Ultrasonic transducer

Abstract

The ultrasonic transducer includes a first acoustic transducer (110), a second acoustic transducer (120), and a bottomed cylindrical housing (130). The second acoustic transducer (120) further includes: an annular portion (121) which is in full contact with the periphery of the second diaphragm portion (122) and supports the second diaphragm portion (122); and an acoustic matching plate (123) which is spaced apart from the second diaphragm portion (122) and is connected to the peripheral wall portion (130s) to form a closed space with the housing (130). An ultrasonic transmission path (T1) is formed in the closed space and is sandwiched between the first diaphragm portion (112) and the second diaphragm portion (122). The maximum inner width (H1) of the ultrasonic transmission path (T1) is smaller than the maximum inner width (H2) of the peripheral wall portion (130s).

Description

Technical Field

[0001] The present invention relates to ultrasonic transducers. Background Art

[0002] As an existing document that discloses an ultrasonic sensor with an acoustic matching layer, there is Japanese Patent Publication No. 2019-193130 (Patent Document 1). The ultrasonic sensor described in Patent Document 1 includes a piezoelectric element and an acoustic matching layer. The piezoelectric element is bonded to the inner side of the top plate of a metal shell with a bottomed cylindrical shape, and the open end is closed by a terminal plate. The acoustic matching layer is bonded to the outer surface of the top plate of the shell.

[0003] The acoustic matching layer is used to efficiently transmit sound between media with greatly different acoustic impedances. Generally, the acoustic impedance of a material is determined by the product of the density of the material and the speed of sound in the material. When the difference in acoustic impedance between different materials is small, sound is transmitted by ultrasonic waves passing through the interface between different materials. However, when the difference in acoustic impedance between different materials is large, ultrasonic waves are reflected at the interface between different materials. In other words, as the difference in acoustic impedance at the interface between different materials increases, the efficiency of sound energy transmission decreases.

[0004] Therefore, as described in Patent Document 1, an acoustic matching layer is used to mitigate the difference in acoustic impedance at the interface between the piezoelectric element and the air. Specifically, ceramics are generally used as the constituent material of the piezoelectric element, and the density of ceramics is extremely high compared to the density of air, and the speed of sound in ceramics is extremely high compared to the speed of sound in air. Therefore, the efficiency of transmitting acoustic energy from the piezoelectric element to the air is very low. In order to solve this problem, an acoustic matching layer having an acoustic impedance value intermediate between the piezoelectric element and the air is sandwiched between the piezoelectric element and the air to improve the efficiency of transmitting acoustic energy.

[0005] As a conventional document that discloses an acoustic matching structure, there is PHYSICAL REVIEW LETTERS 120, 044302 (2018) (Non-Patent Document 1). The acoustic matching structure described in Non-Patent Document 1 includes a first diaphragm portion and a second diaphragm portion.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-193130

[0009] Non-patent literature

[0010] Non-patent document 1: PHYSICAL REVIEW LETTERS 120, 044302 (2018) Summary of the invention

[0011] Problem that the invention aims to solve

[0012] In the ultrasonic sensor described in Patent Document 1, the piezoelectric element is bonded to the top plate of the housing, so the top plate hinders the deformation of the piezoelectric element, causing a decrease in the sound pressure of the ultrasonic wave. In the acoustic matching structure described in Non-Patent Document 1, the ultrasonic transmission path is composed of the peripheral wall portion, so the transmission distance of the ultrasonic wave becomes longer and the transmission attenuation of the ultrasonic wave becomes greater. In addition, even if the structure of the acoustic matching structure is miniaturized, the inner diameter of the ultrasonic transmission path is larger than the outer diameter of the diaphragm portion for transmitting the ultrasonic wave to the high impedance side, so the loss of the transmission distance cannot be minimized.

[0013] The present invention is completed in view of the above-mentioned problems, and its purpose is to provide an ultrasonic transducer, which is configured to have a structure that does not hinder the deformation of the diaphragm portion of the acoustic transducer, thereby ensuring that the displacement of the diaphragm portion is large, and the structural body of the acoustic transducer is larger than the ultrasonic transmission path, thereby shortening the transmission distance of the ultrasonic wave, thereby suppressing the transmission attenuation of the ultrasonic wave and improving efficiency.

