Ultrasonic transducer and parametric speaker equipped with same

Abstract

A first diaphragm (110) resonates and vibrates in antiphase with at least one unimorph piezoelectric transducer (130) in a direction orthogonal to the first diaphragm (110). A dimension (L1) in a lengthwise direction on the inner side of at least one frame body (120) is at least four times greater than a dimension in a widthwise direction orthogonal to the lengthwise direction on the inner side of the at least one frame body (120). A second diaphragm (135), when viewed from a direction orthogonal to the first diaphragm (110), is located in a region between the two edges (120s1, 120s2) in the widthwise direction on the inner peripheral surface of the at least one frame body (120) in the widthwise direction, and an average distance (D1) in the widthwise direction between one edge (120s1) in the widthwise direction on the inner peripheral surface of the at least one frame body (120) and one edge (135s1) in the widthwise direction of the second diaphragm (135) as well as an average distance (D2) in the widthwise direction between the other edge (120s2) in the widthwise direction on the inner peripheral surface of the at least one frame body (120) and the other edge (135s2) in the widthwise direction of the second diaphragm (135) are each no more than 1 / 6 a dimension (L2) in the widthwise direction on the inner side of at the least one frame body (120).

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 consideration 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 with a simple and compact configuration.

[0007] An ultrasonic transducer according to the present invention comprises a first diaphragm, at least one frame, and at least one unimorph piezoelectric vibrator. The at least one frame extends in a longitudinal direction and is bonded to the first diaphragm. The at least one unimorph piezoelectric vibrator is attached to at least one frame. The at least one unimorph piezoelectric vibrator includes a piezoelectric body facing the first diaphragm with a gap therebetween and a second diaphragm provided on the opposite side of the piezoelectric body from the frame. The first diaphragm resonates in an opposite phase to the at least one unimorph piezoelectric vibrator in a direction perpendicular to the first diaphragm. The longitudinal dimension inside the at least one frame is four or more times the lateral dimension inside the at least one frame, which is perpendicular to the longitudinal direction. The second diaphragm is located within a region sandwiched between both ends of the lateral direction on the inner peripheral surface of the at least one frame in the lateral direction, as viewed in a direction perpendicular to the first diaphragm. The second vibration plate has an average distance in the short direction between one edge in the short direction on the inner surface of at least one frame body and one edge in the short direction of the second vibration plate, and an average distance in the short direction between the other edge in the short direction on the inner surface of at least one frame body and the other edge in the short direction of the second vibration plate, each of which is 1 / 6 or less of the dimension in the short direction inside the at least one frame body.

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

[0009] 1 is a longitudinal sectional view showing the configuration of an ultrasonic transducer according to a first embodiment of the present invention. 2 is an exploded perspective view showing the configuration of an ultrasonic transducer according to a first embodiment of the present invention. 3 is a perspective view showing the configuration of a frame included in the ultrasonic transducer according to a first embodiment of the present invention. 4 is a view of the ultrasonic transducer of FIG. 2 as viewed from the direction of arrow IV. 5 is a cross-sectional view showing the configuration of a unimorph-type piezoelectric vibrator included in the ultrasonic transducer according to a first embodiment of the present invention. 6 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer according to a first embodiment of the present invention is transmitting or receiving ultrasonic waves. 7 is a cross-sectional view of the ultrasonic transducer of FIG. 6 as viewed from the direction of the arrows VII-VII. 8 is a graph obtained by simulating and analyzing, using the finite element method, 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. 9 is a graph obtained by simulating and analyzing, using the finite element method, 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. 10 is a graph obtained by simulating and analyzing, using the finite element method, the transition of the sound pressure of ultrasonic waves transmitted from the ultrasonic transducer when the minimum dimension in the second direction (Y-axis direction) of the ultrasonic vibrator is changed. 1 is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a first embodiment, in which the minimum dimension of the piezoelectric body in the second direction (Y-axis direction) is 24 mm, transmits or receives ultrasonic waves; FIG. 2 is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a second embodiment, in which the minimum dimension of the piezoelectric body in the second direction (Y-axis direction) is 16 mm, transmits or receives ultrasonic waves; FIG. 3 is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a third embodiment, in which the minimum dimension of the piezoelectric body in the second direction (Y-axis direction) is 15 mm, transmits or receives ultrasonic waves; and FIG. 4 is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a fourth example, in which the minimum dimension of the piezoelectric body in the second direction (Y-axis direction) is 14.5 mm, transmits or receives ultrasonic waves.15 is a cross-sectional view of the ultrasonic transducer of FIG. 14 as viewed from the direction of the arrows along line XV-XV. It is a view of an ultrasonic transducer according to a fifth example of embodiment 1 of the present invention as viewed from the ultrasonic vibrator side. It is a view of an ultrasonic transducer according to a sixth example of embodiment 1 of the present invention as viewed from the ultrasonic vibrator side. It is a cross-sectional view showing the configuration of an ultrasonic transducer according to a seventh example of embodiment 1 of the present invention. It is a graph obtained by simulating and analyzing, using the finite element method, the progress of the displacement of the first diaphragm when the lateral dimension W of the second diaphragm is changed while the center position of the second diaphragm in the first direction (X-axis direction) is fixed in the first experimental example. It is a cross-sectional view showing the displacement state as simulated and analyzed using the finite element method when an ultrasonic transducer according to a first comparative example, in which the lateral dimension W of the second diaphragm in the first direction (X-axis direction) is 1 mm and the average distances D1 and D2 are each 0.4 mm, is transmitting or receiving ultrasonic waves. 1 is a cross-sectional view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to an eighth embodiment transmits or receives ultrasonic waves, in which the short-side dimension W of the second diaphragm in the first direction (X-axis direction) is 1.5 mm and the average distances D1 and D2 are each 0.15 mm in a first experimental example. 2 is a cross-sectional view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a second comparative example transmits or receives ultrasonic waves, in which the short-side dimension W of the second diaphragm in the first direction (X-axis direction) is 2 mm and the average distances D1 and D2 are each −0.1 mm in a first experimental example. 3 is a graph showing a simulation analysis of the displacement of the first diaphragm when the thickness of the piezoelectric body is changed to 0.2 mm from the analysis conditions of the first experimental example and the short-side dimension W of the second diaphragm is changed while the center position of the second diaphragm in the first direction (X-axis direction) is fixed, in a second experimental example. This graph shows the results of a simulation analysis using the finite element method of the change in displacement of the first diaphragm in the third experimental example when the thickness of the second diaphragm was changed to 0.3 mm from the analysis conditions of the first experimental example, and the center position of the second diaphragm in the first direction (X-axis direction) was fixed while the short-side dimension W of the second diaphragm was changed.

[0033] In a fourth experimental example, the analysis conditions for the first experimental example were changed to a 2.2 mm short side dimension inside the frame, and the short side dimension W of the second diaphragm was changed while the center position of the second diaphragm in the first direction (X-axis direction) was fixed. This graph is a simulation analysis graph using the finite element method showing the change in displacement of the first diaphragm when the analysis conditions for the fifth experimental example were changed to a 0.2 mm thickness of the piezoelectric body and a 2.2 mm short side dimension inside the frame, and the center position of the second diaphragm in the first direction (X-axis direction) was fixed while the short side dimension W of the second diaphragm was changed. In a sixth experimental example, the analysis conditions for the first experimental example were changed to a piezoelectric ceramic material, and the center position of the second diaphragm in the first direction (X-axis direction) was fixed while the short side dimension W of the second diaphragm was changed. This graph is a simulation analysis graph using the finite element method showing the change in displacement of the first diaphragm when the analysis conditions for the first experimental example were changed to a piezoelectric ceramic material, and the center position of the second diaphragm in the first direction (X-axis direction) was fixed while the short side dimension W of the second diaphragm was changed. 10 is a graph showing a simulation analysis using the finite element method of the transition of displacement of the first diaphragm when the center position of the second diaphragm in the first direction (X-axis direction) is shifted in the seventh experimental example.

