Ultrasonic transducer and parametric speaker provided with same

Abstract

The ultrasonic transducer is provided with a first vibrating plate (110), at least one housing (120), and at least one ultrasonic transducer (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 transducer (130) is attached to each of the at least one housing (120), and faces the first vibrating plate (110) at a distance from the first vibrating plate (110). The first vibrating plate (110) resonates in a phase opposite to the at least one ultrasonic transducer (130) in a direction orthogonal to the first vibrating plate (110). The dimension of the inside of the at least one housing (120) in the longitudinal direction is at least four times the dimension of the inside of the at least one housing (120) in the short direction orthogonal to the longitudinal direction.

Description

Technical Field

[0001] The present invention relates to an ultrasonic transducer and a parametric loudspeaker having the ultrasonic transducer. Background Art

[0002] Prior documents that disclose the structure of a super-directional acoustic device include Japanese Patent Publication No. 2003-47085 (Patent Document 1) and Japanese Patent No. 6333480 (Patent Document 2). The super-directional acoustic device described in Patent Document 1 is constructed by spreading a plurality of ultrasonic transducers on a printed circuit board and arranging them so that their outer circumferences are roughly circular. The plurality of ultrasonic transducers are divided into two groups with different installation heights.

[0003] The super-directional acoustic device described in Patent Document 2 includes a first ultrasonic transmitter and a second ultrasonic transmitter. The second ultrasonic transmitter is arranged on the axis of the first ultrasonic transmitter and in front of the radiation surface. The phase of the carrier signal radiated by the second ultrasonic transmitter is inverse to the phase of the carrier signal included in the signal radiated by the first ultrasonic transmitter.

[0004] Prior Art Literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2003-47085

[0007] Patent Document 2: Japanese Patent No. 6333480 Summary of the invention

[0008] Problem that the invention aims to solve

[0009] In the super-directional acoustic device described in Patent Document 1, a plurality of ultrasonic transducers are arranged in two groups at different heights, resulting in a complex structure. In the super-directional acoustic device described in Patent Document 2, a second ultrasonic transmitter is arranged outside a first ultrasonic transmitter, resulting in a large-scale device.

[0010] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an ultrasonic transducer capable of improving the sound pressure level with a simple and compact structure, and a parametric speaker including the ultrasonic transducer.

[0011] Technical solutions to solve problems

[0012] The ultrasonic transducer based on the present invention comprises a first vibration plate, at least one frame, and at least one ultrasonic vibrator. The at least one frame extends in the long side direction and is joined to the first vibration plate. The at least one ultrasonic vibrator is respectively mounted on the at least one frame, and is spaced apart from the first vibration plate and is opposed to the first vibration plate. The first vibration plate resonates and vibrates in a direction orthogonal to the first vibration plate with a phase opposite to that of the at least one ultrasonic vibrator. The dimension of the inner side of the at least one frame in the long side direction is at least 4 times the dimension of the inner side of the at least one frame in the short side direction orthogonal to the long side direction.

[0013] Effects of the Invention

[0014] According to the present invention, in an ultrasonic transducer, the sound pressure level can be increased with a simple and compact structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a longitudinal sectional view showing the structure of the ultrasonic transducer according to the first embodiment of the present invention.

[0016] Figure 2 This is an exploded perspective view showing the structure of the ultrasonic transducer according to Embodiment 1 of the present invention.

[0017] Figure 3 It is a perspective view showing the structure of a housing included in the ultrasonic transducer according to the first embodiment of the present invention.

[0018] Figure 4 This is a cross-sectional view showing the structure of an ultrasonic vibrator included in the ultrasonic transducer according to the first embodiment of the present invention.

[0019] Figure 5 This is a perspective view showing a displacement state of the ultrasonic transducer according to the first embodiment of the present invention when transmitting or receiving ultrasonic waves, which is simulated and analyzed using the finite element method.

[0020] Figure 6 From the direction of the arrow on line VI-VI Figure 5 A cross-sectional view of an ultrasonic transducer for observation.

[0021] Figure 7 This is a graph obtained by simulation analysis using the finite element method on the transition of the resonance frequency of the first diaphragm when the short side dimension inside the frame is fixed and the long side dimension is changed.

[0022] Figure 8 This is a graph obtained by simulation analysis using the finite element method on the transition of the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer when the short side dimension inside the frame is fixed and the long side dimension is changed.

[0023] Fig. 9 It is a perspective view showing the structure of an ultrasonic element array according to a first comparative example.

[0024] Fig.10 This is a graph obtained by simulation analysis using the finite element method on the relationship between the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer and the thickness of the first diaphragm.

[0025] Fig.11 This is a graph obtained by simulation analysis using the finite element method on the relationship between the internal stress (normalized per unit sound pressure) generated in the ultrasonic transducer in the third direction (Z-axis direction) and the thickness of the first diaphragm.

[0026] Fig.12 This is a graph obtained by simulation analysis using the finite element method on the relationship between the displacement of the first vibration plate and the frequency of the ultrasonic vibrator in the ultrasonic transducer according to the present embodiment, the ultrasonic transducer according to the first modification, and the ultrasonic transducer according to the second modification.

[0027] Fig.13 It is a cross-sectional view showing the structure of an ultrasonic transducer according to a third modification.

[0028] Fig.14 It is a cross-sectional view showing the structure of an ultrasonic transducer according to a fourth modification.

[0029] Fig.15 It is a cross-sectional view showing the structure of an ultrasonic transducer according to a fifth modification.

[0030] Fig.16 This is a longitudinal sectional view showing the structure of an ultrasonic transducer according to a sixth modified example of the first embodiment of the present invention.

[0031] Fig.17 This is a side view showing the structure of an ultrasonic transducer according to Embodiment 2 of the present invention.

[0032] Fig.18 From the direction of arrow XVIII Fig.17 The ultrasonic transducer is shown viewed from the rear.

[0033] Fig.19 This 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.

[0034] Fig. 20 This is a plan view showing the positional relationship in the first direction (X-axis direction) in the step of cutting the piezoelectric body of the ultrasonic transducer according to the second embodiment of the present invention.

[0035] Fig.21This is a perspective view showing a displacement state of the ultrasonic transducer according to the second embodiment of the present invention when transmitting or receiving ultrasonic waves, which is simulated and analyzed using the finite element method.