[0014] Solutions for solving problems

[0015] The ultrasonic transducer according to the present invention includes a first acoustic transducer, a second acoustic transducer, and a bottomed cylindrical shell. The first acoustic transducer has a first diaphragm portion that is spaced apart from the first diaphragm portion and is capable of vibrating in the thickness direction. The shell has: a bottom portion that is spaced apart from the first diaphragm portion in the thickness direction; and a peripheral wall portion that is spaced apart from the first diaphragm portion and the second diaphragm portion and surrounds the first diaphragm portion and the second diaphragm portion. The second acoustic transducer also has: an annular portion that is in contact with the periphery of the second diaphragm portion and supports the second diaphragm portion; and an acoustic matching plate that is spaced apart from the second diaphragm portion and is connected to the peripheral wall portion to form a closed space with the shell. An ultrasonic transmission path sandwiched by the first diaphragm portion and the second diaphragm portion is formed in the closed space. The maximum inner width of the ultrasonic transmission path is smaller than the maximum inner widths of the peripheral wall portion, the first diaphragm portion, and the second diaphragm portion.

[0016] Effects of the Invention

[0017] According to the present invention, by adopting a structure that does not hinder the deformation of the diaphragm of the acoustic transducer, the displacement of the diaphragm can be ensured to be large, and by shortening the propagation distance of ultrasonic waves, the propagation attenuation of ultrasonic waves can be suppressed and the efficiency can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a longitudinal sectional view showing the structure of the ultrasonic transducer according to the first embodiment of the present invention.

[0019] Figure 2 This is a diagram schematically showing a configuration located in a propagation path of ultrasonic waves in the ultrasonic transducer according to the first embodiment of the present invention.

[0020] Figure 3 This is a graph showing the relationship between reflectivity and energy transmission rate when ultrasonic waves are transmitted from an ultrasonic wave transmission path to an external space.

[0021] Figure 4 It is a longitudinal sectional view showing the structure of an ultrasonic transducer according to Embodiment 2 of the present invention.

[0022] Figure 5 It is a longitudinal sectional view showing the structure of an ultrasonic transducer according to Embodiment 3 of the present invention.

[0023] Figure 6 It is a longitudinal sectional view showing the structure of an ultrasonic transducer according to a fourth embodiment of the present invention.

[0024] Figure 7 It is a longitudinal sectional view showing the structure of an ultrasonic transducer according to Embodiment 5 of the present invention. DETAILED DESCRIPTION

[0025] Hereinafter, ultrasonic transducers according to various embodiments 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 denoted by the same reference numerals, and their description will not be repeated.

[0026] (Implementation Method 1)

[0027] Figure 1 1 is a longitudinal sectional view showing the structure of an ultrasonic transducer according to Embodiment 1 of the present invention. Figure 1 As shown, the ultrasonic transducer 100 according to the first embodiment of the present invention includes a first acoustic transducer 110 , a second acoustic transducer 120 , and a bottomed cylindrical housing 130 .

[0028] The first acoustic transducer 110 has a first diaphragm portion 112 that flexurally vibrates. The first acoustic transducer 110 is an element having a vibrator made of ceramic or a small mechanical vibrator (MEMS: Micro Electro Mechanical Systems) made by performing micro-machining on semiconductor materials such as Si and functional films. The first acoustic transducer 110 can send and receive ultrasonic waves through the vibration of the first diaphragm portion 112. As a driving source for vibrating the first diaphragm portion 112, a piezoelectric effect, an electrostatic force, or an electromagnetic force can be used. In the ultrasonic transducer 100, in order to achieve a higher transmission efficiency, it is necessary to reduce the transmission path of the ultrasonic wave and reduce the transmission loss of the ultrasonic wave. Therefore, it is effective to make the first acoustic transducer 110 small. Therefore, as the first acoustic transducer 110, it is preferable to use a MEMS element that is easy to miniaturize.

[0029] The first acoustic transducer 110 includes a first diaphragm portion 112 and an annular base portion 111 that is in contact with the entire outer periphery of the first diaphragm portion 112 and supports the first diaphragm portion 112. The base portion 111 is made of Si or SOI (Silicon on Insulator).

[0030] The first diaphragm portion 112 is a portion of the multilayer film provided on the base 111 that extends inward from the inner peripheral edge of the base 111. The total thickness of the stacked thin film layers is, for example, less than 10 μm. The material constituting the multilayer film varies depending on the driving method of the first diaphragm portion 112. For example, in the case of a piezoelectric driving method, the multilayer film is composed of PZT, AlN, lithium niobate or lithium tantalate, etc. In this case, the multilayer film also includes electrode wiring for applying a voltage to the piezoelectric material.

