JP3310764B2 - Ultrasonic transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic transducer for transmitting and receiving ultrasonic waves, and more particularly, to a structure of an ultrasonic transducer which is small, lightweight, excellent in efficiency and sensitivity, and which supports multiple frequencies. About.

[0002]

2. Description of the Related Art Conventionally, the frequency is several tens kHz to several hundred kHz.
A general ultrasonic transducer used in water uses a piezoelectric vibrator. To reduce the size of a part used in water, the piezoelectric vibrator has a small ultrasonic radiation area (for example, one side). (A piezoelectric vibrator having an ultrasonic radiation surface of a square whose wavelength is 1/2 of the wavelength in water at the frequency to be used) has a small capacitance and a high electric impedance. For this reason, in order to obtain a large acoustic output, the transmitter needs to drive 200 to 5
A voltage of about 00 V was required, and the voltage was raised using a transformer or the like.

Further, as a receiver, it is necessary that the amplifier has a high input impedance corresponding to the electrical impedance of the piezoelectric vibrator, and the receiving voltage sensitivity by a wiring cable is required. Is increased, and it is necessary to compensate for this. That is, the peripheral circuit of the piezoelectric vibrator constituting the ultrasonic transducer has become large.

Further, an ultrasonic transducer generally uses a basic mode of a piezoelectric vibrator in order to obtain a large acoustic output, and an ultrasonic transducer which needs to use a plurality of frequencies is used. In the wave device, a plurality of piezoelectric vibrators corresponding to each use frequency are provided. Therefore, the entire ultrasonic transducer becomes large, and various restrictions are imposed on the use conditions of the ultrasonic transducer.

[0005] Techniques for solving the above problems include:
"High-sensitivity high-frequency ultrasonic transmitter using piezoelectric actuator" (Proceedings of the Oceanographic Society of Japan, P49, 199)
The ultrasonic transducer described in 1.5.17) is known as a low-impedance piezoelectric vibrator, which is composed of a piezoelectric actuator in which piezoelectric vibrators are thinly laminated in multiple layers. By utilizing the piezoelectric vibrator, the capacitance of the piezoelectric vibrator is increased to reduce the impedance, and the piezoelectric vibrator can be driven at a low voltage, thereby eliminating the need for a transformer or the like.

[0006] Also, "Characteristic analysis of a composite structure piezoelectric transducer for multi-frequency ultrasonic waves" (IEICE Technical Report, US 91-47, P1, 199).
An ultrasonic transducer described in 1.10.18) is known to transmit and receive a plurality of frequencies with the same piezoelectric vibrator, which partially drives a laminated piezoelectric vibrator. In addition, the same piezoelectric vibrator realizes transmission and reception of a plurality of frequencies, and aims at miniaturization by reducing the number of piezoelectric vibrators provided in the ultrasonic transducer.

[0007] The structure of the piezoelectric vibrator shown in the former article is based on the fact that a very thin vibrator (130 µm) is multi-layered (64 layers).
Therefore, the impedance of the piezoelectric vibrator is 0.5Ω, which is too small for an actual ultrasonic transducer (preferably, about 50Ω). The electric signal is attenuated. That is, the electro-acoustic conversion efficiency deteriorates, and the transmission voltage sensitivity decreases. On the receiving side, since each laminated piezoelectric vibrator is thin, the receiving voltage sensitivity is low, and the minimum receiving sound pressure level obtained by subtracting the receiving sensitivity from the amplification preamplifier noise is increased. That is,
Receiving small sound becomes difficult, and it is not optimal as a piezoelectric vibrator of an actual ultrasonic transducer.

The structure of the piezoelectric vibrator shown in the latter article realizes multi-frequency transmission / reception with the same piezoelectric vibrator element, but partially converts the piezoelectric vibrator in a higher-order resonance mode. It is used for. That is, since only a part of the multilayered piezoelectric vibrator is used to reduce the impedance, the effect of the multilayering does not appear, the electrical impedance increases, and the transmission voltage sensitivity is lower than that of the former paper. It drops as well. Further, in actual ultrasonic transducers, it is common to attach a matching layer or the like to the piezoelectric vibrator in order to perform acoustic matching between the medium transmitting sound waves and the piezoelectric vibrator. Is complicated, so the electricity of the piezoelectric vibrator
It becomes difficult to increase the efficiency of mechanical conversion. That is, it is difficult to increase the sensitivity of the piezoelectric vibrator, and it is not optimal as a piezoelectric vibrator of an actual ultrasonic transducer.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems, and the conversion efficiency between electric signals and ultrasonic waves is high, the sensitivity is high, and the size is small. Another object of the present invention is to provide an ultrasonic transducer that can handle ultrasonic waves of a plurality of frequencies.

More specifically, on the transmission side, the transmission voltage sensitivity can be set to a desired value, and the impedance is matched to the impedance of the amplifier without using a transformer or the like. A piezoelectric vibrator is used and can be driven at a low voltage. On the receiving side, a low-input impedance amplifier can be used, and an ultrasonic transmitting and receiving device having a piezoelectric vibrator having a thin-film multilayer structure having an electrical impedance capable of realizing low noise. Provide a container. Furthermore, in order to handle ultrasonic waves of a plurality of frequencies in a small configuration, a piezoelectric vibrator having a thin-film multilayer structure has a high-order resonance mode.
Another object of the present invention is to provide a high-sensitivity ultrasonic transducer which has high conversion efficiency between an electric signal and an ultrasonic wave even when vibrated by the ultrasonic wave.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric vibrator for converting an electric signal into an ultrasonic wave by electro-mechanical conversion used in an ultrasonic transducer. When using a thin-film type piezoelectric vibrator and using a laminated piezoelectric vibrator to reduce the thermal noise of the piezoelectric vibrator, the thermal noise of the amplifier used in the ultrasonic transducer, This can be achieved by defining the thickness of the piezoelectric vibrator stacked in multiple layers and the number of layers of the thin film type piezoelectric vibrator to be stacked, using the minimum received sound pressure level required for the sound wave transducer as a parameter.

