JP3364546B2 - 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 wave transmitter / receiver for transmitting and receiving ultrasonic waves in the air, underwater, etc. by utilizing electromechanical conversion of a piezoelectric vibrator, and particularly for controlling a directional pattern. , A configuration of an ultrasonic transducer which suppresses a side lobe level in a directional pattern.

[0002]

2. Description of the Related Art In general, sound in an acoustic radiating medium has a directional pattern whose main lobe becomes thin and side lobes are plural when the array area of ultrasonic transducers is increased with respect to the wavelength of the sound. Occurs individually.

In an apparatus for recognizing the shape, direction, distance, etc. of an object, such as an ultrasonic sonar or an ultrasonic diagnostic apparatus, the pointing width is determined according to the size of the object to be detected and the purpose. Specifically, when the sound is transmitted widely or the object to be detected is large and does not require high resolution, the pointing width is wide. Conversely, when the object to be detected is small and the object needs high resolution, the pointing width is wide. Narrow.

Further, in such an apparatus, since the reflected sound reflected by the object is received, if the side lobe is large, the reflected sound in the side lobe direction may be received rather than the sound in the main lobe direction. The distance may be erroneously detected. Therefore, it is desirable to control the directivity width and suppress the side lobe level as much as possible.

As a method for controlling the directivity width, there is, for example, Japanese Patent Laid-Open No. 62-277575. This is provided with a means 30 for selecting a plurality of piezoelectric vibrators 10 arranged on the same plane 20 as shown in FIG. 12, and can be varied depending on the combination of the position and the number of the vibrators 11 to 15 to be selected. It is an ultrasonic wave transmitter / receiver capable of obtaining the directivity of.

As a side lobe suppressing method, there is, for example, Japanese Patent Publication No. 4-81400. As shown in FIG. 13, the electrode surface of the piezoelectric vibrator 40 is divided into a plurality of electrodes 41, 42, voltages of different polarities and amplitudes are applied to the electrodes 41, 42, 43 to control a desired directivity width. The present invention relates to an ultrasonic wave transmitter / receiver that suppresses sidelobe levels.

[0007]

In the structure of the ultrasonic transmitter / receiver disclosed in the former publication, the means for suppressing the sidelobe level is not provided, so that the transmitting / receiving performance by the sidelobe is inferior. To suppress side lobes,
It is necessary to provide a shading amplifier or the like for each piezoelectric vibrator to weight the sensitivity, the number of parts increases, and the shading coefficient of each shading amplifier needs to be changed according to various directivities. It is difficult to control. Therefore, it is not optimal as an ultrasonic transmitter / receiver that controls the directional pattern and suppresses the side lobe level in the directional pattern.

In the structure of the ultrasonic wave transmitter / receiver disclosed in the latter publication, the electrode portion is divided into two parts by a single piezoelectric element in order to suppress the side lobe level. It is difficult to secure the method and dimensional accuracy, and it becomes expensive and complicated because it needs to be manufactured specially.
It is not optimal as an ultrasonic transmitter / receiver that controls the directional pattern and suppresses the side lobe level in the directional pattern.

An object of the present invention is to solve the above-mentioned problems, to control the directional pattern and to suppress the side lobe level in the directional pattern, and to provide a predetermined performance with an inexpensive and simple structure. The purpose of the present invention is to provide an ultrasonic wave transmitter / receiver capable of achieving the above.

[0010]

The above object is to arrange a plurality of laminated piezoelectric vibrators or columnar piezoelectric vibrators having different wave transmission / reception sensitivities in a matrix and connect a plurality of signal transmission cables in parallel. This can be achieved with a simple circuit configuration provided.

Specifically, it is used for an ultrasonic wave transmitter / receiver,
As a piezoelectric vibrator for converting an electric signal into an ultrasonic wave by electro-mechanical conversion, in order to change the electrical impedance of the piezoelectric vibrator, plate-shaped piezoelectric vibrators are laminated in multiple layers and each piezoelectric vibrator Use a multilayer piezoelectric vibrator that pulls out a cable for signal transmission from the above, arrange them in a matrix, and connect the cables for signal transmission from each multilayer piezoelectric vibrator in parallel with a switch circuit. It is achieved by setting the number.