[0031] When observed from the thickness direction of the first diaphragm portion 112, the area of ​​the outer shape of the first diaphragm portion 112 is S10. In the case where the first diaphragm portion 112 is a piezoelectric drive mode, bending vibration is excited in the first diaphragm portion 112 by applying a voltage to the piezoelectric material. The inner diameter S1 of the first diaphragm portion 112 is, for example, greater than 0.7 mm and less than 1.0 mm. In addition, the outer shape of the first diaphragm portion 112 is not limited to a circle, and may also be a rectangle. Therefore, in this specification, the inner diameter refers to the length of the shortest line segment that passes through the center of the inner circumference and connects the inner circumferences to each other.

[0032] A slit is formed in the first diaphragm portion 112. As a result, the residual stress of the first diaphragm portion 112 is reduced. The first diaphragm portion 112 can vibrate at a relatively low frequency due to the reduction of the residual stress generated in the film forming process and the processing process of the thin film layer. Specifically, the first diaphragm portion 112 is configured to bend and vibrate in a low-frequency region above 20 kHz and below 60 kHz, for example, near a mechanical resonance frequency of 40 kHz. As a result, the first acoustic transducer 110 can transmit and receive relatively low-frequency ultrasonic waves.

[0033] Furthermore, when the width of the slit of the first diaphragm portion 112 is narrowed, for example, when the width of the slit of the first diaphragm portion 112 is less than 10 μm, the ultrasonic wave generated by the bending vibration of the first diaphragm portion 112 does not pass through the slit. Thus, it is possible to suppress the ultrasonic wave generated on the second diaphragm portion 122 side described later in the thickness direction of the first diaphragm portion 112 from being attenuated due to interference with the ultrasonic wave of the opposite phase generated on the side opposite to the second diaphragm portion 122 side in the thickness direction of the first diaphragm portion 112. Assuming that the width of the slit of the first diaphragm portion 112 is wide, the ultrasonic waves of the opposite phases generated on both sides in the thickness direction of the first diaphragm portion 112 interfere with each other, thereby reducing the transmission and reception efficiency of the ultrasonic transducer 100.

[0034] The second acoustic transducer 120 has a second diaphragm portion 122 which is spaced apart from the first diaphragm portion 112 and is capable of vibrating in the thickness direction of the first diaphragm portion 112. The second acoustic transducer 120 also has an annular portion 121 which is in contact with the periphery of the second diaphragm portion 122 throughout the entire circumference and supports the second diaphragm portion 122. The annular portion 121 is made of metal, semiconductor, resin, etc., and the constituent material of the annular portion 121 is selected from the viewpoints of processability and acoustic impedance matching. Here, processability refers to the ease of processing in semiconductor micro-processing technology. Acoustic impedance matching refers to making the acoustic impedance of the second acoustic transducer 120 as close as possible to the acoustic impedance of the external medium of the ultrasonic transducer 100. As a material constituting the annular portion 121, Si or Al, etc., which are materials that take into account both processability and acoustic impedance matching, are preferred.

[0035] The second diaphragm portion 122 is a portion of the thin film provided on the annular portion 121 that extends inward from the inner peripheral edge of the annular portion 121. No electrical wiring is provided in the second diaphragm portion 122, so the second diaphragm portion 122 cannot actively vibrate. The second diaphragm portion 122 is made of metal, semiconductor, or resin, etc. From the viewpoint of processability and acoustic impedance matching, Si or Al, etc., are preferably used as the material constituting the second diaphragm portion 122. In addition, the material of the annular portion 121 and the material of the second diaphragm portion 122 may be different from each other.

[0036] The second acoustic transducer 120 further includes an acoustic matching plate 123 which is spaced apart from the second diaphragm portion 122 and faces each other. The acoustic matching plate 123 has a flat plate shape. The acoustic matching plate 123 is made of metal, semiconductor, resin, etc. From the viewpoint of acoustic impedance matching and reliability against interference in the external medium, a material having high rigidity is preferably used as the material constituting the acoustic matching plate 123, for example, Al or polypropylene is preferably used. Interference in the external medium refers to, for example, high-pressure water or flying stones flying at high speed when the ultrasonic transducer 100 is installed on the bumper of a car.