[0041] FIG. 11 is a cross-sectional view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a ninth embodiment transmits or receives ultrasonic waves in the seventh experimental example, in which the short-side dimension W of the second diaphragm in the first direction (X-axis direction) is 1.5 mm, the deviation of the center position of the second diaphragm in the first direction (X-axis direction) is 0.15 mm, the average distance D1 is 0 mm, and the average distance D2 is 0.3 mm.

[0042] FIG. 11 is a cross-sectional view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a third comparative example transmits or receives ultrasonic waves in the seventh experimental example, in which the short-side dimension W of the second diaphragm in the first direction (X-axis direction) is 1.2 mm, the deviation of the center position of the second diaphragm in the first direction (X-axis direction) is 0.3 mm, the average distance D1 is 0 mm, and the average distance D2 is 0.6 mm. 1 is a perspective view of an ultrasonic transducer according to a first modified example of embodiment 1 of the present invention, seen from the second diaphragm side; FIG. 2 is a perspective view of an ultrasonic transducer according to a second modified example of embodiment 1 of the present invention, seen from the first diaphragm side; FIG. 3 is a side view showing the configuration of an ultrasonic transducer according to embodiment 2 of the present invention;Fig. 34 is a rear view of the ultrasonic transducer shown in Fig. 33 as seen from the direction of arrow XXXIV. Fig. 35 is an exploded perspective view showing the stacking state of each component of the ultrasonic transducer according to embodiment 2 of the present invention. Fig. 36 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.

[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 a unimorph piezoelectric 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 an aluminum alloy. Since aluminum alloys have a small Young's modulus, making the first diaphragm 110 out of an aluminum alloy can reduce stress generated within the first diaphragm 110 when the ultrasonic transducer 100 is driven. The thickness of the first diaphragm 110 is, for example, 0.05 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, an iron-nickel alloy (42Ni-Fe), 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 0.6 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 side portions 121 extending in the second direction (Y-axis direction) and a pair of short side portions 122 extending in the first direction (X-axis direction). The pair of long side portions 121 and the pair of short side portions 122 are continuous to form the inner peripheral surface of the frame body 120. The average distance between the short side portions 122 is four or more times the shortest distance between the long side portions 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 four times or more 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] Fig. 4 is a view of the ultrasonic transducer of Fig. 2 as viewed from the direction of arrow IV. As shown in Figs. 1 and 4, the unimorph piezoelectric vibrator 130 is attached to the frame body 120. The unimorph piezoelectric vibrator 130 includes a piezoelectric body 131 that faces the first vibration plate 110 with a gap therebetween, and a second vibration plate 135 that is provided on the side of the piezoelectric body 131 opposite the frame body 120 side. The piezoelectric body 131 has a rectangular parallelepiped shape. The thickness of the piezoelectric body 131 is, for example, not less than 0.1 mm and not more than 0.2 mm. The piezoelectric body 131 is, for example, a piezoelectric ceramic.

[0020] The second diaphragm 135 is formed from a metal such as an aluminum alloy, an iron-nickel alloy (42Ni-Fe), or stainless steel, glass epoxy, or ceramic. In this embodiment, the second diaphragm 135 is made of an iron-nickel alloy (42Ni-Fe). The second diaphragm 135 has a rectangular parallelepiped shape. The second diaphragm 135 is bonded to the piezoelectric body 131. The length of the second diaphragm 135 in the second direction (Y-axis direction) is equal to the length of the piezoelectric body 131 in the second direction (Y-axis direction). The lateral dimension W of the second diaphragm 135 in the first direction (X-axis direction) satisfies the relationship (2 / 3)L2≦W<L2 with respect to the lateral dimension L2 in the first direction (X-axis direction) inside the frame body 120. The thickness of the second diaphragm 135 is, for example, 0.2 mm or more and 0.4 mm or less. When the shape of the second diaphragm 135 is not rectangular but elliptical when viewed from the third direction (Z-axis direction), the short side dimension W is set to an average value.

[0021] As shown in Figure 4, when viewed from a third direction (Z-axis direction) perpendicular to the first vibration plate 110, the second vibration plate 135 is located within the area sandwiched between both end edges 120s1 and 120s2 in the first direction (X-axis direction) on the inner surface of the frame body 120.

[0022] As shown in FIG. 1 , in the second vibration plate 135, the average distance D1 in the first direction (X-axis direction) between one edge 120s1 in the first direction (X-axis direction) on the inner surface of the frame body 120 and one edge 135s1 in the first direction (X-axis direction) of the second vibration plate 135, and the average distance D2 in the first direction (X-axis direction) between the other edge 120s2 in the first direction (X-axis direction) on the inner surface of the frame body 120 and the other edge 135s2 in the first direction (X-axis direction) of the second vibration plate 135, are each 1 / 6 or less of the short-side dimension L2 in the first direction (X-axis direction) inside the frame body 120.

[0023] As shown in FIG. 4 , the longitudinal dimension L1 in the second direction (Y-axis direction) inside the frame 120 is larger than the minimum dimension Lm of the piezoelectric body 131 of the unimorph piezoelectric vibrator 130 in the second direction (Y-axis direction). Here, when the unimorph piezoelectric vibrator 130 has a layered structure in which multiple piezoelectric bodies are stacked, the minimum dimension Lm of the piezoelectric body 131 in the second direction (Y-axis direction) is the minimum dimension in the second direction (Y-axis direction) of the piezoelectric body that has the shortest length in the second direction (Y-axis direction) among the multiple piezoelectric bodies. For example, when the unimorph piezoelectric vibrator 130 has a layered structure in which two piezoelectric bodies 131 are stacked, the polarization directions Dp of the two piezoelectric bodies 131 face each other in the third direction (Z-axis direction). Since the electric fields applied to the two piezoelectric bodies 131 are also opposite to each other in the third direction (Z-axis direction), a unimorph piezoelectric vibrator is configured in which the two piezoelectric bodies 131 flexurally vibrate in the same way.

[0024] 4 shows a state in which the piezoelectric body 131 and the second vibration plate 135 are stacked together without any misalignment in the second direction (Y-axis direction). In this embodiment, the length of the piezoelectric body 131 in the second direction (Y-axis direction) is shorter than the longitudinal dimension L1 in the second direction (Y-axis direction) inside the frame body 120, but is not limited to this and may be equal to or greater than the longitudinal dimension L1 in the second direction (Y-axis direction) inside the frame body 120.

[0025] 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) on the inner surface of the frame body 120 and at least one edge 130e in the second direction (Y-axis direction) of the surface 130s of the piezoelectric body 131 on the frame body 120 side in the unimorph type piezoelectric vibrator 130 shown in Figure 2 is 1.3 times or less the short side dimension L2 in the first direction (X-axis direction) inside the frame body 120.

[0026] 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 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 piezoelectric body 131 in the unimorph piezoelectric vibrator 130 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 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 piezoelectric body 131 in the unimorph piezoelectric vibrator 130 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.