[0036] Fig. 22 It is a perspective view showing the structure of an ultrasonic element array according to a second comparative example.

[0037] Fig.23 This is a graph obtained by actually measuring the transition of attenuation of the sound pressure level due to the propagation distance in the ultrasonic transducer according to the present embodiment and the ultrasonic transducer according to the second comparative example.

[0038] Fig.24 This is a side view showing a state in which an ultrasonic transducer according to a modification of the present embodiment constituting a phased array system radiates ultrasonic waves in a two-dimensional manner in a third direction (Z-axis direction).

[0039] Fig.25 This is a diagram showing the drive start delay time when the ultrasonic transducers A to G are set to the same emission timing of ultrasonic waves in the first state by the processing circuit.

[0040] Fig.26 This is a side view showing a state in which an ultrasonic transducer according to a modification of the present embodiment radiates ultrasonic waves in a planar manner in a direction inclined toward a first direction (X-axis direction) with respect to a third direction (Z-axis direction).

[0041] Fig. 27 This is a diagram showing the drive start delay time in the second state in which the ultrasonic transducers G to A emit ultrasonic waves in this order by the processing circuit.

[0042] Fig.28 This is a side view showing a state in which the ultrasonic transducer according to the modification example of the present embodiment radiates ultrasonic waves in the third direction (Z-axis direction) so as to be concentrated at the center in the first direction (X-axis direction).

[0043] Fig.29 This is a diagram showing the drive start delay time in the third state where the ultrasonic transducers A to D and the ultrasonic transducers G to D are radiated in this order by the processing circuit. DETAILED DESCRIPTION

[0044] Hereinafter, the ultrasonic transducer involved in each embodiment of the present invention will be described with reference to the accompanying drawings. In the description of the following embodiments, the same or equivalent parts in the figures are marked with the same figure marks, and their description will not be repeated. The present invention is applicable to applications of ultrasonic waves that require high sound pressure, such as ultrasonic transducers for parametric speakers, ultrasonic sensors, or non-contact tactile feedback (haptics). In the following embodiments, ultrasonic transducers for parametric speakers are exemplified and described, but the uses of ultrasonic transducers are not limited to this.

[0045] (Implementation method 1)

[0046] Figure 1 This is a longitudinal sectional view showing the structure of the ultrasonic transducer according to the first embodiment of the present invention. Figure 2 FIG. 1 is an exploded perspective view showing the structure of the ultrasonic transducer according to Embodiment 1 of the present invention. Figure 1 as well as Figure 2 As shown, the ultrasonic transducer 100 according to the first embodiment of the present invention includes a first vibration plate 110 , a frame 120 , and an ultrasonic vibrator 130 .

[0047] The first vibration plate 110 has a flat plate shape. The first vibration plate 110 is made of aluminum alloy such as duralumin containing aluminum, or metal such as stainless steel. In the present embodiment, the first vibration plate 110 is made of stainless steel. The thickness of the first vibration plate 110 is, for example, 0.1 mm or more and 0.2 mm or less.

[0048] The frame 120 has a rectangular ring shape. The frame 120 has a short side direction along the first direction (X-axis direction) and a long side direction along the second direction (Y-axis direction). The frame 120 extends in the second direction (Y-axis direction). The axial direction of the frame 120 is along the third direction (Z-axis direction). One end of the frame 120 in the third direction (Z-axis direction) is bonded to the first vibration plate 110 by a bonding agent including epoxy resin or the like.

[0049] The frame 120 is formed of a metal such as an aluminum alloy or stainless steel, glass epoxy or resin. From the viewpoint of suppressing characteristic changes caused by temperature changes of the ultrasonic transducer 100, the frame 120 is preferably made of metal. On the other hand, from the viewpoint of lowering the frequency of the ultrasonic wave transmitted or received by the ultrasonic transducer 100 and miniaturizing the ultrasonic transducer 100, the frame 120 is preferably made of resin. In the present embodiment, the frame 120 is made of stainless steel. The thickness of the frame 120 is, for example, not less than 0.2 mm and not more than 0.8 mm.

[0050] Figure 3 FIG. 1 is a perspective view showing the structure of a frame body included in the ultrasonic transducer according to Embodiment 1 of the present invention. Figure 3 As shown in FIG. 1 , 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 interval between the short sides 122 is at least 4 times the shortest interval between the long sides 121. That is, the long side dimension L1 of the inner side of the frame body 120 in the second direction (Y-axis direction) is at least 4 times the short side dimension L2 of the inner side of the frame body 120 in the first direction (X-axis direction).

[0051] In addition, the corners sandwiched by the long side 121 and the short side 122 may also be chamfered. In addition, when viewed from the third direction (Z-axis direction), the short side 122 is not limited to a straight line, but may be an arc convex toward the inside of the frame 120 or an arc convex toward the outside of the frame 120.

[0052] The resonance frequency of the first vibration plate 110 can be adjusted by changing the short side dimension L2 in the first direction (X-axis direction) inside the frame 120. For example, when the resonance frequency of the first vibration plate 110 is set to 100 kHz or more, the short side dimension L2 is set to 1.5 mm or more and 3 mm or less.

[0053] The long side dimension L1 in the second direction (Y-axis direction) inside the frame 120 is 4 times or more the short side dimension L2 . From the viewpoint of increasing the sound pressure level of the ultrasonic wave transmitted by the ultrasonic transducer 100 , the long side dimension L1 is, for example, 20 mm or more.

[0054] Figure 4 1 is a cross-sectional view showing the structure of an ultrasonic vibrator included in the ultrasonic transducer according to Embodiment 1 of the present invention. Figure 1 As shown, the ultrasonic vibrator 130 is mounted on the frame 120 and faces the first vibration plate 110 at a distance. Specifically, the ultrasonic vibrator 130 is mounted on the other end of the frame 120 in the third direction (Z-axis direction) and faces the first vibration plate 110 with the inner space of the frame 120 interposed therebetween.

[0055] like Figure 1 , Figure 2 as well as Figure 4 As shown in FIG. 1 , the ultrasonic vibrator 130 is a piezoelectric element including a piezoelectric body 131. Figure 4As shown, in the present 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 are opposite to each other in the third direction (Z-axis direction). The two piezoelectric bodies 131 are sandwiched by the first electrode 132 and the second electrode 133, and an intermediate electrode 134 is arranged 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, greater than 0.5 mm and less than 0.85 mm.