[0037] The acoustic matching plate 123 is arranged so as to sandwich the annular portion 121 between the second diaphragm portion 122. That is, in the acoustic matching plate 123, the interval between the opposing portion 123f opposing the second diaphragm portion 122 and the second diaphragm portion 122 is determined by the thickness of the annular portion 121. The acoustic matching plate 123 and the annular portion 121 are connected to each other using an adhesive such as a patch adhesive. Thus, a medium sealing portion T2 is formed in which a medium such as a gas or liquid is sealed and sandwiched between the second diaphragm portion 122 and the opposing portion 123f of the acoustic matching plate 123.

[0038] The second acoustic transducer 120 is a MEMS element having a small mechanical vibrator structure manufactured by a micro-machining process. The second acoustic transducer 120 has the following functions: adjusting the acoustic impedance of the transmission path of the ultrasonic wave from the first acoustic transducer 110 to the external space T0, and suppressing the attenuation of the ultrasonic wave transmitted to the first acoustic transducer 110 or received by the first acoustic transducer 110.

[0039] The housing 130 includes a bottom portion 130b which is spaced apart from the first diaphragm portion 112 in the thickness direction of the first diaphragm portion 112 and faces the first diaphragm portion 112, and a peripheral wall portion 130s which is spaced apart from the first diaphragm portion 112 and the second diaphragm portion 122 and surrounds the first diaphragm portion 112 and the second diaphragm portion 122. The housing 130 also includes an annular protrusion 130p which protrudes toward the inner side of the peripheral wall portion 130s. The housing 130 also includes an open end 130e on the side opposite to the bottom portion 130b.

[0040] In this embodiment, the housing 130 is composed of an annular plate portion 131, a bottomed cylindrical portion 132, and a cylindrical portion 133, and has a bottomed cylindrical shape as a whole. The annular plate portion 131 is located between the bottomed cylindrical portion 132 and the cylindrical portion 133. In the cylindrical portion 133, the end portion on the annular plate portion 131 side protrudes inward.

[0041] In the present embodiment, the bottom 130b of the shell 130 is composed of a bottomed cylindrical portion 132. The peripheral wall portion 130s of the shell 130 is composed of an annular plate portion 131, a bottomed cylindrical portion 132, and a cylindrical portion 133. The protruding portion 130p of the shell 130 is composed of an annular plate portion 131 and a cylindrical portion 133. The annular plate portion 131, the bottomed cylindrical portion 132, and the cylindrical portion 133 are bonded to each other in a liquid-tight manner by bonding materials such as solder or an adhesive. The shell 130 is composed of metal, semiconductor, resin, etc. From the viewpoint of acoustic impedance matching and reliability against interference in the external medium, a material having high rigidity is preferably used as the material constituting the shell 130, for example, Al or polypropylene is preferably preferred.

[0042] The first acoustic transducer 110 is attached to the bottom 130 b side of the protruding portion 130 p of the housing 130 . The surface of the annular plate portion 131 on the bottomed cylindrical portion 132 side is in contact with the base 111 .

[0043] The second acoustic transducer 120 is attached to the open end 130e side of the protruding portion 130p of the housing 130. The cylindrical portion 133 is in contact with the thin film constituting the second diaphragm portion 122.

[0044] The acoustic matching plate 123 and the opening end 130e of the housing 130 are fluid-tightly bonded to each other by a bonding material such as solder or adhesive. Thus, the acoustic matching plate 123 is connected to the peripheral wall portion 130s of the housing 130 to form a sealed space between the acoustic matching plate 123 and the housing 130.

[0045] The sealed space includes an ultrasonic transmission path T1 sandwiched between the first diaphragm 112 and the second diaphragm 122. In the present embodiment, the ultrasonic transmission path T1 is a region surrounded by the first diaphragm 112, the second diaphragm 122, the base 111, and the protrusion 130p of the housing 130.

[0046] The maximum inner width H1 of the ultrasonic transmission path T1 is smaller than the maximum inner width H2 of the peripheral wall portion 130s of the housing 130. The maximum inner width refers to the maximum inner width in a plane parallel to the first diaphragm portion 112. Therefore, the position defining the maximum inner width varies in both the thickness direction and the radial direction of the first diaphragm portion 112.

[0047] Here, a method for manufacturing the ultrasonic transducer 100 according to the first embodiment of the present invention will be described.

