Ultrasonic transducer and parametric speaker provided with same

Abstract

The present invention comprises a first vibration plate (110), at least one frame body (120), and at least one ultrasonic vibrator (130). The at least one frame body (120) extends in the longitudinal direction and is joined to the first vibration plate (110). The at least one ultrasonic vibrator (130) is attached to the at least one frame body (120), and faces the first vibration plate (110) with an interval therebetween. The first vibration plate (110) resonantly vibrates in antiphase with the at least one ultrasonic vibrator (130) in a direction orthogonal to the first vibration plate (110). The dimension of the at least one frame body (120) on the inside thereof in the longitudinal direction is greater than the dimension of the at least one frame body (120) on the inside thereof in the short direction orthogonal to the longitudinal direction. This ultrasonic transducer is provided with at least one opening which connects between an external space on the side opposite to the at least one frame body (120) across the first vibration plate (110) and an internal space inside the at least one frame body.

Description

Ultrasonic transducer and parametric speaker including same

[0001] The present invention relates to an ultrasonic transducer and a parametric speaker including the same.

[0002] Prior documents disclosing the configuration of an ultradirectional acoustic device include Japanese Patent Laid-Open No. 2003-47085 (Patent Document 1) and Japanese Patent No. 6333480 (Patent Document 2). The ultradirectional acoustic device described in Patent Document 1 is configured by deploying multiple ultrasonic transducers on a single printed circuit board and arranging them so that the outer periphery is approximately circular. The multiple ultrasonic transducers are divided into two groups installed at different heights.

[0003] The ultradirectional acoustic device described in Patent Document 2 includes a first ultrasonic emitter and a second ultrasonic emitter. The second ultrasonic emitter is disposed on the axis of the first ultrasonic emitter and in front of the radiation surface. The phase of the carrier signal radiated by the second ultrasonic emitter is opposite to the phase of the carrier signal contained in the signal radiated by the first ultrasonic emitter.

[0004] JP 2003-47085 A Japanese Patent No. 6333480

[0005] The superdirectional acoustic device described in Patent Document 1 has a complex configuration, with multiple ultrasonic transducers arranged in two groups at different installation heights.The superdirectional acoustic device described in Patent Document 2 has a second ultrasonic emitter arranged outside the first ultrasonic emitter, which increases the size of the device.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide an ultrasonic transducer and a parametric speaker including the same that can increase the sound pressure level while reducing internal stress with a simple and compact configuration.

[0007] An ultrasonic transducer according to the present invention comprises a first diaphragm, at least one frame body, and at least one ultrasonic vibrator. The at least one frame body extends in the longitudinal direction and is joined to the first diaphragm. The at least one ultrasonic vibrator is attached to each of the at least one frame body and faces the first diaphragm at a distance. The first diaphragm resonates in an opposite phase to the at least one ultrasonic vibrator in a direction perpendicular to the first diaphragm. The longitudinal dimension inside the at least one frame body is greater than the lateral dimension inside the at least one frame body that is perpendicular to the longitudinal direction. The ultrasonic transducer is provided with at least one opening that connects an external space on the opposite side of the first diaphragm from the at least one frame body with an internal space inside the at least one frame body.

[0008] According to the present invention, it is possible to increase the sound pressure level while reducing the internal stress in an ultrasonic transducer with a simple and compact configuration.

[0009] 6 is a longitudinal sectional view showing the configuration of an ultrasonic transducer according to a first embodiment of the present invention. FIG. 7 is an exploded perspective view showing the configuration of an ultrasonic transducer according to a first embodiment of the present invention. FIG. 8 is a perspective view showing the configuration of a frame included in the ultrasonic transducer according to the first embodiment of the present invention. FIG. 9 is a sectional view showing the configuration of an ultrasonic vibrator included in the ultrasonic transducer according to the first embodiment of the present invention. FIG. 10 is a perspective view showing a displacement state simulated by a finite element method when the ultrasonic transducer according to the first embodiment of the present invention is transmitting or receiving ultrasonic waves. FIG. 11 is a sectional view of the ultrasonic transducer of FIG. 5 as viewed from the direction of the arrows along line VI-VI. FIG. 12 is a graph obtained by a simulation analysis using the finite element method of the transition of the resonance frequency of the first diaphragm when the longitudinal dimension is changed while the lateral dimension inside the frame is fixed in the ultrasonic transducer according to the first embodiment of the present invention. FIG. 13 is a graph obtained by a simulation analysis using the finite element method of the transition of the sound pressure of ultrasonic waves transmitted from the ultrasonic transducer when the longitudinal dimension is changed while the lateral dimension inside the frame is fixed in the ultrasonic transducer according to the first embodiment of the present invention. FIG. 14 is a perspective view showing the configuration of an ultrasonic element array according to a first comparative example. FIG. 15 is a graph obtained by a simulation analysis using the finite element method of the relationship between the sound pressure of ultrasonic waves transmitted from the ultrasonic transducer and the thickness of the first diaphragm. 10 is a graph obtained by simulating and analyzing, using the finite element method, the relationship between the internal stress (a value normalized per sound pressure) in the third direction (Z-axis direction) generated in the ultrasonic transducer and the thickness of the first diaphragm. 11 is a graph obtained by simulating and analyzing, using the finite element method, the relationship between the displacement of the first diaphragm and the frequency of the ultrasonic vibrator in the ultrasonic transducer according to this embodiment, the ultrasonic transducer according to the first modified example, and the ultrasonic transducer according to the second modified example. 12 is a cross-sectional view showing the configuration of an ultrasonic vibrator according to a third modified example. 13 is a cross-sectional view showing the configuration of an ultrasonic vibrator according to a fourth modified example. 14 is a cross-sectional view showing the configuration of an ultrasonic vibrator according to a fifth modified example. 15 is a longitudinal cross-sectional view showing the configuration of an ultrasonic transducer according to a sixth modified example of embodiment 1 of the present invention.19 is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a seventh modified example of embodiment 1 of the present invention, in which the formation positions of each of the two slits are shifted by 2 mm toward the center in the longitudinal direction of the inner side of the frame, is transmitting or receiving ultrasonic waves. FIG. 19 is a side view showing the configuration of an ultrasonic transducer according to embodiment 2 of the present invention. FIG. 19 is a rear view of the ultrasonic transducer shown in FIG. 18, viewed from the direction of arrow XIX. FIG. 19 is an exploded perspective view showing a stacked state in a step of stacking and bonding each component of the ultrasonic transducer according to embodiment 2 of the present invention. FIG. 19 is a plan view showing the positional relationship in a first direction (X-axis direction) in a step of cutting the piezoelectric body of the ultrasonic transducer according to embodiment 2 of the present invention. FIG. 20 is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to embodiment 2 of the present invention is transmitting or receiving ultrasonic waves. FIG. 21 is a perspective view showing the configuration of an ultrasonic element array according to a second comparative example. FIG. 22 is a graph showing actual measurements of the transition of attenuation of sound pressure level with propagation distance in the ultrasonic transducer according to this embodiment and the ultrasonic transducer according to the second comparative example. FIG. 23 is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to embodiment 3 of the present invention is transmitting or receiving ultrasonic waves. 10 is a graph obtained by simulation analysis using the finite element method of the transition of the resonance frequency of the first diaphragm when the longitudinal dimension is changed while the short dimension inside the frame body is fixed in the ultrasonic transducer according to embodiment 3 of the present invention. 11 is a graph obtained by simulation analysis using the finite element method of the transition of the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer when the long dimension is changed while the short dimension inside the frame body is fixed in the ultrasonic transducer according to embodiment 3 of the present invention. 12 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer according to a modified example of embodiment 3 of the present invention is transmitting or receiving ultrasonic waves. 13 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer according to embodiment 4 of the present invention is transmitting or receiving ultrasonic waves.10 is a graph obtained by simulation analysis using the finite element method of the transition of the resonance frequency of the first diaphragm when the longitudinal dimension is changed while the lateral dimension inside the frame is fixed in the ultrasonic transducer according to embodiment 4 of the present invention. 11 is a graph obtained by simulation analysis using the finite element method of the transition of the sound pressure of ultrasonic waves transmitted from the ultrasonic transducer according to embodiment 4 of the present invention when the longitudinal dimension is changed while the lateral dimension inside the frame is fixed in the ultrasonic transducer according to embodiment 4 of the present invention. 12 is a perspective view showing a displacement state obtained by simulation analysis using the finite element method when the ultrasonic transducer according to embodiment 5 of the present invention is transmitting or receiving ultrasonic waves. 13 is a graph obtained by simulation analysis using the finite element method of the transition of the resonance frequency of the first diaphragm when the longitudinal dimension is changed while the lateral dimension inside the frame is fixed in the ultrasonic transducer according to embodiment 5 of the present invention. 14 is a graph obtained by simulation analysis using the finite element method of the transition of the sound pressure of ultrasonic waves transmitted from the ultrasonic transducer according to embodiment 5 of the present invention when the longitudinal dimension is changed while the lateral dimension inside the frame is fixed in the ultrasonic transducer according to embodiment 5 of the present invention. 36. is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a modified example of embodiment 5 of the present invention transmits or receives ultrasonic waves. FIG. 37 is an exploded perspective view showing the configuration of an ultrasonic transducer according to embodiment 6 of the present invention. FIG. 38 is a view of the ultrasonic transducer of FIG. 36 from the direction of arrow XXXVII. FIG. 39 is a cross-sectional view showing the configuration of an ultrasonic vibrator provided in an ultrasonic transducer according to embodiment 6 of the present invention. FIG. 39 is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to embodiment 6 of the present invention transmits or receives ultrasonic waves. FIG. 39 is a graph showing the relationship between the ratio of the length dimension of the slit in the first direction (X-axis direction) to the short side dimension in the first direction (X-axis direction) inside the frame body and the rate of change of internal stress (value normalized per sound pressure) in the third direction (Z-axis direction) generated in the ultrasonic transducer.1 is a graph showing a simulation analysis using the finite element method of the relationship between the position in the longitudinal direction (Y-axis direction) of the first diaphragm and the displacement of the first diaphragm in Samples 1 to 5. FIG. 1 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer of Sample 1 is transmitting or receiving ultrasonic waves. FIG. 2 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer of Sample 2 is transmitting or receiving ultrasonic waves. FIG. 3 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer of Sample 3 is transmitting or receiving ultrasonic waves. FIG. 4 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer of Sample 4 is transmitting or receiving ultrasonic waves. FIG. 5 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer of Sample 5 is transmitting or receiving ultrasonic waves.

