JP5672389B2 - Ultrasonic sensor - Google Patents

Description

  The present invention relates to an ultrasonic sensor having a structure in which a piezoelectric element is bonded to a case, for example, an ultrasonic sensor used for a corner sonar, a back sonar, etc. of an automobile.

  The ultrasonic sensor detects an obstacle or target by intermittently transmitting an ultrasonic pulse signal and receiving a reflected wave reflected after the transmitted ultrasonic pulse signal reaches the obstacle or target. (For example, refer to Patent Document 1). Ultrasonic sensors are used for back sonars, corner sonars of automobiles, and parking spot sensors for detecting distances from obstacles such as side walls in parallel parking.

  FIG. 6A is a cross-sectional view illustrating a configuration example of a conventional ultrasonic sensor. The ultrasonic sensor 101 includes a case 102, a piezoelectric element 103, a damping material 104, a substrate 105, a foamable resin 106, pin terminals 107A and 107B, and lead wires 108A and 108B. The case 102 has a bottomed cylindrical shape and is made of a conductive material such as metal. The piezoelectric element 103 is joined to the inner bottom surface of the case 102 with a conductive adhesive or the like. FIG. 6B is a perspective view illustrating a configuration example of the piezoelectric element 103. The piezoelectric element 103 is made of piezoelectric ceramics, and includes a disk-shaped piezoelectric substrate 103C and electrodes 103A and 103B provided on main surfaces of the piezoelectric substrate 103C facing each other. The piezoelectric element 103 is bonded to the case 102 so that the electrode 103A contacts the inner bottom surface of the opening of the case 102.

  Further, as shown in FIG. 6A, the damping material 104 is provided so as to close the opening of the case 102. The substrate 105 is provided on the damping material 104. The substrate 105 and the damping material 104 are provided with through holes. The foamable resin 106 is injected from one of the through holes into the opening of the case 102 and filled in the case 102 and the through holes. Each of the pin terminals 107A and 107B has a straight bar shape, and is inserted into the opening of the case 102 through one of the through holes. The lead wire 108 </ b> A is joined to the tip of the pin terminal 107 </ b> A and the case 102 by solder in the opening of the case 102, and electrically connects the pin terminal 107 </ b> A and the case 102. For this reason, the pin terminal 107A is electrically connected to the electrode 103A via the lead wire 108A and the case 102. In the opening of the case 102, the lead wire 108B is joined to the tip of the pin terminal 107B and the electrode 103B of the piezoelectric element 103 by soldering, and the tip of the pin terminal 107B and the electrode 103B of the piezoelectric element 103 are electrically connected. Connected.

International Publication WO2007 / 094184

  In the ultrasonic sensor having the conventional configuration as described above, the piezoelectric element is joined to the inner bottom surface of the case opening so that the center position of the piezoelectric element coincides with the center of the inner bottom surface of the case opening. However, depending on the shape of the electrode of the piezoelectric element, the vibration efficiency and the overall sensitivity of the piezoelectric element in the ultrasonic sensor may decrease. In addition, a lead wire is directly connected to one electrode of the piezoelectric element, and a lead wire is indirectly connected to the other electrode via a case. For this reason, it is necessary to perform wiring work twice between the piezoelectric element and the case at the time of manufacture, and the work is complicated.

  In addition, the case needs to be made of a material having good conductivity, and there are significant restrictions on the materials that can be used. Further, when an easily oxidizable metal is used, an anti-oxidation treatment may be required. It was.

  It is also possible to connect the two lead wires directly to the electrode of the piezoelectric element without going through the case. For this purpose, after connecting the lead wire to the electrode of the piezoelectric element, the piezoelectric element is attached to the case. It is necessary to join. In this case, there is a problem that the accuracy of joining the piezoelectric element and the case is lowered, and it is difficult to obtain good vibration efficiency and overall sensitivity.

  Accordingly, an object of the present invention is to realize high bonding accuracy between the piezoelectric element and the case while connecting the wiring member to the electrode of the piezoelectric element without going through the case, and to improve the vibration efficiency and overall sensitivity of the piezoelectric element. It is to realize an ultrasonic sensor having a configuration that can be obtained.