This is, for example, the case where the above-mentioned multilayer piezoelectric vibrator is
If the number of connected cables from the middle multi-layer piezoelectric vibrator is A and the number of connected cables from the multi-layer piezoelectric vibrators on both sides is B, then A
By setting the relation of> B, the side lobe level can be suppressed. Here, when the side lobe level is lowered and the directivity width is widened, the A / B ratio is reduced. Conversely, when raising the side lobe level and narrowing the pointing width,
Increase the A / B ratio. Further, by increasing the number of arrangements of the multi-layer piezoelectric vibrators, the directivity width can be further narrowed, and in order to obtain directivity suitable for the purpose, the number of arrangements of the multi-layer piezoelectric vibrators and the number of cables to be used can be reduced. Determine the number of connections.

The object is to replace the multi-layered piezoelectric vibrator by arranging a plurality of columnar piezoelectric vibrators having different wave-transmission / reception sensitivities, each of which is provided with at least one cable for signal transmission. In the case of arranging in a matrix, it is achieved by connecting each cable in parallel and connecting to at least one transmitting / receiving circuit.

[0014]

With the above-mentioned means, an electric signal for transmission is supplied to each of the multi-layer piezoelectric vibrators or each of the columnar piezoelectric vibrators arranged in a matrix, and the electro-mechanical conversion of each piezoelectric vibrator causes the ultrasonic central axis to be exceeded. Generates sound waves. Further, in the case of reception, each piezoelectric vibrator receives a reflected wave of ultrasonic waves to receive an electric signal by mechanical-electric conversion.

By adjusting the number of piezoelectric vibrators arranged in a matrix, the directivity pattern can be controlled to suppress the side lobe level, and the resolution can be increased by increasing the number of arrays.

When a multilayer piezoelectric vibrator is used, the number of signal transmission cables from each piezoelectric vibrator constituting the multilayer piezoelectric vibrator is adjusted in parallel, and the piezoelectric vibrators are further arranged in a matrix. Adjustment of the parallel connection number A of the cables used from the multilayer piezoelectric oscillator on the acoustic center axis of each multilayer piezoelectric oscillator and the parallel connection number B of the used cables from the multilayer piezoelectric oscillator on the outside thereof By
That is, the sidelobe level can be suppressed by setting the relation of A> B, and the sidelobe level can be lowered by increasing the ratio of A / B.

Further, when the columnar piezoelectric vibrators are used, the wave transmission / reception sensitivities of the columnar piezoelectric vibrators arranged on the acoustic center axis and the outside are made different to obtain the wave transmission / reception sensitivities of the columnar piezoelectric vibrators on the acoustic center axis. The side lobe level can be suppressed and the side lobe level can be lowered by using the one having higher sensitivity than the outer one.

[0018]

EXAMPLES The present invention will be described below with reference to examples. Figure 1
Shows an embodiment of the present invention, in which the directivity pattern is controlled by adjusting the number of connection of signal lines for transmitting and receiving electric signals attached to each piezoelectric vibrator of the multilayer piezoelectric vibrator. The structure of the ultrasonic wave transmitter / receiver which suppresses the side lobe level in a pattern is shown.

The ultrasonic wave transmitter / receiver 7 transmits a transmission / reception electric signal to and from piezoelectric vibrators 0a to 0f, 1a to 1f and 2a to 2f, which are laminated in six layers, for converting vibration energy and electric energy. Signal lines 100a to 100c, 1
01a to 101c and 102a to 102c, a negative electrode of each piezoelectric vibrator is made common, and a signal line 99 using this as a ground line, a switch circuit 4 for connecting the respective signal lines, and switches 4a to 4i And a transmission circuit 5 for generating and amplifying a transmission electric signal and a reception circuit 6 for amplifying a reception electric signal.

In the case of transmission, first, a transmission electric signal such as FM, PCW, CW is generated by the transmission circuit 5 and supplied to the switch circuit 4. In the switch circuit 4, the signal lines 100, 101, 10 required to obtain a desired beam pattern.
2 is selected, and an electric signal for transmission is supplied to each of the multilayer piezoelectric vibrators 0, 1 and 2 through this. The supplied electric signal for transmission is subjected to electromechanical conversion by each of the multilayer piezoelectric vibrators 0, 1 and 2, and an ultrasonic wave is generated around the acoustic axis 3 to the medium 8 such as water or air.

In the case of reception, the operation is opposite to that of transmission, and the ultrasonic waves reflected by the target object arrive at each of the multilayer piezoelectric vibrators 0, 1, 2 and are converted into electrical signals by performing mechanical-electrical conversion. To do. Signal line 1 selected by switch circuit 4
Only the signal 00, 101, and 102 is passed through, and the signal is supplied to the receiving circuit 6, and this electric signal is amplified and detected.