[0010] Hereinafter, ultrasonic transducers according to embodiments of the present invention will be described with reference to the drawings. In the following description of the embodiments, the same or corresponding parts in the drawings will be denoted by the same reference numerals, and their description will not be repeated. The present invention is applicable to applications requiring high sound pressure ultrasonic waves, such as ultrasonic transducers for parametric speakers, ultrasonic sensors, or non-contact haptics. In the following embodiments, an ultrasonic transducer for a parametric speaker will be described as an example, but the use of the ultrasonic transducer is not limited to this.

[0011] (Embodiment 1) Fig. 1 is a longitudinal sectional view showing the configuration of an ultrasonic transducer according to embodiment 1 of the present invention. Fig. 2 is an exploded perspective view showing the configuration of the ultrasonic transducer according to embodiment 1 of the present invention. As shown in Figs. 1 and 2, an ultrasonic transducer 100 according to embodiment 1 of the present invention includes a first diaphragm 110, a frame 120, and an ultrasonic vibrator 130.

[0012] The first diaphragm 110 has a flat plate shape. The first diaphragm 110 is made of an aluminum alloy such as aluminum-containing duralumin, or a metal such as stainless steel. In this embodiment, the first diaphragm 110 is made of stainless steel. The thickness of the first diaphragm 110 is, for example, 0.1 mm or more and 0.2 mm or less.

[0013] The frame body 120 has a rectangular annular shape. The frame body 120 has a short side direction along a first direction (X-axis direction) and a long side direction along a second direction (Y-axis direction). The frame body 120 extends in the second direction (Y-axis direction). The axial direction of the frame body 120 is along a third direction (Z-axis direction). One end of the frame body 120 in the third direction (Z-axis direction) is bonded to the first diaphragm 110 with a bonding agent made of epoxy resin or the like.

[0014] The frame body 120 is formed from a metal such as an aluminum alloy or stainless steel, glass epoxy, or resin. From the viewpoint of suppressing changes in the characteristics of the ultrasonic transducer 100 due to temperature changes, the frame body 120 is preferably made of metal. On the other hand, from the viewpoint of lowering the frequency of the ultrasonic waves transmitted or received by the ultrasonic transducer 100 and from the viewpoint of miniaturizing the ultrasonic transducer 100, the frame body 120 is preferably made of resin. In this embodiment, the frame body 120 is made of stainless steel. The thickness of the frame body 120 is, for example, 0.2 mm or more and 0.8 mm or less.

[0015] 3 is a perspective view showing the configuration of a frame body included in the ultrasonic transducer according to the first embodiment of the present invention. As shown in FIG. 3, the frame body 120 has a pair of long sides 121 extending in the second direction (Y-axis direction) and a pair of short sides 122 extending in the first direction (X-axis direction). The average distance between the short sides 122 is four or more times the shortest distance between the long sides 121. In other words, the longitudinal dimension L1 in the second direction (Y-axis direction) inside the frame body 120 is four or more times the lateral dimension L2 in the first direction (X-axis direction) inside the frame body 120.

[0016] The corners between the long side portion 121 and the short side portion 122 may be chamfered. Furthermore, the short side portion 122 does not have to be linear when viewed from the third direction (Z-axis direction), and may have an arc shape that is convex toward the inside of the frame body 120 or an arc shape that is convex toward the outside of the frame body 120.

[0017] The resonant frequency of the first diaphragm 110 can be adjusted by changing the short-side dimension L2 in the first direction (X-axis direction) inside the frame body 120. For example, when the resonant frequency of the first diaphragm 110 is set to 100 kHz or higher, the short-side dimension L2 is 1.5 mm or more and 3 mm or less.

[0018] The longitudinal dimension L1 in the second direction (Y-axis direction) inside the frame body 120 is larger than the short dimension L2, and from the viewpoint of increasing the sound pressure level of the ultrasound transmitted by the ultrasonic transducer 100, the longitudinal dimension L1 is, for example, 20 mm or more.

[0019] 4 is a cross-sectional view showing the configuration of an ultrasonic vibrator included in the ultrasonic transducer according to embodiment 1 of the present invention. As shown in Fig. 1, the ultrasonic vibrator 130 is attached to the frame body 120 and faces the first diaphragm 110 at a distance. Specifically, the ultrasonic vibrator 130 is attached to the other end of the frame body 120 in the third direction (Z-axis direction), and faces the first diaphragm 110 with the internal space IS inside the frame body 120 sandwiched therebetween.

[0020] The ultrasonic transducer 100 is provided with at least one opening that connects an external space ES on the opposite side of the first diaphragm 110 from the frame body 120 with an internal space IS inside the frame body 120. In this embodiment, as shown in Fig. 2, two openings are formed in the first diaphragm 110. Note that the openings are not limited to being formed in the first diaphragm 110, and an opening may be formed in a portion of the inside of the frame body 120 that is not covered by the first diaphragm 110 because the dimension of the first diaphragm 110 in the second direction (Y-axis direction) is smaller than the longitudinal dimension L1 in the second direction (Y-axis direction) inside the frame body 120.

[0021] Each of the two openings is a slit 110s extending in the first direction (X-axis direction). Each of the two slits 110s extends at least a short-side dimension L2 in the first direction (X-axis direction) inside the frame 120. In this embodiment, the length of the slit 110s in the first direction (X-axis direction) is the same as the short-side dimension L2 in the first direction (X-axis direction) inside the frame 120. The width of the slit 110s in the second direction (Y-axis direction) is 0.4 mm or more and 0.6 mm or less. The slit 110s is formed from a position on the edge of the inner peripheral surface of the frame 120 in the second direction (Y-axis direction) to a position inward in the second direction (Y-axis direction) by the above-mentioned width dimension. The two slits 110s open at both ends in the second direction (Y-axis direction) inside the frame 120.

[0022] As shown in FIGS. 1, 2, and 4, the ultrasonic vibrator 130 is a piezoelectric element including a piezoelectric body 131. As shown in FIG. 4, in this embodiment, the ultrasonic vibrator 130 includes two stacked piezoelectric bodies 131. The polarization directions Dp of the two piezoelectric bodies 131 are different from each other. Specifically, the polarization directions Dp of the two piezoelectric bodies 131 face each other in the third direction (Z-axis direction). The two piezoelectric bodies 131 are sandwiched between a first electrode 132 and a second electrode 133, and an intermediate electrode 134 is disposed between the two piezoelectric bodies 131. The first electrode 132 and the second electrode 133 are electrically connected to a processing circuit 140 capable of applying an AC voltage. The ultrasonic vibrator 130 is a so-called series-type bimorph piezoelectric vibrator. The total thickness of the two piezoelectric bodies 131 is, for example, 0.5 mm or more and 0.85 mm or less.

[0023] FIG. 5 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer according to the first embodiment of the present invention transmits or receives ultrasonic waves. FIG. 6 is a cross-sectional view of the ultrasonic transducer of FIG. 5 as viewed from the direction of the arrows along line VI-VI. The simulation analysis conditions were as follows: the thickness of the first diaphragm 110 was 0.1 mm; the combined thickness of the two piezoelectric bodies 131 was 0.8 mm; the longitudinal dimension L1 inside the frame body 120 was 20 mm; the lateral dimension L2 was 2 mm; and the thickness of the frame body 120 in the third direction (Z-axis direction) was 0.4 mm. Two slits 110s, each 20 mm long, were formed on the inner peripheral surface of the frame body 120, extending from a position on the edge in the second direction (Y-axis direction) to a position 0.5 mm inward in the second direction (Y-axis direction). In other words, the width of the two slits 110s was 0.5 mm.

[0024] 5 and 6, in the vibration mode of the ultrasonic transducer 100 according to the first embodiment of the present invention, the first diaphragm 110 resonates in an opposite phase to the ultrasonic vibrator 130 in a third direction (Z-axis direction) perpendicular to the first diaphragm 110. That is, as shown in Fig. 6, the displacement direction of the resonant vibration Bm of the first diaphragm 110 and the displacement direction of the resonant vibration Bp of the ultrasonic vibrator 130 are opposite to each other in the third direction (Z-axis direction). In this embodiment, the resonant frequencies of the first diaphragm 110 and the ultrasonic vibrator 130 are 100 kHz or higher.

[0025] The portion of the first diaphragm 110 that is located above the internal space IS inside the frame body 120 and between the slits 110s in the second direction (Y-axis direction) becomes a vibration region that resonates. The longitudinal dimension of the vibration region of the first diaphragm 110 is the dimension between the slits 110s, and the lateral dimension of the vibration region of the first diaphragm 110 is the same as the lateral dimension L2 inside the frame body 120. In the first diaphragm 110, a middle portion 110c located at the middle in the longitudinal direction inside the frame body 120 is displaced significantly, while an end portion 110e located outside the slits 110s in the second direction (Y-axis direction) is hardly displaced.

[0026] Here, the relationship between the resonance frequency of the first diaphragm 110 and the longitudinal dimension L1 inside the frame 120 will be described.

[0027] 7 is a graph showing a simulation analysis using the finite element method of the transition of the resonant frequency of the first diaphragm when the longitudinal dimension is changed while the lateral dimension inside the frame body is fixed in the ultrasonic transducer according to the first embodiment of the present invention. In Fig. 7, the vertical axis shows the resonant frequency (kHz) of the first diaphragm 110, and the horizontal axis shows the longitudinal dimension L1 (mm) inside the frame body 120. As a condition for the simulation analysis, the lateral dimension L2 inside the frame body 120 was fixed at 2 mm.

[0028] 7, the resonance frequency of the first diaphragm 110 and the ultrasonic vibrator 130 was approximately constant at 130 kHz, regardless of changes in the longitudinal dimension L1 inside the frame body 120. In other words, the resonance frequency of the first diaphragm 110 is determined by the speed of sound in the first diaphragm 110 and the reflection of vibration with the frame body 120 as the fixed end, but regardless of the longitudinal dimension L1 inside the frame body 120, the influence of the short dimension L2 becomes dominant with respect to the reflection of vibration, and the state of reflection of vibration does not change even if the longitudinal dimension L1 increases.

[0029] Next, the results of a simulation analysis using the finite element method on the relationship between the sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer 100 and the longitudinal dimension L1 inside the frame body 120 will be described.

[0030] 8 is a graph showing a simulation analysis using the finite element method of the transition of the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer according to the first embodiment of the present invention when the longitudinal dimension is changed while the lateral dimension inside the frame body is fixed. In Fig. 8, the vertical axis shows the sound pressure (Pa) transmitted from the ultrasonic transducer 100, and the horizontal axis shows the longitudinal dimension L1 (mm) inside the frame body 120. As a simulation analysis condition, the lateral dimension L2 inside the frame body 120 was fixed to 2 mm, and the sound pressure (Pa) was calculated at a position 30 cm away in the third direction (Z-axis direction) from the first diaphragm 110 on the front side of the ultrasonic transducer 100.