This is because when the thermal noise of the piezoelectric vibrator is larger than the thermal noise of the amplifier, the impedance is lowered by laminating the thin film type piezoelectric vibrators in multiple layers, and the noise of the amplifier is reduced by the piezoelectric vibrator. When the thermal noise is larger than the thermal noise of the ultrasonic transducer, the number of laminated thin-film type piezoelectric vibrators is reduced and the thickness is increased, while maintaining the minimum receiving sound pressure level required for the ultrasonic transducer. The thickness of the piezoelectric vibrator and the number of layers to be laminated are determined so as to lower the impedance by laminating the thin film type piezoelectric vibrators in multiple layers.

More specifically, this is achieved by using a multilayer piezoelectric vibrator in which the thickness and the number of layers of the piezoelectric vibrator are determined by the following equations (1) to (3) having a predetermined relationship.

[0014] _{A N = e E - {20log} (g h × t) -120} ··· (1) where, A _N: amplifier noise sound pressure converted value (dB re 1μP
a) e _E: amplifier noise (dB re 1μPa) g _h: piezoelectric constant (V × m / N × 10 ~ 3) t: the piezoelectric vibrator thickness _{(m) S N = -15 ×} 20logF + 10log {1 + Q M / K 2 F _C / F _S Ω ² ｝ (2) where F _C = t × 10 ³ / (2πRnεεS) S _N : Sensor pressure value of thermal noise of piezoelectric vibrator (DB re 1μP
a) F: application frequency (kHz) Q _M: Mechanical Q K: electromechanical coefficient R: amplifier input impedance (Ω) n: number of laminated layers epsilon: dielectric constant S: piezoelectric vibrator area (m
²⁾ F _S: a resonance frequency _{(kHz) Ω: -F S /} F A N <S N <N L ··· (3) where, N _L: Minimum reception sound pressure that is required by the system (dB
re 1 μPa) Here, as a piezoelectric vibrator, several tens kHz to several hundred kHz
Of ultrasonic waves (for example, if the object transmitting and receiving
100 m or less and 1 m or less, 100
About 500 kHz, and if the distance is 1000 m or more and the size is 10 m or more, 100 kHz or less). Single crystal such as quartz, lithium niobate and lithium tantalate, zircon Piezoelectric ceramics represented by lead titanate-based substances such as lead titanate and lead titanate, polyvinylidene fluoride (PVD
F) and the like (polymers (organic piezoelectric materials)).

In order to realize a high-efficiency, multi-frequency, high-sensitivity ultrasonic transducer, a signal transmission cable is drawn from each thin-film type piezoelectric vibrator of a piezoelectric vibrator laminated in multiple layers.
The piezoelectric vibrator is vibrated in a second or higher order vibration mode (for example, a second or third order higher vibration mode), and the phase of the vibration displacement is reversed in the higher order vibration mode. An ultrasonic transducer for performing electro-mechanical conversion by inverting the polarity of an electric signal transmitted and received by a signal transmission cable is configured for each of the thin film type piezoelectric vibrators.

Further, in order to obtain high efficiency and sensitivity, a predetermined delay is added to the transmission / reception signals of each thin film type piezoelectric vibrator for each thin film type piezoelectric vibrator, and electric signals are adjusted in accordance with the phase characteristics of vibration displacement. An ultrasonic transducer that performs electro-mechanical conversion while adjusting the amount of signal delay can also be used.

An ultrasonic transducer in which a matching layer for performing acoustic matching, for example, a substance having a different acoustic impedance such as an epoxy resin or glass is mounted on a piezoelectric vibrator laminated in multiple layers. In the above, when vibrating in the second or higher order vibration mode, complicated vibration behavior is exhibited. Therefore, use an equivalent circuit of a piezoelectric vibrator equipped with a different substance, represented by Mason's equivalent circuit, etc. Then, in each vibration mode, the positions of nodes and antinodes of the vibration generated in the piezoelectric vibrator on which different materials are mounted are calculated in advance, and the signal transmission cable is applied to each of the laminated thin film piezoelectric vibrators. -An ultrasonic transducer which determines the polarity and the amount of delay of an electric signal to be transmitted / received by the cable and performs the electro-mechanical conversion while adjusting the amount of delay of the electric signal in accordance with the phase characteristics of the vibration displacement.

Further, in a piezoelectric vibrator laminated in multiple layers on which a matching layer or the like is mounted, the matching layer is made of the same material as the piezoelectric vibrator, and is converted into an electric signal including vibration energy generated in the matching layer. Higher efficiency by reverse conversion
A configuration for obtaining high sensitivity may be employed.

Here, the matching layer is a piezoelectric vibrator whose acoustic impedance is matched with that of a medium transmitting ultrasonic waves, and a lead titanate-based material such as lead zirconate titanate or lead titanate described above. The piezoelectric ceramics represented by (1) and (2) include pores for adjusting the acoustic impedance, and polymers represented by polyvinylidene fluoride (PVDF).

[0020]

Generally, the minimum receiving sound pressure level of an ultrasonic transducer using a piezoelectric vibrator is underwater electroacoustic transducers, bus university press and acoustics (1).
991) [Under WaterElectro-acoustic Transdusers,
Bath University Press and Acoustics, (1991)]
As shown by, the noise level is determined by the noise level obtained by subtracting the receiving voltage sensitivity from the noise of the amplifier and the thermal noise of the piezoelectric vibrator.

