Ultrasonic transducer and parametric speaker provided with ultrasonic transducer

Abstract

The present invention is provided with a vibration plate (110), at least one case (120), at least one ultrasonic vibrator (130), and at least one resonator (140). The at least one case (120) extends in the longitudinal direction and is joined to the diaphragm (110). The at least one ultrasonic transducer (130) is attached to each of the at least one housing (120) and faces the vibrating plate (110) with a gap therebetween. The at least one resonating plate (140) faces the vibrating plate (110) on the opposite side of the vibrating plate (110) from the at least one housing (120) with a gap therebetween, and extends in the long axis direction. The vibrating plate (110) resonates and vibrates in a direction orthogonal to the vibrating plate (110) at a phase opposite to that of the at least one ultrasonic vibrator (130). The dimension of the inner side of the at least one housing (120) in the long-axis direction is larger than the dimension of the inner side of the at least one housing (120) in the short-axis direction orthogonal to the long-axis direction. If the wavelength converted from the drive frequency of the at least one ultrasonic transducer (130) is lambda, lambda / 2 air resonance can be generated in the gap in the minor axis direction.

Description

Technical Field

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

[0002] As prior documents that disclose ultrasonic transducers that utilize air resonance to increase the sound pressure level, there are International Publication No. 2012 / 026319 (Patent Document 1) and International Publication No. 2013 / 018579 (Patent Document 2). The ultrasonic transducers described in Patent Document 1 and Patent Document 2 include an ultrasonic generating element and a housing. The ultrasonic generating element has a piezoelectric vibrator. The housing has an ultrasonic release hole and accommodates the ultrasonic generating element. An acoustic path with air as the medium is formed from the piezoelectric vibrator to the ultrasonic release hole by the ultrasonic generating element and the housing. In the acoustic path, air resonance is generated by the ultrasonic wave generated by the piezoelectric vibrator with the ultrasonic release hole as the open end.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2012 / 026319

[0006] Patent Document 2: International Publication No. 2013 / 018579 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] In the ultrasonic transducers described in Patent Documents 1 and 2, there is still room for improving the sound pressure level with a more compact structure.

[0009] 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 compact structure, and a parametric speaker including the ultrasonic transducer.

[0010] Technical solutions to solve problems

[0011] The ultrasonic transducer according to the present invention comprises a vibration plate, at least one housing, at least one ultrasonic vibrator, and at least one resonance board. The at least one housing extends in the long-axis direction and is joined to the vibration plate. The at least one ultrasonic vibrator is respectively mounted on the at least one housing and is spaced apart from the vibration plate. The at least one resonance board is spaced apart from the vibration plate on the opposite side of the at least one housing with respect to the vibration plate and extends along the long-axis direction. The vibration plate resonates and vibrates in a direction orthogonal to the 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 housing in the long-axis direction is larger than the dimension of the inner side of the at least one housing in the short-axis direction orthogonal to the long-axis direction. If the wavelength converted from the driving frequency of the at least one ultrasonic vibrator is set to λ, an air resonance of λ / 2 can be generated in the short-axis direction at the gap.

[0012] Effects of the Invention

[0013] According to the present invention, the sound pressure level can be increased in an ultrasonic transducer with a compact structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a perspective view showing the structure of the ultrasonic transducer according to the first embodiment of the present invention.

[0015] Figure 2 Observe from the direction of the arrow on line II-II Figure 1 A cross-sectional view of an ultrasonic transducer is shown.

[0016] Figure 3 This is an exploded perspective view showing the structure of the ultrasonic transducer according to Embodiment 1 of the present invention.

[0017] Figure 4 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 5 This 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.

[0019] Figure 6 This is a perspective view showing the displacement states of the vibration plate and the ultrasonic vibrator when the ultrasonic transducer according to the first embodiment of the present invention transmits or receives ultrasonic waves, which is simulated and analyzed using the finite element method.

[0020] Figure 7 Observe from the direction of the arrow on line VII-VII Figure 6 Cross-sectional view of an ultrasonic transducer.

[0021] Figure 8The diagram shows displacement states of a diaphragm and an ultrasonic transducer when an ultrasonic wave is transmitted and λ / 2 air resonance is generated in the ultrasonic transducer according to the first embodiment of the present invention, which is simulated and analyzed using the finite element method.

[0022] Fig. 9 This is a diagram showing a sound pressure distribution obtained by simulation analysis using the finite element method when λ / 2 air resonance occurs in the ultrasonic transducer according to the first embodiment of the present invention.

[0023] Fig.10 This is a diagram showing the λ / 2 air resonance generated in the ultrasonic transducer according to the first embodiment of the present invention.

[0024] Fig.11 This is a diagram showing the particle velocity obtained by simulation analysis using the finite element method when λ / 2 air resonance occurs in the ultrasonic transducer according to the first embodiment of the present invention.

[0025] Fig.12 This is a graph obtained by simulation analysis using the finite element method on the relationship between the frequency of air resonance generated in the gap between the diaphragm and the soundboard and the width of the soundboard.

[0026] Fig.13 This is a graph showing the relationship between the frequency of the vibration plate and the ultrasonic vibrator and the displacement of the vibration plate, which was simulated and analyzed using the finite element method.

[0027] Fig.14 This is a graph that uses the finite element method to simulate and analyze the relationship between the sound pressure of the ultrasonic wave emitted from the ultrasonic transducer and the frequency of the vibration plate and the ultrasonic vibrator in an ultrasonic transducer that combines a vibration plate with a resonance frequency of 150kHz and an ultrasonic vibrator with a resonance plate with an air resonance frequency of 150kHz.

[0028] Fig.15 This is a graph showing the relationship between the frequency of air resonance generated in the gap between the diaphragm and the soundboard and the size of the gap between the diaphragm and the soundboard, which was simulated and analyzed using the finite element method.

[0029] Fig.16 This is a graph showing the relationship between the ratio of the size of the gap between the diaphragm and the soundboard to the size of the width of the soundboard and the sound pressure amplification ratio, using the finite element method for simulation analysis.

[0030] Fig.17 This is a graph showing the relationship between the size of the gap between the diaphragm and the soundboard and the sound pressure amplification ratio, using the finite element method for simulation analysis.

[0031] Fig.18This is a graph obtained by simulation analysis using the finite element method on the relationship between the sound pressure of ultrasonic waves transmitted from an ultrasonic transducer and the thickness of a soundboard.

[0032] Fig.19 This is a diagram showing the sound pressure distribution obtained by simulation analysis using the finite element method when a λ / 2 air resonance is generated in an ultrasonic transducer having a soundboard with a thickness of 0.1 mm.

[0033] Fig. 20 This is a diagram showing the sound pressure distribution obtained by simulation analysis using the finite element method when a λ / 2 air resonance is generated in an ultrasonic transducer having a soundboard with a thickness of 0.6 mm.

[0034] Fig.21 It is a perspective view showing the structure of an ultrasonic transducer according to Embodiment 2 of the present invention.

[0035] Fig. 22 This is an exploded perspective view showing the structure of an ultrasonic transducer according to Embodiment 2 of the present invention.

[0036] Fig.23 FIG. 1 is a schematic diagram showing a FEM model of an ultrasonic transducer subjected to simulation analysis.

[0037] Fig.24 This is a graph showing a simulation analysis of the relationship between the sound pressure of ultrasonic waves transmitted from an ultrasonic transducer and the array pitch using the finite element method.

[0038] Fig.25 This is a diagram showing the sound pressure distribution around the ultrasonic transducer when the array pitch is 2.2 mm, which was simulated and analyzed using the finite element method.

[0039] Fig.26 This is a diagram showing the sound pressure distribution around the ultrasonic transducer when the array pitch is 2.6 mm, which is simulated and analyzed using the finite element method.