[0031] 8, as the longitudinal dimension L1 inside the frame body 120 increases, the sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer 100 increases. This means that even when the longitudinal dimension of the vibration region of the first diaphragm 110 is increased, the entire vibration region of the first diaphragm 110 between the slits 110s vibrates. In other words, the area of ​​the vibration region can be increased by the amount that the vibration region of the first diaphragm 110 is longer, and as a result, the change in air pressure due to the vibration of the first diaphragm 110 can be increased, thereby obtaining a high sound pressure.

[0032] In this way, the ultrasonic transducer 100 according to this embodiment can increase the sound pressure while maintaining a substantially constant resonant frequency by increasing the longitudinal dimension of the vibration region of the first diaphragm 110. Furthermore, since there are nodal points at both ends in the longitudinal direction, the ends can be supported or fixed, making it easy to mount the ultrasonic transducer 100.

[0033] Here, an ultrasonic element array according to a first comparative example will be described, which obtains high sound pressure by arranging high-frequency ultrasonic elements side by side.

[0034] 9 is a perspective view showing the configuration of an ultrasonic element array according to a first comparative example. As shown in FIG. 9, in the ultrasonic element array according to the first comparative example, a plurality of ultrasonic elements 800 are arranged in a row at intervals from one another in the second direction (Y-axis direction). In such an ultrasonic element array, there are spaces between the ultrasonic elements 800 where no sound pressure is generated, resulting in low efficiency. Furthermore, because ultrasonic elements 800 with high frequencies of, for example, 100 kHz or more are small in size, it is time-consuming to configure an ultrasonic element array by arranging and mounting a plurality of ultrasonic elements 800.

[0035] The thickness of the first diaphragm 110 included in the ultrasonic transducer 100 according to an embodiment of the present invention will be described in detail below.

[0036] The first diaphragm 110 and the ultrasonic vibrator 130 resonate with each other in opposite phases, resulting in a vibration mode similar to that of a tuning fork. From the viewpoint of maintaining a physical balance between the first diaphragm 110 and the ultrasonic vibrator 130, it is preferable to satisfy the relationship 0.7CpTp / Cv≦Tv≦1.3CpTp / Cv, where Cv is the sound velocity of the shear wave of the first diaphragm 110, Cp is the sound velocity of the shear wave of the piezoelectric body 131, Tv is the thickness of the first diaphragm 110, and Tp is the thickness of the piezoelectric body 131. The sound velocity Cv of the shear wave of the first diaphragm 110 is determined by the material constituting the first diaphragm 110. The sound velocity Cp of the shear wave of the piezoelectric body 131 is determined by the material constituting the piezoelectric body 131. When multiple piezoelectric bodies 131 are stacked in the ultrasonic vibrator 130, the thickness dimension Tp of the piezoelectric body 131 is the sum of the thicknesses of the multiple piezoelectric bodies 131.

[0037] By satisfying the relationship 0.7CpTp / Cv≦Tv≦1.3CpTp / Cv, the physical balance between the first diaphragm 110 and the ultrasonic vibrator 130 during vibration can be maintained, and the amplitude of the resonant vibration of the first diaphragm 110 can be increased to increase the sound pressure and suppress vibration leakage. It is more preferable to satisfy the relationship Tv = CpTp / Cv. From the viewpoint of maintaining the physical balance, when Tp = 0.8, based on the relationship Tv = 0.8Cp / Cv, it is ideal for the thickness dimension Tv of the first diaphragm 110 to be 0.4.

[0038] Fig. 10 is a graph showing the relationship between the sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer and the thickness of the first diaphragm, which was analyzed by simulation using the finite element method. In Fig. 10, the vertical axis represents the sound pressure (Pa) transmitted from the ultrasonic transducer 100, and the horizontal axis represents the thickness (mm) of the first diaphragm. As a condition for the simulation analysis, the total thickness Tp of the two piezoelectric bodies 131 was set to 0.8 mm. As shown in Fig. 10, when the thickness of the first diaphragm 110 was 0.4 mm, the sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer was at its maximum.

[0039] Fig. 11 is a graph showing the relationship between the internal stress (normalized per sound pressure) in the third direction (Z-axis direction) generated in the ultrasonic transducer and the thickness of the first diaphragm, which was analyzed by simulation using the finite element method. In Fig. 11, the vertical axis shows the internal stress in the third direction (Z-axis direction) per sound pressure, and the horizontal axis shows the thickness (mm) of the first diaphragm.

[0040] As shown in FIG. 11 , the thinner the first diaphragm 110, the smaller the internal stress (normalized per sound pressure) in the third direction (Z-axis direction) generated in the ultrasonic transducer 100. In particular, when the thickness of the first diaphragm 110 was 0.24 mm or less, the internal stress (normalized per sound pressure) in the third direction (Z-axis direction) generated in the ultrasonic transducer 100 was significantly smaller. By reducing the internal stress (normalized per sound pressure) in the third direction (Z-axis direction) generated in the ultrasonic transducer 100, it is possible to prevent cracks from occurring due to internal stress at the joint between the first diaphragm 110 and the frame 120 and at the joint between the frame 120 and the ultrasonic vibrator 130. On the other hand, if the thickness of the first diaphragm 110 is thinner than 0.1 mm, the first diaphragm 110 becomes too soft and is no longer suitable as a vibrator for emitting ultrasonic waves.

[0041] That is, from the viewpoint of generating ultrasonic waves with high sound pressure while suppressing the occurrence of cracks due to internal stress, it is preferable to satisfy the relationship 0.25CpTp / Cv≦Tv≦0.6CpTp / Cv. In this embodiment, by setting the thickness of the first diaphragm 110 to be 0.1 mm or more and 0.2 mm or less, it is possible to drive the ultrasonic transducer 100 in a state where the internal stress (a value normalized per sound pressure) generated in the ultrasonic transducer 100 in the third direction (Z-axis direction) is low.

[0042] Here, we will explain the results of a simulation analysis using the finite element method on the drive efficiency of an ultrasonic transducer when the ultrasonic vibrator is a bimorph piezoelectric vibrator and when it is a unimorph piezoelectric vibrator. As simulation analysis conditions, in order to match the conditions with the bimorph ultrasonic vibrator 130 shown in Figure 1, the unimorph ultrasonic vibrator also has a structure in which two piezoelectric bodies 131 are bonded together as shown in Figure 1, and a drive voltage is applied to only one of the two piezoelectric bodies 131, while the other piezoelectric body 131 serves as a second diaphragm to which no drive voltage is applied.

[0043] Specifically, in the ultrasonic transducer of the first modified example, a drive voltage is applied to the piezoelectric body 131 adjacent to the frame body 120, and the piezoelectric body 131 not adjacent to the frame body 120 serves as a second diaphragm to which no drive voltage is applied. In the first modified example, the second diaphragm is provided on the side of the piezoelectric body 131 to which the drive voltage is applied, opposite to the frame body side.

[0044] In the ultrasonic transducer of the second modified example, a drive voltage is applied to the piezoelectric body 131 that is not adjacent to the frame body 120, and the piezoelectric body 131 that is adjacent to the frame body 120 serves as a second vibration plate to which no drive voltage is applied. In the second modified example, the second vibration plate is provided on the frame body side of the piezoelectric body 131 to which the drive voltage is applied.

[0045] 12 is a graph showing the relationship between the displacement of the first diaphragm 110 and the frequency of the ultrasonic vibrator in the ultrasonic transducer according to this embodiment, the ultrasonic transducer according to the first modification, and the ultrasonic transducer according to the second modification, obtained by simulation analysis using the finite element method. In Fig. 12, the vertical axis represents the displacement of the first diaphragm 110, and the horizontal axis represents the frequency (kHz) of the ultrasonic vibrator 130. The data for the ultrasonic transducer 100 according to this embodiment is shown by a solid line, the data for the ultrasonic transducer according to the first modification is shown by a dotted line, and the data for the ultrasonic transducer according to the second modification is shown by a dashed line.

[0046] 12, when the displacement of the first diaphragm 110 in the ultrasonic transducer 100 according to this embodiment is taken as 100%, the displacement of the first diaphragm 110 in the ultrasonic transducer according to the first modified example is 85.6%, and the displacement of the first diaphragm 110 in the ultrasonic transducer according to the second modified example is 23.5%. When the free capacitance of the piezoelectric element in the ultrasonic transducer 100 according to this embodiment is taken as 100%, the free capacitance of the piezoelectric element in the ultrasonic transducer according to the first modified example is 53.5%, and the free capacitance of the piezoelectric element in the ultrasonic transducer according to the second modified example is 60.5%.

[0047] When the piezoelectric element is driven with the same voltage, the smaller the free capacitance of the piezoelectric element, the smaller the power consumption. The ultrasonic transducer according to the first modification example can displace the first diaphragm 110 by nearly 80% of the power consumption of the ultrasonic transducer 100 according to the present embodiment, and is therefore found to be highly efficient.

[0048] In this embodiment, the ultrasonic vibrator 130 is a so-called series-type bimorph piezoelectric vibrator, but the ultrasonic vibrator 130 may be another type of piezoelectric vibrator. Hereinafter, an ultrasonic vibrator of an ultrasonic transducer according to a modification of the first embodiment of the present invention will be described.

[0049] Fig. 13 is a cross-sectional view showing the configuration of an ultrasonic vibrator according to a third modification. As shown in Fig. 13, an ultrasonic vibrator 130a according to the third modification is a piezoelectric element including two stacked piezoelectric bodies 131. The polarization directions Dp of the two piezoelectric bodies 131 are the same. The ultrasonic vibrator 130a is a so-called parallel bimorph piezoelectric vibrator.

[0050] Fig. 14 is a cross-sectional view showing the configuration of an ultrasonic vibrator according to a fourth modification. As shown in Fig. 14, an ultrasonic vibrator 130b according to the fourth modification is a piezoelectric element including four stacked piezoelectric bodies 131. The polarization directions Dp of the two outermost piezoelectric bodies 131 of the four piezoelectric bodies 131 face one side of the first direction (Z-axis direction), and the polarization directions Dp of the two innermost piezoelectric bodies 131 of the four piezoelectric bodies 131 face the other side of the first direction (Z-axis direction). The ultrasonic vibrator 130b is a so-called multimorph piezoelectric vibrator.