  The ultrasonic sensor of the present invention includes a case and a piezoelectric element. The case has a bottom surface portion that is a vibration region and has a bottomed cylindrical shape. The piezoelectric element has a piezoelectric substrate, a first electrode, a second electrode, and a third electrode. The piezoelectric substrate has a first surface and a second surface facing the first surface. The first electrode is provided on the first surface. The second electrode is provided on a part of the second surface. The third electrode is provided apart from the second electrode on a part of the second surface, and is connected to the first electrode. In the piezoelectric element, the first electrode is joined to the bottom surface, and the center of the piezoelectric element is arranged at a position different from the center of the vibration region in plan view.

  In the above-described ultrasonic sensor, it is preferable that the area of the region where the second electrode is provided on the second surface of the piezoelectric substrate is different from the area of the region where the third electrode is provided.

  In the above-described ultrasonic sensor, it is preferable that the second electrode and the third electrode are provided asymmetrically in a plan view of the piezoelectric element.

  In the ultrasonic sensor described above, the vibration region has a planar shape having a longitudinal direction and a short direction when the bottom surface portion is viewed in plan, and the second electrode and the third electrode are arranged in the short direction. It is preferable.

  According to the present invention, since the piezoelectric element is arranged at a position where the center of the piezoelectric element is different from the center of the vibration region in plan view of the bottom surface portion, the vibration efficiency and the overall sensitivity of the piezoelectric element in the ultrasonic sensor are improved. And the characteristics can be improved. In addition, since the second electrode and the third electrode are provided on the second surface of the piezoelectric substrate, a wiring portion such as a flexible substrate or a lead wire can be directly connected without passing through the case. As a result, there are fewer restrictions on the materials that can be used. Furthermore, the connection between the second electrode and the third electrode and the wiring portion can be performed even after the piezoelectric element is bonded to the case, and the bonding accuracy between the piezoelectric element and the case can be increased.

It is a figure which shows the structural example of the ultrasonic sensor which concerns on the 1st Embodiment of this invention. It is a figure explaining a structure and arrangement | positioning of a piezoelectric element. It is a figure explaining the relationship between arrangement | positioning of a piezoelectric element, an electromechanical coupling coefficient, and total sensitivity. It is a figure which shows the structural example of the ultrasonic sensor which concerns on the 2nd Embodiment of this invention. It is a figure which shows the structural example of the ultrasonic sensor which concerns on the modification of this invention. It is sectional drawing which shows the structural example of the conventional ultrasonic sensor, and a perspective view which shows the structural example of the piezoelectric element with which the conventional ultrasonic sensor is equipped.

<< First Embodiment >>
FIG. 1A is a cross-sectional view of the ultrasonic sensor 1 according to the first embodiment of the present invention. FIG. 1B is a plan view of the ultrasonic sensor 1. 1A shows a cross section at a position indicated by AA ′ in FIG. FIG. 1B shows the back surface of the ultrasonic sensor 1.

  The ultrasonic sensor 1 includes a case 2, a piezoelectric element 3, a sound absorbing material 4, a reinforcing material 5, a support material 6, a buffer material 7, a vibration damping material 8, a flexible substrate 9, and a terminal holding material 10. And pin terminals 11A and 11B.

  The case 2 has a bottomed cylindrical shape in which the lower end surface (front surface) in FIG. 1 (A) is closed and the upper end surface (rear surface) in FIG. 1 (A) is open, a cylindrical side wall 2A, and a disk shape. Bottom plate 2B. As shown in FIG. 1B, the opening of the case 2 is circular in plan view. The case 2 is a member made of lightweight aluminum having a high elastic modulus, for example, and is formed by forging. The material of the case 2 is not limited to a conductive material such as aluminum, and may be an insulating material.

  In the side wall 2A, the back side portion is thin and the opening has a large inside diameter, and the bottom plate 2B side portion is thick and the opening has a small inside diameter. The bottom plate 2B includes a recess 2B1 and a step 2B2. Recess 2B1 has a bottom surface portion and a side wall portion, and is provided such that a predetermined direction (lateral direction in FIG. 1B) is a short direction, and a direction orthogonal to the short direction is a long direction. . That is, the recess 2B1 is provided so that both ends in the longitudinal direction reach the side wall 2A. Further, the step 2B2 is provided on both sides in the short direction of the recess 2B1. The bottom surface portion of the recess 2B1 becomes the main vibration region of the case 2, and the ultrasonic sensor 1 has a narrow directivity in the longitudinal direction of the recess 2B1 and a wide directivity in the lateral direction.