[0040] Fig. 27 This is a diagram showing the sound pressure distribution around the ultrasonic transducer when the array pitch is 3.0 mm, which is simulated and analyzed using the finite element method.

[0041] Fig.28 This is a diagram showing the sound pressure distribution around the ultrasonic transducer when the array pitch is 3.6 mm, which was simulated and analyzed using the finite element method.

[0042] Fig.29 This is a diagram showing the sound pressure distribution around the ultrasonic transducer when the array pitch is 4.4 mm, which was simulated and analyzed using the finite element method.

[0043] Fig.30 This is a graph showing a simulation analysis of the relationship between the directivity of ultrasonic waves transmitted from an ultrasonic transducer and the array pitch using the finite element method.

[0044] Fig.31 This is a graph showing the results of actually measuring the output of ultrasonic waves radiated from the ultrasonic transducer while changing the width of the soundboard.

[0045] Fig.32 It is an exploded perspective view showing the structure of an ultrasonic transducer according to Embodiment 3 of the present invention. DETAILED DESCRIPTION

[0046] Hereinafter, the ultrasonic transducer involved in each embodiment of the present invention will be described with reference to the accompanying drawings. In the following description of the embodiments, the same or corresponding parts in the drawings are marked with the same figure marks, and their description will not be repeated. The present invention can be applied to the use of ultrasonic transducers for parametric speakers, ultrasonic sensors or non-contact tactile ultrasound that requires high sound pressure. In the following embodiments, ultrasonic transducers for parametric speakers are exemplified and described, but the use of ultrasonic transducers is not limited to this.

[0047] (Implementation method 1)

[0048] Figure 1 It is a perspective view showing the structure of the ultrasonic transducer according to the first embodiment of the present invention. Figure 2 Observe from the direction of the arrow on line II-II Figure 1 A cross-sectional view of an ultrasonic transducer is shown. Figure 3 FIG. 1 is an exploded perspective view showing the structure of the ultrasonic transducer according to Embodiment 1 of the present invention. Figure 1 to Figure 3 As shown, the ultrasonic transducer 100 according to the first embodiment of the present invention includes a vibration plate 110 , a housing 120 , an ultrasonic vibrator 130 , a resonance plate 140 , and a spacer 150 .

[0049] The vibration plate 110 has a flat plate shape. The vibration plate 110 is made of aluminum alloy such as duralumin containing aluminum or metal such as stainless steel. In the present embodiment, the vibration plate 110 is made of stainless steel. The thickness of the vibration plate 110 is, for example, not less than 0.1 mm and not more than 0.2 mm.

[0050] The housing 120 has a rectangular ring shape. The housing 120 has a short axis direction along the first direction (X-axis direction) and a long axis direction along the second direction (Y-axis direction). The housing 120 extends in the second direction (Y-axis direction). The axial direction of the housing 120 is along the third direction (Z-axis direction). One end of the housing 120 in the third direction (Z-axis direction) is bonded to the vibration plate 110 by a bonding agent including epoxy resin or the like.

[0051] The housing 120 is formed of a metal such as aluminum alloy or stainless steel, glass epoxy or resin. From the viewpoint of suppressing the characteristic change of the ultrasonic transducer 100 caused by the temperature change, the housing 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 housing 120 is preferably made of resin. In the present embodiment, the housing 120 is made of stainless steel. The thickness of the housing 120 is, for example, not less than 0.2 mm and not more than 0.8 mm.

[0052] Figure 4 FIG. 1 is a perspective view showing the structure of a housing provided in the ultrasonic transducer according to Embodiment 1 of the present invention. Figure 4 As shown, the housing 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 more than 4 times the shortest interval between the long sides 121. That is, the long axis dimension L1 in the second direction (Y-axis direction) of the inner side of the housing 120 is more than 4 times the short axis dimension L2 in the first direction (X-axis direction) of the inner side of the housing 120. However, the long axis dimension L1 is not limited to more than 4 times the short axis dimension L2, as long as it is larger than the short axis dimension L2.

[0053] 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 also be an arc convex to the inside of the housing 120 or an arc convex to the outside of the housing 120.

[0054] The resonance frequency of the vibration plate 110 can be adjusted by changing the minor axis dimension L2 in the first direction (X-axis direction) inside the housing 120. For example, when the resonance frequency of the vibration plate 110 is set to 100 kHz or more, the minor axis dimension L2 is set to 1.5 mm or more and 3 mm or less.

[0055] The major axis dimension L1 in the second direction (Y-axis direction) inside the housing 120 is at least 4 times the minor axis dimension L2. From the viewpoint of increasing the sound pressure level of the ultrasonic wave transmitted by the ultrasonic transducer 100, the major axis dimension L1 is, for example, at least 20 mm.

[0056] Figure 5 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 1As shown, the ultrasonic vibrator 130 is mounted in the housing 120 and faces the vibration plate 110 with a gap therebetween. Specifically, the ultrasonic vibrator 130 is mounted at the other end of the housing 120 in the third direction (Z-axis direction) and faces the vibration plate 110 with the inner space of the housing 120 interposed therebetween.

[0057] like Figure 1 , Figure 2 as well as Figure 5 As shown in FIG. 1 , the ultrasonic vibrator 130 is a piezoelectric element including a piezoelectric body 131. Figure 5 As 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 160 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. In addition, the ultrasonic vibrator 130 is not limited to a serial bimorph piezoelectric vibrator, and may be a parallel bimorph piezoelectric vibrator, a multimorph piezoelectric vibrator, or a unimorph piezoelectric vibrator.

[0058] Figure 6 This is a perspective view showing the displacement states of the vibration plate and the ultrasonic vibrator when the ultrasonic transducer according to the first embodiment of the present invention transmits or receives ultrasonic waves, which is simulated and analyzed using the finite element method. Figure 7 Observe from the direction of the arrow on line VII-VII Figure 6 A cross-sectional view of an ultrasonic transducer. Figure 6 as well as Figure 7 , the resonance plate 140 is not shown. As simulation analysis conditions, the thickness of the vibration plate 110 is set to 0.1 mm, the thickness of the two piezoelectric bodies 131 is set to 0.8 mm, the long axis dimension L1 of the inner side of the shell 120 is set to 20 mm, the short axis dimension L2 is set to 2 mm, and the thickness of the shell 120 in the third direction (Z-axis direction) is set to 0.4 mm.

[0059] like Figure 6 as well as Figure 7 As shown, in the vibration mode of the ultrasonic transducer 100 according to the first embodiment of the present invention, the vibration plate 110 resonates and vibrates in a third direction (Z-axis direction) orthogonal to the vibration plate 110 in a phase opposite to that of the ultrasonic vibrator 130. Figure 7As shown, the displacement direction of the resonance vibration Bm of the 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 vibration plate 110 and the ultrasonic vibrator 130 is 100 kHz or more.

[0060] In the vibration plate 110, the middle portion 110c located in the middle of the inner side of the housing 120 in the long axis direction becomes the abdomen of the resonant vibration, and the end portions 110e located at both ends of the inner side of the housing 120 in the long axis direction become the nodes of the resonant vibration. That is, the portion of the vibration plate 110 located above the inner space of the housing 120 becomes the vibration region that performs the resonant vibration. The long axis dimension of the vibration region of the vibration plate 110 is the same as the long axis dimension L1 of the inner side of the housing 120, and the short axis dimension of the vibration region of the vibration plate 110 is the same as the short axis dimension L2 of the inner side of the housing 120.

[0061] The resonant frequency of the vibration plate 110 is determined by the sound velocity of the vibration plate 110 and the reflection of the vibration with the shell 120 as the fixed end. However, from the time when the major axis dimension L1 on the inner side of the shell 120 exceeds 4 times the minor axis dimension L2, the influence of the minor axis dimension L2 becomes dominant with respect to the reflection of the vibration. Even if the major axis dimension L1 becomes larger than 4 times the minor axis dimension L2, the state of the vibration reflection does not change.

