JP7409249B2 - ultrasonic transducer - Google Patents

Description

The present invention relates to an ultrasonic transducer.

Patent Document 1 listed below discloses an ultrasonic transducer using a piezoelectric vibrator. Such an ultrasonic transducer outputs ultrasonic waves and receives ultrasonic waves reflected from an object to be detected.

Japanese Patent Application Publication No. 2004-260239

In the above-mentioned ultrasonic transducer, it is known that reverberation during output of ultrasonic waves deteriorates detection characteristics. The inventors have repeatedly researched the reverberation of ultrasonic transducers, and as a result, they have discovered a new technique that can suppress reverberation.

An object of the present invention is to provide an ultrasonic transducer in which reverberation is suppressed.

An ultrasonic transducer according to an embodiment of the present invention includes a case, a vibrating body having a holding plate whose peripheral portion is held by the case, and a piezoelectric diaphragm stacked on the holding plate, and the tensile elastic modulus of the case is is higher than the tensile modulus of the holding plate of the vibrating body.

In the ultrasonic transducer described above, since the tensile modulus of the case is higher than the tensile modulus of elasticity of the holding plate of the vibrating body, propagation of vibration from the holding plate of the vibrating body to the case is suppressed. That is, vibration of the case caused by oscillation of the vibrating body is suppressed. Therefore, in the above ultrasonic transducer, reverberation is suppressed when outputting ultrasonic waves.

In an ultrasonic transducer according to another embodiment, the peripheral edge of the holding plate is sandwiched between the cases in the extending direction of the cases.

In the ultrasonic transducer according to another embodiment, the end face of the peripheral edge of the holding plate and both main faces facing each other in the extending direction of the case are fixed to the case.

In an ultrasonic transducer according to another embodiment, the holding plate has a recess for accommodating the piezoelectric diaphragm, and the piezoelectric diaphragm is accommodated in the recess.

In an ultrasonic transducer according to another embodiment, the holding plate is made of resin.

In an ultrasonic transducer according to another embodiment, the case is made of resin.

In an ultrasonic transducer according to another embodiment, both the holding plate and the case are made of resin.

According to the present invention, it is possible to provide an ultrasonic transducer in which reverberation is suppressed.

1 is a schematic configuration diagram showing an ultrasonic detection system according to an embodiment. 2 is a schematic cross-sectional view showing the ultrasonic transducer of FIG. 1. FIG. FIG. 2 is a bottom view of the ultrasonic transducer of FIG. 1; FIG. 4 is an enlarged view of a main part of the cross-sectional view shown in FIG. 3; FIG. 2 is a diagram showing signal waveforms in the ultrasonic detection system of FIG. 1, showing (a) an input waveform, (b) a transmitted waveform, and (c) a received waveform. 4 is a sectional view showing a different form from FIG. 3. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same elements or elements having the same function will be denoted by the same reference numerals, and redundant description will be omitted.

In this embodiment, an ultrasonic detection system that detects a target object using ultrasonic waves will be described.

As shown in FIG. 1, the ultrasonic detection system 1 outputs ultrasonic waves to a predetermined object 10 and receives ultrasonic waves reflected from the object 10. The ultrasonic detection system 1 can detect the presence of the object 10 and the distance to the object 10 from the received ultrasonic waves.

The ultrasonic detection system 1 includes a control circuit 20 and an ultrasonic transducer 30.

The control circuit 20 is a circuit that generates a signal of a specific frequency and inputs the signal to the ultrasonic transducer 30 via the signal line 25. Further, the control circuit 20 is a circuit that appropriately amplifies and detects the ultrasonic signal received by the ultrasonic transducer 30. Control circuit 20 can include an LC circuit.

The ultrasonic transducer 30 oscillates in response to a signal input from the control circuit 20 and outputs an ultrasonic signal. Moreover, when the ultrasonic transducer 30 receives an ultrasonic signal from the outside, it transmits the signal to the control circuit 20 .

As shown in FIG. 2, the ultrasonic transducer 30 includes a vibrating body 40 and a housing 50 that holds the vibrating body 40.

The vibrating body 40 includes a holding plate 41 and a piezoelectric diaphragm 42 stacked on the holding plate 41.

The holding plate 41 has a disc-shaped outer shape as shown in FIGS. 2 and 3. A circular recess 43 having a uniform depth is provided in the central region of the upper surface 41a of the holding plate 41. The peripheral edge 44 of the holding plate 41 has a uniform thickness T. In this embodiment, the width W of the annular region from the recess 43 to the end surface 41c of the holding plate 41 is designed to be longer than the thickness T of the peripheral edge 44 of the holding plate 41.

The holding plate 41 is made of resin. In this embodiment, the holding plate 41 is made of polyetheretherketone (PEEK). The tensile modulus of polyetheretherketone constituting the holding plate 41 is 4,300 MPa. The holding plate 41 is not limited to polyetheretherketone, and may be made of polyethylene (PE, tensile modulus: 1,090 MPa), for example.