[0056] Figure 5 This is a perspective view showing a displacement state of the ultrasonic transducer according to the first embodiment of the present invention when transmitting or receiving ultrasonic waves, which is simulated and analyzed using the finite element method. Figure 6 From the direction of the arrow on line VI-VI Figure 5 As simulation analysis conditions, the thickness of the first vibration plate 110 is set to 0.1 mm, the combined thickness of the two piezoelectric bodies 131 is set to 0.8 mm, the inner long side dimension L1 of the frame 120 is set to 20 mm, the short side dimension L2 is set to 2 mm, and the thickness of the frame 120 in the third direction (Z-axis direction) is set to 0.4 mm.

[0057] like Figure 5 as well as Figure 6 As shown, in the vibration mode of the ultrasonic transducer 100 according to the first embodiment of the present invention, the first vibration plate 110 resonates and vibrates in a third direction (Z-axis direction) orthogonal to the first vibration plate 110 in a phase opposite to that of the ultrasonic vibrator 130. That is, Figure 6 As shown, the displacement direction of the resonance vibration Bm of the first vibration plate 110 and the displacement direction of the resonance vibration Bp of the ultrasonic vibrator 130 are opposite to each other in the third direction (Z-axis direction). In this embodiment, the resonance frequency of the first vibration plate 110 and the ultrasonic vibrator 130 is greater than 100 kHz.

[0058] In the first vibration plate 110, the middle portion 110c located in the middle of the long side direction of the inner side of the frame 120 becomes the antinode of the resonant vibration, and the end portions 110e located at both ends of the long side direction of the inner side of the frame 120 become the nodes of the resonant vibration. That is, the portion of the first vibration plate 110 located above the inner space of the frame 120 becomes the vibration region that performs the resonant vibration. The long side dimension of the vibration region of the first vibration plate 110 becomes the same as the long side dimension L1 of the inner side of the frame 120, and the short side dimension of the vibration region of the first vibration plate 110 becomes the same as the short side dimension L2 of the inner side of the frame 120.

[0059] Here, the relationship between the resonance frequency of the first vibration plate 110 and the inner long side dimension L1 of the frame body 120 will be described.

[0060] Figure 7 This is a graph obtained by simulation analysis using the finite element method on the change in the resonance frequency of the first vibration plate when the short side dimension of the inner side of the frame is fixed and the long side dimension is changed. Figure 7 In FIG. 1 , the vertical axis shows the resonance frequency (kHz) of the first vibration plate 110 , and the horizontal axis shows the inner long side dimension L1 (mm) of the frame body 120 . As a simulation analysis condition, the inner short side dimension L2 of the frame body 120 is fixed to 2 mm.

[0061] like Figure 7 As shown, when the long side dimension L1 of the inner side of the frame 120 is 2 mm, the resonance frequency of the first vibration plate 110 is 220 kHz. When the long side dimension L1 increases to 8 mm and the long side dimension of the vibration region of the first vibration plate 110 increases, the resonance frequency of the first vibration plate 110 decreases to 122 kHz. Then, even if the long side dimension L1 of the inner side of the frame 120 becomes larger than 8 mm and the long side dimension of the vibration region of the first vibration plate 110 further increases, the resonance frequency of the first vibration plate 110 becomes substantially fixed at 122 kHz.

[0062] That is, the following situation is shown, namely, the resonant frequency of the first vibration plate 110 is determined by the sound velocity of the first vibration plate 110 and the reflection of the vibration with the frame 120 as the fixed end, but from the time when the long side dimension L1 on the inner side of the frame 120 exceeds 4 times the short side dimension L2, the influence of the short side dimension L2 dominates the reflection of the vibration, and even if the long side dimension L1 becomes larger than 4 times the short side dimension L2, the state of the vibration reflection will not change.

[0063] Next, the result of simulation analysis using the finite element method on the relationship between the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer 100 and the inner long side dimension L1 of the housing 120 will be described.

[0064] Figure 8 This is a graph obtained by simulation analysis using the finite element method on the change in the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer when the short side dimension of the inner side of the frame is fixed and the long side dimension is changed. Figure 8In FIG. 1 , the vertical axis shows the sound pressure (Pa) transmitted from the ultrasonic transducer 100, and the horizontal axis shows the inner long side dimension L1 (mm) of the frame 120. As a simulation analysis condition, the inner short side dimension L2 of the frame 120 is fixed to 2 mm, and the sound pressure (Pa) at a position 30 cm away from the first vibration plate 110 in the front of the ultrasonic transducer 100 in the third direction (Z-axis direction) is calculated.

[0065] like Figure 8 As shown in FIG. 1 , as the long side dimension L1 of the inner side of the frame 120 increases, the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer 100 increases. This means that even when the long side dimension of the vibration region of the first vibration plate 110 is increased, the entire vibration region of the first vibration plate 110 between the two end portions 110e vibrates. That is, the area of ​​the vibration region can be increased by the amount by which the vibration region of the first vibration plate 110 becomes longer, and as a result, the pressure change of the air caused by the vibration of the first vibration plate 110 can be increased to obtain a high sound pressure.

[0066] As described above, the ultrasonic transducer 100 according to the present embodiment can maintain the resonance frequency substantially constant and increase the sound pressure by increasing the long side dimension of the vibration region of the first vibration plate 110. In addition, since there are nodes at both ends in the long side direction, the two ends can be supported or fixed, so the ultrasonic transducer 100 is easy to install.

[0067] Here, an ultrasonic element array according to a first comparative example in which high-frequency ultrasonic elements are arranged in an array to obtain a high sound pressure will be described.

[0068] Fig. 9 1 is a perspective view showing the structure of the ultrasonic element array according to the first comparative example. Fig. 9 As shown, in the ultrasonic element array according to the first comparative example, a plurality of ultrasonic elements 800 are arranged at intervals in the second direction (Y-axis direction). In such an ultrasonic element array, there is a space between the ultrasonic elements 800 where no sound pressure is generated, so the efficiency is reduced. In addition, since the ultrasonic element 800 of a high frequency of, for example, 100 kHz or more is small in size, it takes a lot of effort to arrange and install a plurality of ultrasonic elements 800 to form an ultrasonic element array.