[0062] As the long-axis dimension L1 of the inner side of the housing 120 increases, the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer 100 increases. This means that even when the long-axis dimension of the vibration region of the vibration plate 110 is increased, the entire vibration region of the 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 vibration plate 110 is lengthened, and as a result, the pressure change of the air caused by the vibration of the vibration plate 110 can be increased, thereby obtaining a high sound pressure.

[0063] 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-axis dimension of the vibration region of the vibration plate 110. In addition, since both ends in the long-axis direction have nodes, the two ends can be supported or fixed, making it easy to install the ultrasonic transducer 100.

[0064] like Figure 1 as well as Figure 3As shown, the two spacers 150 are respectively arranged at nodes with less vibration in the vibration plate 110. In the present embodiment, the two spacers 150 are respectively arranged at the ends of the vibration plate 110 in the second direction (Y-axis direction), but when the resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130 is a low frequency of, for example, about 40 kHz, the two spacers 150 may be respectively arranged at the ends of the vibration plate 110 in the first direction (X-axis direction).

[0065] The sound plate 140 is arranged on the two spacers 150. The sound plate 140 is opposed to the vibration plate 110 with a gap on the side opposite to the housing 120 with respect to the vibration plate 110, and extends along the second direction (Y-axis direction). The central axis of the sound plate 140 extending in the second direction (Y-axis direction) is along the central axis of the vibration region of the vibration plate 110 extending in the second direction (Y-axis direction). Ideally, the central axis of the sound plate 140 extending in the second direction (Y-axis direction) overlaps with the central axis of the vibration region of the vibration plate 110 extending in the second direction (Y-axis direction) when viewed from the third direction (Z-axis direction).

[0066] The dimension of the gap between the vibration plate 110 and the sounding plate 140 in the third direction (Z-axis direction) is defined by the spacer 150. The spacer 150 may be formed of a metal plate with an adhesive material applied to both sides, or may be formed of a double-sided tape. As described later, the thickness of the spacer 150 is determined by the frequency of the air resonance generated in the gap between the vibration plate 110 and the sounding plate 140. The thickness of the spacer 150 is about 0.1 mm when the frequency of the air resonance is 150 kHz, and is greater than or equal to 0.1 mm and less than or equal to 0.2 mm when the frequency of the air resonance is 100 kHz.

[0067] The length of the sounding plate 140 in the second direction (Y-axis direction) is substantially the same as the length of the vibration plate 110 in the second direction (Y-axis direction). The thinner the thickness of the sounding plate 140 is, the easier it is to cause air resonance in the gap between the vibration plate 110 and the sounding plate 140. In the present embodiment, the sounding plate 140 is made of stainless steel. The material of the sounding plate 140 is not limited to stainless steel, and may also be an aluminum alloy or a resin with high rigidity. The thickness of the sounding plate 140 is, for example, not less than 0.1 mm and not more than 0.2 mm. Regarding the width of the sounding plate 140 in the first direction (X-axis direction), when the frequency of the air resonance is 150 kHz, it is not less than 0.7 mm and not more than 0.9 mm, and when the frequency of the air resonance is 100 kHz, it is not less than 1.1 mm and not more than 1.4 mm.

[0068] In the ultrasonic transducer according to the first embodiment of the present invention, if the wavelength converted from the driving frequency of the ultrasonic vibrator 130 is set to λ, it is possible to generate air resonance of λ / 2 in the first direction (X-axis direction) at the gap between the vibration plate 110 and the sounding plate 140. Each structure of the ultrasonic transducer 100 is designed so that the frequency of the air resonance generated at the gap between the vibration plate 110 and the sounding plate 140 is within ±10% of the resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130.

[0069] Figure 8 FIG. 1 is a diagram showing the displacement states of the vibration plate and the ultrasonic vibrator when the ultrasonic transducer according to Embodiment 1 of the present invention transmits ultrasonic waves and generates λ / 2 air resonance, which is simulated and analyzed using the finite element method. Figure 8 As shown, since the displacement of the resonant vibration of the vibration plate 110 is larger than the displacement of the resonant vibration of the ultrasonic vibrator 130 , the main ultrasonic wave is radiated in the third direction (Z-axis direction) perpendicular to the vibration plate 110 .

[0070] Fig. 9 1 is a diagram showing the sound pressure distribution obtained by simulation analysis using the finite element method when a λ / 2 air resonance occurs in the ultrasonic transducer according to the first embodiment of the present invention. Fig. 9 In FIG. 1 , it is shown that in the portion where air exists, the sound pressure increases as the color changes from black to white. Fig. 9 In the illustrated state, the sound pressure is high in the gap Rg between the diaphragm 110 and the sound plate 140 , and the sound pressure is low in the region Rf just above the sound plate 140 .

[0071] Fig.10 1 is a diagram showing the λ / 2 air resonance generated in the ultrasonic transducer according to the first embodiment of the present invention. When the vibration plate 110 is displaced upward, the area on the central axis extending in the second direction (Y-axis direction) of the vibration area of ​​the vibration plate 110 is compressed between the resonance plate 140, so that the sound pressure increases. Fig.10 As shown in FIG. 1 , the region outside the gap Rg between the vibration plate 110 and the resonance plate 140 is open to air. Fig.10 As shown, it becomes a node of the air resonance Wr. That is, the area outside the gap Rg between the diaphragm 110 and the resonance plate 140 becomes an open end of the air resonance Wr.

[0072] Fig.11 1 is a graph showing the particle velocity obtained by simulation analysis using the finite element method when a λ / 2 air resonance is generated in the ultrasonic transducer according to the first embodiment of the present invention. The particle velocity shows the flow of air. Fig.11, the vibration plate 110 is shown to be displaced downward. Fig.11 As shown, when the vibration plate 110 is displaced downward, the air in the area Rf directly above the sounding plate 140 is sucked into the gap Rg between the vibration plate 110 and the sounding plate 140. Conversely, when the vibration plate 110 is displaced upward, the air in the gap Rg between the vibration plate 110 and the sounding plate 140 is released to the area Rf directly above the sounding plate 140.

[0073] As described above, when the λ / 2 air resonance is generated, a virtual sound source whose sound pressure fluctuates is formed in the region Rf directly above the sound plate 140 due to the inflow and outflow of air centered on the region Rf directly above the sound plate 140. As a result, the sound pressure caused by the virtual sound source is superimposed on the ultrasonic transducer 100 when the λ / 2 air resonance is generated, so that ultrasonic waves of a high sound pressure level can be radiated.

[0074] Fig.12 This is a graph that uses the finite element method to simulate the relationship between the frequency of air resonance generated in the gap between the vibration plate and the soundboard and the width of the soundboard. Fig.12 In FIG. 1 , the vertical axis shows the frequency (kHz) of air resonance generated in the gap Rg between the diaphragm 110 and the sounding plate 140 , and the horizontal axis shows the width (mm) of the sounding plate 140 .

[0075] like Fig.12 As shown, the frequency of the air resonance becomes lower as the width of the sound plate 140 in the first direction (X-axis direction) becomes wider. This is because as the width of the sound plate 140 in the first direction (X-axis direction) becomes wider, the length λ / 2 of the air resonance becomes longer, and therefore the value of the frequency of the air resonance obtained by dividing the speed of sound of the air by λ / 2 becomes smaller.

[0076] Fig.13 This is a graph that uses the finite element method to simulate the relationship between the frequency of the vibration plate and the ultrasonic vibrator and the displacement of the vibration plate. Fig.13 In FIG. 1 , the vertical axis shows the displacement (nm) of the vibration plate 110 , and the horizontal axis shows the frequency (kHz) of the vibration plate 110 and the ultrasonic vibrator 130 . Fig.13 In the example shown, when the frequency of the vibration plate 110 and the ultrasonic vibrator 130 is 150 kHz, the displacement of the vibration plate 110 becomes maximum, indicating that the resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130 is 150 kHz. The resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130 changes according to the thickness of the vibration plate 110 and the width of the vibration plate 110 in the first direction (X-axis direction).