The piezoelectric diaphragm 42 has a disc-shaped outer shape. The piezoelectric diaphragm 42 includes a piezoelectric layer (not shown) and a pair of terminal electrodes. A pair of terminal electrodes of the piezoelectric diaphragm 42 are electrically connected to the signal line 25 via a pair of wiring (or leads) 26, respectively. The piezoelectric diaphragm 42 vibrates in response to a signal input from the signal line 25. The piezoelectric diaphragm 42 vibrates in the thickness direction and also in a direction perpendicular to the thickness direction. The piezoelectric layer of the piezoelectric diaphragm 42 may have a single layer structure including one piezoelectric material layer, or may have a multilayer structure in which a plurality of piezoelectric material layers and internal electrode layers are alternately stacked. The piezoelectric material layer of the piezoelectric diaphragm 42 can be made of a piezoelectric ceramic material such as PZT.

The piezoelectric diaphragm 42 is stacked on the holding plate 41 so as to be accommodated in the recess 43 of the holding plate 41. As shown in FIG. 2, when the thickness of the piezoelectric diaphragm 42 is thicker than the depth of the recess 43 of the holding plate 41, the piezoelectric diaphragm 42 protrudes from the upper surface 41a of the holding plate 41. The thickness of the piezoelectric diaphragm 42 may be thinner than the depth of the recess 43 of the holding plate 41, and the piezoelectric diaphragm 42 may be completely accommodated in the recess 43. By providing the recess 43 in which the piezoelectric diaphragm 42 is accommodated in the holding plate 41, the contact surface between the holding plate 41 and the piezoelectric diaphragm 42 is made smaller than when the piezoelectric diaphragm 42 is placed on a flat surface. This increases the vibration propagation efficiency between the holding plate 41 and the piezoelectric diaphragm 42. In this case, the output efficiency of the ultrasonic transducer increases and the reception sensitivity also increases.

The housing 50 includes a cylindrical portion 52, a frame portion 54, and a lid portion 56.

The cylindrical portion 52 (case) has a cylindrical shape as shown in FIGS. 2 and 3. The cylindrical portion 52 has a clamping portion 53 near the lower opening. In the holding part 53 of the cylindrical part 52, as shown in FIG. A peripheral edge portion 44 of 41 is held between the inner surface of the cylindrical portion 52. The holding plate 41 is held between the holding parts 53 of the cylindrical part 52 and closes the lower opening of the cylindrical part 52. The peripheral edge part 44 of the holding plate 41 is sandwiched between the cylinder parts 52 in the extending direction of the cylinder part 52 (arrow A1 direction in FIG. 4), and the end surface 41c and the upper and lower surfaces 41a of the peripheral edge part 44 of the holding plate 41 , 41b (that is, both principal surfaces facing each other in the A1 direction) are fixed to the cylindrical portion 52. The holding plate 41 of the vibrating body 40 is fixed to the cylindrical portion 52 by caulking, for example. The holding plate 41 and the cylindrical portion 52 of the vibrating body 40 can be fixed with an adhesive. The holding plate 41 and the cylindrical portion 52 of the vibrating body 40 can be integrated by insert molding.

The cylindrical portion 52 is made of resin, and in this embodiment is made of polybutylene terephthalate (PBT). The tensile modulus of polybutylene terephthalate constituting the cylindrical portion 52 is 10,300 MPa. That is, the tensile modulus of the cylindrical portion 52 (10,300 MPa) is higher than the tensile modulus of the retaining plate 41 (4,300 MPa). The cylindrical portion 52 is not limited to polybutylene terephthalate, and may be made of, for example, LCP (tensile modulus of 14,014 MPa).

The frame portion 54 is provided at the upper end of the cylindrical portion 52 and has an annular shape. The lid portion 56 is provided at the inner opening of the frame portion 54 and cooperates with the frame portion 54 to close the upper opening of the cylindrical portion 52. The lid part 56 is connected to the end of the signal line 25 and is provided so as to be able to hold the end of the signal line 25. The frame portion 54 can be made of, for example, nitrile rubber (NBR), and the lid portion 56 can be made of, for example, urethane.

In the ultrasonic transducer 30 described above, when a signal is input from the control circuit 20 via the signal line 25, the piezoelectric diaphragm 42 vibrates, and an ultrasonic signal is output from the lower surface 41b side of the holding plate 41. . Furthermore, when the ultrasonic transducer 30 receives an external ultrasonic signal on the lower surface 41 b of the holding plate 41 , it is converted into a voltage signal on the piezoelectric diaphragm 42 and sent to the control circuit 20 via the signal line 25 .

FIG. 5 is a diagram showing signal waveforms in the ultrasonic detection system 1. FIG. 5A shows the waveform of the signal output from the control circuit 20, that is, the waveform of the signal input to the ultrasonic transducer 30 (input signal). FIG. 5B shows a waveform of a signal (transmission signal) transmitted from the ultrasonic transducer 30 to the outside. As shown in FIG. 5(b), the waveform of the transmission signal contains a slight reverberation component compared to the waveform of the input signal due to the LC circuit of the control circuit 20. FIG. 5(c) shows a waveform of a signal (received signal) obtained by amplifying the signal received by the ultrasonic transducer 30 from the transmitted signal reflected by the object 10 in the control circuit 20. As shown in FIG. 5(c), the waveform of the received signal includes a reverberation component. It is thought that a part of the reverberation component included in the waveform of the received signal is caused by the resonance of the piezoelectric diaphragm 42. In particular, when the distance between the ultrasonic transducer 30 and the target object 10 is short, reverberation components in the received signal are likely to interfere, leading to a decrease in detection accuracy.