Equation (1) shows the sound pressure conversion level A _N of the amplifier thermal noise, and equation (2) shows the sound pressure conversion level S _N of the thermal noise of the piezoelectric vibrator. Is determined so that the values of Equations (1) and (2) are as close as possible and satisfy the inequality of Equation (3), that is, the optimum value at which the receiver can receive the smallest sound. If the thickness t of the multilayered piezoelectric vibrator and the number n of the thin film type piezoelectric vibrators are selected by using the equations (1) and (2) so that A wave filter is obtained.

However, in order to reduce the size of the ultrasonic transducer, it is desirable that the piezoelectric vibrator has a low impedance when the piezoelectric vibrator is used for both the transducer and the transducer. The thickness of the element is reduced, the number n of layers to be stacked is increased, and the receiving sensitivity is lowered to lower the impedance within a range satisfying the required minimum receiving sound pressure level _NL .

As described above, by selecting the thickness t of the piezoelectric vibrator and the number n of laminated thin-film piezoelectric vibrators, the electrical impedance of the piezoelectric vibrator, which is generally high, can be reduced. Can be optimized. That is, the impedance can be reduced so as to match the input impedance of the amplifier, and a small-sized and low-noise amplifier can be used.

Further, since the electric impedance of the piezoelectric vibrator is small, the size of the peripheral circuit of the ultrasonic transducer can be reduced, for example, the piezoelectric vibrator can be driven at a low voltage. Therefore, by optimizing the electrical impedance of the piezoelectric vibrator, it is possible to apply small-sized, light-weight, small-scale, general-purpose electronic equipment, and to realize reduction in size and weight.

Further, in order to realize an ultrasonic transducer capable of handling a plurality of frequencies in a compact and economical manner, one piezoelectric vibrator laminated in multiple layers is vibrated in a plurality of vibration modes.
It is necessary to share the piezoelectric vibrator. Hereinafter, a more specific description will be given with reference to FIGS.

FIG. 5 is a model diagram showing the vibration state of the piezoelectric vibrator laminated in multiple layers. In each vibration mode,
FIG. 4 shows a state in which a piezoelectric vibrator laminated in multiple layers is vibrating. The broken line in the figure indicates the velocity distribution of the piezoelectric vibrator, and the broken line in the upper half of the center line indicates the speed component in the left direction, and the broken line in the lower half indicates the speed component in the right direction. The point where the center line and the broken line intersect is the node where the vibration is minimum, and the point where the solid line and the broken line on the outer periphery are in contact is the antinode where the vibration is the maximum.

FIG. 5A shows the vibration in the basic vibration mode, in which six laminated piezoelectric vibrators a,
In b, c, d, e, and f, the piezoelectric vibrators a, b, and c vibrate in the left direction, and the piezoelectric vibrators d, e, and f vibrate in the right direction, and all vibrate around the nodes. In other words, the piezoelectric vibrators vibrate in a state where there is nothing to press the vibrations between the piezoelectric vibrators.

FIG. 5B shows the vibration in the secondary vibration mode. The six piezoelectric vibrators a, b, and
As for c, d, e, and f, the piezoelectric vibrators a and f vibrate in the left direction and the piezoelectric vibrators c and d move in the right direction centering on the nodes of the piezoelectric vibrators b and e. In other words, the right piezoelectric vibrators d, e, and d extend in the direction in which the left piezoelectric vibrators a, b, and c extend.
f vibrates in the shrinking direction (the shrinking portion is indicated by oblique lines).

FIG. 5C shows the vibration in the tertiary vibration mode in which the middle piezoelectric vibrators c and d are contracted, and the piezoelectric vibrators a, b and e on both sides are shrunk. f vibrates in the extending direction, and the piezoelectric vibrators vibrate so as to cancel the vibration, similarly to the secondary vibration mode. As described above, in a piezoelectric vibrator laminated in multiple layers, there are directions in which each piezoelectric vibrator extends and contracts. Therefore, in a cable for transmitting and receiving electric signals wired in the polarization direction of each piezoelectric vibrator, an electric signal is transmitted. The phase of the signal will be inverted. That is, if the polarity of each cable and the amount of signal delay are not adjusted, the electric signals from the piezoelectric vibrators are output so as to cancel each other out, or large vibration does not occur even if the electric signals are input. .

FIG. 6 is a diagram showing the relationship between the wiring of the signal cables provided on the piezoelectric vibrators stacked in multiple layers and the respective vibration modes. It shows the state of the electro-mechanical conversion.

That is, FIG. 6A shows the case where the polarization directions of the respective piezoelectric vibrators are set to be the same and the wirings of the respective piezoelectric vibrators are connected in parallel. ), The received electric signal is canceled by the secondary resonance, and the sensitivity is improved at an odd multiple of the fundamental wave. Conversely, when the wirings of the right half and the left half of the piezoelectric vibrator are reversed, the received electric signal is canceled at the basic resonance, and the sensitivity becomes the best at the secondary resonance. Therefore, even in a higher-order resonance, the reception voltage sensitivity is improved by delaying and adding the electric signals from the respective piezoelectric vibrators so that they are in phase with each other.

In the case of wave transmission, the polarity of the cable wired with respect to the polarization direction of the piezoelectric vibrator is changed as shown in FIG.
Assuming that each piezoelectric vibrator is the same, the piezoelectric vibrators vibrate in the same phase at the fundamental frequency as shown by the characteristic curve (indicated by ●) in FIG. Is supplied with an electric signal so as to vibrate in the opposite direction to the vibration mode, the transmission voltage sensitivity decreases. Therefore, the transmission voltage sensitivity is improved if the electric signal supplied to each piezoelectric vibrator is delayed or the polarity is changed and supplied to the piezoelectric vibrator in the same way as the case of receiving wave. I do.