  The piezoelectric element 3 has a flat plate shape and spreads in the in-plane direction and vibrates when a driving voltage is applied. The piezoelectric element 3 is disposed inside the recess 2B1 of the case 2 and joined to the bottom plate 2B. Specifically, the piezoelectric element 3 is bonded to the bottom surface portion of the recess 2B1. The piezoelectric element 3 and the bottom plate 2B are joined together to form a bimorph vibrator, and the bottom plate 2B (recessed portion 2B1) bends and vibrates in the vertical direction in FIG.

  The sound absorbing material 4 is a flat plate made of polyester felt, for example, and is provided to absorb unnecessary ultrasonic waves emitted from the piezoelectric element 3 to the opening side of the case 2. The sound absorbing material 4 is disposed in the recess 2 </ b> B <b> 1 of the case 2 and is bonded onto the piezoelectric element 3.

  The reinforcing material 5 is a ring-shaped member having an opening at the center, and has high acoustic impedance. The reinforcing member 5 is made of a material having higher density and higher rigidity than the material constituting the case 2 such as stainless steel or zinc so as to function as a weight. Note that. The reinforcing material 5 may be made of the same material (aluminum) as the case 2 by adjusting the size such as thickness. The reinforcing member 5 is disposed on the bottom plate 2B of the case 2 so as to contact the inner peripheral surface of the side wall 2A on the bottom plate 2B side, that is, the thick portion, and the stepped portion 2B2. Thus, by providing the reinforcing material 5, the rigidity of the surrounding portion surrounding the recess 2 </ b> B <b> 1 of the case 2 is increased, and vibrations in the bottom plate 2 </ b> B of the case 2 can be prevented from being transmitted to the side wall 2 </ b> A of the case 2.

  The support member 6 is a ring-shaped member having an opening in the center, and is provided between the side wall 2 </ b> A of the case 2 and the buffer material 7 in order to support the buffer material 7 without contacting the case 2. . By providing the support material 6, it is possible to suppress the vibration in the bottom plate 2 </ b> B of the case 2 from being transmitted to the buffer material 7 through the side wall 2 </ b> A.

  The buffer material 7 is a cup-shaped member made of an elastic body such as silicone rubber or urethane resin. The shock-absorbing material 7 is provided at the lower portion, and has a convex portion that engages with the opening of the reinforcing member 5, and an opening that is provided at the upper portion and engages with the terminal holding material 10. By providing the buffer material 7, it is possible to suppress the vibration in the bottom plate 2 </ b> B of the case 2 from being transmitted to the terminal holding material 10 through the side wall 2 </ b> A.

  The terminal holding member 10 is an L-shaped member made of a resin such as polybutylene terephthalate (PBT), and holds the pin terminals 11A and 11B in a state along an axis passing through the center of the opening of the case 2. The lower portion of the terminal holding member 10 is bent so as to engage with an opening provided in the upper portion of the cushioning member 7. The terminal holding material 10 has a convex portion provided on the bottom surface. Further, two through holes through which the pin terminals 11 </ b> A and 11 </ b> B are inserted are provided in the central portion of the terminal holding material 10.

  The pin terminals 11 </ b> A and 11 </ b> B are metal linear pins to which the driving voltage of the piezoelectric element 3 is applied, and are held by the terminal holding material 10. Specifically, the pin terminals 11 </ b> A and 11 </ b> B are inserted into the through holes of the terminal holding material 10, respectively. The lower ends of the pin terminals 11 </ b> A and 11 </ b> B protrude from the through hole of the terminal holding material 10 and are arranged in the opening of the case 2. The upper ends of the pin terminals 11 </ b> A and 11 </ b> B protrude from the upper end of the terminal holding member 10 and are arranged outside the case 2.

  The flexible substrate 9 has a wide band shape, and is a wiring portion that electrically connects the pin terminals 11 </ b> A and 11 </ b> B and the piezoelectric element 3. The flexible substrate 9 is bent and disposed in the opening of the case 2, and a part thereof is disposed between the support material 6 and the buffer material 7. The flexible substrate 9 has a first end and a second end. The first end extends along the same direction as the lower ends of the pin terminals 11A and 11B and is connected to the pin terminals 11A and 11B. The second end is connected to the piezoelectric element 3 by a conductive adhesive. Since the flexible substrate 9 is connected to the piezoelectric element 3 by a conductive adhesive, the weight of the wiring portion can be reduced as compared with the case where the lead wire is connected to the piezoelectric element by solder as in a conventional ultrasonic sensor. Can do. Thereby, the vibration of the piezoelectric element 3 can be brought closer to an ideal one.