[0051] Fig. 15 is a cross-sectional view showing the configuration of an ultrasonic vibrator according to a fifth modified example. As shown in Fig. 15, an ultrasonic vibrator 130c according to the fifth modified example is a piezoelectric element including one piezoelectric body 131. Specifically, the piezoelectric body 131 is sandwiched between a first electrode 132 and a second vibration plate 135 made of metal. The ultrasonic vibrator 130c is a so-called unimorph piezoelectric vibrator.

[0052] Fig. 16 is a longitudinal cross-sectional view showing the configuration of an ultrasonic transducer according to a sixth modified example of the first embodiment of the present invention. As shown in Fig. 16, the ultrasonic transducer 100a according to the sixth modified example of the first embodiment of the present invention includes a first diaphragm 110, a frame body 120a, and an ultrasonic vibrator 130. The frame body 120a has a cylindrical shape with a bottom. The frame body 120a is made of metal. A piezoelectric body 131 is attached to the outer bottom surface of the frame body 120a, thereby forming an ultrasonic vibrator that is a unimorph type piezoelectric vibrator.

[0053] Here, the position and size of the slits will be described in detail. FIG. 17 is a perspective view showing a displacement state, simulated and analyzed using the finite element method, when an ultrasonic transducer according to a seventh modification of the first embodiment of the present invention, in which the positions of the two slits are shifted by 2 mm toward the center in the longitudinal direction inside the frame body, transmits or receives ultrasonic waves. In the ultrasonic transducer 100b according to the seventh modification of the first embodiment of the present invention, the slit 110sb is formed from a position 2 mm inward in the second direction (Y-axis direction) from a position on the edge of the inner peripheral surface of the frame body 120 in the second direction (Y-axis direction) to a position 0.5 mm inward. That is, the length dimension of each of the two slits 110s was 20 mm and the width dimension was 0.5 mm. The other simulation analysis conditions were the same as those of the ultrasonic transducer 100 shown in FIG. 5.

[0054] 17, in an ultrasonic transducer 100b according to a seventh modification of the first embodiment of the present invention, a portion of the first diaphragm 110 that is located above the internal space IS inside the frame body 120 and between the slits 110sb in the second direction (Y-axis direction) becomes a vibration region that resonates. In the first diaphragm 110, a middle portion 110c that is located at the middle in the longitudinal direction inside the frame body 120 is displaced greatly, and an end portion 110e that is located outside the slits 110sb in the second direction (Y-axis direction) is hardly displaced.

[0055] Therefore, in the ultrasonic transducer 100b according to the seventh modification of the first embodiment of the present invention, the area of ​​the vibration region of the first diaphragm 110 is reduced, and the change in air pressure due to the vibration of the first diaphragm 110 is reduced, resulting in a lower sound pressure, compared to the ultrasonic transducer 100 according to the first embodiment of the present invention. Therefore, as in the ultrasonic transducer 100 according to the first embodiment of the present invention, it is preferable that the slits 110s are formed near positions on the edge in the second direction (Y-axis direction) on the inner circumferential surface of the frame body 120.

[0056] It is preferable that the length dimension of the slit 110s in the first direction (X-axis direction) be equal to or greater than the short dimension L2 in the first direction (X-axis direction) inside the frame body 120, from the viewpoint of preventing fixed ends from appearing at both ends in the second direction (Y-axis direction) in the vibration region where the first vibration plate 110 resonates.

[0057] The width dimension of the slits 110s in the second direction (Y-axis direction) is preferably as small as possible from the viewpoint of increasing the area of ​​the vibration region of the first diaphragm 110. When the first diaphragm 110 and the frame 120 are joined with an adhesive, the width dimension of the slits 110s in the second direction (Y-axis direction) is preferably 0.4 mm or more and 0.6 mm or less to prevent the slits 110s formed near the edge of the inner peripheral surface of the frame 120 in the second direction (Y-axis direction) from being blocked by the adhesive that has seeped into the slits 110s. Alternatively, the slits 110s are preferably formed with a width dimension of 0.2 mm or more and 0.4 mm or less inward in the second direction (Y-axis direction) from a position 0.2 mm inward in the second direction (Y-axis direction) from the edge of the inner peripheral surface of the frame 120 in the second direction (Y-axis direction). Furthermore, when the slit 110s is formed at a position on the edge of the inner surface of the frame body 120 in the second direction (Y-axis direction), the amount of stacking misalignment between the first vibration plate 110 and the frame body 120 and the amount of adhesive that has seeped out inside the frame body 120 can be visually confirmed through the slit 110s, and therefore the slit 110s can be used to improve the assembly accuracy of the ultrasonic transducer 100.

[0058] The ultrasonic transducer 100 according to the first embodiment of the present invention includes a first diaphragm 110, at least one frame body 120, and at least one ultrasonic vibrator 130. The at least one frame body 120 extends in the longitudinal direction and is joined to the first diaphragm 110. The at least one ultrasonic vibrator 130 is attached to the at least one frame body 120 and faces the first diaphragm 110 at an interval. The first diaphragm 110 resonates in an opposite phase to the at least one ultrasonic vibrator 130 in a direction perpendicular to the first diaphragm 110. A dimension L1 in the longitudinal direction inside the at least one frame body 120 is greater than a dimension L2 in a lateral direction perpendicular to the longitudinal direction inside the at least one frame body 120. The ultrasonic transducer 100 has at least one opening that connects an external space ES on the opposite side of the first vibration plate 110 from the at least one frame body 120 with an internal space IS inside the at least one frame body 120.

[0059] As a result, the internal space IS and the external space ES are connected through the opening, which reduces pressure changes in the internal space IS when, for example, the adhesive that bonds the first diaphragm 110 and the frame body 120 is heated and hardened, thereby preventing an increase in internal stress within the ultrasonic transducer 100. Furthermore, the area adjacent to the opening becomes the free end of the resonantly vibrating first diaphragm 110 and is therefore more likely to displace, thereby reducing internal stress generated within the resonantly vibrating first diaphragm 110. Therefore, in the ultrasonic transducer 100, it is possible to increase the sound pressure level while reducing internal stress with a simple and compact configuration.

[0060] In the ultrasonic transducer 100 according to the first embodiment of the present invention, at least one opening is formed in the first diaphragm 110. This makes it possible to appropriately set the position where the opening is provided.

[0061] In the ultrasonic transducer 100 according to the first embodiment of the present invention, at least one opening is a slit 110s extending in the short-side direction, which prevents a reduction in the area of ​​the vibration region of the resonant vibration due to the provision of the slit 110s, thereby enabling a high sound pressure to be obtained.

[0062] In the ultrasonic transducer 100 according to the first embodiment of the present invention, at least one opening has a short-side dimension L2 or greater in the first direction (X-axis direction) inside at least one frame 120. This allows the area adjacent to the opening to be the free end of the first diaphragm 110 that is vibrating in resonance, making it easier for the first diaphragm 110 to displace. This in turn makes it possible to increase the sound pressure level.

[0063] In the ultrasonic transducer 100 according to the first embodiment of the present invention, the two openings are respectively open at both ends in the second direction (Y-axis direction) inside at least one frame body 120. This makes it possible to maintain the resonance frequencies of the first diaphragm 110 and the ultrasonic vibrator 130 substantially constant regardless of the longitudinal dimension L1 inside the frame body 120.

[0064] In a parametric speaker including the ultrasonic transducer 100 according to the first embodiment of the present invention, it is possible to reproduce audible sound by modulating the ultrasonic waves emitted from the ultrasonic transducer 100 through modulation driving of the ultrasonic transducer 100. Modulation methods include an AM modulation method (amplitude modulation method) and an FM modulation method (frequency modulation method).

[0065] In the ultrasonic transducer 100 according to the first embodiment of the present invention, the resonant frequency of the first diaphragm 110 and the ultrasonic vibrator 130 is 100 kHz or higher. As a result, as will be described later, when the resonant frequency is 100 kHz or higher, the attenuation of sound waves over the propagation distance is large, and therefore, a parametric speaker including the ultrasonic transducer 100 can reproduce audible sound only in a limited space.

[0066] In the ultrasonic transducer 100 according to the first embodiment of the present invention, when the sound velocity of the shear wave in the first diaphragm 110 is Cv, the sound velocity of the shear wave in the piezoelectric body 131 is Cp, the thickness dimension of the first diaphragm 110 is Tv, and the thickness dimension of the piezoelectric body 131 is Tp, the relationship 0.25CpTp / Cv≦Tv≦0.6CpTp / Cv is satisfied. This makes it possible to drive the ultrasonic transducer 100 in a state where the internal stress (a value normalized per sound pressure) in the third direction (Z-axis direction) generated in the ultrasonic transducer 100 is low. Consequently, it is possible to generate ultrasonic waves with high sound pressure while suppressing the occurrence of cracks due to internal stress at each of the joint between the first diaphragm 110 and the frame body 120 and the joint between the frame body 120 and the ultrasonic vibrator 130.

[0067] In the ultrasonic transducer 100 according to the first embodiment of the present invention, the relationship 0.7CpTp / Cv≦Tv≦1.3CpTp / Cv is satisfied, where Cv is the sound velocity of the shear wave in the first diaphragm 110, Cp is the sound velocity of the shear wave in the piezoelectric body 131, Tv is the thickness of the first diaphragm 110, and Tp is the thickness of the piezoelectric body 131. This allows the physical balance between the first diaphragm 110 and the ultrasonic vibrator 130 to be maintained during vibration, and increases the amplitude of the resonant vibration of the first diaphragm 110, thereby increasing the sound pressure and suppressing vibration leakage.

[0068] In the first modified example of the ultrasonic transducer 100 according to the first embodiment of the present invention, the ultrasonic vibrator is a unimorph piezoelectric vibrator, and a second diaphragm is provided on the side opposite to the frame body side of the piezoelectric body 131. This makes it possible to maintain a high displacement of the first diaphragm 110 while reducing power consumption, thereby improving the efficiency of the ultrasonic transducer.

[0069] (Embodiment 2) An ultrasonic transducer according to embodiment 2 of the present invention will be described below with reference to the drawings. The ultrasonic transducer according to embodiment 2 of the present invention differs from the ultrasonic transducer according to embodiment 1 of the present invention in that a plurality of ultrasonic vibrators are arranged in an array, and therefore, description of the configuration that is the same as that of the ultrasonic transducer according to embodiment 1 of the present invention will not be repeated.

[0070] Fig. 18 is a side view showing the configuration of an ultrasonic transducer according to embodiment 2 of the present invention, Fig. 19 is a rear view of the ultrasonic transducer shown in Fig. 18 as seen from the direction of arrow XIX.