[0077] Fig.14This is a chart that uses the finite element method to simulate and analyze the relationship between the sound pressure of the ultrasonic wave emitted from the ultrasonic transducer and the frequency of the vibration plate and the ultrasonic vibrator in an ultrasonic transducer that combines a vibration plate with a resonance frequency of 150kHz and an ultrasonic vibrator with a resonance plate with an air resonance frequency of 150kHz. Fig.14 In FIG. 1 , the vertical axis shows the sound pressure (Pa) of the ultrasonic wave transmitted from the ultrasonic transducer 100 , and the horizontal axis shows the frequency (kHz) of the vibration plate 110 and the ultrasonic vibrator 130 . Fig.14 In the figure, the data of the ultrasonic transducer equipped with a sound board is shown by a solid line, and the data of the ultrasonic transducer without a sound board is shown by a dotted line. The sound pressure is shown at a point 30 cm away from the front of the ultrasonic transducer in the third direction (Z-axis direction).

[0078] like Fig.14 As shown, the ultrasonic transducer provided with the sound plate 140 that generates air resonance at a frequency substantially the same as the resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130 can radiate ultrasonic waves with a higher sound pressure than the ultrasonic transducer without the sound plate.

[0079] Fig.15 This is a graph that uses the finite element method to simulate the relationship between the frequency of air resonance generated in the gap between the diaphragm and the soundboard and the size of the gap between the diaphragm and the soundboard. Fig.12 In FIG. 1 , the vertical axis shows the frequency (kHz) of air resonance generated in the gap Rg between the diaphragm 110 and the sounding plate 140 , and the horizontal axis shows the dimension (mm) of the gap Rg between the diaphragm 110 and the sounding plate 140 in the third direction (Z-axis direction).

[0080] like Fig.15 As shown, the frequency of air resonance becomes higher as the dimension of the gap Rg between the vibration plate 110 and the sounding plate 140 in the third direction (Z-axis direction) becomes smaller. The reason is described below. The smaller the dimension of the gap Rg between the vibration plate 110 and the sounding plate 140 in the third direction (Z-axis direction) becomes, the smaller the volume of the gap Rg becomes. According to Boyle's law, the smaller the volume of the gap Rg between the vibration plate 110 and the sounding plate 140 becomes, the greater the change in pressure relative to the displacement of the vibration plate 110 becomes. When the dimension of the gap Rg between the vibration plate 110 and the sounding plate 140 in the third direction (Z-axis direction) is small, the air compressed between the vibration plate 110 and the sounding plate 140 due to the displacement of the vibration plate 110 becomes hard, and the speed of sound in the air increases. Therefore, as the dimension of the gap Rg between the diaphragm 110 and the sound plate 140 in the third direction (Z-axis direction) becomes smaller, the speed of sound of the air in the gap Rg becomes higher, and even if the length of λ / 2 of the air resonance is fixed, the frequency of the air resonance becomes higher.

[0081] Next, conditions for effectively generating the λ / 2 air resonance in the first direction (X-axis direction) will be described in detail. Fig.16 This is a graph that uses the finite element method to simulate and analyze the relationship between the ratio of the gap between the vibration plate and the soundboard to the width of the soundboard and the sound pressure amplification ratio. Fig.16 In FIG. 1 , the vertical axis shows the sound pressure amplification ratio, and the horizontal axis shows the ratio of the dimension (mm) of the gap Rg between the vibration plate 110 and the sounding plate 140 in the third direction (Z-axis direction) to the width of the sounding plate 140 in the first direction (X-axis direction). Fig.16 In the figure, the solid line shows the data when the resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130 and the frequency of the air resonance generated in the gap between the vibration plate 110 and the sound plate 140 are each 150kHz, the dotted line shows the data when the resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130 and the frequency of the air resonance generated in the gap between the vibration plate 110 and the sound plate 140 are each 100kHz, and the single-dash line shows the data when the resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130 and the frequency of the air resonance generated in the gap between the vibration plate 110 and the sound plate 140 are each 80kHz.

[0082] For example, when the frequency of the air resonance generated at the gap between the vibration plate 110 and the sounding board 140 is 80 kHz, when the dimension of the gap Rg between the vibration plate 110 and the sounding board 140 in the third direction (Z-axis direction) is 0.1 mm, the dimension of the width of the sounding board 140 in the first direction (X-axis direction) is 1.8 mm, and therefore the ratio of the dimension of the gap Rg in the third direction (Z-axis direction) to the dimension of the width of the sounding board 140 in the first direction (X-axis direction) is 0.1 / 1.8=0.056. When the resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130 is 80 kHz, the value of the sound pressure at a point 30 cm away in the third direction (Z-axis direction) from the front face of the ultrasonic transducer without the sounding board 140 is 0.276 Pa, and the value of the sound pressure at a point 30 cm away in the third direction (Z-axis direction) from the front face of the ultrasonic transducer of the sounding board 140 where the above-mentioned gap Rg is arranged and the dimension ratio of the width in the first direction (X-axis direction) of the sounding board 140 is 0.056 is 0.522 Pa. Therefore, the sound pressure amplification ratio is 0.522 / 0.276=1.89.

[0083] like Fig.16As shown, when the ratio of the dimension of the gap Rg in the third direction (Z-axis direction) to the dimension of the width of the sound plate 140 in the first direction (X-axis direction) is 1 or less, that is, when the dimension in the short-axis direction of the sound plate 140 is larger than the dimension of the gap Rg in the direction orthogonal to the vibration plate 110, the effect of increasing the sound pressure of the ultrasonic wave radiated from the ultrasonic transducer at any of the above three frequencies can be obtained. When the dimension in the short-axis direction of the sound plate 140 is 2.5 times or more and 5 times or less of the dimension of the gap Rg in the direction orthogonal to the vibration plate 110, the effect of increasing the sound pressure of the ultrasonic wave radiated from the ultrasonic transducer by more than 2 times can be obtained.

[0084] On the other hand, if the dimension of the gap Rg in the third direction (Z-axis direction) becomes too small, the rebound force caused by air resonance and air compression when the vibration plate 110 is displaced becomes large, and the displacement of the vibration plate 110 becomes small. Fig.16 As shown, when the ratio of the dimension of the gap Rg in the third direction (Z-axis direction) to the width of the sound plate 140 in the first direction (X-axis direction) is 0.1 or less, the sound pressure amplification ratio is low.

[0085] In addition, by appropriately generating a rebound force due to air resonance and air compression when the vibration plate 110 is displaced, the amplitude of the vibration plate 110 can be reduced, and the internal stress in the third direction (Z-axis direction) generated in the ultrasonic transducer 100 relative to the radiated sound pressure can be reduced. In other words, the sound pressure of the ultrasonic wave radiated from the ultrasonic transducer 100 can be maintained, and the internal stress in the third direction (Z-axis direction) generated in the ultrasonic transducer 100 can be reduced.

[0086] Fig.17 This is a graph that uses the finite element method to simulate the relationship between the size of the gap between the vibration plate and the sound plate and the sound pressure amplification ratio. Fig.17 In FIG. 1 , the vertical axis shows the sound pressure amplification ratio, and the horizontal axis shows the dimension (mm) of the gap Rg between the vibration plate 110 and the sounding plate 140 in the third direction (Z-axis direction). Fig.17 In the figure, the solid line shows the data when the resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130 and the frequency of the air resonance generated in the gap between the vibration plate 110 and the sound plate 140 are each 150kHz, the dotted line shows the data when the resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130 and the frequency of the air resonance generated in the gap between the vibration plate 110 and the sound plate 140 are each 100kHz, and the single-dash line shows the data when the resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130 and the frequency of the air resonance generated in the gap between the vibration plate 110 and the sound plate 140 are each 80kHz.