[0048] The first acoustic transducer 110 and the second acoustic transducer 120 are formed by photolithography or etching, etc. After the first acoustic transducer 110 is die-bonded to the annular plate portion 131 , the bottomed cylindrical portion 132 is bonded to the annular plate portion 131 using a bonding material such as solder.

[0049] After the second acoustic transducer 120 is mounted on the cylindrical portion 133 by chip bonding or flip chip bonding, the annular plate portion 131 and the cylindrical portion 133 are bonded using a bonding material such as solder. At this time, the ultrasonic transmission path T1 is filled with a gas or liquid medium.

[0050] The ultrasonic transducer 100 according to the first embodiment of the present invention is manufactured through the above-mentioned steps.

[0051] Hereinafter, the operation of the ultrasonic transducer 100 according to the first embodiment of the present invention will be described. Figure 2 This is a diagram schematically showing a configuration located in a propagation path of ultrasonic waves in the ultrasonic transducer according to the first embodiment of the present invention.

[0052] like Figure 1 As shown in FIG. 1 , the ultrasonic wave W1 transmitted from the first acoustic transducer 110 is reflected at the interface between the second diaphragm portion 122 and the ultrasonic transmission path T1 and the interface between the acoustic matching plate 123 and the dielectric sealing portion T2 in the initial stage. When the second diaphragm portion 122 starts to vibrate upon receiving the ultrasonic wave W1, the second diaphragm portion 122 transmits the ultrasonic wave in the thickness direction of the second diaphragm portion 122, canceling the reflected wave from the above-mentioned interface. As a result, the ultrasonic wave is transmitted from the first diaphragm portion 112 in the same direction as the direction in which the ultrasonic wave is transmitted, as shown in FIG. Figure 1 and Figure 2 As shown, the ultrasonic wave is transmitted to the external space T0 via the acoustic matching plate 123 .

[0053] The ultrasonic wave W2 propagating to the external space T0 is reflected by the detection target object, propagates in the reverse order to the above, excites the vibration of the first diaphragm portion 112, and is received.

[0054] Here, when ultrasonic waves are transmitted between different components, the energy transfer rate is determined by the acoustic impedance value of each component. The acoustic impedance value is uniquely determined by the density and rigidity of the material constituting the component, so there are limitations on the materials that can be used to achieve efficient acoustic transmission. However, in the ultrasonic transducer 100 of embodiment 1 of the present invention, the second acoustic transducer 120 that transmits ultrasonic waves by vibrating the second diaphragm portion 122 is provided in the path of ultrasonic transmission, so that the acoustic impedance value can be set in a wide range not only according to material selection but also according to structural design.

[0055] Specifically, the acoustic impedance value can be adjusted by changing any one of the mass of the second diaphragm portion 122 and the distance between the second diaphragm portion 122 and the facing portion 123 f.

[0056] For example, when the ultrasonic transmission path T1 is filled with air and the medium of the external space T0 is also air, the acoustic impedance value of the ultrasonic transmission path T1 and the external space T0 is set to Za. If the acoustic impedance value of the second acoustic transducer 120 is set to Zm, the reflectivity (Ra-m) of the ultrasonic wave generated by the first acoustic transducer 110 when it is transmitted from the ultrasonic transmission path T1 to the external space T0 becomes (Zm-Za) / (Zm+Za).

[0057] Figure 3 This is a graph showing the relationship between the reflectivity (Ra-m) and the energy transfer rate when ultrasonic waves are transmitted from the ultrasonic transmission path T1 to the external space T0. Figure 3 In FIG. 1 , the horizontal axis represents the reflectivity (Ra-m) when the ultrasonic wave is transmitted from the ultrasonic wave transmission path T1 to the external space T0, and the vertical axis represents the energy transfer rate when the ultrasonic wave is transmitted from the ultrasonic wave transmission path T1 to the external space T0.

[0058] like Figure 3 As shown in Figure 2, when the absolute value of the reflectivity (Ra-m) is less than 0.22, Figure 3 The energy transfer rate on the upper side of point line A reaches a range of more than 90%. At this time, the energy transfer rate from the time the ultrasonic wave is sent to the time it is received becomes more than 80%. According to the relationship between the above-mentioned reflectivity (Ra-m) and the acoustic impedance values ​​Za and Zm, Za / 1.6<Zm<1.6Za is satisfied.