[0071] 18 and 19 , in an ultrasonic transducer 200 according to embodiment 2 of the present invention, ultrasonic transducers 100 according to embodiment 1 arranged in an array in a first direction (X-axis direction) are integrally configured. The ultrasonic transducer 200 includes a first diaphragm 210, a plurality of frame bodies 220, and a plurality of ultrasonic vibrators 130. A plurality of frame bodies 220 are bonded to the first diaphragm 210, and a plurality of ultrasonic vibrators 130 are bonded to the plurality of frame bodies 220, respectively.

[0072] Here, a description will be given of a manufacturing method of the ultrasonic transducer 200. Fig. 20 is an exploded perspective view showing a stacked state in the process of stacking and bonding the components of the ultrasonic transducer according to the second embodiment of the present invention.

[0073] 20 , the first diaphragm 210 has a flat plate shape and has a plurality of slits 211 extending in the second direction (Y-axis direction) formed at intervals in the first direction (X-axis direction). The first diaphragm 210 has a plurality of slits 210s formed therein as a plurality of openings that connect the external space on the opposite side of the first diaphragm 210 from the plurality of frame bodies 220 with the internal space inside the plurality of frame bodies 220. The positional relationship between the frame body 220 and the slits 210s is the same as the positional relationship between the frame body 120 and the slits 110s in the first embodiment.

[0074] The first diaphragm 210 is made of an aluminum alloy such as aluminum-containing duralumin, or a metal such as stainless steel. In this embodiment, the first diaphragm 210 is made of stainless steel. The plurality of slits 211 and the plurality of slits 210s are formed by etching, cutting, or the like.

[0075] Each of the multiple frame bodies 220 has a rectangular ring shape. Each of the multiple frame bodies 220 has a short side direction along a first direction (X-axis direction) and a long side direction along a second direction (Y-axis direction). Each of the multiple frame bodies 220 extends in the second direction (Y-axis direction). The axial direction of each of the multiple frame bodies 220 is along a third direction (Z-axis direction). Each of the multiple frame bodies 220 has a pair of long side portions 221 extending in the second direction (Y-axis direction) and a pair of short side portions 222 extending in the first direction (X-axis direction). The shortest distance between the long side portions 221 is greater than the shortest distance between the short side portions 222.

[0076] The multiple frame bodies 220 are arranged side by side in a first direction (X-axis direction). A slit 223 is formed between adjacent frame bodies 220 in the first direction (X-axis direction). The multiple slits 223 are formed by etching, cutting, or the like. Adjacent long side portions 221 of adjacent frame bodies 220 in the first direction (X-axis direction) are separated from each other by the slits 223.

[0077] The frame bodies 220 adjacent to each other in the first direction (X-axis direction) are connected to each other at the short side portions 222. That is, among the multiple frame bodies 220, the frame bodies 220 adjacent to each other in the short side direction are connected to each other at both ends in the longitudinal direction.

[0078] Each of the plurality of frame bodies 220 is formed from a metal such as an aluminum alloy or stainless steel, glass epoxy, resin, etc. In this embodiment, the plurality of frame bodies 220 are formed from a single thin plate, but this is not limiting, and the plurality of frame bodies 220, each formed from a plurality of thin plates, may be integrated by joining the short side portions 222 of the frame bodies 220 together.

[0079] In this embodiment, each of the plurality of ultrasonic vibrators 130 includes two stacked piezoelectric bodies 131. As shown in Fig. 20, the two piezoelectric bodies 131 constituting the plurality of ultrasonic vibrators 130 are stacked and joined in the form of two thin plates.

[0080] 21 is a plan view showing the positional relationship in the first direction (X-axis direction) in the process of cutting the piezoelectric body of the ultrasonic transducer according to embodiment 2 of the present invention. In FIG. 21, only one piezoelectric body 131 is shown.

[0081] 21 , the slits 211 and 223 are arranged at the same position in the first direction (X-axis direction) so as to overlap with each other in the third direction (Z-axis direction). The piezoelectric body 131 is cut and divided by a dicer or the like along a plurality of cut lines LC extending in the second direction (Y-axis direction) so as to overlap with the slits 211 and 223 in the third direction (Z-axis direction). As a result, the ultrasonic transducer 200 shown in FIGS. 18 and 19 is formed.

[0082] FIG. 22 is a perspective view showing a displacement state obtained by simulation analysis using the finite element method when the ultrasonic transducer according to the second embodiment of the present invention transmits or receives ultrasonic waves.

[0083] 22 , the portions of the first diaphragm 210 that are located above the internal space inside each frame 220 and between the slits 210s in the second direction (Y-axis direction) become vibration regions that resonate. The longitudinal dimension of the vibration region of the first diaphragm 210 is the dimension between the slits 210s in the second direction (Y-axis direction), and the lateral dimension of the vibration region of the first diaphragm 210 is the same as the lateral dimension inside each frame 220. In the first diaphragm 210, intermediate portions 210c located at the middle of the longitudinal direction inside each frame 220 are displaced significantly, while end portions 210e located on both ends of the longitudinal direction inside each frame 220 are hardly displaced.

[0084] The ultrasonic transducer 100 according to the first embodiment has nodal points at both ends in the second direction (Y-axis direction), which is the longitudinal direction, and therefore even if the ultrasonic transducers 100 according to the first embodiment are connected to each other at the both ends to form an array to form the ultrasonic transducer 200 according to the second embodiment, the resonant vibration of each ultrasonic transducer 100 is not inhibited. Therefore, by increasing the number of ultrasonic transducers 100 that form the ultrasonic transducer 200 according to the second embodiment, the sound pressure level can be easily increased.

[0085] In a parametric speaker equipped with the ultrasonic transducer 200 according to the second embodiment of the present invention, it is possible to modulate the ultrasonic waves emitted from the ultrasonic transducer 200 by modulating the ultrasonic waves to reproduce audible sounds.

[0086] Here, the results of a simulation analysis using the finite element method on the relationship between the frequency of ultrasonic waves and the attenuation of the sound pressure level due to the propagation distance will be described. As the simulation analysis conditions, the finite element method was used to simulate and analyze the transition of attenuation due to the propagation distance of a 4 kHz audible sound reproduced from ultrasonic waves with a resonance frequency of 146 kHz transmitted from the ultrasonic transducer 200 according to this embodiment, and a 4 kHz audible sound reproduced from ultrasonic waves with a resonance frequency of 40 kHz transmitted from the ultrasonic element array according to the second comparative example.

[0087] Fig. 23 is a perspective view showing the configuration of an ultrasonic element array according to Comparative Example 2. As shown in Fig. 23, in the ultrasonic element array according to Comparative Example 2, 50 ultrasonic elements 900 are arranged in a matrix at intervals from one another.

[0088] Fig. 24 is a graph showing actual measurements of the transition of attenuation of sound pressure level over propagation distance in the ultrasonic transducer according to this embodiment and the ultrasonic transducer according to the second comparative example. In Fig. 24, the vertical axis represents sound pressure level (dB) and the horizontal axis represents propagation distance (cm). The solid line represents data for the ultrasonic transducer 200 according to this embodiment, and the dotted line represents data for the ultrasonic transducer according to the second comparative example. The sound pressure level is a value normalized by setting the sound pressure level of an audible sound with a frequency of 4 kHz at a point 30 cm away in the third direction (Z-axis direction) from the front of each of the ultrasonic transducer and the ultrasonic element array to 0 dB.

[0089] 24, the audible sound reproduced from the ultrasonic waves having a resonant frequency of 146 kHz transmitted from the ultrasonic transducer 200 according to this embodiment was attenuated more due to the propagation distance than the audible sound reproduced from the ultrasonic waves having a resonant frequency of 40 kHz transmitted from the ultrasonic element array according to the second comparative example. This is because high-frequency ultrasonic waves are easily absorbed by the air as heat, and therefore audible sounds reproduced using high-frequency ultrasonic waves as carrier waves are attenuated more due to the propagation distance.

[0090] In this way, a parametric speaker including the ultrasonic transducer 200 according to this embodiment, which transmits ultrasonic waves at high frequencies of 100 kHz or higher, can reproduce audible sound only in a limited space, suppressing sound from traveling unnecessarily far and sound leakage due to unnecessary reflections. Furthermore, the ultrasonic transducer 200 can increase the attenuation of audible sound over the propagation distance without providing a configuration for transmitting an opposite-phase carrier wave as in Patent Document 2, allowing for a simple and compact configuration. Furthermore, because ultrasonic waves at high frequencies of 100 kHz or higher are outside the audible range of animals such as dogs and cats, the effects on these animals can be suppressed.

[0091] As shown in Figure 24, in order for audible sound to attenuate after a propagation distance of 30 cm, the distance must be kept within 30 cm. The Rayleigh distance R0 is given by R0 = (k × a 2) / 2, where k is the wave number and a is the radius of the sound source. Therefore, if the speed of sound in air is 340 m / s, when the frequency of the ultrasonic waves is 100 kHz, the longitudinal dimension of the vibration region of first diaphragm 210 is 36 mm or less, when the frequency of the ultrasonic waves is 150 kHz, the longitudinal dimension of the vibration region of first diaphragm 210 is 29.4 mm or less, and when the frequency of the ultrasonic waves is 200 kHz, the longitudinal dimension of the vibration region of first diaphragm 210 is 25.5 mm or less.

[0092] The ultrasonic transducer 200 according to this embodiment can be used as a phased array system.

[0093] In the ultrasonic transducer 200 according to the second embodiment of the present invention, at least one frame body 220 is arranged in a plurality of rows in the short side direction and joined to the first vibration plate 210, and adjacent frame bodies 220 in the short side direction of at least one frame body 220 are connected to each other at both ends in the long side direction. This makes it possible to easily increase the sound pressure level.

[0094] (Embodiment 3) An ultrasonic transducer according to embodiment 3 of the present invention will be described below with reference to the drawings. The ultrasonic transducer according to embodiment 3 of the present invention differs from the ultrasonic transducer according to embodiment 1 of the present invention in the positions and number of openings, and therefore, description of the configuration that is the same as that of the ultrasonic transducer according to embodiment 1 of the present invention will not be repeated.

[0095] 25 is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to embodiment 3 of the present invention transmits or receives ultrasonic waves. As shown in FIG. 25 , in the ultrasonic transducer 300 according to embodiment 3 of the present invention, an intermediate slit 110cs is formed in the first diaphragm 110 as an opening located at the center of the longitudinal direction inside the frame body 120. The length dimension of the intermediate slit 110cs in the first direction (X-axis direction) is the same as the short side dimension L2 in the first direction (X-axis direction) inside the frame body 120. The width dimension of the intermediate slit 110cs in the second direction (Y-axis direction) is 0.2 mm or more and 0.6 mm or less. Other simulation analysis conditions were the same as those of the simulation analysis shown in FIG. 5 .