[0069] Hereinafter, the thickness of the first vibration plate 110 included in the ultrasonic transducer 100 according to one embodiment of the present invention will be described in detail.

[0070] The first vibration plate 110 and the ultrasonic vibrator 130 resonate and vibrate in opposite phases to each other, forming a vibration mode like the vibration of a tuning fork. From the perspective of maintaining the physical balance between the first vibration plate 110 and the ultrasonic vibrator 130, if the sound velocity of the transverse wave of the first vibration plate 110 is set to Cv, the sound velocity of the transverse wave of the piezoelectric body 131 is set to Cp, the thickness of the first vibration plate 110 is set to Tv, and the thickness of the piezoelectric body 131 is set to Tp, it is preferable to satisfy the relationship of 0.7CpTp / Cv≤Tv≤1.3CpTp / Cv. The sound velocity Cv of the transverse wave of the first vibration plate 110 is determined by the material constituting the first vibration plate 110. The sound velocity Cp of the transverse wave of the piezoelectric body 131 is determined by the material constituting the piezoelectric body 131. When a plurality of piezoelectric bodies 131 are stacked in the ultrasonic transducer 130 , the thickness dimension Tp of the piezoelectric body 131 is the total value of the thicknesses of the plurality of piezoelectric bodies 131 .

[0071] By satisfying the relationship of 0.7CpTp / Cv≤Tv≤1.3CpTp / Cv, it is possible to maintain physical balance when the first vibration plate 110 and the ultrasonic vibrator 130 vibrate, increase the amplitude of the resonant vibration of the first vibration plate 110, increase the sound pressure, and suppress vibration leakage. In addition, it is more preferable to satisfy the relationship of Tv=CpTp / Cv. From the perspective of maintaining physical balance, when Tp=0.8, according to the relationship of Tv=0.8Cp / Cv, it is ideal that the thickness dimension Tv of the first vibration plate 110 is 0.4.

[0072] Fig.10 This is a graph showing the relationship between the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer and the thickness of the first vibration plate, which was simulated and analyzed using the finite element method. Fig.10 In FIG. 1 , the vertical axis shows the sound pressure (Pa) transmitted from the ultrasonic transducer 100, and the horizontal axis shows the thickness (mm) of the first vibration plate. As a simulation analysis condition, the total value Tp of the thickness of the two piezoelectric bodies 131 is set to 0.8 mm. Fig.10 As shown, when the thickness of the first diaphragm 110 is 0.4 mm, the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer becomes maximum.

[0073] Fig.11 This is a graph that uses the finite element method to simulate and analyze the relationship between the internal stress (normalized per unit sound pressure) generated in the third direction (Z-axis direction) of the ultrasonic transducer and the thickness of the first vibration plate. Fig.11 In FIG. 1 , the vertical axis shows the internal stress in the third direction (Z-axis direction) per unit sound pressure, and the horizontal axis shows the thickness (mm) of the first diaphragm.

[0074] like Fig.11As shown in FIG. 1 , the thinner the thickness of the first vibration plate 110 is, the smaller the internal stress (normalized value per unit sound pressure) generated in the ultrasonic transducer 100 in the third direction (Z-axis direction). In particular, when the thickness of the first vibration plate 110 is 0.24 mm or less, the internal stress (normalized value per unit sound pressure) generated in the ultrasonic transducer 100 in the third direction (Z-axis direction) is significantly reduced. By reducing the internal stress (normalized value per unit sound pressure) generated in the ultrasonic transducer 100 in the third direction (Z-axis direction), it is possible to suppress the occurrence of cracks due to internal stress at the joint between the first vibration plate 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 vibration plate 110 becomes thinner than 0.1 mm, the first vibration plate 110 becomes too soft and is not suitable as a vibrating body for oscillating ultrasonic waves.

[0075] That is, from the viewpoint of suppressing the generation of cracks caused by internal stress and generating ultrasonic waves of high sound pressure, it is preferable to satisfy the relationship of 0.25CpTp / Cv≤Tv≤0.6CpTp / Cv. In the present embodiment, by setting the thickness of the first vibration plate 110 to be greater than or equal to 0.1 mm and less than or equal to 0.2 mm, the ultrasonic transducer 100 can be driven in a state where the internal stress (normalized per unit sound pressure) in the third direction (Z-axis direction) generated in the ultrasonic transducer 100 is reduced.

[0076] Here, the results of simulation analysis using the finite element method on the driving efficiency of ultrasonic transducers when the ultrasonic transducers are bimorph-type piezoelectric transducers and unimorph-type piezoelectric transducers are described. Figure 1 The bimorph type ultrasonic transducer 130 shown in FIG. 1 is consistent with the bimorph type ultrasonic transducer 130 shown in FIG. 1 . Figure 1 As shown in the figure, the two piezoelectric bodies 131 are bonded together, and a driving voltage is applied to only one of the two piezoelectric bodies 131, and the other piezoelectric body 131 serves as a second vibration plate to which no driving voltage is applied.

[0077] Specifically, in the ultrasonic transducer of the first modified example, a driving voltage is applied to the piezoelectric body 131 adjacent to the frame 120, and the piezoelectric body 131 not adjacent to the frame 120 becomes the second vibration plate to which the driving voltage is not applied. In the first modified example, the second vibration plate is provided on the side of the piezoelectric body 131 to which the driving voltage is applied, which is opposite to the frame side.

[0078] In the ultrasonic transducer of the second modification, a driving voltage is applied to the piezoelectric body 131 not adjacent to the frame 120, and the piezoelectric body 131 adjacent to the frame 120 becomes a second vibration plate to which no driving voltage is applied. In the second modification, the second vibration plate is provided on the frame side of the piezoelectric body 131 to which the driving voltage is applied.

[0079] Fig.12 This is a graph showing a simulation analysis of the relationship between the displacement of the first vibration plate and the frequency of the ultrasonic vibrator in the ultrasonic transducer according to the present embodiment, the ultrasonic transducer according to the first variant, and the ultrasonic transducer according to the second variant using the finite element method. Fig.12 In FIG. 1 , the vertical axis shows the displacement of the first vibration plate 110, and the horizontal axis shows the frequency (kHz) of the ultrasonic vibrator 130. The data of the ultrasonic transducer 100 according to the present embodiment is shown by a solid line, the data of the ultrasonic transducer according to the first modification is shown by a dotted line, and the data of the ultrasonic transducer according to the second modification is shown by a dashed dotted line.