  The damping material 8 is made of an elastic body such as silicone resin or urethane resin. The damping material 8 is filled in the case 2 and seals the lower ends of the pin terminals 11 </ b> A and 11 </ b> B and the flexible substrate 9 disposed in the opening of the case 2. However, since the space on the bottom plate 2 </ b> B side of the case 2 is covered with the support material 6 and the buffer material 7, the vibration damping material 8 is filled only in the space on the opening side of the case 2. The damping material 8 has a function of suppressing vibration of the side wall 2 </ b> A of the case 2 and also has a function of preventing the support material 6 and the buffer material 7 from being detached from the case 2.

  In the ultrasonic sensor 1 having such a configuration, the vibration in the bottom plate 2B of the case 2 is attenuated by the sound absorbing material 4, the support material 6, and the buffer material 7, and thus almost propagates to the terminal holding material 10 and the pin terminals 11A and 11B. There is nothing. Therefore, vibration leakage from the pin terminals 11A and 11B to the external substrate that occurs when the ultrasonic sensor 1 is mounted on the external substrate is greatly reduced.

  Note that it is preferable that the support material 6 and the buffer material 7 are difficult to propagate vibration, and the vibration damping material 8 is one that suppresses (vibrates) the vibration of the side wall 2A of the case 2. The support material 6 and the buffer material 7 preferably have a lower elastic modulus than the vibration damping material 8. More specifically, the elastic modulus includes a storage elastic modulus and a loss elastic modulus. It is preferable that the support material 6 and the buffer material 7 have a small storage elastic modulus, and the damping material 8 has a large loss elastic modulus. For example, the support material 6 and the buffer material 7 are preferably made of a silicone resin (silicone rubber), and the vibration damping material 8 is preferably made of a urethane resin.

  FIG. 2A is a perspective view for explaining a detailed configuration of the piezoelectric element 3. FIG. 2B is a plan view of the ultrasonic sensor 1 as seen through the state in which the piezoelectric element 3 is bonded to the case 2.

  The piezoelectric element 3 includes electrodes 3A to 3D and a piezoelectric substrate 3E. The piezoelectric substrate 3E is made of a lead zirconate titanate piezoelectric ceramic and has a rectangular flat plate shape in plan view. The electrode 3A corresponds to the first electrode in the present embodiment, and is provided on the entire lower surface, which is the first surface of the piezoelectric substrate 3E. The electrode 3A is joined to the bottom plate 2B of the case 2. Specifically, the electrode 3A is joined to the bottom surface of the recess 2B1. The electrode 3B corresponds to the second electrode in the present embodiment, and is provided on a part of the upper surface which is the second surface of the piezoelectric substrate 3E. The electrode 3C corresponds to the third electrode in the present embodiment, and is provided on a part of the upper surface that is the second surface of the piezoelectric substrate 3E. The electrode 3D is provided on one side surface of the piezoelectric substrate 3E, and is connected to the electrode 3A and the electrode 3C. For this reason, the electrode 3A and the electrode 3C are electrically connected. Between the region where the electrode 3B is provided on the upper surface of the piezoelectric substrate 3E and the region where the electrode 3C is provided, a linear piezoelectric substrate exposure region parallel to the longitudinal direction of the piezoelectric substrate 3E is provided. . Thereby, the electrode 3B and the electrode 3C are separated from each other by a predetermined distance, and are arranged in the short direction on the upper surface of the piezoelectric substrate 3E, and are not electrically connected to each other. The area where the electrode 3B is provided on the upper surface of the piezoelectric substrate 3E is different from the area where the electrode 3C is provided, and the area where the electrode 3B is provided is the area where the electrode 3C is provided. Is larger than the area. That is, the area of the electrode 3B is larger than that of the electrode 3C.