The ultrasonic transducer 30 described above is designed so that the tensile modulus of the cylindrical portion 52 is higher than the tensile modulus of the retaining plate 41. Therefore, from the viewpoint of the constituent materials, the vibrating body 40 is designed to vibrate relatively easily, while the cylindrical portion 52 is designed to be relatively difficult to vibrate. Therefore, the propagation of vibrations from the holding plate 41 to the cylindrical portion 52 is effectively suppressed. As a result, the vibration of the cylinder portion 52 caused by the oscillation of the vibrating body 40 is suppressed, thereby suppressing reverberation when outputting ultrasonic waves. Therefore, even if the distance between the ultrasonic transducer 30 and the target object 10 is short, the reverberation components in the received signal are unlikely to interfere, and detection accuracy can be improved.

Furthermore, in the ultrasonic transducer 30, since the peripheral edge portion 44 of the retaining plate 41 is sandwiched between the cylindrical portions 52 in the extending direction of the cylindrical portion 52, the vibrations propagated from the retaining plate 41 to the cylindrical portion 52 are The vibration mainly becomes longitudinal vibration (vibration in the direction of arrow A1 in FIG. 4), and the transverse vibration (vibration in the direction of arrow A2 in FIG. 4), which causes reverberation, is hardly propagated. Therefore, the ultrasonic transducer 30 can achieve further suppression of reverberation.

Further, in the ultrasonic transducer 30, the end surface 41c and the upper and lower surfaces 41a and 41b of the peripheral portion 44 of the holding plate 41 are fixed to the cylindrical portion 52 by caulking. When fixed by caulking, the retaining plate 41 and the cylindrical part 52 are in direct contact with each other without interposing an adhesive or the like between the retaining plate 41 and the cylindrical part 52. By caulking and fixing the holding plate 41 and the cylindrical portion 52, it is possible to suppress variations in characteristics among a plurality of products. In addition, by fixing by caulking, the thickness of the cylindrical part 52 at the upper and lower parts of the clamping part 53 (the length in the direction of arrow A2 in FIG. 4) can be kept approximately the same, so the characteristics between multiple products can be maintained Variations can be suppressed. Note that if the thickness of the cylindrical portion 52 at the upper and lower portions of the holding portion 53 is different, vibrations may be inhibited around the holding portion 53.

Although the preferred embodiments of the present invention have been described above, the present invention is not necessarily limited to the above-described embodiments, and various changes can be made without departing from the gist thereof.

For example, in the form shown in FIG. 6, the cylindrical portion 52 can hold the vibrating body 40. In the form shown in FIG. 6(a), the end surface 41c of the holding plate 41 is in contact with the inner surface of the cylindrical portion 52 at the clamping portion 53 of the cylindrical portion 52. As shown in FIG. In this case, the holding plate 41 is held within the cylindrical portion 52, for example, via an adhesive. In the form shown in FIG. 6(b), the retaining plate 41 closes the lower opening of the cylindrical portion 52 so that the lower end surface of the cylindrical portion 52 and the upper surface 41a of the retaining plate 41 are in contact with each other. In this case, the lower end surface of the cylindrical portion 52 and the upper surface 41a of the holding plate 41 are fixed, for example, via an adhesive.

Further, the material constituting the cylinder portion 52 and the retaining plate 41 is not limited to the above-mentioned materials, and can be appropriately selected from known resin materials.

DESCRIPTION OF SYMBOLS 1... Ultrasonic detection system, 10... Target object, 20... Control circuit, 30... Ultrasonic transducer, 40... Vibrating body, 41... Holding plate, 42... Piezoelectric diaphragm, 43... Recessed part, 44... Peripheral part, 50... Housing, 52...cylindrical part, 53... clamping part.

Claims (7)

case and
A vibrating body including a holding plate having a disc-shaped outer shape and a peripheral portion held by the case, and a piezoelectric diaphragm stacked on the holding plate,
The ultrasonic transducer, wherein the case has a tensile modulus higher than that of the holding plate of the vibrating body. The ultrasonic transducer according to claim 1, wherein a peripheral edge of the holding plate is sandwiched between the cases in an extending direction of the cases. The ultrasonic transducer according to claim 1 or 2, wherein an end face of a peripheral portion of the holding plate and both main faces facing each other in the extending direction of the case are fixed to the case. The ultrasonic transducer according to claim 1, wherein the holding plate has a recess for accommodating the piezoelectric diaphragm, and the piezoelectric diaphragm is accommodated in the recess. The ultrasonic transducer according to claim 1, wherein the holding plate is made of resin. The ultrasonic transducer according to claim 1, wherein the case is made of resin. The ultrasonic transducer according to claim 1, wherein both the holding plate and the case are made of resin.

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