That is, the characteristic curve of FIG.
As shown in FIG. 6A, as shown in FIG. 6A, when the same is applied to each piezoelectric vibrator, high sensitivity is exhibited at the fundamental resonance and the third resonance, but
At the secondary resonance frequency, the transmission voltage sensitivity decreases. Therefore,
When transmitting the secondary resonance frequency, a method of using only a part of the piezoelectric vibrator with the wiring shown in FIG. 6B has been conventionally used. Also in this method, the sensitivity at the basic resonance is reduced, but the sensitivity at the secondary resonance is improved, as shown by the characteristic curve (indicated by a circle) in FIG.

Further, according to the structure of the present invention, FIG.
According to the method of changing the polarity of the signal by using all of the piezoelectric vibrators in the wiring shown in FIG. 6, as shown by the characteristic curve (indicated by the circle) in FIG. An all-piezoelectric vibrator having the best sensitivity at resonance can be utilized, and a highly efficient and highly sensitive ultrasonic transducer can be realized. Of course, instead of changing the polarity of the signal, a method of giving a delay to the signal may be used. When a matching layer or the like is mounted on the above-described piezoelectric vibrator, the velocity distribution between the piezoelectric vibrator and the matching layer becomes complicated.

FIG. 7 shows a piezoelectric vibrator provided with a matching layer.
It is a model diagram showing a vibration state, wherein the multilayer piezoelectric vibrator,
In each of the vibration modes, a state of vibration is shown. As shown in the figure, in each vibration mode, since the velocity distribution between the piezoelectric vibrator and the matching layer becomes complicated and the position of the node moves, the polarity of each piezoelectric vibrator is simply changed as described above. It is not possible to obtain a high-efficiency, high-sensitivity ultrasonic transducer only by doing so. Therefore, the operation of the piezoelectric vibrator equipped with different materials is calculated from the equivalent circuit using the analysis method typified by Mason's equivalent circuit analysis method for the expansion part and the contraction part. A high-efficiency, high-sensitivity ultrasonic transducer using all piezoelectric transducers is realized.

Further, when the vibrator is made of piezoelectric ceramic, matching can be achieved by using a ceramic containing air bubbles as the matching layer, and the vibration energy of the matching layer can be utilized. An ultrasonic transducer with high efficiency and high sensitivity can be obtained.

As described above, corresponding to each vibration mode,
By adjusting the signal polarity of each piezoelectric vibrator and giving the optimal amount of delay for each frequency, high efficiency, multi-frequency,
A highly sensitive ultrasonic transducer can be realized.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, a piezoelectric vibrator according to the present invention will be described. The piezoelectric vibrator includes a plurality of piezoelectric vibrators and signal lines for transmitting and receiving electric signals attached to the respective piezoelectric vibrators. A detailed description will be given of an embodiment of an ultrasonic transducer in which high-efficiency electro-mechanical conversion is performed by adjusting a delay amount and impedance is optimized with equipment such as an amplifier.

<Embodiment 1> In this embodiment, by adjusting the polarity of the electric signal of the signal line for transmitting and receiving electric signals attached to each piezoelectric vibrator of the multilayer laminated piezoelectric vibrator, a highly efficient electric -The configuration of an ultrasonic transducer that performs mechanical conversion and optimizes impedance with equipment such as an amplifier is shown.

(1) Configuration of Ultrasonic Wave Transmitter / Receiver FIG. 1 is a sectional view showing a main part of an ultrasonic wave transmitter / receiver according to the present invention. The ultrasonic transducer 1 has a vibration energy
Vibrators 1a to 1f (to be described in detail later), which perform conversion between energy and electric energy, a backing 3 for reflecting sound, and positioning of the piezoelectric vibrators 1a to 1f. Frame 2 to be transmitted, an acoustic window 4 for transmitting an acoustic signal, a signal line 5 connected to each of the piezoelectric vibrators 1a to 1f and transmitting an electric signal to be transmitted and received, and a frequency used as the ultrasonic transducer 1 Signal line 5 of each of the piezoelectric vibrators 1a to 1f
And a matching circuit unit 6 for converting the wiring to adjust the polarity and amplifying the transmitted and received electric signals, and a case for transmitting and receiving electric signals such as a power supply, a control signal, FM, and PCW to and from an external device (not shown). And a mounting bracket 8 for connecting and holding the matching circuit 6, the frame 2, and the cable 7. Note that 6
It is also possible to arrange a plurality of piezoelectric vibrators 1a to 1f stacked in layers in parallel to control the directivity of ultrasonic transmission and reception. Further, as shown in a second embodiment described later, in the matching circuit section 6, instead of converting the wiring of the signal line 5, a predetermined delay can be given to the signal line 5.

(2) Configuration of Piezoelectric Vibrator The configuration of the laminated piezoelectric vibrator used in the ultrasonic transducer 1 of the present embodiment will be described below. FIG. 7 shows the above-mentioned equations (1) to
A piezoelectric vibrator showing an example of the structure of the laminated piezoelectric vibrator and its characteristics (relationship between the number of layers of the piezoelectric vibrator, the operating frequency, and the lowest received sound pressure level) obtained by equation (3). FIG. In this embodiment, the material of each piezoelectric vibrator is PZ
The area that radiates sound is 10mm x 1 using T ceramic.
0 mm square, the thickness of the laminated piezoelectric vibrator is 22 mm
In this case, a laminated piezoelectric vibrator formed of six piezoelectric vibrators was used.