[0027] 5 is a cross-sectional view showing the configuration of a unimorph piezoelectric vibrator included in the ultrasonic transducer according to embodiment 1 of the present invention. As shown in Fig. 1, the unimorph piezoelectric vibrator 130 is attached to the frame body 120 and faces the first diaphragm 110 with a gap therebetween. Specifically, the unimorph piezoelectric vibrator 130 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 inner space of the frame body 120 sandwiched therebetween.

[0028] 1, 2, and 5, the unimorph piezoelectric vibrator 130 is a piezoelectric element including a piezoelectric body 131. As shown in Fig. 5, in this embodiment, the piezoelectric body 131 is sandwiched between a first electrode 132 and a second electrode 133. The polarization direction Dp of the piezoelectric body 131 is along the third direction (Z-axis direction). The first electrode 132 and the second electrode 133 are electrically connected to a processing circuit 140 to which an AC voltage can be applied.

[0029] Fig. 6 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer according to embodiment 1 of the present invention transmits or receives ultrasonic waves. Fig. 7 is a cross-sectional view of the ultrasonic transducer of Fig. 6 as viewed from the direction of the arrow VII-VII. The simulation analysis conditions were as follows: the thickness of the first diaphragm 110 was 0.1 mm, the thickness of the piezoelectric body 131 was 0.1 mm, the thickness of the second diaphragm 135 was 0.2 mm, the longitudinal dimension L1 inside the frame body 120 was 20 mm, the lateral dimension L2 was 1.8 mm, and the thickness of the frame body 120 in the third direction (Z-axis direction) was 0.4 mm.

[0030] 6 and 7, 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 unimorph piezoelectric vibrator 130 in a third direction (Z-axis direction) perpendicular to the first diaphragm 110. That is, as shown in Fig. 7, the displacement direction of the resonant vibration Bm of the first diaphragm 110 and the displacement direction of the resonant vibration Bp of the unimorph piezoelectric 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 unimorph piezoelectric vibrator 130 are 100 kHz or higher.

[0031] In first diaphragm 110, middle portion 110c located at the middle in the longitudinal direction inside frame body 120 becomes the antinode of the resonant vibration, and end portions 110e located at both ends in the longitudinal direction inside frame body 120 become nodes of the resonant vibration. In other words, the portion of first diaphragm 110 located above the internal space of frame body 120 becomes the vibration region that resonates. The longitudinal dimension of the vibration region of first diaphragm 110 is the same as longitudinal dimension L1 inside frame body 120, and the lateral dimension of the vibration region of first diaphragm 110 is the same as lateral dimension L2 inside frame body 120.

[0032] Here, the relationship between the resonance frequency of the first diaphragm 110 and the longitudinal dimension L1 inside the frame 120 will be described.

[0033] Fig. 8 is a graph showing the results of a simulation analysis using the finite element method of the change in the resonant frequency of the first diaphragm 110 when the longitudinal dimension is changed while the transverse dimension inside the frame is fixed. In Fig. 8, the vertical axis represents the resonant frequency (kHz) of the first diaphragm 110, and the horizontal axis represents the longitudinal dimension L1 (mm) inside the frame 120. As a condition for the simulation analysis, the transverse dimension L2 inside the frame 120 was fixed at 2 mm.

[0034] 8, when the longitudinal dimension L1 inside the frame 120 is 2 mm, the resonant frequency of the first diaphragm 110 is 220 kHz, and when the longitudinal dimension L1 increases to 8 mm and the longitudinal dimension of the vibration region of the first diaphragm 110 increases, the resonant frequency of the first diaphragm 110 decreases to 122 kHz. Thereafter, even when the longitudinal dimension L1 inside the frame 120 exceeds 8 mm and the longitudinal dimension of the vibration region of the first diaphragm 110 further increases, the resonant frequency of the first diaphragm 110 remains substantially constant at 122 kHz.

[0035] In other words, the resonant frequency of the first vibration plate 110 is determined by the speed of sound of the first vibration plate 110 and the reflection of vibration with the frame body 120 as the fixed end, but once the longitudinal dimension L1 inside the frame body 120 exceeds four times the lateral dimension L2, the influence of the lateral dimension L2 becomes dominant with respect to the reflection of vibration, and the state of vibration reflection does not change even if the longitudinal dimension L1 becomes even larger than four times the lateral dimension L2.

[0036] 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.

[0037] 9 is a graph showing the results of a simulation analysis using the finite element method of the transition of the sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer when the longitudinal dimension is changed while the lateral dimension inside the frame body is fixed. In FIG. 9, the vertical axis represents the sound pressure (Pa) transmitted from the ultrasonic transducer 100, and the horizontal axis represents 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 at 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.

[0038] 9, 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 both end portions 110e 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.

[0039] 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.

[0040] 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 and the minimum dimension Lm of the piezoelectric body 131 in the second direction (Y-axis direction) will be described.

[0041] Fig. 10 is a graph showing the results of a 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 minimum dimension of the ultrasonic vibrator in the second direction (Y-axis direction) is changed. In Fig. 10, the vertical axis shows the sound pressure (Pa) transmitted from the ultrasonic transducer, and the horizontal axis shows the minimum dimension Lm (mm) of the piezoelectric body in the second direction (Y-axis direction).

[0042] The simulation analysis conditions were as follows: the outer dimensions of the frame body 120 in the second direction (Y-axis direction) were 24 mm, the outer dimensions in the first direction (X-axis direction) were 2.6 mm, the thickness of the frame body 120 in the third direction (Z-axis direction) was 0.4 mm, and the longitudinal dimension L1 and lateral dimension L2 of the inner frame body 120 were 20 mm and 1.8 mm, respectively. The outer dimensions of the first vibration plate 110 were the same as those of the frame body 120, and the thickness of the first vibration plate 110 was 0.1 mm. The dimension of the piezoelectric body 131 in the first direction (X-axis direction) was 2.4 mm, and the thickness of the piezoelectric body 131 was 0.1 mm. The piezoelectric body 131 was positioned point-symmetrically with respect to the center of the frame body 120 when viewed from the third direction (Z-axis direction). The dimension of the second vibration plate 135 in the first direction (X-axis direction) was 1.5 mm, and the thickness of the second vibration plate 135 was 0.2 mm. The dimensions of the piezoelectric body 131 and the second diaphragm 135 in the second direction (Y-axis direction) were the same. 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.

[0043] FIG. 11 is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a first embodiment, in which the minimum dimension of the piezoelectric body in the second direction (Y-axis direction) is 24 mm, transmits or receives ultrasonic waves. FIG. 12 is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a second embodiment, in which the minimum dimension of the piezoelectric body in the second direction (Y-axis direction) is 16 mm, transmits or receives ultrasonic waves. FIG. 13 is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a third embodiment, in which the minimum dimension of the piezoelectric body in the second direction (Y-axis direction) is 15 mm, transmits or receives ultrasonic waves. FIG. 14 is a perspective view showing a displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a fourth embodiment, in which the minimum dimension of the piezoelectric body in the second direction (Y-axis direction) is 14.5 mm, transmits or receives ultrasonic waves. FIG. 15 is a cross-sectional view of the ultrasonic transducer of FIG. 14 as viewed from the direction of the arrows XV-XV.