[0096] Fig. 26 is a graph showing a simulation analysis using the finite element method of the transition of the resonant frequency of the first diaphragm when the longitudinal dimension is changed while the lateral dimension inside the frame body is fixed in the ultrasonic transducer according to the third embodiment of the present invention. In Fig. 26, the vertical axis shows the resonant frequency (kHz) of the first diaphragm 110, and the horizontal axis shows the longitudinal dimension L1 (mm) inside the frame body 120. As a condition for the simulation analysis, the lateral dimension L2 inside the frame body 120 was fixed at 2 mm.

[0097] 26, the resonance frequency of the first diaphragm 110 and the ultrasonic vibrator 130 was approximately constant at 130 kHz, regardless of changes in the longitudinal dimension L1 inside the frame body 120. In other words, the resonance frequency of the first diaphragm 110 is determined by the speed of sound in the first diaphragm 110 and the reflection of vibration with the frame body 120 as the fixed end, but regardless of the longitudinal dimension L1 inside the frame body 120, the influence of the short dimension L2 becomes dominant with respect to the reflection of vibration, and the state of reflection of vibration does not change even if the longitudinal dimension L1 increases.

[0098] 27 is a graph showing a simulation analysis using the finite element method of the transition of the sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer according to the third embodiment of the present invention when the longitudinal dimension is changed while the lateral dimension inside the frame body is fixed. In Fig. 27, the vertical axis shows the sound pressure (Pa) transmitted from the ultrasonic transducer 100, and the horizontal axis shows the longitudinal dimension L1 (mm) inside the frame body 120. As a simulation analysis condition, the lateral dimension L2 inside the frame body 120 was fixed to 2 mm, and the sound pressure (Pa) was calculated at a position 30 cm away in the third direction (Z-axis direction) from the first diaphragm 110 on the front side of the ultrasonic transducer 300.

[0099] 27, as the longitudinal dimension L1 inside the frame body 120 increases, the sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer 300 increases. This means that even when the longitudinal dimension of the vibration region of the first diaphragm 110 is increased, the entire vibration region of the first diaphragm 110 between the slits 110s vibrates. In other words, the area of ​​the vibration region can be increased by the amount that the vibration region of the first diaphragm 110 is longer, and as a result, the change in air pressure due to the vibration of the first diaphragm 110 can be increased, thereby obtaining a high sound pressure.

[0100] In this way, also in the ultrasonic transducer 300 according to this embodiment, by increasing the longitudinal dimension of the vibration region of the first diaphragm 110, it is possible to increase the sound pressure while maintaining the resonance frequency substantially constant.

[0101] The intermediate slit may be opened at a position shifted from the center in the longitudinal direction inside the frame body 120. Fig. 28 is a perspective view showing a displacement state simulated by a finite element method when an ultrasonic transducer according to a modification of the third embodiment of the present invention transmits or receives ultrasonic waves. As shown in Fig. 28, in an ultrasonic transducer 300a according to a modification of the third embodiment of the present invention, an intermediate slit 110as is formed in the first diaphragm 110 as an opening that opens at a position shifted from the center in the longitudinal direction inside the frame body 120 toward the end.

[0102] (Embodiment 4) An ultrasonic transducer according to embodiment 4 of the present invention will be described below with reference to the drawings. The ultrasonic transducer according to embodiment 4 of the present invention differs from the ultrasonic transducer according to embodiment 1 of the present invention in the positions and number of openings, and therefore, description of the configuration that is the same as that of the ultrasonic transducer according to embodiment 1 of the present invention will not be repeated.

[0103] Fig. 29 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer according to the fourth embodiment of the present invention transmits or receives ultrasonic waves. As shown in Fig. 29, in the ultrasonic transducer 400 according to the fourth embodiment of the present invention, one opening is opened at one of both longitudinal end portions inside the frame body 120. In other words, only one slit 110s is formed. The other simulation analysis conditions were the same as those of the simulation analysis shown in Fig. 5.

[0104] Fig. 30 is a graph showing a simulation analysis using the finite element method of the transition of the resonant frequency of the first diaphragm when the longitudinal dimension is changed while the lateral dimension inside the frame body is fixed in the ultrasonic transducer according to embodiment 4 of the present invention. In Fig. 30, the vertical axis shows the resonant frequency (kHz) of the first diaphragm 110, and the horizontal axis shows the longitudinal dimension L1 (mm) inside the frame body 120. As a condition for the simulation analysis, the lateral dimension L2 inside the frame body 120 was fixed at 2 mm.

[0105] 30, in the range where the longitudinal dimension L1 inside the frame body 120 is more than twice the lateral dimension L2, the resonant frequency of the first diaphragm 110 and the ultrasonic vibrator 130 is approximately constant at 130 kHz. In other words, the resonant frequency of the first diaphragm 110 is determined by the speed of sound in the first diaphragm 110 and the reflection of vibration with the frame body 120 as the fixed end, but when the longitudinal dimension L1 inside the frame body 120 is more than twice the lateral dimension L2, the influence of the lateral dimension L2 becomes dominant with respect to the reflection of vibration, and even if the longitudinal dimension L1 becomes further larger, the state of reflection of vibration does not change.

[0106] 31 is a graph showing a simulation analysis using the finite element method of the transition of the sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer according to the fourth embodiment of the present invention when the longitudinal dimension is changed while the lateral dimension inside the frame body is fixed. In Fig. 31, the vertical axis shows the sound pressure (Pa) transmitted from the ultrasonic transducer 100, and the horizontal axis shows the longitudinal dimension L1 (mm) inside the frame body 120. As a simulation analysis condition, the lateral dimension L2 inside the frame body 120 was fixed to 2 mm, and the sound pressure (Pa) was calculated at a position 30 cm away in the third direction (Z-axis direction) from the first diaphragm 110 on the front side of the ultrasonic transducer 400.

[0107] 31 , as the longitudinal dimension L1 inside the frame body 120 increases, the sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer 400 increases. This means that even when the longitudinal dimension of the vibration region of the first diaphragm 110 is increased, the entire vibration region of the first diaphragm 110 vibrates. In other words, the area of ​​the vibration region can be increased by the amount that the vibration region of the first diaphragm 110 is longer, and as a result, the change in air pressure due to the vibration of the first diaphragm 110 can be increased, thereby obtaining a high sound pressure.

[0108] In this way, in the ultrasonic transducer 400 according to this embodiment, by making the longitudinal dimension of the vibration region of the first vibration plate 110 more than twice the short dimension, the sound pressure can be increased while maintaining the resonant frequency approximately constant.

[0109] (Embodiment 5) An ultrasonic transducer according to embodiment 5 of the present invention will be described below with reference to the drawings. The ultrasonic transducer according to embodiment 5 of the present invention differs from the ultrasonic transducer according to embodiment 1 of the present invention in the positions of the openings and the number of openings, and therefore, the description of the configuration that is the same as that of the ultrasonic transducer according to embodiment 1 of the present invention will not be repeated.

[0110] 32 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer according to the fifth embodiment of the present invention transmits or receives ultrasonic waves. As shown in FIG. 32, in the ultrasonic transducer 500 according to the fifth embodiment of the present invention, one opening is opened in the center of the longitudinal direction inside the frame body 120. That is, only the intermediate slit 110cs is formed. The other simulation analysis conditions were the same as those of the simulation analysis shown in FIG. 5.

[0111] Fig. 33 is a graph showing a simulation analysis using the finite element method of the transition of the resonant frequency of the first diaphragm when the longitudinal dimension is changed while the lateral dimension inside the frame body is fixed in the ultrasonic transducer according to the fifth embodiment of the present invention. In Fig. 33, the vertical axis shows the resonant frequency (kHz) of the first diaphragm 110, and the horizontal axis shows the longitudinal dimension L1 (mm) inside the frame body 120. As a condition for the simulation analysis, the lateral dimension L2 inside the frame body 120 was fixed at 2 mm.

[0112] 33, when the longitudinal dimension L1 inside the frame body 120 is four times or more the lateral dimension L2, the resonance frequency of the first diaphragm 110 and the ultrasonic vibrator 130 is approximately constant at 130 kHz. In other words, the resonance frequency of the first diaphragm 110 is determined by the speed of sound in the first diaphragm 110 and the reflection of vibration with the frame body 120 as the fixed end, but when the longitudinal dimension L1 inside the frame body 120 is four times or more the lateral dimension L2, the influence of the lateral dimension L2 becomes dominant with respect to the reflection of vibration, and even if the longitudinal dimension L1 becomes even larger, the state of reflection of vibration does not change.

[0113] Fig. 34 is a graph showing a simulation analysis using the finite element method of the transition of the sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer according to embodiment 5 of the present invention when the longitudinal dimension is changed while the lateral dimension inside the frame body is fixed. In Fig. 34, the vertical axis shows the sound pressure (Pa) transmitted from the ultrasonic transducer 100, and the horizontal axis shows the longitudinal dimension L1 (mm) inside the frame body 120. As a simulation analysis condition, the lateral dimension L2 inside the frame body 120 was fixed to 2 mm, and the sound pressure (Pa) was calculated at a position 30 cm away in the third direction (Z-axis direction) from the first diaphragm 110 on the front side of the ultrasonic transducer 500.

[0114] 34, as the longitudinal dimension L1 inside the frame body 120 increases, the sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer 400 increases. This means that even when the longitudinal dimension of the vibration region of the first diaphragm 110 is increased, the entire vibration region of the first diaphragm 110 vibrates. In other words, the area of ​​the vibration region can be increased by the amount that the vibration region of the first diaphragm 110 is longer, and as a result, the change in air pressure due to the vibration of the first diaphragm 110 can be increased, thereby obtaining a high sound pressure.

[0115] In this way, in the ultrasonic transducer 500 according to this embodiment, by making the longitudinal dimension of the vibration region of the first vibration plate 110 four or more times larger than the short dimension, the sound pressure can be increased while maintaining the resonant frequency approximately constant.

[0116] The intermediate slit may be opened at a position shifted from the center in the longitudinal direction inside the frame body 120. Fig. 35 is a perspective view showing a displacement state simulated by analysis using the finite element method when an ultrasonic transducer according to a modification of the fifth embodiment of the present invention is transmitting or receiving ultrasonic waves. As shown in Fig. 35, in an ultrasonic transducer 500a according to a modification of the fifth embodiment of the present invention, an intermediate slit 110as is formed in the first diaphragm 110 as an opening that opens at a position shifted from the center in the longitudinal direction inside the frame body 120 toward the end.