More specifically, FIG. 7 shows the calculated value of the minimum received sound pressure level when the number of stacked piezoelectric vibrators is changed. The thin solid line in the graph indicates the preamplifier noise. the value of a _N of the formula (1) is, a broken line indicates a value of S _N of the formula (2) is a piezoelectric vibrator thermal noise. From the calculation results, if the ultrasonic transducer 1 of the present embodiment is used only as a receiver, the optimum number that satisfies the relationship of Expression (3) is obtained when n = 3 (three sheets). . But,
Generally, the minimum received sound pressure level N _L is systematically determined depending on the purpose of use and environment of the ultrasonic transducer 1. For example, as in the present embodiment, the ultrasonic transducer 1
However, if it is used at a frequency of 100 kHz or less, if the required minimum received sound pressure level is 30 dB or less, it becomes smaller than underwater noise, and the intended use of the ultrasonic transducer 1 can be achieved.

That is, when n = 3 (three sheets),
Since the noise margin is as large as about 6 dB, the electrical impedance can be reduced by further laminating the layers.
Therefore, from the calculation result, the optimum number is n = 6 (the number of stacked layers is 6).
Sheets). As described above, if the environment (size, frequency band, sound pressure level) in which the ultrasonic transducer is used is determined, the relationship as described above has the optimum impedance as a communication system, and Since a laminated piezoelectric vibrator having a desired electro-mechanical conversion efficiency can be easily selected, a compact ultrasonic transducer having excellent characteristics can be realized.

(3) Transmitting and Receiving Operation In the following, the ultrasonic transducer 1 of this embodiment shown in FIG.
The transmitting and receiving operations will be described in detail with reference to the drawings. FIG. 2 is a block diagram showing a detailed configuration of the ultrasonic transducer 1 according to the present embodiment. Ultrasonic transducer 1
Are connected to a piezoelectric vibrator 1A in which piezoelectric vibrators 1a to 1f, electrodes 51a to 51g are alternately stacked and laminated in six layers, and electrodes 51a to 51g that are in contact with each of the piezoelectric vibrators 1a to 1f. The wires of the signal lines 5a to 5g of each of the piezoelectric vibrators 1a to 1f are converted according to the transducers 1a to 1f, the signal lines 5a to 5g for transmitting the transmission and reception electric signals, and the frequency used as the ultrasonic transducer 1. Switching circuit 11 comprising contacts 11a to 11g and contacts 111 to 118
The transmission amplifier 12 and the reception amplifier 13 for amplifying the transmission and reception electric signals are transmitted at least to the matching circuit unit 6 and the transmission and reception electric signals such as the power supply, the control signal, the FM, and the PCW to and from an external device (not shown). Cable 7. Note that, in FIG.
g, and reflects the sound wave. The sound wave is transmitted and received from the electrode 51a through the acoustic window 4 shown in FIG.

In the case of wave transmission, first, transmission electric signals such as FM and PCW are transmitted to the matching circuit unit 6 through the cable 7. The transmitted electric signal is amplified by a power amplifier 12, passes through a switching circuit 11 that changes with frequency, and is transmitted to each of the piezoelectric vibrators 1a to 1f such as a piezoelectric ceramic. Each of the piezoelectric vibrators 1a to 1f performs an electro-mechanical conversion, transmits the vibration after the mechanical conversion to the electrode 51a, and transmits an ultrasonic wave from the acoustic window. In addition, the backing 3 reflects the vibration transmitted to the back to the front, and enables high-efficiency wave transmission. More specifically, the switching circuit 11
In each vibration mode, the electrical polarity of the piezoelectric vibrators 1a to 1f is connected so as to be inverted between the extended portion and the contracted portion. For example, in the case of the basic vibration mode, the piezoelectric vibrators 1a to 1f are extended portions as shown in FIG. 5A, and therefore have the same polarity as shown in FIG. 6A. Preferably, each contact is a contact 11a and a contact 1
12, contact 11b and contact 113, contact 11c and contact 11
4. Contact 11d and contact 115, contact 11e and contact 11
6, contact 11f and contact 117, contact 11g and contact 118
And connect. In the case of the secondary vibration mode, FIG.
As shown in FIG. 6B, each of the piezoelectric vibrators 1a to 1f has an extended portion and a contracted portion. Therefore, as shown in FIG. Are contact 11a and contact 112, contact 11b and contact 1
13, the contact 11c and the contact 114 are connected, and further, the contact 11d and the contact 114, the contact 11e and the contact 115, the contact 11f and the contact 116, and the contact 11g and the contact 117 are connected. In this embodiment, the amplifier 12 and the amplifier 1
3 is provided between the switching circuit 11 and the cable 7, but the piezoelectric vibrator 1 laminated with the switching circuit 11
A may be arranged for each of the piezoelectric vibrators 1a to 1f. Further, a switch switching mechanism may be provided in the matching circuit unit 6 and a vibration mode notification signal may be added to a control signal transmitted from the cable 7, thereby switching from an external device.

In the case of receiving waves, the operation is the reverse of the case of transmitting waves, and the sound that has passed through the acoustic window 4 passes through the electrode 51a and is transmitted to each of the piezoelectric vibrators 1a to 1f. Each of the piezoelectric vibrators 1a to 1
f converts the acoustic signal into a mechanical-electrical signal, and is transmitted to the switching circuit 11 as an electric signal. The electric polarity of the piezoelectric vibrators 1a to 1f in each vibration mode, that is, the connection of the respective contacts is the same as in the case of the wave transmission. The received electric signal is amplified by the amplifier 13 and transmitted by the cable 7 as a received signal. Here, backing 3 is
It performs the same function as transmitting waves.