[0044] 11 and 12, in the ultrasonic transducer 101 according to the first embodiment and the ultrasonic transducer 102 according to the second embodiment, in which the minimum dimension of the piezoelectric body 131 in the second direction (Y-axis direction) is 16 mm or more, the first diaphragm 110 vibrated in a tuning-fork vibration mode in which the intermediate portion 110c of the first diaphragm 110 serves as an antinode of the resonant vibration. As shown in Fig. 13, in the ultrasonic transducer 103 according to the third embodiment, in which the minimum dimension of the piezoelectric body 131 in the second direction (Y-axis direction) is 15 mm, the first diaphragm 110 vibrated in a vibration mode in which large displacement portions 110p, with the largest displacement, appeared near each of both longitudinal ends of the first diaphragm 110 inside the frame 120. However, the two large displacement portions 110p vibrated in the same phase, and the vibrations in the first diaphragm 110 were in the same phase.

[0045] 14 and 15 , in the ultrasonic transducer 104 according to the fourth example in which the minimum dimension of the piezoelectric body 131 in the second direction (Y-axis direction) is 14.5 mm, the first diaphragm 110 vibrated in a vibration mode in which reverse displacement portions 110b displacing in a displacement direction Ds opposite to the displacement direction Dm of the intermediate portion 110c appeared in the first diaphragm 110 near each of both longitudinal ends inside the frame body 120. That is, in the first diaphragm 110, vibrations of an opposite phase to that of the intermediate portion 110c were generated in the first diaphragm 110 near each of both longitudinal ends inside the frame body 120.

[0046] As a result, as shown in Figure 10, the sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer 104 of the fourth embodiment, in which the minimum dimension of the piezoelectric body 131 in the second direction (Y-axis direction) is 14.5 mm, was approximately half the sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer 102 of the second embodiment, in which the minimum dimension of the piezoelectric body 131 in the second direction (Y-axis direction) is 16 mm.

[0047] In the ultrasonic transducer 104 according to the fourth embodiment, 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 peripheral surface 120s of the frame body 120 and at least one edge 130e in the second direction (Y-axis direction) of the surface 130s of the unimorph piezoelectric vibrator 130 facing the frame body 120 is 2.75 mm, which is about 1.5 times the short-side dimension L2 in the first direction (X-axis direction) inside the frame body 120. In other words, when the average distance L3 is about 1.5 times the short-side dimension L2 in the first direction (X-axis direction) inside the frame body 120, antiphase vibrations are generated in the first diaphragm 110.

[0048] Although there are some variations due to changes in the length dimension in the second direction (Y-axis direction) of the unimorph piezoelectric vibrator 130 and the short-side dimension L2 in the first direction (X-axis direction) inside the frame body 120, it has been confirmed by simulation analysis using the finite element method that, as long as the average distance L3 is 1.3 times or less the short-side dimension L2 in the first direction (X-axis direction) inside the frame body 120, no anti-phase vibrations occur in the first diaphragm 110. In other words, as long as the average distance L3 is 1.3 times or less the short-side dimension L2 in the first direction (X-axis direction) inside the frame body 120, it is possible to reduce power consumption while maintaining a high sound pressure of the ultrasonic waves transmitted from the ultrasonic transducer.

[0049] Here, we will explain the power consumption of an ultrasonic transducer. The piezoelectric body 131 that constitutes the unimorph piezoelectric vibrator 130, particularly piezoelectric ceramic, has a large dielectric constant and electrical characteristics similar to those of a capacitor. The impedance of a capacitor is proportional to 1 / ωC, where ω is the frequency of the AC current and C is the capacitance. Therefore, as the frequency of the voltage applied to the piezoelectric body 131 increases, the impedance of the piezoelectric body 131 decreases, and current consumption increases. On the other hand, if the area of ​​the piezoelectric body 131 is reduced, the capacitance decreases, and current consumption decreases.

[0050] In the ultrasonic transducer 101 according to the first embodiment in which the minimum dimension of the unimorph piezoelectric vibrator 130 in the second direction (Y-axis direction) is 24 mm, the ends 110e of the first diaphragm 110 located on both ends in the longitudinal direction inside the frame 120 become nodes of the resonant vibration and hardly vibrate, as shown in Figure 11. In other words, both ends of the unimorph piezoelectric vibrator 130 in the second direction (Y-axis direction) hardly vibrate and do not work.

[0051] Therefore, in this embodiment, as shown in Fig. 4, the minimum dimension Lm of the piezoelectric body 131 in the second direction (Y-axis direction) is made smaller than the longitudinal dimension L1 in the second direction (Y-axis direction) inside the frame body 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 body 120 and at least one edge 130e in the second direction (Y-axis direction) of the surface 130s of the piezoelectric body 131 on the frame body 120 side shown in Fig. 2. This makes it possible to eliminate both ends in the second direction (Y-axis direction) of the unimorph piezoelectric vibrator 130, which are parts that consume power but do not work as shown in Fig. 11, and therefore the power consumption of the unimorph piezoelectric vibrator 130 can be reduced and efficiency can be improved.

[0052] Furthermore, since the gap is formed, the internal space inside the frame body 120 communicates with the external space outside the frame body 120. This reduces pressure changes in the internal space when, for example, an adhesive bonding the first diaphragm 110 and the frame body 120 is heated and cured, thereby preventing an increase in internal stress within the ultrasonic transducer 100. When the first diaphragm 110 and the frame body 120 are bonded together with an adhesive, the average distance L3 of the gap in the second direction (Y-axis direction) is preferably 0.2 mm or more to prevent the gap from being blocked by the adhesive that has been applied to the long side portion 121 of the frame body 120 and has penetrated into the gap. That is, the average distance L3 of the gap in the second direction (Y-axis direction) is preferably 0.2 mm or more and 1.3 times or less the short-side dimension L2 in the first direction (X-axis direction) inside the frame body 120.

[0053] FIG. 16 is a diagram showing an ultrasonic transducer according to a fifth example of the first embodiment of the present invention, viewed from the ultrasonic vibrator side. As shown in Figure 16, in the ultrasonic transducer 105 relating to the fifth example of embodiment 1 of the present invention, 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 piezoelectric body 131 in the unimorph piezoelectric vibrator 130 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 no gap is formed 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 piezoelectric body 131 in the unimorph piezoelectric vibrator 130 facing the frame body 120. That is, only one of the two end portions in the second direction (Y-axis direction) of the unimorph type piezoelectric vibrator 130 shown in FIG. 11, which is the portion that consumes power but does not work, may be removed.

[0054] 17 is a view of an ultrasonic transducer according to a sixth example of embodiment 1 of the present invention as viewed from the ultrasonic vibrator side. As shown in Fig. 17, in the ultrasonic transducer 106 according to the sixth example of embodiment 1 of the present invention, when viewed from the third direction (Z-axis direction), an edge 130e on one side in the second direction (Y-axis direction) of a surface 130s of the piezoelectric body 131 of the unimorph piezoelectric vibrator 130 on the frame body 120 side is not positioned parallel to at least one edge 120e in the second direction (Y-axis direction) of an inner peripheral surface 120s of the frame body 120. In such a case, 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) on the inner surface 120s of the frame body 120 and one edge 130e in the second direction (Y-axis direction) of the surface 130s of the piezoelectric body 131 on the frame body 120 side of the unimorph type piezoelectric vibrator 130 shown in Figure 2 is the average value of the shortest distance between the edge 120e and the edge 130e, which changes depending on the position in the first direction (X-axis direction), and the average distance L3 should be 1.3 times or less the short side dimension L2 in the first direction (X-axis direction) inside the frame body 120.