[0087] like Fig.17 As shown in FIG. 1 , the higher the resonant frequency of the vibration plate 110 and the ultrasonic vibrator 130 and the frequency of the air resonance become, the more the peak value of the sound pressure amplification ratio moves toward the smaller side of the dimension in the third direction (Z-axis direction) of the gap Rg. Specifically, when the resonant frequency of the vibration plate 110 and the ultrasonic vibrator 130 and the frequency of the air resonance are 80 kHz, the sound pressure amplification ratio reaches a peak value at a dimension of 0.2 mm in the third direction (Z-axis direction) of the gap Rg, when the resonant frequency of the vibration plate 110 and the ultrasonic vibrator 130 and the frequency of the air resonance are 100 kHz, the sound pressure amplification ratio reaches a peak value at a dimension of 0.15 mm in the third direction (Z-axis direction) of the gap Rg, and when the resonant frequency of the vibration plate 110 and the ultrasonic vibrator 130 and the frequency of the air resonance are 150 kHz, the sound pressure amplification ratio reaches a peak value at a dimension of 0.07 mm in the third direction (Z-axis direction) of the gap Rg. According to this result, the sound pressure amplification ratio can be brought closer to the peak value by changing the dimension of the gap Rg in the third direction (Z-axis direction) according to the resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130 and the frequency of air resonance.

[0088] Hereinafter, the thickness of the sounding board 140 included in the ultrasonic transducer 100 according to one embodiment of the present invention will be described. Fig.18 This is a graph that uses the finite element method to simulate and analyze the relationship between the sound pressure of the ultrasonic wave sent from the ultrasonic transducer and the thickness of the soundboard. Fig.18 In FIG. 1 , the vertical axis shows the sound pressure (Pa) of the ultrasonic wave transmitted from the ultrasonic transducer 100, and the horizontal axis shows the thickness (mm) of the sound board 140. The sound pressure is shown at a point 30 cm away in the third direction (Z-axis direction) from the front of the ultrasonic transducer. Fig.18 As shown, as the sound board 140 becomes thicker, the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer 100 decreases.

[0089] Fig.19 This is a diagram showing the sound pressure distribution obtained by simulation analysis using the finite element method when a λ / 2 air resonance is generated in an ultrasonic transducer having a soundboard with a thickness of 0.1 mm. Fig. 20 This is a diagram showing the sound pressure distribution obtained by simulation analysis using the finite element method when a λ / 2 air resonance is generated in an ultrasonic transducer having a soundboard with a thickness of 0.6 mm.

[0090] like Fig.19 As shown in FIG. 1 , when the thickness of the sound board is 0.1 mm, the virtual sound source is concentrated in the area Rf just above the sound board 140, but as shown in FIG. Fig. 20As shown in FIG. 1 , when the thickness of the sound board 140 is 0.6 mm, the imaginary sound source is dispersed in the upper part of the sound board 140, and the front sound pressure becomes smaller. That is, as the thickness of the sound board 140 increases, the inflow and outflow of air centered on the area Rf directly above the sound board 140 when the λ / 2 air resonance is generated becomes weaker, and the effect of superimposing the sound pressure caused by the imaginary sound source becomes lower. Therefore, the thickness of the sound board 140 is preferably 0.3 mm or less. In addition, if the thickness of the sound board 140 is less than 0.05 mm, even if the sound board 140 is made of a highly rigid metal such as stainless steel, the rigidity becomes low, and warping occurs in the sound board 140, making it difficult to accurately ensure the gap between the vibration plate 110 and the sound board, and the possibility of unnecessary vibration due to the rebound of air caused by the resonance increases. Therefore, the thickness of the sound board 140 is more preferably 0.05 mm or more and 0.3 mm or less.

[0091] The ultrasonic transducer 100 according to the first embodiment of the present invention includes a vibration plate 110, at least one housing 120, at least one ultrasonic vibrator 130, and at least one sounding board 140. The at least one housing 120 extends in the long-axis direction and is bonded to the vibration plate 110. The at least one ultrasonic vibrator 130 is mounted on the at least one housing 120 and faces the vibration plate 110 with a gap therebetween. The at least one sounding board 140 faces the vibration plate 110 with a gap Rg therebetween on the opposite side of the at least one housing 120 with respect to the vibration plate 110 and extends along the long-axis direction. The vibration plate 110 resonates and vibrates in a direction orthogonal to the vibration plate 110 with 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 housing 120 in the long-axis direction is larger than the dimension L2 of the inner side of the at least one housing 120 in the short-axis direction orthogonal to the long-axis direction. If the wavelength converted from the driving frequency of the at least one ultrasonic vibrator 130 is set to λ, air resonance of λ / 2 can be generated in the short axis direction at the gap Rg. Thus, in the ultrasonic transducer 100, the sound pressure level can be increased with a compact structure.

[0092] In the ultrasonic transducer 100 according to the first embodiment of the present invention, the dimension L1 of the inner side of the at least one housing 120 in the long axis direction is 4 times or more the dimension L2 of the inner side of the at least one housing 120 in the short axis direction orthogonal to the long axis direction. Thus, in the ultrasonic transducer 100, the sound pressure level can be increased with a simple and miniaturized structure.

[0093] In the ultrasonic transducer 100 according to the first embodiment of the present invention, the frequency of the air resonance is within ±10% of the resonance frequency of the vibration plate 110 and the at least one ultrasonic vibrator 130. Thus, the sound pressure caused by the air resonance can be superimposed on the sound pressure of the ultrasonic wave radiated by the resonance of the vibration plate 110 and the ultrasonic vibrator 130, so that the ultrasonic transducer 100 can radiate ultrasonic waves with high sound pressure.

[0094] In the ultrasonic transducer 100 according to the first embodiment of the present invention, the dimension of at least one of the resonance plates 140 in the minor axis direction is larger than the dimension of the gap Rg in the direction orthogonal to the vibration plate 110. Thus, the sound pressure of the ultrasonic wave radiated from the ultrasonic transducer 100 can be increased, and the internal stress in the third direction (Z-axis direction) generated in the ultrasonic transducer 100 relative to the radiated sound pressure can be reduced.

[0095] In the ultrasonic transducer 100 according to the first embodiment of the present invention, the dimension of at least one sounding plate 140 in the minor axis direction is 2.5 to 5 times the dimension of the gap Rg in the direction perpendicular to the vibration plate 110. Thus, the sound pressure of the ultrasonic wave radiated from the ultrasonic transducer 100 can be increased by more than 2 times as compared with an ultrasonic transducer not provided with the sounding plate 140, and the internal stress in the third direction (Z-axis direction) generated in the ultrasonic transducer 100 relative to the radiated sound pressure can be reduced.

[0096] In the ultrasonic transducer 100 according to the first embodiment of the present invention, the thickness of at least one resonance plate 140 is 0.3 mm or less. Thus, the sound pressure caused by air resonance can be effectively superimposed on the sound pressure of the ultrasonic wave radiated by the resonance of the vibration plate 110 and the ultrasonic vibrator 130, so that the ultrasonic transducer 100 can radiate ultrasonic waves of high sound pressure.

[0097] In the 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 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).

[0098] (Implementation method 2)

[0099] 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.

[0100] Fig.21 It is a perspective view showing the structure of an ultrasonic transducer according to Embodiment 2 of the present invention. Fig. 22 FIG. 2 is an exploded perspective view showing the structure of an ultrasonic transducer according to Embodiment 2 of the present invention. Fig.21 as well as Fig. 22 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 vibration plate 210, a plurality of housings 220, a plurality of ultrasonic vibrators 130, and a plurality of resonance plates 240. The plurality of housings 220 are bonded to the vibration plate 210, and the plurality of ultrasonic vibrators 130 are bonded to the plurality of housings 220, respectively.