As described above, according to the ultrasonic transducer of the present invention, one multilayer piezoelectric vibrator can be provided only by switching the polarity of each electric signal input / output to the piezoelectric vibrators stacked in multiple layers. For example, an ultrasonic transducer capable of transmitting and receiving ultrasonic waves of a plurality of frequencies from a fundamental vibration mode to a higher-order vibration mode can be realized.
Since the mechanical conversion operation can be used, an efficient ultrasonic transducer can be realized. That is, according to the present invention, it is possible to realize a high-efficiency ultrasonic transducer that is small and can handle a plurality of frequencies. Furthermore, from a simple calculation formula, it is possible to determine the configuration of the laminated piezoelectric vibrator having an impedance that matches the input / output impedance of a general-purpose communication device such as an amplifier, which is suitable for transmitting and receiving an electric signal. An ultrasonic transducer such as a piezoelectric vibrator can be easily designed, a general-purpose communication device can be used for a switch or an amplifier for processing an electric signal, and a compact and economical ultrasonic transducer can be realized. .

<Embodiment 2> In this embodiment, a highly efficient electro-mechanical device is provided by adjusting the amount of delay of a signal line for transmitting and receiving electric signals attached to each piezoelectric vibrator of a multilayer laminated piezoelectric vibrator. Another configuration example of an ultrasonic transducer that performs conversion and optimizes impedance with equipment such as an amplifier is shown.

FIG. 3 is a block diagram showing a detailed configuration of the ultrasonic transducer 1. In the present embodiment, the ultrasonic transducer 1 according to the first embodiment has a switching circuit 11 in which the polarity of each electric signal is adjusted. By providing a plurality of different delay elements and passing each electric signal through these delay elements, the amount of delay of each electric signal is adjusted, and highly efficient electro-mechanical conversion is performed. Specifically, in the present embodiment, 0 ° (no delay), 90 ° (１ ／)
Phase delay), 180 ° (reverse phase delay), 270 ° (3/4 phase delay), four types of delay elements 14a, 14b, 14c, 1
4d is provided in the matching circuit section 6. Of course, the 0 ° delay element 14a is a through element, and may have an unnecessary configuration. Each of the delay elements 14a to 14d is a contact 1 which is a terminal on the matching circuit unit 6 side of each of the signal lines 5a to 5g.
Terminals 14a1 to 14a7 for connecting to 1a to 11g
, 14b1 to 14b7, 14c1 to 14c7, and 1
4d1 to 14d7 are provided, and according to each vibration mode,
By connecting the contacts 11a to 11g and these terminals, transmission and reception of electric signals with each piezoelectric vibrator are performed.

Of course, the number of these terminals is increased or decreased according to the number of layers of the piezoelectric vibrator or the situation where the ultrasonic transducer is used. The configuration of the piezoelectric vibrator, the electrodes, the amplifier, and the like of the present embodiment was the same as that of the ultrasonic transducer shown in the first embodiment.

In the present embodiment, in the case of the basic vibration mode, as shown in FIG.
Since 1f is an extended portion, it is desirable that it has the same polarity as shown in FIG. 6A. That is, since it is not necessary to adjust the amount of delay for each signal, each contact is Contact 11a and terminal 14a1, contact 11b and terminal 1
4a2, the contact 11c and the terminal 14a3, the contact 11d and the terminal 14a4, the contact 11e and the terminal 14a5, the contact 11f and the terminal 14a6, the contact 11g and the terminal 14a7, and all signals are connected to the delay element 14a without delay. I do.

In the case of the secondary vibration mode, FIG.
As shown in FIG. 6B, since each of the piezoelectric vibrators 1a to 1f has an extended portion and a contracted portion, a signal of a portion which is inverted between the extended portion and the contracted portion as shown in FIG. Each of the contacts connects the contacts 11a, 11b, 11c, and 11d to the terminals 14a1 to 14a7 of the delay element 14a so as to be in phase with the delay, and further, contacts 11e, 11f, and 11g. And 180
° Terminals 14c1-1 of delay element 14c for delaying a signal
4c7.

In this embodiment, the amplifiers 12 and 13 are provided between the delay elements 14a to 14d and the cable 7, but the delay elements 14a to 14d are provided in the same manner as in the first embodiment.
A piezoelectric vibrator 1A may be disposed between the piezoelectric vibrator 14d and the piezoelectric vibrator 1A. Further, the matching circuit unit 6 is provided with a switching mechanism for connection between the contact of the signal line and the terminal of the delay element, and a vibration mode notification signal is added to the control signal transmitted from the cable 7 to thereby control the external device. It is also possible to adopt a configuration in which switching is performed from the device of (1). Since the impedance of the laminated piezoelectric vibrator 1A is adjusted to match the impedance of the general-purpose communication device, a delay element composed of a commercially available coil or the like is used as each delay element.

FIG. 4 is a block diagram showing a detailed configuration of another embodiment of the ultrasonic transducer according to the present invention.
In the present embodiment, the above-described ultrasonic transducer has a fixed delay, selects a plurality of delay elements, and adjusts a delay amount of an electric signal in a signal line connected to each piezoelectric vibrator. On the other hand, a delay element capable of setting a variable delay amount is provided for each signal line, and the delay amount of an electric signal input / output to / from each piezoelectric vibrator of the laminated piezoelectric vibrator is finely adjusted according to each vibration mode. The adjustment is performed to further improve the electro-mechanical conversion efficiency. More specifically, the four kinds of delay elements 14a, 14b, 1
In place of 4c and 14d, variable delay elements 141 to 147 each having a variable delay amount or a plurality of input / output terminals having different delay amounts are provided in each of signal lines 5a to 5g.
The delay amount of input / output is selected according to each vibration mode. This embodiment is also similar to the above-described embodiment in that the delay amount can be set and switched externally, and a commercially available variable delay element is used.