  Thus, the electrodes 3B and 3C are arranged side by side while being separated by a predetermined distance, so that the electrodes 3B and 3C are directly connected to the connection region 9A at the second end of the flexible substrate 9. The connection region 9A is connected to the electrode 3B and the electrode 3C in the center in the longitudinal direction of the piezoelectric element 3 and in the region around the electrode non-formation region. Since the electrodes 3 </ b> A to 3 </ b> D are configured as described above, the connection region 9 </ b> A of the flexible substrate 9 is connected to the piezoelectric element 3 after the piezoelectric element 3 is joined to the bottom plate 2 </ b> B of the case. Thereby, the joining accuracy of the piezoelectric element 3 and the case 2 can be increased.

  The piezoelectric element 3 having such a configuration vibrates when a driving voltage is applied between the electrodes 3A and 3B, and a region sandwiched between the electrodes 3A and 3B in the piezoelectric substrate 3E is deformed. It will be. On the other hand, the region sandwiched between the electrodes 3A and 3C in the piezoelectric substrate 3E hardly deforms and therefore hardly contributes to vibration. The area of the area where the electrode 3B is provided on the upper surface, which is the second surface of the piezoelectric substrate 3E, is different from the area of the area where the electrode 3C is provided. Since the electrode 3C is provided asymmetrically, the region contributing to vibration in the piezoelectric element 3 is asymmetrical.

  The piezoelectric element 3 is joined to the concave portion 2B1 so that the longitudinal direction of the piezoelectric element 3 coincides with the longitudinal direction of the concave portion 2B1 and the short side direction thereof coincides with the short direction of the concave portion 2B1. ing. Then, the piezoelectric element 3 has a plan view of the recess 2B1 so that the center position of the short side direction of the piezoelectric element 3 is different from the center position of the short side direction of the recess 2B1, that is, the center of the short side direction of the piezoelectric element 3 is. Further, the concave portion 2B1 is disposed so as to be offset from the center in the short direction to the one side of the stepped portion 2B2. The piezoelectric element 3 is arranged such that its longitudinal center coincides with the longitudinal center of the recess 2B1.

  Thus, in consideration of the fact that the region that effectively acts on the vibration in the piezoelectric element 3 is asymmetric, the center of the piezoelectric element 3 is different from the center position of the piezoelectric element 3 and the center position of the recess 2B1. Is offset from the center of the recess 2B1, and the offset dimension of the piezoelectric element 3, that is, the distance between the position of the center of the piezoelectric element 3 and the position of the center of the recess 2B1 is appropriately determined. The vibration efficiency and the overall sensitivity of the element 3 can be improved and the characteristics can be improved.

  Further, by making the short direction of the piezoelectric element 3 coincide with the short direction of the recess 2B1, a region sandwiched between the electrodes 3A and 3C in the piezoelectric substrate 3E that hardly contributes to vibration is defined as a bottom plate of the case. Since it can be arranged close to the step 2B2 that is a node of vibration in 2B, it is possible to prevent the vibration of the piezoelectric element 3 from being obstructed and bring the vibration of the ultrasonic sensor 1 closer to an ideal one. it can.

  In addition, the connection region 9A at the second end of the flexible substrate 9 is connected to the electrode 3B and the electrode 3C at the center in the longitudinal direction of the piezoelectric element 3 and in the region around the electrode non-formation region. Since 9A can be arranged close to the step 2B2 that becomes a vibration node in the bottom plate 2B of the case, the vibration of the piezoelectric sensor 3 is prevented from being obstructed, and the vibration of the ultrasonic sensor 1 is made more ideal. You can get closer to things. Here, the flexible substrate 9 (not shown) is drawn from the connection region 9A to the electrode 3C side. Thereby, the symmetry of the vibration of the piezoelectric element 3 can be improved, and the vibration of the ultrasonic sensor 1 can be brought closer to an ideal one.

  A specific example of setting the dimensions will be described. The recess 2B1 has a dimension in the short side direction of 7.0 mm. The piezoelectric element 3 has a short-side dimension of 5.2 mm and a long-side dimension of 6.5 mm. The electrode 3C has a dimension in the short (width) direction of 0.9 mm. The dimension in the short (width) direction of the electrode non-formation region at the boundary between the electrode 3C and the electrode 3B is 0.4 mm. The electrode 3B has a short (width) dimension of 3.9 mm. The offset dimension between the center of the piezoelectric element 3 and the center of the recess 2B1 is 0.4 mm. That is, the center of the recess 2B1 is positioned at 2.2 mm from the end of the piezoelectric element 3 on the electrode 3B side and at a position of 3.0 mm from the end on the electrode 3C side.