Here, these ultrasonic transducers are shown in FIGS.
The structure of the piezoelectric oscillator shown in FIG. 7, the following formula expressing a specific relationship in the equivalent circuit, and the structure (thickness, material, It is possible to suppress the sidelobe level by setting the number of layers, etc.) and combining them.

<When receiving waves>

[0024]

[Equation 3]

[0025]

[Equation 4]

<In case of wave transmission>

[0027]

[Equation 5]

As the piezoelectric vibrator, several + kHz to
It transmits and receives ultrasonic waves of several MHz, and examples thereof include piezoelectric ceramics such as lead zirconate titanate and polymers such as polyvinylidene fluoride (PVDF).

FIG. 2 shows an electrical equivalent circuit of the piezoelectric vibrator during transmission. Here, Ri is a mechanical load and an acoustic load,
Ii is the vibration speed of the piezoelectric vibrator, Li is the mechanical mass, Ci is the mechanical stiffness, Ci ′ is the capacitance of the piezoelectric vibrator,
Ci ″ indicates the cable capacity. The electrical equivalent circuit of the piezoelectric vibrator at the time of reception is shown in FIG. 3, which is a circuit obtained by loading the target equivalent circuit of FIG. 2 with electromotive force ei.

When the piezoelectric vibrators are laminated in multiple layers and the respective piezoelectric elements are coupled in parallel, Ri becomes small and Ci becomes large, and apparently the electric impedance of the piezoelectric vibrator becomes small, and the piezoelectric vibrator thickness t. Is smaller, eo is also smaller.

Now, as shown in FIG. 4, + -electrodes 50a, 50
When three piezoelectric elements 0, 1, 2 provided with b, 51a, 51b, 52a, 52b are arranged and the signal transmission cables 100, 101, 102 from the respective piezoelectric elements 0, 1, 2 are coupled in parallel, The equivalent circuit during reception is as shown in FIG. Where R is the input impedance of the amplifier for amplification, V
Can be represented by the sum of the voltages generated by the respective electromotive forces e ₀ , e ₁ , e ₂ . Electromotive force ei (e ₀ , of each piezoelectric element,
The voltage Vi generated in the resistor R by e ₁ , e ₂ ) changes due to the electrical impedance of the other two piezoelectric vibrators.

In the case of wave reception, the voltage V ₀ generated by the electromotive force e ₀ can be expressed by equation 3. Therefore, as can be seen from FIG. 6, the voltage V ₀ is represented by the impedance Z ₀ consisting of the mechanical circuit constant of the middle piezoelectric element ₀ and the impedances Z ₁ , Z ₂ and C, R of the outer piezoelectric elements ₁ , _2. It is the voltage division ratio with the impedance.

Now, consider multi-layer piezoelectric vibrators 0, 1 and 6 in each of which piezoelectric vibrators are laminated in six layers as shown in FIG. If the materials and thicknesses of the piezoelectric vibrators 0, 1 and 2 are the same, the electromotive forces ei generated from the piezoelectric vibrators are all equal. Therefore, in such a case, V ₀ increases as Z ₁ and Z ₂ increase.

If the voltages generated by the electromotive forces e ₁ and e ₂ are V ₁ and V _{2 in the} same manner, the voltage V is the power addition of these voltages V ₀ , V ₁ and V ₂ , and is expressed by _equation (6). .

[0035]

[Equation 6]

Here, the sensitivity coefficients of the piezoelectric elements 1 and 2 on both sides with respect to the piezoelectric element 0 on the acoustic axis are │V ₁ │ / │V ₀ │, │V
₂ | / | V ₀ | Therefore, when the relationship of Z ₀ <Z ₁ = Z _{2 is established, the} equation 7 is obtained, and the piezoelectric elements 1 and 2 on both sides of the apparent piezoelectric element 0 are weighted. It is equivalent to what was done, shading can be applied, and side lobes can be suppressed.

[0037]

[Equation 7]

As for the electric impedance of the piezoelectric element, when the same plate-shaped piezoelectric vibrators are used and are connected in parallel, the larger the number of connected piezoelectric elements, the smaller the electric impedance. Therefore, if the number A of piezoelectric elements stacked on the acoustic center axis is B <A
When the number of sheets is determined according to the relation, Z ₀ <Z ₁ = Z ₂ is established.

Even if the material, thickness, etc. of the piezoelectric vibrator are different, side lobes can be suppressed by selecting the structure of the piezoelectric vibrator so as to satisfy the expressions (4) and (5).