[0055] 18 is a cross-sectional view showing the configuration of an ultrasonic transducer according to a seventh example of the first embodiment of the present invention. As shown in FIG. 18, 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 peripheral surface of the frame body 120 and at least one edge 130e in the second direction (Y-axis direction) of the surface 130s of the unimorph piezoelectric vibrator 130 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. This allows the ultrasonic transducer 100d to have a simple and compact configuration, while reducing power consumption and increasing the sound pressure level.

[0056] A portion of surface 131b of piezoelectric body 131 opposite to frame 120 is not covered by second diaphragm 135. Specifically, because second diaphragm 135 is disposed offset in the second direction (Y-axis direction) with respect to piezoelectric body 131, a portion of surface 131b of piezoelectric body 131 opposite to frame 120 is exposed and not covered by second diaphragm 135. This makes it possible to easily connect wiring 10 for supplying power to piezoelectric body 131 to a portion of surface 131b of piezoelectric body 131 opposite to frame 120, which is not covered by second diaphragm 135. Note that the dimension of second diaphragm 135 in the second direction (Y-axis direction) may be larger, smaller, or the same as the dimension of piezoelectric body 131 in the second direction (Y-axis direction).

[0057] Here, we will explain the results of a first experimental example in which simulation analysis was performed on the relationship between the average distance D1 in the first direction (X-axis direction) between one edge 120s1 in the first direction (X-axis direction) on the inner surface of the frame body 120 and one edge 135s1 in the first direction (X-axis direction) of the second vibration plate 135, and the average distance D2 in the first direction (X-axis direction) between the other edge 120s2 in the first direction (X-axis direction) on the inner surface of the frame body 120 and the other edge 135s2 in the first direction (X-axis direction) of the second vibration plate 135, and the displacement of the first vibration plate 110.

[0058] Fig. 19 is a graph obtained by simulating and analyzing using the finite element method the change in displacement of the first diaphragm when the short-side dimension W of the second diaphragm is changed while the center position of the second diaphragm in the first direction (X-axis direction) is fixed in the first experimental example. In Fig. 19, the vertical axis represents the displacement (μm) of the first diaphragm 110, and the horizontal axis represents the short-side dimension W (mm) of the second diaphragm.

[0059] The simulation analysis conditions for the first experimental example were as follows: the thickness of first diaphragm 110 in the third direction (Z-axis direction) was 0.1 mm; the longitudinal dimension of piezoelectric body 131 in the second direction (Y-axis direction) was 18 mm; the thickness of piezoelectric body 131 in the third direction (Z-axis direction) was 0.1 mm; the longitudinal dimension L1 on the inside of frame 120 was 20 mm, the lateral dimension L2 was 1.8 mm; the thickness of frame 120 in the third direction (Z-axis direction) was 0.4 mm; the thickness of second diaphragm 135 in the third direction (Z-axis direction) was 0.2 mm; and the longitudinal dimension of second diaphragm 135 in the second direction (Y-axis direction) was 18 mm. The material of first diaphragm 110 was an aluminum alloy, the material of frame 120 was stainless steel, and the material of second diaphragm 135 was an iron-nickel alloy (42Ni-Fe). The center position of the second diaphragm 135 in the first direction (X-axis direction) is aligned with the center position of the inner space of the frame 120 in the first direction (X-axis direction).

[0060] Figure 20 is a cross-sectional view showing the displacement state simulated and analyzed using the finite element method when an ultrasonic transducer according to a first comparative example, in which the short side dimension W of the second diaphragm in the first direction (X-axis direction) is 1 mm and the average distances D1 and D2 are each 0.4 mm, is transmitting or receiving ultrasonic waves in the first experimental example.

[0061] Figure 21 is a cross-sectional view showing the displacement state simulated and analyzed using the finite element method when the ultrasonic transducer of Example 8, in which the short side dimension W of the second diaphragm in the first direction (X-axis direction) is 1.5 mm and the average distance D1 and average distance D2 are each 0.15 mm, is transmitting or receiving ultrasonic waves in the first experimental example.

[0062] 22 is a cross-sectional view showing the displacement state obtained by simulation analysis using the finite element method when an ultrasonic transducer according to a second comparative example, in which the short-side dimension W of the second diaphragm in the first direction (X-axis direction) is 2 mm and the average distances D1 and D2 are each −0.1 mm, transmits or receives ultrasonic waves in the first experimental example. Figures 20 to 22 are shown in the same cross-sectional view as Figure 7, and are shown in grayscale, with white indicating a higher tensile stress in the first direction (X-axis direction) and black indicating a higher compressive stress in the first direction (X-axis direction).

[0063] As shown in Figure 19, in the first experimental example, when the short side dimension W of the second vibration plate in the first direction (X-axis direction) was 1.2 mm or more and 1.8 mm or less, that is, when the average distance D1 and the average distance D2 were each 0 mm or more and 0.3 mm or less, the displacement of the first vibration plate 110 could be ensured at a high level of 0.56 μm or more within the resonant frequency range of 150 kHz or more and 160 kHz or less, and the transmission sound pressure and reception sensitivity of the ultrasonic transducer 100 could be increased.

[0064] As shown in Figure 20, when the average distance D1 and the average distance D2 are each 0.3 mm or more, the stress distribution within the piezoelectric body 131 is such that areas where tensile stress occurs and areas where compressive stress occurs are dispersed, the vibration efficiency of the piezoelectric body 131 decreases, and the displacement of the first vibration plate 110 becomes smaller.

[0065] As shown in Figure 21, when the average distance D1 and the average distance D2 are each between 0 and 0.3 mm, there are areas in the stress distribution within the piezoelectric body 131 where high compressive stress occurs throughout, improving the vibration efficiency of the piezoelectric body 131 and increasing the displacement of the first vibration plate 110.

[0066] 22 , when the second diaphragm 135 is positioned so as to protrude outside the region sandwiched between both edges in the first direction (X-axis direction) on the inner peripheral surface of the frame body 120 in the first direction (X-axis direction) when viewed from the third direction (Z-axis direction) perpendicular to the first diaphragm 110, the piezoelectric body 131 is constrained and becomes less likely to vibrate, and the stress inside the piezoelectric body 131 is generally lowered. As a result, the vibration efficiency of the piezoelectric body 131 decreases, and the displacement of the first diaphragm 110 becomes smaller.

[0067] According to the mechanism of action shown in Figures 20 to 22, when the center position of the second vibration plate 135 in the first direction (X-axis direction) coincides with the center position of the internal space of the frame body 120 in the first direction (X-axis direction), it is considered that when each of the average distance D1 and the average distance D2 in the second vibration plate 135 is 1 / 6 or less of the short side dimension L2 in the first direction (X-axis direction) inside the frame body 120, the displacement of the first vibration plate 110 can be increased, thereby increasing the transmission sound pressure and reception sensitivity of the ultrasonic transducer 100.

[0068] Below, we will explain the results of analysis performed by changing the simulation analysis conditions from those in Experimental Example 1. The following analysis results will only describe the conditions that were changed from those in Experimental Example 1, and conditions that are not described are the same as the analysis conditions in Experimental Example 1.

[0069] Figure 23 is a graph showing the results of a simulation analysis using the finite element method of the change in displacement of the first vibration plate in the second experimental example when the thickness of the piezoelectric body is changed to 0.2 mm from the analysis conditions of the first experimental example, and the short-side dimension W of the second vibration plate is changed while the center position of the second vibration plate in the first direction (X-axis direction) is fixed.