[0117] (Embodiment 6) An ultrasonic transducer according to embodiment 6 of the present invention will be described below with reference to the drawings. The ultrasonic transducer according to embodiment 6 of the present invention differs from the ultrasonic transducer according to embodiment 1 of the present invention in that the minimum dimension of the ultrasonic vibrator in the second direction (Y-axis direction) is smaller than the inner longitudinal dimension of the frame body, and therefore the description of the same configuration as the ultrasonic transducer according to embodiment 1 of the present invention will not be repeated.

[0118] 36 is an exploded perspective view showing the configuration of an ultrasonic transducer according to embodiment 6 of the present invention. As shown in Fig. 36, an ultrasonic transducer 600 according to embodiment 6 of the present invention includes a first diaphragm 110, a frame body 120, and an ultrasonic vibrator 630.

[0119] Figure 37 is a view of the ultrasonic transducer of Figure 36 as viewed from the direction of arrow XXXVII. As shown in Figure 37, the ultrasonic vibrator 630 has a rectangular outer shape. The longitudinal dimension L1 in the second direction (Y-axis direction) inside the frame body 120 is greater than the minimum dimension Lm of the ultrasonic vibrator 630 in the second direction (Y-axis direction). Here, when the ultrasonic vibrator 630 has a layered structure in which multiple piezoelectric elements are stacked, the minimum dimension Lm in the second direction (Y-axis direction) of the piezoelectric element with the shortest length in the second direction (Y-axis direction) among the multiple piezoelectric elements is the minimum dimension in the second direction (Y-axis direction) of the piezoelectric element with the shortest length in the second direction (Y-axis direction) among the multiple piezoelectric elements. Figure 37 shows a layered structure in which multiple piezoelectric elements are stacked without any misalignment in the second direction (Y-axis direction).

[0120] The average distance L3 in the second direction (Y-axis direction) of the gap between at least one edge 120e in the second direction (Y-axis direction) of the inner surface 120s of the frame body 120 and at least one edge 130e in the second direction (Y-axis direction) of the surface 130s on the frame body 120 side of the ultrasonic vibrator 630 shown in Figure 36 is 1.3 times or less the short side dimension L2 in the first direction (X-axis direction) inside the frame body 120.

[0121] In this embodiment, the average distance L3 in the second direction (Y-axis direction) of the gap between the edge 120e on one side in the second direction (Y-axis direction) of the inner surface 120s of the frame body 120 and the edge 130e on one side in the second direction (Y-axis direction) of the surface 130s of the ultrasonic vibrator 630 facing the frame body 120 is 1.3 times or less the short side dimension L2 in the first direction (X-axis direction) inside the frame body 120, and the average distance L3 in the second direction (Y-axis direction) of the gap between the edge 120e on the other side in the second direction (Y-axis direction) of the inner surface 120s of the frame body 120 and the edge 130e on the other side in the second direction (Y-axis direction) of the surface 130s of the ultrasonic vibrator 630 facing the frame body 120 is 1.3 times or less the short side dimension L2 in the first direction (X-axis direction) inside the frame body 120.

[0122] Fig. 38 is a cross-sectional view showing the configuration of an ultrasonic vibrator included in an ultrasonic transducer according to embodiment 6 of the present invention. As shown in Fig. 37, the ultrasonic vibrator 630 is attached to the frame body 120 and faces the first diaphragm 110 with a gap therebetween. Specifically, the ultrasonic vibrator 630 is attached to the other end in the third direction (Z-axis direction) of each of the pair of long side portions 121 of the frame body 120, and faces the first diaphragm 110 with the internal space of the frame body 120 sandwiched therebetween.

[0123] As shown in Figures 37 and 38 , the ultrasonic vibrator 630 is a piezoelectric element including a piezoelectric body 131. As shown in Figure 38 , in this embodiment, the ultrasonic vibrator 630 has a layered structure in which a plurality of piezoelectric bodies 131 are stacked. Specifically, the ultrasonic vibrator 630 includes two stacked piezoelectric bodies 131. Of the two piezoelectric bodies 131, the piezoelectric body 131 in contact with the frame body 120 is polarized, and the piezoelectric body 131 not in contact with the frame body 120 is not polarized.

[0124] 39 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer according to the sixth embodiment of the present invention transmits or receives ultrasonic waves. The simulation analysis conditions were as follows: the thickness of the first diaphragm 110 was 0.1 mm; the combined thickness of the two piezoelectric bodies 131 was 0.8 mm; the longitudinal dimension L1 inside the frame body 120 was 20 mm; the lateral dimension L2 inside the frame body 120 was 1.8 mm; and the thickness of the frame body 120 in the third direction (Z-axis direction) was 0.4 mm. The length dimension of the slit 110s in the first direction (X-axis direction) was 80.1% of the lateral dimension L2 in the first direction (X-axis direction) inside the frame body 120. The width dimension of the slit 110s in the second direction (Y-axis direction) was 0.5 mm. The slit 110s is formed from a position on the edge of the inner peripheral surface of the frame body 120 in the second direction (Y-axis direction) to a position inward by the width dimension in the second direction (Y-axis direction). The two slits 110s are open at both ends in the second direction (Y-axis direction) inside the frame body 120, respectively.

[0125] 39 , in the vibration mode of the ultrasonic transducer 600 according to the sixth embodiment of the present invention, the first diaphragm 110 resonates in an antiphase with the ultrasonic vibrator 630 in a third direction (Z-axis direction) perpendicular to the first diaphragm 110. In this embodiment, the resonant frequency of the first diaphragm 110 and the ultrasonic vibrator 630 is approximately 150 kHz.

[0126] In this embodiment, as shown in FIG. 37 , the minimum dimension Lm of the ultrasonic vibrator 630 in the second direction (Y-axis direction) is set smaller than the longitudinal dimension L1 in the second direction (Y-axis direction) inside the frame 120 so that a gap is formed between at least one edge 120e in the second direction (Y-axis direction) of the inner peripheral surface 120s of the frame 120 and at least one edge 130e in the second direction (Y-axis direction) of the surface 130s of the ultrasonic vibrator 630 facing the frame 120, as shown in FIG. 36 . This reduces the power consumption of the ultrasonic vibrator 630 and improves efficiency. Furthermore, because the piezoelectric body 131 not bonded to the frame 120 is not driven, the free capacitance of the piezoelectric element is reduced, allowing the first diaphragm 110 to be displaced efficiently.

[0127] Here, we will explain the relationship between the ratio of the length dimension of the slit 110s in the first direction (X-axis direction) to the short side dimension L2 in the first direction (X-axis direction) inside the frame body 120 and the rate of change of the internal stress (value normalized per sound pressure) in the third direction (Z-axis direction) generated within the ultrasonic transducer.

[0128] Figure 40 is a graph showing the relationship between the ratio of the length dimension of the slit in the first direction (X-axis direction) to the short-side dimension in the first direction (X-axis direction) inside the frame body and the rate of change of internal stress (value normalized per sound pressure) in the third direction (Z-axis direction) generated in the ultrasonic transducer. In Figure 40, the vertical axis represents the rate of change (%) of internal stress in the third direction (Z-axis direction) per sound pressure, and the horizontal axis represents the rate (%) of the length dimension of the slit 110s in the first direction (X-axis direction) to the short-side dimension L2 in the first direction (X-axis direction) inside the frame body 120. The rate of change of internal stress in the third direction (Z-axis direction) per sound pressure is the rate of change relative to the internal stress in the third direction (Z-axis direction) per sound pressure when the ratio of the length dimension of the slit 110s in the first direction (X-axis direction) to the short-side dimension L2 in the first direction (X-axis direction) inside the frame body 120 is 0%.

[0129] 40 , when the ratio of the length dimension of the slit 110s in the first direction (X-axis direction) to the short-side dimension L2 in the first direction (X-axis direction) inside the frame body 120 is 60% or more and 95% or less, the rate of change in internal stress in the third direction (Z-axis direction) per sound pressure is −15% or more. In other words, when the short-side dimension of at least one opening is 60% or more and 95% or less of the short-side dimension inside at least one frame body, the internal stress in the third direction (Z-axis direction) generated in the ultrasonic transducer 600 (a value normalized per sound pressure) can be effectively reduced. Consequently, the occurrence of cracks due to internal stress can be effectively suppressed at the joint between the first diaphragm 110 and the frame body 120 and at the joint between the frame body 120 and the ultrasonic vibrator 630.

[0130] Next, for sample 1 where the ratio of the length dimension of the slit 110s in the first direction (X-axis direction) to the short side dimension L2 in the first direction (X-axis direction) inside the frame body 120 is 0%, sample 2 where it is 55.6%, sample 3 where it is 77.8%, sample 4 where it is 88.9%, and sample 5 where it is 100%, a simulation analysis was performed using the finite element method to examine the relationship between the position of the first vibration plate 110 in the longitudinal direction (Y-axis direction) and the displacement of the first vibration plate 110.

[0131] Fig. 41 is a graph showing the relationship between the position of the first diaphragm in the longitudinal direction (Y-axis direction) and the displacement of the first diaphragm in Samples 1 to 5, obtained by simulation analysis using the finite element method. In Fig. 41, the vertical axis shows the displacement of the first diaphragm (μm), and the horizontal axis shows the position of the first diaphragm in the longitudinal direction (Y-axis direction) (mm). The position of one edge of the first diaphragm 110 in the longitudinal direction (Y-axis direction) was set to 0 mm, and the position of the other edge of the first diaphragm 110 in the longitudinal direction (Y-axis direction) was set to 22 mm.

[0132] Fig. 42 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer of Sample 1 transmits or receives ultrasonic waves. Fig. 43 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer of Sample 2 transmits or receives ultrasonic waves. Fig. 44 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer of Sample 3 transmits or receives ultrasonic waves. Fig. 45 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer of Sample 4 transmits or receives ultrasonic waves. Fig. 46 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer of Sample 5 transmits or receives ultrasonic waves.

[0133] As shown in Figures 41 and 42, in the ultrasonic transducer 700 of sample 1, the middle portion 710c of the first vibration plate 710, which is located at the middle of the longitudinal direction inside the frame body 120, is displaced significantly, and the displacement becomes smaller as it approaches the end portion 710e in the second direction (Y-axis direction).