  Here, the vibration characteristic of the ultrasonic sensor 1 will be described based on the FEM analysis result. FIG. 3A shows the relationship between the electromechanical coupling coefficient Kp /% in the bimorph vibrator including the case 2 and the piezoelectric element 3 and the offset dimension (element shift amount) of the piezoelectric element 3 in the dimension setting example described above. FIG.

  As shown in FIG. 3A, in the configuration in which the center of the piezoelectric element 3 coincides with the center of the recess 2B1, that is, the offset dimension of the piezoelectric element 3 is larger than the configuration in which the offset dimension of the piezoelectric element 3 is zero. The electromechanical coupling coefficient Kp /% becomes large. The electromechanical coupling coefficient Kp /% is maximized when the offset dimension of the piezoelectric element 3 is a predetermined value (0.4 mm), and in the configuration in which the offset dimension of the piezoelectric element 3 is larger than the predetermined value, the electromechanical coupling coefficient Kp / % Is smaller than the maximum value. Therefore, at least in terms of vibration efficiency of the ultrasonic sensor, it can be seen that vibration efficiency can be maximized by setting the piezoelectric element 3 to a predetermined offset dimension.

  Next, sensitivity characteristics of the ultrasonic sensor 1 will be described based on sample test results (n = 3). FIG. 3B is a diagram showing the relationship between the total sensitivity Vpp of the ultrasonic sensor 1 and the offset dimension of the piezoelectric element 3 in the above dimension setting example.

  The total sensitivity Vpp of the ultrasonic sensor 1 has a positive correlation with the offset dimension of the piezoelectric element 3, and the total sensitivity Vpp is high when the offset dimension is large. Accordingly, it can be seen that at least in terms of the total sensitivity Vpp of the ultrasonic sensor 1, it is desirable that the offset dimension of the piezoelectric element 3 be large (for example, 0.5 mm).

  However, in reality, if the offset dimension of the piezoelectric element 3 is too large, the arrangement of the flexible substrate 9 connected to the piezoelectric element 3 is also greatly offset, and the flexible substrate 9 easily interferes with the side wall 2A of the case 2. . When the flexible substrate 9 interferes with the side wall 2A of the case 2, unnecessary vibrations are transmitted from the flexible substrate 9 to the side wall 2A, which may deteriorate the characteristics. Therefore, in order to improve vibration characteristics and sensitivity characteristics while preventing such interference, an example of setting the offset dimension of the piezoelectric element 3 described above is an example of setting the offset dimension to 0.4 mm. It was.

  If the direction in which the flexible substrate 9 is pulled out is the longitudinal direction of the piezoelectric element 3, interference between the flexible substrate 9 and the side wall 2A of the case 2 is less likely to occur. In that case, the offset dimension may be increased to the limit, and the overall sensitivity of the ultrasonic sensor 1 can be further improved.

<< Second Embodiment >>
Next, an ultrasonic sensor 21 according to a second embodiment of the present invention will be described.

  FIG. 4 is a schematic cross-sectional view of the ultrasonic sensor 21 according to the present embodiment.

  The ultrasonic sensor 21 includes lead wires 29A and 29B instead of the flexible substrate 9 of the ultrasonic sensor 1 according to the above-described embodiment. The other configuration of the ultrasonic sensor 21 is the same as that of the ultrasonic sensor 1 according to the above-described embodiment. The lead wires 29A and 29B are directly connected to the electrodes 3B and 3C (not shown) of the piezoelectric element 3, respectively. In this way, the ultrasonic sensor 21 may be configured. Even in this case, the present invention can be suitably implemented by directly connecting the piezoelectric element 3 and the pin terminals 11A and 11B without using the case 2 and by arranging the piezoelectric element 3 in an offset manner.

≪Modification≫
Next, ultrasonic sensors 31 to 51 according to modifications of the present invention will be described.

In the piezoelectric element 33, the electrodes 3 </ b> B and 3 </ b> C are provided side by side in the longitudinal direction of the piezoelectric element 33 while being separated by a predetermined distance. The piezoelectric element 33 is arranged offset in the longitudinal direction of the recess 2B1. In such a configuration, the symmetry of the directional beam can be enhanced in the short direction of the recess 2B1. Further, the region sandwiched between the electrode 3A (not shown) and the electrode 3C in the piezoelectric substrate 3E (not shown) that hardly contributes to vibration does not interfere with the side wall 2A or the step 2B2, and the piezoelectric element 33 The size can be increased.