[0080] like Fig.12 As shown in FIG. 1 , when the displacement of the first vibration plate 110 in the ultrasonic transducer 100 according to the present embodiment is set to 100%, the displacement of the first vibration plate 110 in the ultrasonic transducer according to the first variant is 77.2%, and the displacement of the first vibration plate 110 in the ultrasonic transducer according to the second variant is 36.9%. When the free capacitance of the piezoelectric element in the ultrasonic transducer 100 according to the present embodiment is set to 100%, the free capacitance of the piezoelectric element in the ultrasonic transducer according to the first variant is 54.2%, and the free capacitance of the piezoelectric element in the ultrasonic transducer according to the second variant is 59.2%.

[0081] When the piezoelectric element is driven with the same voltage, the smaller the free capacitance of the piezoelectric element, the smaller the power consumption. It can be seen that the ultrasonic transducer involved in the first variant can displace the first vibration plate 110 by nearly 80% of the ultrasonic transducer 100 involved in the present embodiment with about half the power consumption of the ultrasonic transducer 100 involved in the present embodiment, and has good efficiency.

[0082] In this embodiment, the ultrasonic vibrator 130 is a so-called tandem 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.

[0083] Fig.13 FIG. 4 is a cross-sectional view showing the structure of an ultrasonic vibrator according to the third modified example. Fig.13As shown, the ultrasonic transducer 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 transducer 130a is a so-called parallel-type bimorph piezoelectric transducer.

[0084] Fig.14 4 is a cross-sectional view showing the structure of an ultrasonic vibrator according to the fourth modification. Fig.14 As shown, the ultrasonic vibrator 130b according to the fourth modification is a piezoelectric element including four stacked piezoelectric bodies 131. The polarization direction Dp of the two piezoelectric bodies 131 located on the outside of the four piezoelectric bodies 131 faces one side of the first direction (Z-axis direction), and the polarization direction Dp of the two piezoelectric bodies 131 located on the inside of the four piezoelectric bodies 131 faces the other side of the first direction (Z-axis direction). The ultrasonic vibrator 130b is a so-called multimorph-type piezoelectric vibrator.

[0085] Fig.15 1 is a cross-sectional view showing the structure of the ultrasonic vibrator according to the fifth modification. Fig.15 As shown, the ultrasonic vibrator 130c according to the fifth modification 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 type piezoelectric vibrator.

[0086] Fig.16 FIG. 2 is a longitudinal sectional view showing the structure of an ultrasonic transducer according to a sixth variation of the first embodiment of the present invention. Fig.16 As shown in FIG. 1 , an ultrasonic transducer 100a according to the sixth variation of the first embodiment of the present invention includes a first vibration plate 110, a frame 120a, and an ultrasonic vibrator 130. The frame 120a has a bottomed cylindrical shape. The frame 120a is made of metal. A piezoelectric body 131 is attached to the bottom surface of the outer side of the frame 120a, forming an ultrasonic vibrator as a single piezoelectric chip type piezoelectric vibrator.

[0087] In the ultrasonic transducer 100 according to the first embodiment of the present invention, there is provided a first vibration plate 110, at least one frame 120, and at least one ultrasonic vibrator 130. The at least one frame 120 extends in the longitudinal direction and is bonded to the first vibration plate 110. The at least one ultrasonic vibrator 130 is respectively mounted on the at least one frame 120 and is spaced apart from the first vibration plate 110 and faces the at least one ultrasonic vibrator 130. The first vibration plate 110 resonates and vibrates in a direction orthogonal to the first vibration plate 110 in a phase opposite to that of the at least one ultrasonic vibrator 130. The dimension L1 of the inner side of the at least one frame 120 in the longitudinal direction is at least 4 times the dimension L2 of the inner side of the at least one frame 120 in the short side direction orthogonal to the longitudinal direction. Thus, in the ultrasonic transducer 100, the sound pressure level can be improved with a simple and compact structure.

[0088] In the parametric speaker including the ultrasonic transducer 100 according to the first embodiment of the present invention, the ultrasonic wave radiated from the ultrasonic transducer 100 can be modulated to reproduce audible sound by modulating the ultrasonic wave radiated from the ultrasonic transducer 100 through modulation driving of the ultrasonic transducer 100. As modulation methods, there are AM modulation method (amplitude modulation method) and FM modulation method (frequency modulation method).

[0089] In the ultrasonic transducer 100 according to the first embodiment of the present invention, the resonance frequency of the first vibration plate 110 and the ultrasonic vibrator 130 is 100 kHz or more. As described later, when the resonance frequency is 100 kHz or more, the attenuation of the sound wave relative to the propagation distance is large, so by setting the resonance frequency of the first vibration plate 110 and the ultrasonic vibrator 130 to 100 kHz or more, the parametric speaker including the ultrasonic transducer 100 can reproduce audible sound only in a limited space.

[0090] In the ultrasonic transducer 100 according to the first embodiment of the present invention, when the acoustic velocity of the transverse wave of the first vibration plate 110 is Cv, the acoustic velocity of the transverse wave of the piezoelectric body 131 is Cp, the thickness of the first vibration plate 110 is Tv, and the thickness of the piezoelectric body 131 is Tp, the relationship of 0.25CpTp / Cv≤Tv≤0.6CpTp / Cv is satisfied. Thus, the ultrasonic transducer 100 can be driven in a state where the internal stress (normalized value per unit sound pressure) in the third direction (Z-axis direction) generated in the ultrasonic transducer 100 is reduced. Furthermore, the occurrence of cracks due to the internal stress can be suppressed at the joint between the first vibration plate 110 and the frame 120 and the joint between the frame 120 and the ultrasonic vibrator 130, respectively, and ultrasonic waves with high sound pressure can be generated.