[0070] As shown in Figure 23, in the second experimental example, when the short side dimension W of the second vibration plate in the first direction (X-axis direction) was 1.2 mm or more and 1.8 mm or less, that is, when the average distance D1 and the average distance D2 were each 0 mm or more and 0.3 mm or less, the displacement of the first vibration plate 110 could be ensured at a high level of 0.31 μm or more within the resonant frequency range of 158 kHz or more and 159 kHz or less, and the transmission sound pressure and reception sensitivity of the ultrasonic transducer 100 could be increased.

[0071] Figure 24 is a graph showing the results of a simulation analysis using the finite element method of the change in displacement of the first diaphragm in the third experimental example when the thickness of the second diaphragm was changed to 0.3 mm from the analysis conditions of the first experimental example, and the short-side dimension W of the second diaphragm was changed while the center position of the second diaphragm in the first direction (X-axis direction) was fixed.

[0072] As shown in Figure 24, in the third experimental example, when the short dimension W of the second vibration plate in the first direction (X-axis direction) was 1.2 mm or more and 1.8 mm or less, that is, when the average distance D1 and the average distance D2 were each 0 mm or more and 0.3 mm or less, the displacement of the first vibration plate 110 could be ensured at a high level of 0.55 μm or more within the resonant frequency range of 150 kHz or more and 160 kHz or less, and the transmission sound pressure and reception sensitivity of the ultrasonic transducer 100 could be increased.

[0073] Figure 25 is a graph showing the results of a simulation analysis using the finite element method of the change in displacement of the first diaphragm in the fourth experimental example when the short dimension inside the frame body was changed to 2.2 mm from the analysis conditions of the first experimental example, and the short dimension W of the second diaphragm was changed while the center position of the second diaphragm in the first direction (X-axis direction) was fixed.

[0074] As shown in Figure 25, in the fourth experimental example, when the short side dimension W of the second vibration plate in the first direction (X-axis direction) was 1.6 mm or more and 2.2 mm or less, that is, when the average distance D1 and the average distance D2 were each 0 mm or more and 0.3 mm or less, the displacement of the first vibration plate 110 could be ensured at a high level of 0.65 μm or more within the resonant frequency range of 100 kHz or more and 110 kHz or less, and the transmission sound pressure and reception sensitivity of the ultrasonic transducer 100 could be increased.

[0075] Figure 26 is a graph showing the results of a simulation analysis using the finite element method of the change in displacement of the first vibration plate in the fifth experimental example when the thickness of the piezoelectric body was changed to 0.2 mm and the short dimension inside the frame body to 2.2 mm from the analysis conditions of the first experimental example, and the short dimension W of the second vibration plate was changed while the center position of the second vibration plate in the first direction (X-axis direction) was fixed.

[0076] As shown in Figure 26, in the fifth experimental example, when the short side dimension W of the second vibration plate in the first direction (X-axis direction) was 1.6 mm or more and 2.2 mm or less, that is, when the average distance D1 and the average distance D2 were each 0 mm or more and 0.3 mm or less, the displacement of the first vibration plate 110 could be ensured at a high level of 0.44 μm or more at a resonant frequency of 108 kHz, and the transmission sound pressure and reception sensitivity of the ultrasonic transducer 100 could be increased.

[0077] Figure 27 is a graph showing the results of a simulation analysis using the finite element method of the change in displacement of the first diaphragm in the sixth experimental example when the material of the second diaphragm was changed from the analysis conditions of the first experimental example to a piezoelectric ceramic, and the central position of the second diaphragm in the first direction (X-axis direction) was fixed while the short-side dimension W of the second diaphragm was changed.

[0078] As shown in Figure 27, in the sixth experimental example, when the short dimension W of the second vibration plate in the first direction (X-axis direction) was 1.2 mm or more and 1.8 mm or less, that is, when the average distance D1 and the average distance D2 were each 0 mm or more and 0.3 mm or less, the displacement of the first vibration plate 110 could be ensured at a high level of 0.55 μm or more within the resonant frequency range of 150 kHz or more and 160 kHz or less, and the transmission sound pressure and reception sensitivity of the ultrasonic transducer 100 could be increased.

[0079] Next, we will explain the results of the seventh experimental example, in which a simulation analysis was performed using the finite element method to determine the progression of the displacement of the first diaphragm when the center position of the second diaphragm in the first direction (X-axis direction) was shifted while the short-side dimension W of the second diaphragm was changed.

[0080] Fig. 28 is a graph showing the results of a simulation analysis using the finite element method of the change in displacement of the first diaphragm when the center position of the second diaphragm in the first direction (X-axis direction) is shifted in the seventh experimental example. In Fig. 28, the vertical axis represents the displacement (μm) of the first diaphragm 110, and the horizontal axis represents the amount of shift (mm) of the center position of the second diaphragm in the first direction (X-axis direction). In Fig. 28, the data for the short-side dimension W of the second diaphragm of 1.5 mm is shown by the solid line, the data for 1.4 mm by the dotted line, the data for 1.3 mm by the dashed-dot line, and the data for 1.2 mm by the dashed-dot line.

[0081] The other conditions for the simulation analysis in Experimental Example 7 were the same as those in Experimental Example 1. In addition, the direction in which the center position of the second diaphragm was shifted was one of the first directions (X-axis direction), and the center position of the second diaphragm was shifted until the average distance D1 became 0 mm.

[0082] Figure 29 is a cross-sectional view showing the displacement state simulated and analyzed using the finite element method when the ultrasonic transducer of the ninth embodiment, in which the short dimension W of the second vibration plate in the first direction (X-axis direction) is 1.5 mm, the deviation of the center position of the second vibration plate in the first direction (X-axis direction) is 0.15 mm, the average distance D1 is 0 mm, and the average distance D2 is 0.3 mm, is transmitting or receiving ultrasonic waves in the seventh experimental example.

[0083] Figure 30 is a cross-sectional view showing the displacement state simulated and analyzed using the finite element method when the ultrasonic transducer of the third comparative example, in which the short dimension W of the second vibration plate in the first direction (X-axis direction) is 1.2 mm, the deviation of the center position of the second vibration plate in the first direction (X-axis direction) is 0.3 mm, the average distance D1 is 0 mm, and the average distance D2 is 0.6 mm, is transmitting or receiving ultrasonic waves in the seventh experimental example.

[0084] As shown in Figure 28, in the seventh experimental example, when the short dimension W of the second vibration plate in the first direction (X-axis direction) is 1.2 mm, and the deviation of the center position of the second vibration plate in the first direction (X-axis direction) is 0 mm, that is, when the average distance D1 and the average distance D2 are each 0.3 mm, the displacement of the first vibration plate 110 can be ensured at a high level of 0.56 μm or more, and the transmission sound pressure and reception sensitivity of the ultrasonic transducer 100 can be increased.

[0085] When the short side dimension W of the second vibration plate in the first direction (X-axis direction) is 1.3 mm, and the deviation of the center position of the second vibration plate in the first direction (X-axis direction) is within 0.1 mm, that is, when the average distance D2 is within 0.35 mm, the displacement of the first vibration plate 110 can be ensured at a high level of 0.56 μm or more, and the transmission sound pressure and reception sensitivity of the ultrasonic transducer 100 can be increased.

[0086] When the short side dimension W of the second vibration plate in the first direction (X-axis direction) is 1.4 mm, and the deviation of the center position of the second vibration plate in the first direction (X-axis direction) is within 0.15 mm, that is, when the average distance D2 is within 0.35 mm, the displacement of the first vibration plate 110 can be ensured at a high level of 0.56 μm or more, and the transmission sound pressure and reception sensitivity of the ultrasonic transducer 100 can be increased.