An equivalent circuit for transmitting waves is shown in FIG. When the drive voltage of the piezoelectric element is E, the same voltage is applied to the terminals of each piezoelectric element 0, 1, 2. The sensitivity coefficient of the piezoelectric element in the case of transmission can be represented by the ratio of particle velocities of the piezoelectric element during transmission, and is | I ₁ | / | I ₀ |, | I ₂ | / | I ₀ |. Therefore, the smaller the impedance of the piezoelectric element, the more Ii
Is large, and when the relationship of Z ₀ <Z ₁ = Z ₂ is established,
Therefore, like the received wave, the directivity can be shaded and the side lobe can be suppressed.

[0041]

[Equation 8]

8 (a) to 8 (c) show concrete examples of the ultrasonic transmitter / receiver of FIG. FIG. 8A is a directional pattern at the time of reception when all the switches of the switch circuit 4 are connected. The 0 ° direction in FIG. 8A corresponds to the acoustic axis 3 in FIG. 1 and is the center of the main lobe with the highest sensitivity. Here, the solid line indicates the calculated value, and ∘ indicates the measured value, and a side lobe of -16 dB is generated near ± 70 °. Further, the directivity width (-3 dB width) is about ± 18 °.

FIG. 8B shows the switch 4 of the switch circuit 4.
It is a directional pattern at the time of reception when b to 4f and 4h and 4i are connected. Compared to FIG. 8A, the side lobe becomes −20 dB in the vicinity of ± 80 °, which is reduced by about 4 dB, and the directivity width (−3 dB width) is slightly widened to about ± 20 °.

FIG. 8C shows the switch 4 of the switch circuit 4.
This is a directional pattern at the time of reception when connecting c to 4f and 4i. Compared to FIG. 8A, the side lobe disappears and the directivity width (−3 dB width) becomes wide, about ± 30 °.

As described above, the directional pattern is controlled by adjusting the number of connection of the signal lines for transmitting and receiving electric signals attached to each piezoelectric vibrator of the multilayer piezoelectric vibrator, and the side of the directional pattern is controlled. The lobe level can be suppressed.

FIG. 9 shows the circuit constant of each equivalent circuit and the sensitivity coefficient calculated from the equation (4). 8 (a), 8 (b) and 8
The sensitivity coefficients in (c) are 1.0, 0.74,
The value becomes 0.16, and the sensitivity coefficient becomes smaller as the number of signal lines connected to the piezoelectric vibrators 1 and 2 is reduced, which is equivalent to that in which the weighting is apparently increased.

FIG. 10 shows another embodiment in which three columnar piezoelectric vibrators 0, 1, 2 which are not laminated are arranged. Here, the piezoelectric vibrators 0, 1, and 2 are selected so as to satisfy Expression 9, Expression 10, and Expression 3, and the piezoelectric vibrators are connected in parallel. In this case, the directional pattern is fixed, but considering the selection of the piezoelectric vibrator material and the setting of the thickness,
The directional pattern can be changed.

FIG. 11 shows another embodiment in which the number of laminated piezoelectric vibrators 0, 1 and 2 is changed, satisfying the expressions 9, 9 and 3 and transmitting and receiving ultrasonic waves all connected in parallel. It is a vessel.
Although the directional pattern is fixed as in FIG. 10, the directional pattern can be changed in consideration of the selection of the piezoelectric vibrator material and the setting of the thickness.

[0049]

[Equation 9]

[0050]

[Equation 10]

[0051]

According to the ultrasonic wave transmitter / receiver of the present invention, the structure (material,
If several piezoelectric vibrator matrices are provided by simply selecting the number of laminated layers, thickness, etc., control of the directional pattern and side lobe level in the directional pattern can be suppressed, and it is inexpensive and simple. The structure can achieve desired performance.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an ultrasonic wave transceiver according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram at the time of transmission of the ultrasonic transducer according to the embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram at the time of reception of the ultrasonic transmitter / receiver according to an embodiment of the present invention.

FIG. 4 is a perspective view of a 1 × 3 matrix piezoelectric vibrator of an ultrasonic transducer according to an embodiment of the present invention.

FIG. 5 is an equivalent circuit diagram of an ultrasonic wave transceiver according to an embodiment of the present invention.

FIG. 6 is an equivalent circuit diagram (at the time of reception) of an ultrasonic wave transmitter / receiver according to an embodiment of the present invention.

FIG. 7 is an equivalent circuit diagram (during transmission) of the ultrasonic wave transceiver according to the embodiment of the present invention.

FIG. 8 is an explanatory diagram of a directional pattern of an ultrasonic wave transmitter / receiver according to an embodiment of the present invention.