[0059] When the acoustic impedance values ​​Za and Zm do not satisfy the above relationship, the sensitivity of the ultrasonic transducer 100 decreases, and the detectable distance to the detection object becomes shorter. If you want to compensate for this sensitivity reduction, in order to increase the ultrasonic wave generated by the first acoustic transducer 110, it is necessary to increase the deformation of the first diaphragm portion 112 by applying a large voltage to the piezoelectric material of the first diaphragm portion 112. At this time, there is a concern that the mechanical reliability of the vibrator of the first acoustic transducer 110 caused by the large deformation of the first diaphragm portion 112 during driving and the generation of heat energy loss caused by the application of a large voltage will be reduced. Therefore, it is considered that the acoustic impedance values ​​Za and Zm preferably satisfy the above relationship.

[0060] When the acoustic impedance values ​​Za and Zm satisfy the above relationship, the combined acoustic impedance of the medium filling the sealed space between the housing 130 and the acoustic matching plate 123 and the second acoustic transducer 120 is 1 / 1.6 to 1.6 times the value Za of the acoustic impedance of air.

[0061] For example, when the enclosed space between the shell 130 and the acoustic matching plate 123 is filled with air, the external space T0 is also filled with air, the acoustic matching plate 123 is made of Al, the second diaphragm portion 122 is made of an active layer of SOI, and the annular portion 121 is made of a supporting substrate of SOI, by setting the thickness of the second diaphragm portion 122 to 144 μm and setting the interval between the second diaphragm portion 122 and the relative portion 123f to 6.69 μm, it is possible to ensure an energy transfer rate of more than 90% for sound waves in the ultrasonic frequency band of 40 kHz.

[0062] In the ultrasonic transducer 100 of the first embodiment of the present invention, the first diaphragm portion 112 of the first acoustic transducer 110 is spaced apart from the bottom 130b of the housing 130 and is surrounded by the peripheral wall portion 130s with a gap. Therefore, it is possible to ensure that the displacement of the first diaphragm portion 112 is large. In addition, the maximum inner width H1 of the ultrasonic transmission path T1 is smaller than the maximum inner width H2 of the peripheral wall portion 130s, the inner diameter S1 of the first diaphragm portion 112, and the inner diameter S2 of the second diaphragm portion 122, respectively, so that the transmission attenuation of the ultrasonic wave caused by the increase in the transmission distance of the ultrasonic wave can be suppressed. Furthermore, the ultrasonic transducer 100 can be made more efficient.

[0063] In the ultrasonic transducer 100 according to the first embodiment of the present invention, the first acoustic transducer 110 is a MEMS element. Therefore, since a multi-layer thin film can be formed thinly, relatively low-frequency ultrasonic waves can be transmitted, and the ultrasonic transducer 100 can be miniaturized.

[0064] In the ultrasonic transducer 100 of embodiment 1 of the present invention, the combined acoustic impedance of the medium filling the enclosed space between the shell 130 and the acoustic matching plate 123 and the second acoustic transducer 120 is 1 / 1.6 times or more and 1.6 times or less than the acoustic impedance of air, so that ultrasonic waves can be transmitted and received with low loss by utilizing the acoustic impedance matching between the enclosed space and the external space T0.

[0065] (Implementation Method 2)

[0066] Hereinafter, an ultrasonic transducer according to a second embodiment of the present invention will be described with reference to the accompanying drawings. The ultrasonic transducer according to the second embodiment of the present invention is different from the ultrasonic transducer 100 according to the first embodiment of the present invention mainly in that a concave portion is provided in the acoustic matching plate, and therefore the same structure as that of the ultrasonic transducer 100 according to the first embodiment of the present invention will not be described repeatedly.

[0067] Figure 4 2 is a longitudinal sectional view showing the structure of an ultrasonic transducer according to Embodiment 2 of the present invention. Figure 4As shown, in the second acoustic transducer 220 of the ultrasonic transducer 200 according to the second embodiment of the present invention, a recessed portion 223c is provided at a position of the acoustic matching plate 223 that is opposite to the second diaphragm portion 122. That is, in the acoustic matching plate 223, the interval between the opposing portion 223f that is opposite to the second diaphragm portion 122 and the second diaphragm portion 122 is defined by the depth of the recessed portion 223c. The recessed portion 223c of the acoustic matching plate 223 is formed by etching or machining.