[0087] When the short side dimension W of the second vibration plate in the first direction (X-axis direction) is 1.5 mm, and the deviation of the central position of the second vibration plate in the first direction (X-axis direction) is within 0.15 mm, that is, when the average distance D2 is within 0.3 mm, the displacement of the first vibration plate 110 can be ensured at a high level of 0.56 μm or more, and the transmission sound pressure and reception sensitivity of the ultrasonic transducer 100 can be increased.

[0088] As shown in Figure 29, when the average distance D2 is 0.3 mm, the stress distribution within the piezoelectric body 131 shows that high compressive stress occurs in the part above the second vibration plate 135 and high tensile stress occurs in the part corresponding to the average distance D2, but the vibration mode is maintained and no significant decrease in the displacement of the first vibration plate 110 is observed.

[0089] As shown in Figure 30, when the average distance D2 is 0.6 mm, the stress distribution within the piezoelectric body 131 shows that high compressive stress occurs in the part above the second vibration plate 135 and high tensile stress occurs in the part corresponding to the average distance D2, the vibration mode changes, the first vibration plate 110 is deformed into an irregular shape, and a large decrease in the displacement of the first vibration plate 110 is observed.

[0090] According to the mechanism of action shown in Figures 29 and 30, when the central position of the second vibration plate 135 in the first direction (X-axis direction) is shifted from the central position of the inner space of the frame body 120 in the first direction (X-axis direction), if each of the average distance D1 and the average distance D2 is 1 / 6 or less of the short-side dimension L2 in the first direction (X-axis direction) inside the frame body 120, it is possible to ensure a high level of displacement of 0.56 μm or more, and it is considered that the transmission sound pressure and reception sensitivity of the ultrasonic transducer 100 can be increased.

[0091] From the results of the above-described first to seventh experimental examples, it was found that the second diaphragm 135 is located in a region sandwiched between both end edges in the first direction (X-axis direction) on the inner peripheral surface of the frame body 120 in the first direction (X-axis direction) when viewed from the third direction (Z-axis direction) perpendicular to the first diaphragm 110, and that the second diaphragm 135 is located in a region sandwiched between both end edges in the first direction (X-axis direction) on the inner peripheral surface of the frame body 120 and one end edge 135s1 in the first direction (X-axis direction) of the second diaphragm 135 When the average distance D1 between the first edge 120s2 in the first direction (X-axis direction) on the inner surface of the frame body 120 and the average distance D2 in the first direction (X-axis direction) between the other edge 120s2 in the first direction (X-axis direction) of the second vibration plate 135 and the other edge 135s2 in the first direction (X-axis direction) of the second vibration plate 135 is each 1 / 6 or less of the short-side dimension L2 in the first direction (X-axis direction) inside the frame body 120, it is considered that the displacement of the first vibration plate 110 can be increased, and the transmission sound pressure and reception sensitivity of the ultrasonic transducer 100 can be increased.

[0092] 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).

[0093] 31 is a perspective view of an ultrasonic transducer according to a first modification of the first embodiment of the present invention, viewed from the second diaphragm side. As shown in FIG. 31 , in the ultrasonic transducer 100a according to the first modification of the first embodiment of the present invention, the length of the second diaphragm 135 in the second direction (Y-axis direction) is longer than the length of the piezoelectric body 131 in the second direction (Y-axis direction). The frame body 120 and the second diaphragm 135 are each plated with Ag or the like. The frame body 120 and the piezoelectric body 131 are electrically connected by pressure bonding, and the piezoelectric body 131 and the second diaphragm 135 are also electrically connected by pressure bonding. This allows wiring 10 for supplying power to the piezoelectric body 131 to be easily connected to the ends of the frame body 120 and the second diaphragm 135 in the second direction (Y-axis direction).

[0094] FIG. 32 is a perspective view of an ultrasonic transducer according to a second modified example of the first embodiment of the present invention, as viewed from the first diaphragm side. As shown in FIG. 32, in the ultrasonic transducer 100b according to the second modified example of the first embodiment of the present invention, a slit 110s extending in a first direction (X-axis direction) is formed in the first diaphragm 110. In this modified example, the length dimension 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 body 120. The width dimension 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 body 120 in the second direction (Y-axis direction) to a position inward by the above 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.

[0095] As a result, the internal space inside the frame body 120 is connected to the external space outside the frame body 120 through the slits 110s, which reduces pressure changes in the internal space when, for example, an adhesive that bonds the first diaphragm 110 and the frame body 120 is heated and cured, thereby preventing an increase in internal stress within the ultrasonic transducer 100. Furthermore, the areas adjacent to the slits 110s become free ends of the resonantly vibrating first diaphragm 110 and are 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.

[0096] (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 unimorph piezoelectric 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.

[0097] Fig. 33 is a side view showing the configuration of an ultrasonic transducer according to embodiment 2 of the present invention. Fig. 34 is a rear view of the ultrasonic transducer shown in Fig. 33 as seen from the direction of arrow XXXIV. Fig. 35 is an exploded perspective view showing the stacked state of each component of the ultrasonic transducer according to embodiment 2 of the present invention.

[0098] 33 to 35, 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 unimorph piezoelectric vibrators 230. The plurality of frame bodies 220 are bonded to the first diaphragm 210, and the plurality of unimorph piezoelectric vibrators 230 are respectively bonded to the plurality of frame bodies 220.

[0099] Here, a method for manufacturing the ultrasonic transducer 200 will be described. As shown in Fig. 35, the first diaphragm 210 has a flat plate shape, and a plurality of slits 211 extending in the second direction (Y-axis direction) are formed at intervals in the first direction (X-axis direction). 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 are formed by etching, cutting, or the like.

[0100] 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 four or more times the shortest distance between the short side portions 222.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 36 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. As shown in FIG. 36, 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 using a dicer or the like along multiple 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).

[0105] 35 , adjacent second diaphragms 235 in the first direction (X-axis direction) are connected to each other by connecting portions 236 at positions near both ends in the second direction (Y-axis direction). The connecting portions 236 extend in the first direction (X-axis direction). The connecting portions 236 are formed by etching, pressing, cutting, or the like.

[0106] A recess 237 is formed in the connecting portion 236 in a portion facing the gap between the piezoelectric bodies 131 adjacent in the first direction (X-axis direction) in the plurality of unimorph piezoelectric vibrators 230. The recess 237 is formed by half etching, pressing, cutting, or the like.

[0107] The second vibration plate 235 is bonded to the piezoelectric body 131 with an adhesive so that the recess 237 faces the cut line LC in the third direction (Z-axis direction). As a result, as shown in Fig. 34, each of the multiple unimorph piezoelectric vibrators 230 includes the piezoelectric body 131 facing the first vibration plate 210 at a distance, and multiple second vibration plates 235 provided on the side of the piezoelectric body 131 opposite the frame body 220 side. The multiple unimorph piezoelectric vibrators 230 are arranged side by side in the first direction (X-axis direction).

[0108] The recess 237 functions as a reservoir for the adhesive and prevents the adhesive from seeping into the cut line LC, thereby preventing the adjacent unimorph piezoelectric vibrators 230 from interfering with each other and deteriorating the characteristics of the ultrasonic transducer 200.