FIG. 9 is an explanatory diagram of circuit constants of an ultrasonic wave transceiver according to an embodiment of the present invention.

FIG. 10 is a configuration diagram of an ultrasonic wave transmitter / receiver according to another embodiment of the present invention.

FIG. 11 is a configuration diagram of an ultrasonic wave transmitter / receiver according to another embodiment of the present invention.

FIG. 12 is a configuration diagram of a conventional ultrasonic transducer.

FIG. 13 is a configuration diagram of a conventional ultrasonic transmitter / receiver device.

[Explanation of symbols]

0,0a to 0f, 1,1a to 1f, 1a 'to 1b',
2, 2a to 2f, 2a 'to 2b' ... Piezoelectric vibrator, 3 ... Acoustic axis, 4, 4a-4i ... Switch, 5 ... Transmitting circuit, 6 ...
Receiver circuit, 7 ... Ultrasonic wave transmitter / receiver, 8 ... Medium, 50a-5
0b, 51a to 51b, 52a to 52b ... Electrode 100,
100a to 100c, 101, 101a to 101c, 1
02, 102a to 102c ... Signal cables.

Front page continuation (72) Inventor Kazuhiko Iwata 216 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa Hitachi, Ltd. Information & Communication Division (56) Reference JP-A-6-181925 (JP, A) JP-A-6 -90950 (JP, A) JP 5-76527 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04R 17/00 332 H04R 17/00 330 G01S 7/52

Claims (3)

(57) [Claims] 1. An ultrasonic wave transmitter that generates an ultrasonic wave by inputting an electric signal to a piezoelectric vibrator as a drive signal, and the piezoelectric vibrator performs electromechanical conversion, and an ultrasonic wave as a drive signal. An ultrasonic wave receiver for generating an electric signal by inputting to a piezoelectric vibrator and performing mechanical-electric conversion by the piezoelectric vibrator, wherein the piezoelectric vibrator is a plate-shaped piezoelectric vibrator having the same material and thickness. In the ultrasonic transmitter / receiver in which a plurality of piezoelectric vibrators in which a plurality of piezoelectric vibrators are stacked perpendicularly to the acoustic radiation surface are arranged in a matrix in the horizontal direction with respect to the acoustic center axis, A signal line is drawn out from both electrode surfaces of at least one piezoelectric vibrator forming the piezoelectric vibrator, and the number of signal lines used by the multilayer piezoelectric vibrator on the acoustic center axis is A, and the acoustic Many on the central axis Let B be the number of signal lines of another multilayer piezoelectric oscillator outside the layer piezoelectric oscillator, and C, D be the number of signal lines of another multilayer piezoelectric oscillator outside the other multilayer piezoelectric oscillator. The ultrasonic wave transmitter / receiver is characterized in that each signal line is connected in parallel in such a relationship that A>B>C>D>. 2. The ultrasonic wave transceiver according to claim 1, further comprising a switch circuit for selecting each signal line to be used. 3. An ultrasonic wave transmitter that inputs an electric signal as a drive signal to a piezoelectric vibrator, and the piezoelectric vibrator performs an electromechanical conversion to generate an ultrasonic electric signal that generates an ultrasonic wave, and An ultrasonic wave receiver that inputs an ultrasonic wave as a drive signal to a piezoelectric vibrator, and the piezoelectric vibrator performs an electromechanical conversion to generate an electric signal, and the piezoelectric vibrator is made of a material or a thickness. In a ultrasonic transducer in which a plurality of laminated or single-layered piezoelectric vibrators of different types are used and the pressure transducers are arranged in a matrix in the horizontal direction with respect to the acoustic center axis, The number of the vibrator is 0, the number of the other piezoelectric vibrator outside the piezoelectric vibrator on the acoustic center axis is 1, and the number of the other piezoelectric vibrator outside the other piezoelectric vibrator is 1 2, 3, ... i,
and i + 1 · · n, and the electrical Inpi of each piezoelectric vibrator - dancing, respectively reception output voltage in correspondence with the number of each piezoelectric vibrator _{Z 0, Z 1, Z 2} , Z 3, ... Z _i, Z _i + _{1
... Z n, V 0, V} 1, V 2, V 3 ... V i, when the _{V i + 1 ... V n,} 1 number when received wave, the number 2 the relationship case of transmitting, each piezoelectric An ultrasonic wave transmitter / receiver characterized in that the material, thickness, or the number of laminated layers of the vibrators are selected, and that each piezoelectric vibrator is connected in parallel. [Equation 1] [Equation 2]