[0068] The acoustic matching plate 223 and the film constituting the second diaphragm section 122 are connected to each other by an adhesive such as a die bonding agent, thereby forming a medium sealing portion T2 sandwiched between the second diaphragm section 122 and the facing portion 223f of the acoustic matching plate 223 and sealing a gas or liquid medium.

[0069] In the ultrasonic transducer 200 according to the second embodiment of the present invention as well, the efficiency of the ultrasonic transducer 200 can be improved by ensuring a large displacement amount of the first diaphragm portion 112 and suppressing attenuation of ultrasonic waves.

[0070] In the ultrasonic transducer 200 according to the second embodiment of the present invention, a recessed portion 223c is provided at a position of the acoustic matching plate 223 that is opposite to the second diaphragm portion 122, so that the dimension of the interval between the second diaphragm portion 122 and the opposite portion 223f is the same as the dimension of the depth of the recessed portion 223c. In the case of this structure, the mass of the second diaphragm portion 122 and the interval between the second diaphragm portion 122 and the opposite portion 223f of the acoustic matching plate 223, which are related to the acoustic impedance, can be adjusted by separate processing. Therefore, the mass of the second diaphragm portion 122 and the interval between the second diaphragm portion 122 and the opposite portion 223f of the acoustic matching plate 223 can be adjusted separately, so that the adjustable range of the acoustic impedance value of the second acoustic transducer 220 can be increased.

[0071] (Implementation 3)

[0072] Hereinafter, an ultrasonic transducer according to a third embodiment of the present invention will be described with reference to the accompanying drawings. In addition, the ultrasonic transducer according to the third embodiment of the present invention is different from the ultrasonic transducer 100 according to the first embodiment of the present invention in that the second diaphragm portion 122 and the annular portion 121 of the second acoustic transducer 120 are formed of the same member, and therefore, the same structure as that of the ultrasonic transducer 100 according to the first embodiment of the present invention will not be described repeatedly.

[0073] Figure 5 2 is a longitudinal sectional view showing the structure of an ultrasonic transducer according to Embodiment 3 of the present invention. Figure 5As shown, in the second acoustic transducer 120 of the ultrasonic transducer 300 according to the third embodiment of the present invention, the second diaphragm portion 122 and the annular portion 121 are formed by processing an integral material. As a result, since the second diaphragm portion 122 and the annular portion 121 are formed by the same member, it is possible to suppress the occurrence of peeling at the interface between the second diaphragm portion 122 and the annular portion 121 and improve reliability. In addition, the second diaphragm portion 122 and the annular portion 121 can be easily formed by etching or the like.

[0074] (Implementation 4)

[0075] Hereinafter, an ultrasonic transducer according to a fourth embodiment of the present invention will be described with reference to the accompanying drawings. In addition, the ultrasonic transducer according to the fourth embodiment of the present invention is different from the ultrasonic transducer 300 according to the third embodiment of the present invention in that the outer shape area S20 of the second diaphragm portion 122 is larger than the outer shape area S10 of the first diaphragm portion 112, and therefore the same structure as that of the ultrasonic transducer 300 according to the third embodiment of the present invention will not be described repeatedly.

[0076] Figure 6 1 is a longitudinal sectional view showing the structure of an ultrasonic transducer according to Embodiment 4 of the present invention. Figure 6 As shown, in the ultrasonic transducer 400 according to the fourth embodiment of the present invention, when viewed from the thickness direction of the second diaphragm portion 122, the outer shape area S20 of the second acoustic transducer 120 is larger than the outer shape area S10 of the first diaphragm portion 112 of the first acoustic transducer 110. Thus, the second diaphragm portion 122 can fully receive the acoustic energy of the ultrasonic wave W1 transmitted from the first diaphragm portion 112, thereby reducing the transmission loss of the ultrasonic wave.

[0077] (Implementation method 5)

[0078] Hereinafter, an ultrasonic transducer according to a fifth embodiment of the present invention will be described with reference to the accompanying drawings. In addition, the ultrasonic transducer according to the fifth embodiment of the present invention is different from the ultrasonic transducer 400 according to the fourth embodiment of the present invention mainly in the structure of the housing, and therefore the same structure as the ultrasonic transducer 400 according to the fourth embodiment of the present invention will not be described repeatedly.

[0079] Figure 7 1 is a longitudinal sectional view showing the structure of an ultrasonic transducer according to Embodiment 5 of the present invention. Figure 7 As shown, in the ultrasonic transducer 500 according to the fifth embodiment of the present invention, the housing 130 is composed only of the bottomed cylindrical portion 132 .