[0091] In the ultrasonic transducer 100 according to the first embodiment of the present invention, when the acoustic velocity of the transverse wave of the first vibration plate 110 is Cv, the acoustic velocity of the transverse wave of the piezoelectric body 131 is Cp, the thickness of the first vibration plate 110 is Tv, and the thickness of the piezoelectric body 131 is Tp, the relationship of 0.7CpTp / Cv≤Tv≤1.3CpTp / Cv is satisfied. Thus, the physical balance between the first vibration plate 110 and the ultrasonic vibrator 130 can be maintained during vibration, the amplitude of the resonant vibration of the first vibration plate 110 can be increased to increase the sound pressure, and vibration leakage can be suppressed.

[0092] 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 vibration plate is provided on the side opposite to the frame side of the piezoelectric body 131. Thus, the power consumption can be reduced and the displacement of the first vibration plate 110 can be maintained high, thereby improving the efficiency of the ultrasonic transducer.

[0093] (Implementation method 2)

[0094] Hereinafter, an ultrasonic transducer according to Embodiment 2 of the present invention will be described with reference to the drawings. The ultrasonic transducer according to Embodiment 2 of the present invention is different 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, the same structure as that of the ultrasonic transducer according to Embodiment 1 of the present invention will not be described again.

[0095] Fig.17 This is a side view showing the structure of an ultrasonic transducer according to Embodiment 2 of the present invention. Fig.18 From the direction of arrow XVIII Fig.17 The ultrasonic transducer is shown viewed from the rear.

[0096] like Fig.17 as well as Fig.18 As shown, in the ultrasonic transducer 200 according to the second embodiment of the present invention, the ultrasonic transducer 100 according to the first embodiment arranged in an array in the first direction (X-axis direction) is integrally configured. The ultrasonic transducer 200 includes a first vibration plate 210, a plurality of frames 220, and a plurality of ultrasonic vibrators 130. The plurality of frames 220 are joined to the first vibration plate 210, and the plurality of ultrasonic vibrators 130 are joined to each of the plurality of frames 220.

[0097] Here, a method for manufacturing the ultrasonic transducer 200 will be described. Fig.19 This 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.

[0098] like Fig.19 As shown, the first vibration plate 210 has a flat plate shape, and a plurality of slits 211 extending in the second direction (Y-axis direction) are formed in the first direction (X-axis direction) at intervals. The first vibration plate 210 is made of an aluminum alloy such as aluminum-containing duralumin, or a metal such as stainless steel. In this embodiment, the first vibration plate 210 is made of stainless steel. The plurality of slits 211 are formed by etching or cutting.

[0099] Each of the plurality of frames 220 has a rectangular ring shape. Each of the plurality of frames 220 has a short side direction along the first direction (X-axis direction) and a long side direction along the second direction (Y-axis direction). Each of the plurality of frames 220 extends in the second direction (Y-axis direction). Each of the axis directions of the plurality of frames 220 is along the third direction (Z-axis direction). Each of the plurality of frames 220 has a pair of long sides 221 extending in the second direction (Y-axis direction) and a pair of short sides 222 extending in the first direction (X-axis direction). The shortest interval between the long sides 221 is more than 4 times the shortest interval between the short sides 222.

[0100] The plurality of frames 220 are arranged in a first direction (X-axis direction). Slits 223 are formed between the frames 220 adjacent to each other in the first direction (X-axis direction). The plurality of slits 223 are formed by etching or cutting. The long sides 221 adjacent to each other in the frames 220 adjacent to each other in the first direction (X-axis direction) are separated from each other by the slits 223.

[0101] 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, the frame bodies 220 adjacent to each other in the short side direction among the plurality of frame bodies 220 are connected to each other at both ends in the long side direction.

[0102] The plurality of frames 220 are each formed of a metal such as aluminum alloy or stainless steel, glass epoxy or resin, etc. In the present embodiment, the plurality of frames 220 are formed by a single thin plate, but are not limited thereto, and the short sides 222 of the plurality of frames 220 respectively formed by a plurality of thin plates may be joined to form a whole.

[0103] In this embodiment, each of the plurality of ultrasonic vibrators 130 includes two stacked piezoelectric bodies 131. Fig.19 As shown, two piezoelectric bodies 131 constituting the plurality of ultrasonic vibrators 130 are stacked and bonded in the state of two thin plates.

[0104] Fig. 20 1 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 the second embodiment of the present invention. Fig. 20 In the figure, only one piezoelectric body 131 is shown.

[0105] like Fig. 20 As shown in FIG. 1 , the slits 211 and 223 are arranged at the same position in the first direction (X-axis direction) so as to overlap each other in the third direction (Z-axis direction). The piezoelectric body 131 is cut and divided by a cutting machine or the like along a plurality of cutting lines LC extending in the second direction (Y-axis direction) so as to overlap the slits 211 and 223 in the third direction (Z-axis direction). As a result, Fig.17 as well as Fig.18 An ultrasonic transducer 200 is shown.

[0106] Fig.21 This is a perspective view showing a displacement state of the ultrasonic transducer according to the second embodiment of the present invention when transmitting or receiving ultrasonic waves, which is simulated and analyzed using the finite element method.

[0107] like Fig.21 As shown, in the first vibration plate 210, the middle portion 210c located in the middle of the long side direction of the inner side of each frame 220 becomes the antinode of the resonant vibration, and the end portions 210e located at both ends of the long side direction of the inner side of each frame 220 become the nodes of the resonant vibration. That is, the portion of the first vibration plate 210 located above the inner space of each frame 220 becomes the vibration region that performs resonant vibration. The long side dimension of the vibration region of the first vibration plate 210 becomes the same as the long side dimension of the inner side of each frame 220, and the short side dimension of the vibration region of the first vibration plate 210 becomes the same as the short side dimension of the inner side of each frame 220.

[0108] In the ultrasonic transducer 100 according to the first embodiment, there are nodes at both ends in the second direction (Y-axis direction) which is the long-side direction. Therefore, even if the ultrasonic transducers 100 according to the first embodiment are connected to each other at the both ends and arrayed to constitute the ultrasonic transducer 200 according to the second embodiment, the resonant vibration in each ultrasonic transducer 100 is not hindered. Therefore, by increasing the number of ultrasonic transducers 100 constituting the ultrasonic transducer 200 according to the second embodiment, the sound pressure level can be easily increased.