[0101] The vibration plate 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 vibration plate 210 is made of an aluminum alloy such as duralumin containing aluminum or a metal such as stainless steel. In the present embodiment, the vibration plate 210 is made of stainless steel. The plurality of slits 211 are formed by etching or cutting.

[0102] Each of the multiple shells 220 has a rectangular ring shape. Each of the multiple shells 220 has a short axis direction along the first direction (X-axis direction) and a long axis direction along the second direction (Y-axis direction). Each of the multiple shells 220 extends in the second direction (Y-axis direction). The axial direction of each of the multiple shells 220 is along the third direction (Z-axis direction). Each of the multiple shells 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 distance between the long sides 221 is more than 4 times the shortest distance between the short sides 222. However, the shortest distance between the long sides 221 is not limited to more than 4 times the shortest distance between the short sides 222, as long as it is wider than the shortest distance between the short sides 222.

[0103] The plurality of shells 220 are arranged in a first direction (X-axis direction). Slits 223 are formed between the shells 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 shells 220 adjacent to each other in the first direction (X-axis direction) are separated from each other by the slits 223.

[0104] The housings 220 adjacent to each other in the first direction (X-axis direction) are connected to each other at the short sides 222. That is, among the plurality of housings 220, the housings 220 adjacent to each other in the short axis direction are connected to each other at both ends in the long axis direction.

[0105] The multiple housings 220 are each formed of a metal such as aluminum alloy or stainless steel, glass epoxy or resin, etc. In the present embodiment, the multiple housings 220 are formed by a single thin plate, but the present invention is not limited thereto, and the multiple housings 220 can also be integrated by mutually joining the short sides 222 of the multiple housings 220 respectively formed by the multiple thin plates.

[0106] In this embodiment, each of the plurality of ultrasonic vibrators 130 includes two stacked piezoelectric bodies 131. The two piezoelectric bodies 131 constituting the plurality of ultrasonic vibrators 130 are stacked and bonded in the state of two thin plates.

[0107] like Fig. 22 As shown, 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 cutter or the like at 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).

[0108] like Fig.21 as well as Fig. 22 As shown, the two spacers 250 are respectively arranged at nodes with less vibration in the vibration plate 210. In the present embodiment, the two spacers 250 are respectively arranged at the ends of the vibration plate 210 in the second direction (Y-axis direction).

[0109] The plurality of sounding plates 240 are arranged at intervals from each other so as to be arranged in a first direction (X-axis direction). Among the plurality of sounding plates 240, the sounding plates 240 adjacent to each other in the first direction (X-axis direction) are connected to each other at both ends in a second direction (Y-axis direction) by connecting portions 241. The two connecting portions 241 each extend in the first direction (X-axis direction) and are arranged on the spacer 250.

[0110] Here, the result of simulation analysis using the finite element method on the relationship between the array pitch, which is the arrangement interval of the plurality of ultrasonic transducers 100 , and the air resonance will be described. Fig.23 Schematic diagram of an FEM model of an ultrasonic transducer subjected to simulation analysis. As simulation analysis conditions, a vibration source VS located at the interface between the vibration plate 210 and the air vibrates at a speed of 1 m / s in the third direction (Z-axis direction) at the gap between the vibration plate 210 and the resonance plate 240, and the interval between the ultrasonic transducers 100 adjacent to each other in the first direction (X-axis direction) is set to Fig.23The array pitch PA shown in FIG. 1 is changed, and the sound pressure at a point 30 cm away in the third direction (Z-axis direction) from the front of the ultrasonic transducer 200 including the five ultrasonic transducers 100 at this time and the sound pressure distribution around the ultrasonic transducer 200 are simulated and analyzed using the finite element method. The frequency of air resonance is set to 150 kHz, and the width of the sound board 140 in the first direction (X-axis direction) is set to 0.9 mm.

[0111] Fig.24 This is a graph that uses the finite element method to simulate and analyze the relationship between the sound pressure of the ultrasonic wave sent from the ultrasonic transducer and the array spacing. Fig.24 In FIG. 1 , the vertical axis shows the sound pressure (Pa) of the ultrasonic wave transmitted from the ultrasonic transducer 200, and the horizontal axis shows the array pitch (mm). The sound pressure is shown at a point 30 cm away in the third direction (Z-axis direction) from the front of the ultrasonic transducer 200. Fig.24 In FIG. 1 , the reference sound pressure indicated by the two-dot chain line is a sound pressure obtained by quintupling the sound pressure at a point 30 cm away from the front surface of one ultrasonic transducer 100 in the third direction (Z-axis direction).

[0112] When the sound pressure of the ultrasonic wave sent from the ultrasonic transducer 200 is higher than the reference sound pressure, the arraying of the ultrasonic transducer 100 causes the sound pressures to reinforce each other. When the sound pressure of the ultrasonic wave sent from the ultrasonic transducer 200 is lower than the reference sound pressure, the arraying of the ultrasonic transducer 100 causes the sound pressures to weaken each other.

[0113] Fig.25 This is a diagram showing the sound pressure distribution around the ultrasonic transducer when the array pitch is 2.2 mm, which was simulated and analyzed using the finite element method. Fig.26 This is a diagram showing the sound pressure distribution around the ultrasonic transducer when the array pitch is 2.6 mm, which is simulated and analyzed using the finite element method. Fig. 27 This is a diagram showing the sound pressure distribution around the ultrasonic transducer when the array pitch is 3.0 mm, which is simulated and analyzed using the finite element method. Fig.28 This is a diagram showing the sound pressure distribution around the ultrasonic transducer when the array pitch is 3.6 mm, which was simulated and analyzed using the finite element method. Fig.29 This is a diagram showing the sound pressure distribution around the ultrasonic transducer when the array pitch is 4.4 mm, which was simulated and analyzed using the finite element method.

[0114] like Fig.25As shown in FIG. 1 , when the array pitch is 2.2 mm, which is too narrow, the anti-cord of the sound pressure at the gap Rg between the vibration plate 210 and the sounding plate 240 becomes extended in the first direction (X-axis direction) and collapses, and no air resonance occurs, so the gap area Rs between the adjacent sounding plates 240 and the gap Rg become substantially white. Fig.24 As shown, the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer 200 becomes lower than the reference sound pressure.

[0115] like Fig.26 As shown in the figure, when the array pitch is 2.6 mm, the gap Rg becomes white, the area Rs becomes black, and air resonance begins to occur. Fig.24 As shown, the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer 200 becomes slightly higher than the reference sound pressure.

[0116] like Fig. 27 As shown in FIG. 1 , when the array pitch is 3.0 mm, the gap Rg becomes white, the area Rs becomes black, and the area Rf directly above the soundboard 140 also becomes black, forming a virtual sound source in the area Rf. Fig.24 As shown, the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer 200 increases to near the peak.

[0117] like Fig.28 As shown in FIG. 1 , when the array pitch is 3.6 mm, the air resonances in the individual ultrasonic transducers 100 are substantially not affected by each other. Fig.24 As shown, the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer 200 becomes slightly higher than the reference sound pressure.

[0118] like Fig.29 As shown in FIG. 1 , when the array pitch is 4.4 mm, the gap Rg and the region Rs become white, and the gap between the gap Rg and the region Rs becomes black. The sound pressures of the ultrasonic waves sent from the adjacent ultrasonic transducers 100 cancel each other out, causing air resonance with a reduced front sound pressure. Fig.24 As shown, the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer 200 becomes lower than the reference sound pressure.

[0119] Fig.30 This is a graph that uses the finite element method to simulate and analyze the relationship between the directivity of ultrasonic waves sent from an ultrasonic transducer and the array spacing. Fig.30 In FIG. 1 , the vertical axis shows the sound pressure level (dB) of the ultrasonic wave transmitted from the ultrasonic transducer 200 , and the directivity angle is shown in a semicircular shape. Line A shows the data with an array pitch of 2.2 mm, line B shows the data with an array pitch of 3.0 mm, and line C shows the data with an array pitch of 4.8 mm.