  The ultrasonic sensor 41 includes a piezoelectric element 43 instead of the piezoelectric element 3 of the above-described embodiment. The other configuration of the ultrasonic sensor 41 is the same as that of the ultrasonic sensor 1 according to the above-described embodiment. FIG. 5B is a plan view of the ultrasonic sensor 41 as seen through the state in which the piezoelectric element 43 is bonded to the case 2.

  In the piezoelectric element 43, the electrodes 3 </ b> B and 3 </ b> C are provided side by side in the short direction of the piezoelectric element 43 while being separated by a predetermined distance. The piezoelectric element 43 is arranged with its own longitudinal direction as the short direction of the recess 2B1 and offset in the longitudinal direction of the recess 2B1.

  The ultrasonic sensor 51 includes a piezoelectric element 53 instead of the piezoelectric element 3 of the above-described embodiment. The other configuration of the ultrasonic sensor 51 is the same as that of the ultrasonic sensor 1 according to the above-described embodiment. FIG. 5C is a plan view of the ultrasonic sensor 51 as seen through the state in which the piezoelectric element 53 is bonded to the case 2.

  In the piezoelectric element 53, the electrodes 3 </ b> B and 3 </ b> C are provided side by side in the longitudinal direction of the piezoelectric element 53 while being separated by a predetermined distance. The piezoelectric element 53 is arranged with its own longitudinal direction as the short direction of the recess 2B1, and offset in the short direction of the recess 2B1.

  As described in the above embodiments, the present invention can be implemented, but the specific configuration of the ultrasonic sensor is not limited to the above-described one. For example, any specific shape or material such as cushioning material, support material, reinforcement material, support material, sound absorbing material may be used, and cushioning material, support material, reinforcement material, support material, sound absorption material may be It is not always necessary to provide each.

1, 2, 31, 41, 51 ... Ultrasonic sensor 2 ... Case 2A ... Side wall 2B ... Bottom plate 2B1 ... Recess 2B2 ... Steps 3, 33, 43, 53 ... Piezoelectric elements 3A to 3D ... Drive electrode 3E ... Piezoelectric substrate 4 ... Sound absorbing material 5 ... Reinforcement material 6 ... Support material 7 ... Buffer material 8 ... Damping material 9 ... Flexible substrate 9A ... Connection region 10 ... Terminal holding materials 11A and 11B ... Pin terminals 29A and 29B ... Lead wires

Claims (6)

A bottomed cylindrical case having a bottom plate ;
A piezoelectric substrate having a first surface and a second surface opposite to the first surface, a first electrode provided on the first surface, and a portion of the second surface A second electrode that is provided, and a third electrode that is provided apart from the second electrode on a part of the second surface and is connected to the first electrode, A piezoelectric element bonded to the bottom plate via the first electrode;
Equipped with a,
The bottom plate has a flat bottom surface formed with the thinnest thickness,
The piezoelectric element, the bottom plate is bonded to the bottom portion is their center at the center is different from the position of the bottom surface portion in plan view, and ultrasonic sensors that vibrate the said bottom portion as a vibrating region.   The ultrasonic sensor according to claim 1, wherein the second electrode is disposed so as to overlap a center of the bottom surface portion when the bottom surface portion is viewed in plan. Wherein the area of a region where the the area of the region where the in the second surface of the piezoelectric substrate is the second electrode is provided third electrode is provided are different, according to claim 1 or claim 2 Ultrasonic sensor. The ultrasonic sensor according to claim 1 , wherein the second electrode and the third electrode are provided asymmetrically when the piezoelectric element is viewed in plan. The bottom surface portion has a planar shape having a longitudinal direction and a lateral direction in plan view,
The ultrasonic sensor according to claim 1 , wherein the second electrode and the third electrode are arranged in the short direction.   The bottom surface portion has a planar shape having a longitudinal direction and a lateral direction in plan view,
  The second electrode and the third electrode are arranged with the lateral direction or the longitudinal direction as an arrangement direction,
  The ultrasonic sensor according to claim 1, wherein the piezoelectric element is arranged to be shifted from the center of the bottom surface portion toward the third electrode along the arrangement direction.

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