[0109] In the parametric speaker including the ultrasonic transducer 200 according to the second embodiment of the present invention, the ultrasonic transducer 200 can be modulated and driven to reproduce audible sound by modulating the ultrasonic wave radiated from the ultrasonic transducer 200 .

[0110] Here, the results of simulation analysis of the relationship between the frequency of ultrasonic waves and the attenuation of the sound pressure level caused by the propagation distance using the finite element method are described. As simulation analysis conditions, the finite element method is used to simulate the transition of attenuation caused by the propagation distance of the audible sound with a frequency of 4 kHz reproduced by the ultrasonic wave with a resonance frequency of 146 kHz transmitted from the ultrasonic transducer 200 involved in the present embodiment and the audible sound with a frequency of 4 kHz reproduced by the ultrasonic wave with a resonance frequency of 40 kHz transmitted from the ultrasonic element array involved in the second comparative example.

[0111] Fig. 22 2 is a perspective view showing the structure of an ultrasonic element array according to the second comparative example. Fig. 22 As shown, in the ultrasonic element array according to the second comparative example, 50 ultrasonic elements 900 are arranged in a matrix at intervals from each other.

[0112] Fig.23 Graphs showing actual measured changes in attenuation of the sound pressure level due to propagation distance in the ultrasonic transducer according to the present embodiment and the ultrasonic transducer according to the second comparative example. Fig.23 , the vertical axis shows the sound pressure level (dB) and the horizontal axis shows the propagation distance (cm). The data of the ultrasonic transducer 200 according to the present embodiment are shown by a solid line, and the data of the ultrasonic transducer according to the second comparative example are shown by a dotted line. The sound pressure level is a value normalized by setting the sound pressure level of an audible sound of a frequency of 4 kHz at a point 30 cm away from the front surface of the ultrasonic transducer and the ultrasonic element array in the third direction (Z-axis direction) to 0 dB.

[0113] like Fig.23 As shown, the attenuation caused by the propagation distance of the audible sound reproduced by the ultrasonic wave with a resonance frequency of 146 kHz transmitted from the ultrasonic transducer 200 according to the present embodiment is greater than the audible sound reproduced by the ultrasonic wave with a resonance 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 air as heat, and therefore the attenuation caused by the propagation distance of the audible sound reproduced using the high-frequency ultrasonic wave as a carrier wave is greater.

[0114] As described above, in the parametric speaker of the ultrasonic transducer 200 according to the present embodiment that transmits high-frequency ultrasonic waves of 100 kHz or more, it is possible to suppress the sound from reaching far away unnecessarily and the sound leakage caused by unnecessary reflection, thereby reproducing the audible sound only in a limited space. In addition, in the ultrasonic transducer 200, it is possible to increase the attenuation caused by the propagation distance of the audible sound without providing a structure that transmits a carrier wave of opposite phase as in Patent Document 2, so that a simple and miniaturized structure can be provided. Furthermore, the high-frequency ultrasonic waves of 100 kHz or more are outside the audible range of animals such as dogs or cats, so the influence on these animals can be suppressed.

[0115] like Fig.23 As shown in the figure, in order to make the audible sound attenuate after the propagation distance is 30cm, the Rayleigh distance needs to be set within 30cm. The Rayleigh distance R0 satisfies R0=(k×a 2 ) / 2. k is the wave number, and a is the radius of the sound source. Therefore, if the sound speed of air is set to 340m / s, when the frequency of the ultrasonic wave is 100kHz, the long side dimension of the vibration area of ​​the first vibration plate 210 is less than 36mm, when the frequency of the ultrasonic wave is 150kHz, the long side dimension of the vibration area of ​​the first vibration plate 210 is less than 29.4mm, and when the frequency of the ultrasonic wave is 200kHz, the long side dimension of the vibration area of ​​the first vibration plate 210 is less than 25.5mm. When the frequency of the ultrasonic wave is above 100kHz, the long side dimension L1 is more than 4 times and less than 24 times the short side dimension L2.

[0116] The ultrasonic transducer 200 according to the present embodiment can be used as a phased array system.

[0117] Fig.24 1 is a side view showing a state where an ultrasonic transducer according to a modification of the present embodiment constituting a phased array system emits ultrasonic waves in a planar manner in the third direction (Z-axis direction). Fig.24 As shown, the ultrasonic transducer 200 a according to the modification of the present embodiment includes a processing circuit 240 capable of controlling the emission timing of ultrasonic waves by each of the ultrasonic transducers A to G.

[0118] Fig.25 1 is a diagram showing the drive start delay time when the ultrasonic wave emission timing of the ultrasonic transducers A to G is set to the same first state by the processing circuit. Fig.25 As shown, in the first state where the ultrasonic emission timings of the ultrasonic transducers A to G are set to be the same by the processing circuit 240, as shown in FIG. Fig.24 As shown, the ultrasonic wave Da is emitted in a planar manner in the third direction (Z-axis direction).

[0119] Fig.26 This is a side view showing a state in which an ultrasonic transducer according to a modification of the present embodiment radiates ultrasonic waves in a planar manner in a direction inclined toward a first direction (X-axis direction) with respect to a third direction (Z-axis direction). Fig. 27 1 is a diagram showing the driving start delay time in the second state in which the ultrasonic transducers G to A emit ultrasonic waves in the order of each other by the processing circuit. Fig. 27 As shown in FIG. 1 , in the second state where the driving start delay time is increased in the order of the ultrasonic transducers G to A by the processing circuit 240, as shown in FIG. Fig.24 As shown in FIG. 1 , the ultrasonic wave Db is emitted in a planar manner in a direction inclined toward the first direction (X-axis direction) with respect to the third direction (Z-axis direction).

[0120] Fig.28 This is a side view showing a state in which the ultrasonic transducer according to the modification example of the present embodiment radiates ultrasonic waves in the third direction (Z-axis direction) so as to be concentrated at the center in the first direction (X-axis direction). Fig.29 1 is a diagram showing the driving start delay time in the third state in which the ultrasonic transducers A to D and the ultrasonic transducers G to D are radiated in the order of the processing circuit. Fig.29 As shown, in the third state where the driving start delay time is increased in the order of ultrasonic transducers A to D by the processing circuit 240 and the driving start delay time is increased in the order of ultrasonic transducers G to D, as shown in FIG. Fig.28 As shown, the ultrasonic wave Dc is emitted in the third direction (Z-axis direction) so as to be concentrated on the center of the ultrasonic transducer 200 a in the first direction (X-axis direction).