According to the ultrasonic transducer of the present embodiment, the phase of each electric signal can be adjusted more finely than that of the first embodiment in which the polarity of each electric signal is switched. If provided, an ultrasonic transducer capable of transmitting and receiving ultrasonic waves of a plurality of frequencies from the fundamental vibration mode to higher-order vibration modes with higher efficiency can be realized. In particular, an ultrasonic transducer using a variable delay element is capable of precise phase adjustment, and also has a matching layer for acoustic matching, as shown in the following example, and performs complex vibration. Effective for ultrasonic transducers.

<Embodiment 3> In this embodiment, in order to facilitate transmission of sound waves between a transmission medium such as water or air which actually transmits ultrasonic waves and a piezoelectric vibrator, acoustic matching is performed. The configuration of an ultrasonic transducer with a matching layer added for this purpose. Here, the matching layer is for performing acoustic matching between the piezoelectric vibrator and the medium, and is provided between the acoustic window 4 and the piezoelectric vibrator 1a in the case of the ultrasonic transducer of FIG. Things. As the material of the matching layer, generally, a material in which glass or a metal having a high specific gravity is mixed into an epoxy resin or the like to change the acoustic impedance is applied. If such a matching layer is used, wiring of electric signals is limited to each piezoelectric vibrator portion as shown in FIG.

Further, as in the present invention, for example, a piezoelectric ceramic is used as a piezoelectric vibrator, and a matching layer is further provided.
If the piezoelectric ceramic is made of a material in which pores are inserted and acoustic impedance is adjusted, a signal line can be wired from the matching layer. In any case, the mounting of the matching layer complicates the vibration state depending on the vibration mode. Therefore, the configuration of the ultrasonic transducer of the present invention shown in the first and second embodiments is different from that of the present embodiment. , It becomes more effective.

FIG. 8 is an explanatory view of a main part showing the relationship between the structure of a laminated piezoelectric vibrator having a structure in which a matching layer is mounted on the piezoelectric vibrator and the vibration mode. In the present embodiment, as the piezoelectric vibrator,
The matching layers M1 and M having a thickness of about 3 mm were prepared by using the same six layers 1a to 1f as in the above-described embodiment, and adjusting the acoustic impedance by inserting pores in the same PZT ceramic as the piezoelectric vibrator.
2 is mounted between the piezoelectric vibrator 1 a and the acoustic window 4. Further, since the matching layers M1 and M2 can also be used as a piezoelectric vibrator, they are not shown in FIG.
3, the electrodes are also connected to the matching layers M1 and M2, and the signal lines connect between the electrodes and the matching circuit section to input and output electric signals. The matching layers M1 and M2 are also configured to transmit and receive sound waves by electro-mechanical conversion. Note that the vibration states of the piezoelectric vibrator and the matching layer in each vibration mode shown in the figure show the results obtained from Mason's equivalent circuit using an equivalent circuit analysis method.

In the case of this embodiment, in the basic vibration mode shown in FIG. 8A, since the matching layers and the piezoelectric vibrators vibrate in the same phase, the polarities of the electric signals are wired in the same phase. The same delay amount may be set.

Further, in the secondary vibration mode shown in FIG. 8B, there are two vibration nodes (marked by ●), but in the case of only the piezoelectric vibrator as in the above-described embodiment, The state of vibration changes, and the portions of the matching layers M1 and M2 and the other portions of the piezoelectric vibrator vibrate in opposite phases. Therefore, the polarity of the electric signal may be reversed between the portions of the matching layers M1 and M2 and the portion of the piezoelectric vibrator, or one of the signals may be delayed by 180 °. Furthermore, if the phase of each signal is adjusted by adjusting the amount of delay of the variable delay element provided on each signal line by the amount that the position of the node is shifted, compared with the case of only the piezoelectric vibrator, higher efficiency can be achieved. Electrical-mechanical conversion can be performed.

In the tertiary vibration mode shown in FIG. 8C, there are three vibration nodes (marked by ●), the matching layer M2, the parts 1a and 1b of the piezoelectric vibrator, and the other parts. The matching layer M1 and the piezoelectric vibrators 1c to 1f vibrate in opposite phases.
Therefore, the matching layer M2 and the portions 1a, 1a,
b, the matching layer M1, and the piezoelectric vibrators 1c to 1c
It is sufficient to wire the electrical signal f in the opposite polarity or to delay any signal by 180 °. Further, as in the case of the secondary vibration mode, the delay amount of the variable delay element provided on each signal line is adjusted by the amount by which the position of the node is shifted, and the phase of each signal is changed. , A more efficient electro-mechanical conversion can be performed.

As in the present invention, for example, a piezoelectric material made of a piezoelectric ceramic such as lead zirconate titanate is used as a piezoelectric vibrator, and an acoustic impedance in which pores are formed in such a piezoelectric ceramic is used as a matching layer. By using a material that has been adjusted to the above, signal lines can be routed from the matching layer, and even if the vibration state becomes complicated due to the mounting of the matching layer, the polarity of the electric signal and the amount of delay can be reduced. Since the adjustment can be performed, an ultrasonic transducer having good electro-mechanical conversion efficiency can be realized.

<Embodiment 4> In the above embodiments, a piezoelectric vibrator having a configuration in which rectangular parallelepiped piezoelectric vibrators are stacked in multiple layers is used. A piezoelectric vibrator in a small ultrasonic transducer that transmits and receives ultrasonic waves of multiple frequencies from the fundamental vibration mode to higher-order vibration modes by adjusting the polarity and delay amount of the signal. Is not limited to a rectangular parallelepiped piezoelectric vibrator.

