anacoustic zone Ns, and thus, the output sound pressure falls rapidly.
As shown in
In contrast, when the frequency difference between the low-frequency side peak Lp and the high-frequency side peak Hp is 10.5 kHz or 14.0 kHz, even if the temperature of the usage environment falls, the output sound pressure falls less than when the frequency difference is 5.5 kHz or 8.0 kHz. This seems because, even if the frequency of the anacoustic zone Ns approaches the frequency of the driving signal (frequency near the low-frequency side peak Lp) with a fall in temperature of the usage environment, the output sound pressure does not fall since both the frequencies are sufficiently apart from each other.
It is known from the above that, when the frequency difference between the low-frequency side peak Lp and the high-frequency side peak Hp is set at 10 kHz or more as in the present invention, even if the temperature of the usage environment changes, the output sound pressure does not fall and a stable output sound pressure can be obtained.
Next, a description will be given of a method for setting the frequency difference between the low-frequency side peak Lp and the high-frequency side peak Hp at 10 kHz or more in the present invention. To set the frequency difference between the low-frequency side peak Lp and the high-frequency side peak Hp at 10 kHz or more in the present invention, it is only necessary to adjust (design) the dimensions of the members and parts that constitute the ultrasonic generation device so that each of the frequency of the low-frequency side peak Lp and the frequency of the high-frequency side peak Lp takes a desired value.
The low-frequency side peak Lp can be set at a desired frequency by adjusting the length of the acoustic path (first acoustic path R1) from the vicinity of the vibration surface F1 of the first bimorph piezoelectric vibrator 3 to the vicinity of the ultrasonic emission ports 8b or the size or shape of the ultrasonic emission ports 8b. Specifically, the frequency of the low-frequency side peak Lp can be moved to a lower side by increasing the length of the acoustic path (first acoustic path R1) from the vicinity of the vibration surface F1 of the first bimorph piezoelectric vibrator 3 to the vicinity of the ultrasonic emission ports 8b. Alternatively, the frequency of the low-frequency side peak Lp can be moved to the lower side by reducing the size of the ultrasonic emission ports 8b.
The high-frequency side peak Hp can be set at a desired frequency by adjusting the size of the ultrasonic generation element 1 or the housing. Specifically, the frequency of the high-frequency side peak Hp can be moved to a lower side by increasing the size of the ultrasonic generation element 1 or the housing.
When the frequency of the high-frequency side peak Hp is moved by adjusting the size of the ultrasonic generation element or the housing, the frequency of the low-frequency side peak Lp also moves. Specifically, when the frequency of the high-frequency side peak Hp is moved to the lower side by adjusting the size of the ultrasonic generation element or the housing, the frequency of the low-frequency side peak Lp also moves to the lower side. That is, when the dimensions of the members and parts that constitute the ultrasonic generation device are adjusted to move the frequency of the high-frequency side peak Hp, the frequency of the low-frequency side peak Lp is also influenced. Therefore, the frequency of the high-frequency side peak Hp and the frequency of the low-frequency side peak Lp are preferably adjusted not by only the size of the ultrasonic generation element or the housing, by a combination of the size of the ultrasonic generation element or the housing and the size or shape of the ultrasonic emission ports. Specifically, for example, the frequency difference between the low-frequency side peak Lp and the high-frequency side peak Hp may be controlled by adjusting the size or shape of the ultrasonic emission ports, and the frequency of the low-frequency side peak Lp may be controlled by adjusting the size of the ultrasonic generation element or the housing.
The ultrasonic generation device 100 having the above-described structure according to the embodiment of the present invention is manufactured by the following method, for example.
First, the first bimorph piezoelectric vibrator 3 and the second bimorph piezoelectric vibrator 4 are produced. Specifically, a plurality of piezoelectric ceramic green sheets each having a predetermined shape are prepared, and conductive paste for forming the inner electrodes 3b and 4b and the outer electrodes 3c, 3d, 4c, and 4d is printed on surfaces of the piezoelectric ceramic green sheets in a predetermined shape. Next, the predetermined piezoelectric ceramic green sheets are stacked, pressed, and fired at a predetermined profile, and the first bimorph piezoelectric vibrator 3 with the inner electrode 3b and the outer electrodes 3c and 3d and the second bimorph piezoelectric vibrator 4 with the inner electrode 4b and the outer electrodes 4c and 4d are obtained. The outer electrodes 3c, 3d, 4c, and 4d may be formed by printing or sputtering after the stacked piezoelectric ceramic green sheets are fired.
Next, the frame 2 previously formed in a predetermined shape is prepared, and the first bimorph piezoelectric vibrator 3 and the second bimorph piezoelectric vibrator 4 are bonded to both principal surfaces of the frame 2 with the adhesives 5a and 5b, respectively, so that the ultrasonic generation element 1 is obtained.
Next, the extended electrodes 6a, 6b, 6c, and 6d are formed at four corners of the ultrasonic generation element 1 by a technique such as sputtering.
Next, the substrate 7 and the cover member 8 each previously formed in a predetermined shape are prepared, the ultrasonic generation element 1 is mounted on the substrate 7 with the conductive adhesive 9, and the cover member 8 is bonded to the upper principal surface of the substrate 7 with adhesive (not illustrated), so that the ultrasonic generation device 100 is completed.
The structure, the driving state, and the exemplary manufacturing method for the ultrasonic generation device 100 according to the first embodiment of the present invention have been described above. However, the ultrasonic generation device of the present invention is not limited to the above description, and various changes can be made in accordance with the purport of the invention.
For example, the first and second vibrators that constitute the ultrasonic generation element 1 may be vibrators of other types, such as unimorph piezoelectric vibrators or multimorph piezoelectric vibrators, instead of the first and second bimorph piezoelectric vibrators 3 and 4.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-219541 | Oct 2011 | JP | national |
The present application is a continuation of PCT/JP2012/074025 filed Sep. 20, 2012, which claims priority to Japanese Patent Application No. 2011-219541, filed Oct. 3, 2011, the entire contents of each of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2012/074025 | Sep 2012 | US |
| Child | 14223357 | US |