[0120] like Fig.30 As shown in FIG. 1 , as the array pitch increases, the side lobes increase and protrude toward the front side. That is, if the array pitch increases too much, the radiation efficiency of the ultrasonic transducer 200 toward the front side of the ultrasonic wave decreases.

[0121] Therefore, as a range in which the radiation efficiency of the ultrasonic wave of the ultrasonic transducer 200 toward the front is suppressed from decreasing and the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer 200 becomes higher than the reference sound pressure, it is preferable to Fig.24 The range surrounded by the dotted line L11 and the dotted line L13 is shown. If the dimension of the sounding board 240 in the first direction (X-axis direction) is set to Ds, the wavelength of the ultrasonic wave in the air is set to λa, and the array pitch which is the arrangement pitch of the ultrasonic transducers 130 in the first direction (X-axis direction) is set to PA, then in order to fall within the preferred range, the relationship Ds+3λa / 4≤PA≤Ds+5λa / 4 must be satisfied.

[0122] For example, when the frequency of air resonance is set to 150 kHz and the width of the sound board 140 in the first direction (X-axis direction) is set to 0.9 mm, it is preferable to be within the following range, that is, with an array pitch of PA=Ds+λa=3.16 mm. Fig.24 The single-point dash line L12 is shown as the center, with an array pitch of PA = Ds + λa-λa / 4 = Ds + 3λa / 4 = 2.6 mm. Fig.24 The dotted line L11 shown is the lower limit, and the array spacing is PA = Ds + λa + λa / 4 = Ds + 5λa / 4 = 3.7 mm. Fig.24 The dotted line L13 shown is the upper limit. It has been confirmed that even when the dimension of the gap between the vibration plate 110 and the sounding plate 240 in the third direction (Z-axis direction) is doubled and the width of the sounding plate 140 in the first direction (X-axis direction) is changed to change the resonance frequency, the radiation efficiency of the ultrasonic wave of the ultrasonic transducer 200 toward the front is suppressed from decreasing and the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer 200 is made higher than the reference sound pressure by satisfying the relationship Ds+3λa / 4≤PA≤Ds+5λa / 4.

[0123] Fig.31 : is a graph showing the results of measuring the output of ultrasonic waves radiated from the ultrasonic transducer while changing the width of the soundboard. Fig.31 In FIG. 1 , the vertical axis shows the output, and the horizontal axis shows the width of the soundboard (mm). Fig.31In the figure, the width of the sounding plate is 0, which is the data when the sounding plate is not configured. The resonance frequency of the vibration plate 110 and the ultrasonic vibrator 130 is set to 141 kHz, the dimension of the gap between the vibration plate 110 and the sounding plate 240 in the third direction (Z-axis direction) is set to 0.2 mm, and the array pitch is set to 2.8 mm.

[0124] like Fig.31 As shown in FIG. 1 , when the width of the sounding board 240 in the first direction (X-axis direction) is 0.8 mm, the output is approximately twice that when the sounding board is not provided. Based on this result, it can be confirmed that the ultrasonic transducer 200 involved in this embodiment can radiate ultrasonic waves at a high output compared to an ultrasonic transducer without a sounding board.

[0125] 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 .

[0126] In the parametric speaker having the ultrasonic transducer 200 of the present embodiment that transmits high-frequency ultrasonic waves of 100 kHz or more, it is possible to suppress the unnecessary sound reaching far away and the sound leakage caused by unnecessary reflection and reproduce the audible sound only in a limited space. The high-frequency ultrasonic waves of 100 kHz or more are outside the audible range of animals such as dogs and cats, so the influence on these animals can be suppressed.

[0127] In order to attenuate the audible sound after the propagation distance is 30cm, the Rayleigh distance needs to be 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 major axis dimension of the vibration area of ​​the vibration plate 210 is less than 36mm, when the frequency of the ultrasonic wave is 150kHz, the major axis dimension of the vibration area of ​​the vibration plate 210 is less than 29.4mm, and when the frequency of the ultrasonic wave is 200kHz, the major axis dimension of the vibration area of ​​the vibration plate 210 is less than 25.5mm. When the frequency of the ultrasonic wave is above 100kHz, the major axis dimension L1 is more than 4 times and less than 24 times the minor axis dimension L2.

[0128] In the ultrasonic transducer 200 according to the second embodiment of the present invention, at least one housing 220 is configured in plurality so as to be arranged in the short-axis direction and joined to the vibration plate 210. In at least one housing 220, the housings 220 adjacent in the short-axis direction are connected to each other at both ends in the long-axis direction. At least one resonance plate 240 is configured in plurality so as to be arranged in the short-axis direction. In at least one resonance plate 240, the resonance plates 240 adjacent in the short-axis direction are connected to each other at both ends in the long-axis direction. Thus, the sound pressure level can be easily increased.

[0129] In the ultrasonic transducer 200 according to the second embodiment of the present invention, when the dimension of at least one sounding board 240 in the short-axis direction is set to Ds, the wavelength of the ultrasonic wave in the air is set to λa, and the arrangement pitch of at least one ultrasonic vibrator 130 in the short-axis direction is set to PA, the relationship Ds+3λa / 4≤PA≤Ds+5λa / 4 is satisfied. Thus, it is possible to suppress the reduction in the radiation efficiency of the ultrasonic wave of the ultrasonic transducer 200 toward the front and increase the sound pressure of the ultrasonic wave transmitted from the ultrasonic transducer 200.

[0130] (Implementation method 3)

[0131] Hereinafter, an ultrasonic transducer according to Embodiment 3 of the present invention will be described with reference to the drawings. The ultrasonic transducer according to Embodiment 3 of the present invention is different from the ultrasonic transducer according to Embodiment 1 of the present invention in that a slit is formed in the vibration plate, and therefore, the same structure as that of the ultrasonic transducer according to Embodiment 1 of the present invention will not be described again.

[0132] Fig.32 FIG. 2 is an exploded perspective view showing the structure of an ultrasonic transducer according to Embodiment 3 of the present invention. Fig.32 As shown in FIG. 1 , an ultrasonic transducer 300 according to Embodiment 3 of the present invention includes a vibration plate 310, a housing 120, an ultrasonic vibrator 130, a resonance plate 140, and a spacer 150. At least one slit 310s extending in a first direction (X-axis direction) is formed in the vibration plate 310. In this embodiment, two slits 310s are formed at positions on the edge in a second direction (Y-axis direction) of the inner peripheral surface of the housing 120.

[0133] The two slits 310s each extend longer than the short axis dimension L2 in the first direction (X-axis direction) of the inner side of the housing 120. In the present embodiment, the length dimension of the slit 310s in the first direction (X-axis direction) is the same as the short axis dimension L2 in the first direction (X-axis direction) of the inner side of the housing 120. The width dimension of the slit 310s in the second direction (Y-axis direction) is greater than 0.4 mm and less than 0.6 mm. The slit 310s is formed from a position on the end edge in the second direction (Y-axis direction) of the inner peripheral surface of the housing 120 to a position close to the above width dimension in the second direction (Y-axis direction). The two slits 310s are open at both ends in the second direction (Y-axis direction) of the inner side of the housing 120.

[0134] The portion of the vibration plate 110 located above the internal space inside the housing 120 and between the slits 310s in the second direction (Y-axis direction) becomes a vibration region that resonates. The long-axis dimension of the vibration region of the vibration plate 110 becomes the dimension between the slits 310s, and the short-axis dimension of the vibration region of the vibration plate 110 becomes the same as the short-axis dimension L2 inside the housing 120. In the vibration plate 110, the middle portion located in the middle in the long-axis direction inside the housing 120 is greatly displaced, and the end portion located outside the slits 310s in the second direction (Y-axis direction) is hardly displaced.