FIG. 9 is a block diagram showing the configuration of another embodiment of the ultrasonic transducer according to the present invention. In this embodiment, cylindrical piezoelectric vibrators 15 are stacked in multiple layers, and signal lines are output from the respective vibrators. Cylindrical piezoelectric vibrator 1
In the case of No. 5, since a vibration mode in the cylinder and in the height direction is also generated, a fine slit 1 is formed in the piezoelectric vibrator 15 as shown in FIG.
5a was inserted to construct an ultrasonic transducer.

[0065]

As has been described in detail above, the intended object has been achieved by the present invention. In other words, it is possible to easily configure a multi-layer laminated piezoelectric vibrator having an impedance that matches the input / output impedance of a general-purpose communication device, switch the polarity of each electric signal input / output to / from this piezoelectric vibrator, and reduce the amount of delay. Just by adjusting, if one multi-layer piezoelectric vibrator is provided, it is possible to transmit and receive ultrasonic waves of multiple frequencies from the fundamental vibration mode to higher-order vibration modes. A wave device can be realized. Further, a general-purpose communication device can be used for a switch or an amplifier for processing an electric signal, and a compact and economical ultrasonic transducer can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of an essential part of an ultrasonic transducer according to an embodiment of the present invention.

FIG. 2 is a block diagram of the ultrasonic transducer.

FIG. 3 is a block diagram of an ultrasonic transducer according to another embodiment.

FIG. 4 is a block diagram of an ultrasonic transducer according to still another embodiment.

FIG. 5 is a model diagram showing a vibration state of a multilayer piezoelectric vibrator.

FIG. 6 is a model diagram showing a relationship between signal wiring of a multilayer piezoelectric vibrator and a vibration state.

FIG. 7 is a characteristic diagram of the piezoelectric vibrator of the ultrasonic transducer according to the present invention.

FIG. 8 is a model diagram showing a vibration state of the multilayer piezoelectric vibrator with a matching layer.

FIG. 9 is a block diagram of an ultrasonic transducer according to another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ultrasonic transducer 1a, 1b, 1c, 1d, 1e, 1f ... Piezoelectric vibrator, 1A ... Multilayer piezoelectric vibrator, 2 ... Frame, 3 ... Backing, 4 ... Acoustic window, 5 ... Signal line Reference numeral 6: Matching circuit section 7: Cable 8: Mounting bracket 11: Switching circuit 12, 13: Amplifier 14a, 14b, 14c, 14d: Delay element

Claims (5)

(57) [Claims] An electric signal is input to a piezoelectric vibrator as a drive signal, and the piezoelectric vibrator performs an electro-mechanical conversion.
An ultrasonic wave transmitter for generating an ultrasonic wave, and an ultrasonic wave receiver for inputting an ultrasonic wave as a drive signal to a piezoelectric vibrator and performing an electromechanical conversion by the piezoelectric vibrator to generate an electric signal An ultrasonic transducer using a multi-layer piezoelectric vibrator in which a plurality of piezoelectric vibrator materials are laminated in a multilayer as the piezoelectric vibrator, wherein an electric signal is input / output to / from the plurality of piezoelectric vibrator materials. Signal transmitting means, and a phase control means for adjusting a phase of the electric signal, wherein the phase control means
Is an arrangement for switching the polarity of the input / output signal of the signal transmission means.
And a line switching means for inputting the plurality of piezoelectric vibrator materials.
The polarity of each electric signal to be output,
An ultrasonic transducer configured to convert the electric signal switched and phase-adjusted into a sound wave. 2. The apparatus according to claim 1, wherein said phase control means includes signal delay means for delaying input / output signals of said signal transmission means, and applies respective electric signals input / output to / from said plurality of piezoelectric vibrator members to said delay means. 2. The ultrasonic transducer according to claim 1 , wherein the ultrasonic transducer is configured to be able to be delayed and converted into a sound wave. 3. The ultrasonic transducer according to claim 1 , wherein the multi-layer piezoelectric vibrator is a vibration mode selected from a plurality of vibration modes including a basic vibration mode and a second or higher order vibration mode. Selecting means for vibrating in a mode, wherein the selecting means controls the phase control means and converts the electric signal whose phase has been adjusted into a sound wave in accordance with the selected vibration mode. The ultrasonic transducer according to claim 1 or 2 . 4. A matching layer for acoustic matching including a piezoelectric vibration material is provided between the multilayer piezoelectric vibrator and a transmission medium for transmitting a sound wave, and an electric signal is also input to the matching layer. The signal transmission means for outputting, and the phase control means for adjusting the phase of the electric signal, wherein the matching layer is also configured to be able to convert the electric signal whose phase has been adjusted to a sound wave. 3. The ultrasonic transducer according to any one of 3 . 5. An electric signal is input to a piezoelectric vibrator as a drive signal, and the piezoelectric vibrator performs an electro-mechanical conversion.
An ultrasonic wave transmitter for generating an ultrasonic wave, and an ultrasonic wave receiver for inputting an ultrasonic wave as a drive signal to a piezoelectric vibrator and performing an electromechanical conversion by the piezoelectric vibrator to generate an electric signal In the ultrasonic transducer using a multilayer piezoelectric vibrator in which a plurality of piezoelectric vibrator materials are laminated in a multilayer as the piezoelectric vibrator, the number of layers of the piezoelectric vibrator material is set to In the range where the thermal noise sound pressure conversion value is smaller than the minimum receiving sound pressure required for the ultrasonic transmitter and larger than the thermal noise sound pressure conversion value of the electric signal amplifying means connected to the multilayer piezoelectric vibrator, The ultrasonic transducer according to any one of claims 1 to 4, wherein the impedance of the piezoelectric vibrator is set to be substantially the same as the impedance of the amplifying means.