[0080] In the present embodiment, the first acoustic transducer 110 and the second acoustic transducer 120 are bonded to each other using a known wafer bonding method such as metal bonding or anodic bonding. Specifically, the base 111 and the annular portion 121 are bonded to each other. In addition, when observed from the thickness direction of the second diaphragm portion 122, the outer shape area S20 of the second diaphragm portion 122 of the second acoustic transducer 120 is larger than the outer shape area S10 of the first diaphragm portion 112 of the first acoustic transducer 110.

[0081] In the present embodiment, the ultrasonic transmission path T1 is a region surrounded by the first diaphragm portion 112, the second diaphragm portion 122, and the base portion 111. Therefore, the length of the ultrasonic transmission path T1 is equal to the thickness of the annular base portion 111 that contacts the outer periphery of the first diaphragm portion 112 and supports the first diaphragm portion 112.

[0082] In the ultrasonic transducer 500 according to the fifth embodiment of the present invention, the length of the ultrasonic transmission path T1 can be shortened, and therefore the efficiency of the ultrasonic transducer 500 can be improved by suppressing the attenuation of ultrasonic waves.

[0083] In the ultrasonic transducer 500 according to the fifth embodiment of the present invention, the length of the ultrasonic transmission path T1 can be shortened, and the housing 130 is formed only of the bottomed cylindrical portion 132 , so that the length of the housing 130 can be shortened. Therefore, the ultrasonic transducer 500 can be miniaturized.

[0084] In the description of the above-mentioned embodiments, it is also possible to combine the structures that can be combined with each other.

[0085] The embodiments disclosed this time should be considered in all aspects as illustrative and non-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.

[0086] Description of Reference Numerals

[0087] 100, 200, 300, 400, 500, ultrasonic transducer; 110, first acoustic transducer; 111, base; 112, first diaphragm; 120, 220, second acoustic transducer; 121, annular portion; 122, second diaphragm; 123, 223, acoustic matching plate; 123f, 223f, opposite portion; 130, housing; 130b, bottom; 130e, opening end ; 130p, protrusion; 130s, peripheral wall portion; 131, annular plate portion; 132, cylindrical portion with bottom; 133, cylindrical portion; 223c, recessed portion; A, dotted line; H1, H2, maximum inner width; S1, S2, inner diameter; S10, S20, area; T0, external space; T1, ultrasonic transmission path; T2, medium sealing portion; W1, W2, ultrasonic wave; Za, Zm, acoustic impedance value.

Claims

1. An ultrasonic transducer, wherein: The ultrasonic transducer includes: a first acoustic transducer having a first diaphragm portion that flexurally vibrates; a second acoustic transducer including a second diaphragm portion which is opposed to the first diaphragm portion with a gap therebetween and is capable of vibrating in a thickness direction; and A bottomed cylindrical housing having a bottom opposed to the first diaphragm portion at a distance in the thickness direction and a peripheral wall portion which is spaced apart from the first diaphragm portion and the second diaphragm portion by a gap and surrounds the first diaphragm portion and the second diaphragm portion, The second acoustic transducer further comprises: an annular portion which contacts the entire periphery of the second diaphragm portion and supports the second diaphragm portion; and an acoustic matching plate which is spaced apart from the second diaphragm portion and is opposite to the second diaphragm portion and is connected to the peripheral wall portion to form a closed space between the housing and the acoustic matching plate. An ultrasonic transmission path sandwiched by the first diaphragm portion and the second diaphragm portion is formed in the sealed space. The maximum inner width of the ultrasonic transmission path is smaller than the maximum inner width of the peripheral wall portion.

2. The ultrasonic transducer according to claim 1, wherein: A recessed portion is provided at a position of the acoustic matching plate facing the second diaphragm portion.

3. The ultrasonic transducer according to claim 1 or 2, wherein: The second diaphragm portion and the annular portion are formed of the same member.

4. The ultrasonic transducer according to any one of claims 1 to 3, wherein: When viewed in the thickness direction, the outer shape area of ​​the second diaphragm portion is larger than the outer shape area of ​​the first diaphragm portion.

5. The ultrasonic transducer according to any one of claims 1 to 4, wherein: The length of the ultrasonic transmission path is equal to the thickness of an annular base portion that contacts the entire outer periphery of the first diaphragm portion and supports the first diaphragm portion.

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