[0135] In the ultrasonic transducer 300 according to the third embodiment of the present invention, the internal space inside the housing 120 and the external space outside the housing are connected through the slit 310s. Therefore, for example, the pressure change in the internal space when the adhesive material joining the vibration plate 110 and the housing 120 is heated and cured can be reduced, thereby suppressing the increase of the internal stress in the ultrasonic transducer 300. In addition, the portion adjacent to the slit 310s becomes the free end of the vibration plate 110 that performs resonant vibration and becomes easily displaced, so that the internal stress generated in the vibration plate 110 that performs resonant vibration can be reduced. Therefore, in the ultrasonic transducer 300, the internal stress can be reduced and the sound pressure level can be improved with a simple and compact structure.

[0136] (Note)

[0137] It will be understood by those skilled in the art that the above-described exemplary embodiments are specific examples of the following aspects.

[0138] <1>

[0139] An ultrasonic transducer having:

[0140] Vibration plate;

[0141] at least one housing extending in the long axis direction and coupled to the vibration plate;

[0142] at least one ultrasonic vibrator, mounted on the at least one housing, and opposed to the vibration plate with a gap therebetween; and

[0143] at least one sounding board, which is opposed to the vibration plate with a gap therebetween on the opposite side of the at least one housing and extends along the long axis direction,

[0144] The vibration plate resonates and vibrates in a direction orthogonal to the vibration plate in a phase opposite to that of the at least one ultrasonic vibrator.

[0145] The dimension of the inner side of the at least one shell in the long axis direction is larger than the dimension of the inner side of the at least one shell in the short axis direction orthogonal to the long axis direction.

[0146] If the wavelength converted from the driving frequency of the at least one ultrasonic transducer is set to λ, air resonance of λ / 2 can be generated in the gap in the short-axis direction.

[0147] <2>

[0148] The ultrasonic transducer according to <1>, wherein:

[0149] The dimension of the inner side of the at least one shell in the long axis direction is 4 times or more the dimension of the inner side of the at least one shell in the short axis direction.

[0150] <3>

[0151] The ultrasonic transducer according to <1> or <2>, wherein:

[0152] The frequency of the air resonance is within ±10% of the resonance frequency of the vibration plate and the at least one ultrasonic vibrator.

[0153] <4>

[0154] The ultrasonic transducer according to any one of <1> to <3>, wherein:

[0155] The dimension of the at least one sound plate in the short-axis direction is larger than the dimension of the gap in the direction orthogonal to the vibration plate.

[0156] <5>

[0157] The ultrasonic transducer according to <4>, wherein:

[0158] The dimension of the at least one soundboard in the minor axis direction is 2.5 times or more and 5 times or less of the dimension of the gap in a direction orthogonal to the diaphragm.

[0159] <6>

[0160] The ultrasonic transducer according to any one of <1> to <5>, wherein:

[0161] The at least one soundboard has a thickness of 0.3 mm or less.

[0162] <7>

[0163] The ultrasonic transducer according to any one of <1> to <6>, wherein:

[0164] The at least one housing is configured in plurality so as to be arranged in the short axis direction and to be joined to the vibration plate.

[0165] In the at least one shell, the shells adjacent to each other in the short axis direction are connected to each other at both ends in the long axis direction.

[0166] The at least one soundboard is configured in plurality so as to be arranged in the direction of the short axis,

[0167] In the at least one sounding board, the sounding boards adjacent to each other in the short-axis direction are connected to each other at both ends in the long-axis direction.

[0168] <8>

[0169] The ultrasonic transducer according to <7>, wherein:

[0170] If the dimension of the at least one soundboard in the short axis direction is set to Ds, the wavelength of the ultrasonic wave in the air is set to λa, and the arrangement pitch of the at least one ultrasonic vibrator in the short axis direction is set to PA, the following relationship is satisfied:

[0171] Ds+3λa / 4≤PA≤Ds+5λa / 4.

[0172] In the description of the above-mentioned embodiments, it is also possible to combine the structures that can be combined with each other.

[0173] 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.

[0174] Description of Reference Numerals

[0175] 100, 200: ultrasonic transducer;

[0176] 110, 210: vibration plate;

[0177] 110c: middle part;

[0178] 110e: end;

[0179] 120, 220: housing;

[0180] 121, 221: long side;

[0181] 122, 222: short side;

[0182] 130: ultrasonic vibrator;

[0183] 131: piezoelectric;

[0184] 132: first electrode;

[0185] 133: second electrode;

[0186] 134: middle electrode;

[0187] 140, 240: sounding board;

[0188] 150, 250: spacers;

[0189] 160: processing circuit;

[0190] 211, 223: slits;

[0191] 241: connection part;

[0192] A, B, C: lines;

[0193] Bm, Bp: resonant vibration;

[0194] Dp: polarization direction;

[0195] L1: major axis dimension;

[0196] L2: minor axis dimension;

[0197] LC: cutting line;

[0198] PA: array spacing;

[0199] Rg: gap;

[0200] VS: vibration source;

[0201] Wr: Air resonance.

Claims

1. An ultrasonic transducer comprising: Vibration plate; at least one housing extending in the long axis direction and coupled to the vibration plate; at least one ultrasonic vibrator, mounted on the at least one housing, and opposed to the vibration plate with a gap therebetween; and at least one sounding board, which is opposed to the vibration plate with a gap therebetween on the opposite side of the at least one housing and extends along the long axis direction, The vibration plate resonates and vibrates in a direction orthogonal to the 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 shell in the long axis direction is larger than the dimension of the inner side of the at least one shell in the short axis direction orthogonal to the long axis direction. If the wavelength converted from the driving frequency of the at least one ultrasonic transducer is set to λ, air resonance of λ / 2 can be generated in the gap in the short-axis direction.

2. The ultrasonic transducer according to claim 1, wherein: The dimension of the inner side of the at least one shell in the long axis direction is 4 times or more the dimension of the inner side of the at least one shell in the short axis direction.

3. The ultrasonic transducer according to claim 1 or claim 2, wherein: The frequency of the air resonance is within ±10% of the resonance frequency of the vibration plate and the at least one ultrasonic vibrator.

4. The ultrasonic transducer according to any one of claims 1 to 3, wherein: The dimension of the at least one sound plate in the short-axis direction is larger than the dimension of the gap in the direction orthogonal to the vibration plate.

5. The ultrasonic transducer according to claim 4, wherein: The dimension of the at least one soundboard in the minor axis direction is 2.5 times or more and 5 times or less of the dimension of the gap in a direction orthogonal to the diaphragm.

6. The ultrasonic transducer according to any one of claims 1 to 5, wherein: The at least one soundboard has a thickness of 0.3 mm or less.

7. The ultrasonic transducer according to any one of claims 1 to 6, wherein: The at least one housing is configured in plurality so as to be arranged in the short axis direction and to be joined to the vibration plate. In the at least one shell, the shells adjacent to each other in the short axis direction are connected to each other at both ends in the long axis direction. The at least one soundboard is configured in plurality so as to be arranged in the direction of the short axis, In the at least one sounding board, the sounding boards adjacent to each other in the short-axis direction are connected to each other at both ends in the long-axis direction.

8. The ultrasonic transducer according to claim 7, wherein: If the dimension of the at least one soundboard in the short axis direction is set to Ds, the wavelength of the ultrasonic wave in the air is set to λa, and the arrangement pitch of the at least one ultrasonic vibrator in the short axis direction is set to PA, the following relationship is satisfied: Ds+3λa / 4≤PA≤Ds+5λa / 4.

9. A parametric loudspeaker, wherein: A method of manufacturing the ultrasonic transducer according to any one of claims 1 to 8, Audible sound is reproduced by modulated driving of the ultrasonic transducer.

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