[0121] In the ultrasonic transducer 200 according to the second embodiment of the present invention, a plurality of at least one frame body 220 are arranged in the short-side direction and bonded to the first vibration plate 210, and frame bodies 220 adjacent to each other in the short-side direction in at least one frame body 220 are connected to each other at both ends in the long-side direction. Thus, the sound pressure level can be easily increased.

[0122] The ultrasonic transducer 200 a according to the modification of Embodiment 2 of the present invention can function as a phased array system.

[0123] (Note)

[0124] Those skilled in the art will appreciate that the above-described exemplary embodiments are specific examples of the following aspects.

[0125] <1>

[0126] An ultrasonic transducer having:

[0127] The first vibration plate;

[0128] at least one frame extending in the longitudinal direction and joined to the first vibration plate; and

[0129] at least one ultrasonic vibrator is mounted on the at least one frame and faces the first vibration plate with a gap therebetween.

[0130] The first vibration plate resonates and vibrates in a direction orthogonal to the first vibration plate in a phase opposite to that of the at least one ultrasonic vibrator.

[0131] The dimension of the inner side of the at least one frame in the longitudinal direction is 4 times or more the dimension of the inner side of the at least one frame in the transverse direction perpendicular to the longitudinal direction.

[0132] <2>

[0133] according to <1> The ultrasonic transducer, wherein:

[0134] The at least one ultrasonic vibrator is a piezoelectric element including a piezoelectric body.

[0135] <3>

[0136] according to <1> or <2> The ultrasonic transducer, wherein:

[0137] The resonance frequency of the first vibration plate and the at least one ultrasonic vibrator is 100 kHz or more.

[0138] <4>

[0139] according to <2> The ultrasonic transducer, wherein:

[0140] If the acoustic velocity of the transverse wave of the first vibration plate is Cv, the acoustic velocity of the transverse wave of the piezoelectric body is Cp, the thickness of the first vibration plate is Tv, and the thickness of the piezoelectric body is Tp, then

[0141] The relationship of 0.25CpTp / Cv≤Tv≤0.6CpTp / Cv is satisfied.

[0142] <5>

[0143] according to <2> The ultrasonic transducer, wherein:

[0144] If the acoustic velocity of the transverse wave of the first vibration plate is Cv, the acoustic velocity of the transverse wave of the piezoelectric body is Cp, the thickness of the first vibration plate is Tv, and the thickness of the piezoelectric body is Tp, then

[0145] The relationship of 0.7CpTp / Cv≤Tv≤1.3CpTp / Cv is satisfied.

[0146] <6>

[0147] according to <1> to <5> The ultrasonic transducer as described in any one of the preceding claims, wherein:

[0148] The at least one frame is arranged in plurality so as to be aligned in the short side direction and bonded to the first vibration plate.

[0149] In the at least one frame body, frame bodies adjacent to each other in the short-side direction are connected to each other at both ends in the long-side direction.

[0150] <7>

[0151] according to <2> The ultrasonic transducer, wherein:

[0152] The at least one ultrasonic vibrator is a unimorph piezoelectric vibrator,

[0153] A second vibration plate is provided on the side of the piezoelectric body opposite to the frame body side.

[0154] In the description of the above-mentioned embodiments, it is also possible to combine the structures that can be combined with each other.

[0155] The embodiments disclosed this time should be considered as illustrative in all aspects and not restrictive. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0156] Description of Reference Numerals

[0157] 100, 100a, 200, 200a: ultrasonic transducer; 110, 210: first vibration plate; 110c, 210c: middle part; 110e, 210e: end part; 120, 120a, 220: frame; 121, 221: long side; 122, 222: short side; 130, 130a, 130b, 130c: ultrasonic vibrator; 131: piezoelectric body; 132: first electrode; 133: second electrode; 134: middle electrode; 135: second vibration plate; 140, 240: processing circuit; 211, 223: slit; 800, 900: ultrasonic element.

Claims

1. An ultrasonic transducer comprising: The first vibration plate; at least one frame extending in the longitudinal direction and joined to the first vibration plate; and at least one ultrasonic vibrator is mounted on the at least one frame and faces the first vibration plate with a gap therebetween. The first vibration plate resonates and vibrates in a direction orthogonal to the first vibration plate in a phase opposite to that of the at least one ultrasonic vibrator. The dimension of the inner side of the at least one frame in the longitudinal direction is 4 times or more the dimension of the inner side of the at least one frame in the transverse direction perpendicular to the longitudinal direction.

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

3. The ultrasonic transducer according to claim 1 or claim 2, wherein: The resonance frequency of the first vibration plate and the at least one ultrasonic vibrator is 100 kHz or more.

4. The ultrasonic transducer according to claim 2, wherein: If the acoustic velocity of the transverse wave of the first vibration plate is Cv, the acoustic velocity of the transverse wave of the piezoelectric body is Cp, the thickness of the first vibration plate is Tv, and the thickness of the piezoelectric body is Tp, then The relationship of 0.25CpTp / Cv≤Tv≤0.6CpTp / Cv is satisfied.

5. The ultrasonic transducer according to claim 2, wherein: If the acoustic velocity of the transverse wave of the first vibration plate is Cv, the acoustic velocity of the transverse wave of the piezoelectric body is Cp, the thickness of the first vibration plate is Tv, and the thickness of the piezoelectric body is Tp, then The relationship of 0.7CpTp / Cv≤Tv≤1.3CpTp / Cv is satisfied.

6. The ultrasonic transducer according to any one of claims 1 to 5, wherein: The at least one frame is arranged in plurality so as to be aligned in the short side direction and bonded to the first vibration plate. In the at least one frame body, frame bodies adjacent to each other in the short-side direction are connected to each other at both ends in the long-side direction.

7. The ultrasonic transducer according to claim 2, wherein: The at least one ultrasonic vibrator is a unimorph piezoelectric vibrator, A second vibration plate is provided on the side of the piezoelectric body opposite to the frame body side.

8. A parametric speaker comprising the ultrasonic transducer according to any one of claims 1 to 7, Audible sound is reproduced by modulated driving of the ultrasonic transducer.

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