[0109] In this embodiment, each of the frame body 220 and the second diaphragm 235 is plated with Ag or the like. The frame body 220 and the piezoelectric body 131 are electrically connected by pressure and compression, and the piezoelectric body 131 and the second diaphragm 235 are electrically connected by pressure and compression. As a result, as shown in Fig. 34, by connecting wiring 10 for supplying power to the piezoelectric body 131 to only two locations on the ends of the frame body 220 and the second diaphragm 235 in the second direction (Y-axis direction), it is possible to drive a plurality of unimorph piezoelectric vibrators 230.

[0110] 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.

[0111] 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.

[0112] A parametric speaker equipped with 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 requiring 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.

[0113] In order for audible sound to attenuate after a propagation distance of 30 cm, the Rayleigh distance must be 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 ultrasonic frequency is 100 kHz, the longitudinal dimension of the vibration region of first diaphragm 210 is 36 mm or less, when the ultrasonic frequency is 150 kHz, the longitudinal dimension of the vibration region of first diaphragm 210 is 29.4 mm or less, and when the ultrasonic frequency is 200 kHz, the longitudinal dimension of the vibration region of first diaphragm 210 is 25.5 mm or less. When the ultrasonic frequency is 100 kHz or more, the longitudinal dimension L1 is between 4 and 24 times the lateral dimension L2.

[0114] (Note) It will be understood by those skilled in the art that the exemplary embodiments described above are specific examples of the following aspects.

[0115] <1> A piezoelectric 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 unimorph piezoelectric vibrator attached to the at least one frame body, the unimorph piezoelectric vibrator including a piezoelectric body facing the first vibration plate with a gap therebetween and a second vibration plate provided on the opposite side of the piezoelectric body from the frame body side, wherein the first vibration plate resonates and vibrates in an opposite phase to the at least one unimorph piezoelectric vibrator in a direction perpendicular to the first vibration plate, and the longitudinal dimension inside the at least one frame body is four times or more the lateral dimension inside the at least one frame body perpendicular to the longitudinal direction, An ultrasonic transducer in which the second vibration plate is located in an area sandwiched between both short-side edges of the inner surface of the at least one frame body in the short direction when viewed from a direction perpendicular to the first vibration plate, and the average distance in the short direction between one short-side edge of the inner surface of the at least one frame body and one short-side edge of the second vibration plate, and the average distance in the short direction between the other short-side edge of the inner surface of the at least one frame body and the other short-side edge of the second vibration plate, are each 1 / 6 or less of the short-side dimension inside the at least one frame body.

[0116] <2> The ultrasonic transducer described in <1>, wherein the longitudinal dimension inside the at least one frame body is larger than the smallest dimension of the piezoelectric body in the longitudinal direction of the at least one unimorph piezoelectric vibrator, and the average distance in the longitudinal direction of the gap between at least one longitudinal edge of the inner surface of the at least one frame body and at least one longitudinal edge of the frame-side surface of the piezoelectric body in the at least one unimorph piezoelectric vibrator is 1.3 times or less the short side dimension inside the at least one frame body.

[0117] <3> The ultrasonic transducer described in <1> or <2>, wherein the at least one frame body is arranged in a plurality of positions aligned in the short side direction and joined to the first vibration plate, the at least one frame body adjacent to each other in the short side direction are connected to each other at both ends in the longitudinal direction, and the at least one unimorph type piezoelectric vibrator is arranged in a plurality of positions aligned in the short side direction.

[0118] <4> The ultrasonic transducer described in <3>, wherein the second vibration plates adjacent to each other in the short direction in the at least one unimorph type piezoelectric vibrator are connected by a connecting portion extending in the short direction at positions near both ends in the longitudinal direction of each other, and a recess is formed in the connecting portion in a portion facing a gap between the piezoelectric bodies adjacent to each other in the short direction in the at least one unimorph type piezoelectric vibrator.

[0119] <5> A parametric speaker comprising the ultrasonic transducer according to any one of <1> to <4>, and reproducing an audible sound by modulating and driving the ultrasonic transducer.

[0120] In the above-described embodiments and examples, configurations that can be combined may be combined with each other.

[0121] 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.

[0122] 10 Wiring, 100, 100a, 100b, 100d, 101, 102, 103, 104, 105, 106, 200 Ultrasonic transducer, 110, 210 First vibration plate, 110b Reverse displacement portion, 110c Intermediate portion, 110e End portion, 110p Large displacement portion, 110s, 211, 223 Slit, 120, 220 Frame body, 120e, 120s1, 120s2, 130e, 135s1, 135s2 Edge, 120s Inner surface, 121, 221 Long side portion, 122, 222 Short side portion, 130, 230 Unimorph type piezoelectric vibrator, 130s, 131b Surface, 131 Piezoelectric body, 132 First electrode, 133 Second electrode, 135, 235 Second diaphragm, 140 Processing circuit, 236 Connection portion, 237 Recess.

Claims

1. A piezoelectric transducer comprising: a first vibration plate; at least one frame extending in a longitudinal direction and joined to the first vibration plate; and at least one unimorph type piezoelectric vibrator attached to each of the at least one frame and including a piezoelectric body facing the first vibration plate with a gap therebetween and a second vibration plate provided on the opposite side of the piezoelectric body to the frame side, wherein the first vibration plate resonates and vibrates in an opposite phase to the at least one unimorph type piezoelectric vibrator in a direction perpendicular to the first vibration plate, and the longitudinal dimension inside the at least one frame is four or more times the transverse dimension perpendicular to the longitudinal direction inside the at least one frame, An ultrasonic transducer, wherein the second vibration plate is located in an area sandwiched between both short edge portions of the inner surface of the at least one frame body in the short side direction when viewed from a direction perpendicular to the first vibration plate, and the average distance in the short side direction between one short edge portion of the inner surface of the at least one frame body and one short edge portion of the second vibration plate, and the average distance in the short side direction between the other short edge portion of the inner surface of the at least one frame body and the other short edge portion of the second vibration plate, are each 1 / 6 or less of the short side dimension inside the at least one frame body.

2. An ultrasonic transducer as described in claim 1, wherein the longitudinal dimension inside the at least one frame body is greater than the smallest dimension of the piezoelectric body in the longitudinal direction of the at least one unimorph type piezoelectric vibrator, and the average distance in the longitudinal direction of the gap between at least one longitudinal edge of the inner surface of the at least one frame body and at least one longitudinal edge of the frame side surface of the piezoelectric body in the at least one unimorph type piezoelectric vibrator is 1.3 times or less than the short side dimension inside the at least one frame body.

3. An ultrasonic transducer as described in claim 1 or claim 2, wherein the at least one frame body is arranged in a plurality of positions aligned in the short side direction and joined to the first vibration plate, the at least one frame body adjacent to each other in the short side direction are connected to both ends in the longitudinal direction, and the at least one unimorph type piezoelectric vibrator is arranged in a plurality of positions aligned in the short side direction.

4. An ultrasonic transducer as described in claim 3, wherein the second vibration plates adjacent to each other in the short direction in the at least one unimorph type piezoelectric vibrator are connected by a connecting portion extending in the short direction at positions near both ends in the longitudinal direction of each of the second vibration plates, and a recess is formed in the connecting portion in a portion facing a gap between the piezoelectric bodies adjacent to each other in the short direction in the at least one unimorph type piezoelectric vibrator.

5. A parametric speaker comprising the ultrasonic transducer according to any one of claims 1 to 4, which reproduces an audible sound by modulating the ultrasonic transducer.

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