[0134] As shown in Figures 41 and 43, in the ultrasonic transducer 600a of sample 2, the middle portion 110c of the first vibration plate 110, which is located at the middle of the longitudinal direction inside the frame body 120, is displaced significantly, and the displacement becomes smaller as it approaches the slit 110s in the second direction (Y-axis direction).

[0135] 41 and 44, in the ultrasonic transducer 600b according to Sample 3, the middle portion 110c of the first diaphragm 110 was displaced significantly, and the displacement became smaller as it approached the slit 110s in the second direction (Y-axis direction). However, compared to Samples 1 and 2, Sample 3 had a smaller difference between the displacement in the middle portion 110c and the displacement at a position near the slit 110s within the vibration region.

[0136] As shown in FIGS. 41 and 45, in the ultrasonic transducer 600c according to Sample 4, the position near the slit 110s in the vibration region of the first diaphragm 110 was displaced slightly more than the middle portion 110c.

[0137] As shown in Figures 41 and 46, in the ultrasonic transducer 600d of sample 5, the first vibration plate 110 was displaced significantly at a position near the slit 110s within the vibration region, and the displacement became smaller as it approached the intermediate portion 110c in the second direction (Y-axis direction).

[0138] From the above results, it was found that as the ratio of the length dimension of the slit 110s in the first direction (X-axis direction) to the short side dimension L2 in the first direction (X-axis direction) inside the frame body 120 increases, the peak position of the displacement in the first vibration plate 110 shifts from the middle portion 110c in the second direction (Y-axis direction) to both ends.

[0139] The maximum stress in the third direction (Z-axis direction) generated within the ultrasonic transducer when driven can be reduced if the displacement of the first diaphragm 110 is evenly distributed in the longitudinal direction of the frame body 120. Due to this mechanism of action, it is believed that when the ratio of the length dimension of the slit 110s in the first direction (X-axis direction) to the short side dimension L2 in the first direction (X-axis direction) inside the frame body 120 is 60% or more and 95% or less, as shown in Figure 40, it is possible to effectively reduce the internal stress (value normalized per sound pressure) in the third direction (Z-axis direction) generated within the ultrasonic transducer 600.

[0140] Furthermore, when the ratio of the length dimension of the slit 110s in the first direction (X-axis direction) to the short side dimension L2 in the first direction (X-axis direction) inside the frame body 120 is 60% or more and 95% or less, the effect of effectively reducing the internal stress (value normalized per sound pressure) in the third direction (Z-axis direction) generated within the ultrasonic transducer 600 can be similarly obtained for the transducers 100 and 200 according to each of embodiments 1 and 2.

[0141] (Note) It will be understood by those skilled in the art that the exemplary embodiments described above are specific examples of the following aspects.

[0142] <1> An ultrasonic transducer comprising: a first vibration plate; at least one frame body extending in a longitudinal direction and joined to the first vibration plate; and at least one ultrasonic vibrator attached to each of the at least one frame body and facing the first vibration plate with a gap therebetween, wherein the first vibration plate resonates and vibrates in an opposite phase to the at least one ultrasonic vibrator in a direction perpendicular to the first vibration plate, the longitudinal dimension inside the at least one frame body is greater than the lateral dimension inside the at least one frame body perpendicular to the longitudinal direction, and at least one opening is provided to connect an external space on the opposite side of the first vibration plate from the at least one frame body with an internal space inside the at least one frame body.

[0143] <2> The ultrasonic transducer according to <1>, wherein the at least one opening is formed in the first diaphragm.

[0144] <3> The ultrasonic transducer according to <2>, wherein the at least one opening is a slit extending in the short-side direction.

[0145] <4> The ultrasonic transducer according to <3>, wherein the at least one opening extends to a dimension equal to or greater than the short-side dimension inside the at least one frame body.

[0146] <5> The ultrasonic transducer according to any one of <1> to <4>, wherein one opening as the at least one opening is open at one of both end portions in the longitudinal direction inside the at least one frame body.

[0147] <6> The ultrasonic transducer according to any one of <1> to <4>, wherein two openings as the at least one opening are opened at both ends in the longitudinal direction inside the at least one frame body.

[0148] <7> The ultrasonic transducer according to any one of <1> to <6>, wherein the at least one ultrasonic vibrator is a piezoelectric element including a piezoelectric body.

[0149] <8> The ultrasonic transducer according to any one of <1> to <7>, wherein the first diaphragm and the at least one ultrasonic vibrator have a resonance frequency of 100 kHz or higher.

[0150] <9> The ultrasonic transducer according to <7>, wherein the relationship of 0.25CpTp / Cv≦Tv≦0.6CpTp / Cv is satisfied, where Cv is the sound velocity of a shear wave in the first diaphragm, Cp is the sound velocity of a shear wave in the piezoelectric body, Tv is the thickness dimension of the first diaphragm, and Tp is the thickness dimension of the piezoelectric body.

[0151] <10> The ultrasonic transducer according to <7>, wherein the relationship of 0.7CpTp / Cv≦Tv≦1.3CpTp / Cv is satisfied, where Cv is the sound velocity of a shear wave in the first diaphragm, Cp is the sound velocity of a shear wave in the piezoelectric body, Tv is the thickness dimension of the first diaphragm, and Tp is the thickness dimension of the piezoelectric body.

[0152] <11> The ultrasonic transducer according to any one of <1> to <10>, wherein the at least one frame body is arranged in a plurality of rows in the short side direction and joined to the first vibration plate, and adjacent frame bodies in the short side direction of the at least one frame body are connected to each other at both ends in the long side direction.

[0153] <12> The ultrasonic transducer according to <7>, wherein the at least one ultrasonic vibrator is a unimorph piezoelectric vibrator, and a second vibration plate is provided on the side of the piezoelectric body opposite to the frame body side.

[0154] <13> The ultrasonic transducer according to <5>, wherein the longitudinal dimension on the inside of the at least one frame body is at least twice the lateral dimension on the inside of the at least one frame body.

[0155] <14> The ultrasonic transducer according to any one of <1> to <13>, wherein the dimension of the short side of the at least one opening is 60% or more and 95% or less of the dimension of the short side inside the at least one frame body.

[0156] <15> A parametric speaker comprising the ultrasonic transducer according to any one of <1> to <14>, and reproducing an audible sound by modulating and driving the ultrasonic transducer.

[0157] In the above-described embodiments, configurations that can be combined may be combined with each other.

[0158] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0159] 100, 100a, 100b, 200, 300, 300a, 400, 500, 500a, 600, 600a, 600b, 600c, 600d, 700 ultrasonic transducer, 110, 210, 710 first diaphragm, 110as, 110cs intermediate slit, 110c, 210c, 710c intermediate portion, 110e, 210e, 710e end portion, 110s, 110sb, 210s, 211, 223 slit, 120, 120a, 220 frame, 120e, 130e edge, 120s inner peripheral surface, 121, 221 long side portion, 122, 222 Short side portion, 130, 130a, 130b, 130c, 630 ultrasonic vibrator, 130s surface of ultrasonic vibrator on the frame body side, 131 piezoelectric body, 132 first electrode, 133 second electrode, 134 intermediate electrode, 135 second diaphragm, 140 processing circuit, 800, 900 ultrasonic element, Bm, Bp resonant vibration, Cp, Cv sound speed, Dp polarization direction, ES external space, IS internal space, L1 longitudinal dimension, L2 transverse dimension, LC cut line, R0 Rayleigh distance.

Claims

1. A first diaphragm; At least one frame extending in a longitudinal direction and joined to the first diaphragm; at least one ultrasonic transducer attached to each of the at least one frame bodies and facing the first vibration plate with a gap therebetween; the first vibration plate resonates in an antiphase with the at least one ultrasonic transducer in a direction perpendicular to the first vibration plate, a longitudinal dimension on an inner side of the at least one frame body is greater than a lateral dimension on an inner side of the at least one frame body that is perpendicular to the longitudinal direction, An ultrasonic transducer having at least one opening that connects an external space on the opposite side of the first vibration plate from the at least one frame body with an internal space inside the at least one frame body.

2. The ultrasonic transducer of claim 1 , wherein the at least one opening is formed in the first diaphragm.

3. The ultrasonic transducer according to claim 2 , wherein the at least one opening is a slit extending in the short direction.

4. The ultrasonic transducer according to claim 3 , wherein the at least one opening extends beyond a dimension of the short side of the inner side of the at least one frame body.

5. The ultrasonic transducer according to claim 4 , wherein one opening as the at least one opening is open at one of both ends in the longitudinal direction on the inside of the at least one frame body.

6. The ultrasonic transducer according to claim 4 , wherein the at least one opening includes two openings that open at both ends in the longitudinal direction on the inside of the at least one frame body.

7. The ultrasonic transducer according to claim 1 , wherein the at least one ultrasonic vibrator is a piezoelectric element including a piezoelectric body.

8. The ultrasonic transducer of claim 1 , wherein the first diaphragm and the at least one ultrasonic vibrator have a resonant frequency of 100 kHz or more.

9. If the sound velocity of the shear wave of the first diaphragm is Cv, the sound velocity of the shear wave of the piezoelectric body is Cp, the thickness dimension of the first diaphragm is Tv, and the thickness dimension of the piezoelectric body is Tp, then 8. The ultrasonic transducer according to claim 7, which satisfies the relationship: 0.25CpTp / Cv≦Tv≦0.6CpTp / Cv.

10. If the sound velocity of the shear wave of the first diaphragm is Cv, the sound velocity of the shear wave of the piezoelectric body is Cp, the thickness dimension of the first diaphragm is Tv, and the thickness dimension of the piezoelectric body is Tp, then 8. The ultrasonic transducer according to claim 7, which satisfies the relationship: 0.7CpTp / Cv≦Tv≦1.3CpTp / Cv.

11. The ultrasonic transducer of claim 1, wherein the at least one frame body is arranged in a plurality of rows in the short side direction and joined to the first vibration plate, and adjacent frame bodies in the at least one frame body in the short side direction are connected to each other at both ends in the long side direction.

12. The at least one ultrasonic transducer is a unimorph type piezoelectric transducer, The ultrasonic transducer according to claim 7 , further comprising a second diaphragm provided on a side of the piezoelectric body opposite to a side of the frame body.

13. The ultrasonic transducer according to claim 5 , wherein the longitudinal dimension on an inside of the at least one frame body is at least twice as large as the lateral dimension on an inside of the at least one frame body.

14. The ultrasonic transducer according to claim 1 , wherein the short-side dimension of the at least one opening is 60% or more and 95% or less of the short-side dimension inside the at least one frame body.

15. The ultrasonic transducer according to any one of claims 1 to 14, A parametric speaker that reproduces audible sound by modulating the ultrasonic transducer.