JPH01101800A - Ultrasonic wave transducer in liquid - Google Patents

Abstract

PURPOSE:To attain electronic scanning of each parallel stripe form electrode and to decrease the insertion loss to a degree capable of processing a signal by arranging the parallel stripe form electrode on one face of a piezoelectric high polymer film. CONSTITUTION:A piezoelectric substrate 1 is made of a piezoelectric high polymer film and a parallel stripe form electrode 2 whose number of electrode fingers N is 20, electrode finger pitch (p) is 100mum, electrode finger width (a) is 80mum, and electrode cross length (b) is 6mm while being excited at a frequency (f) of 12MHz is formed on one side of the substrate 1, an opposite electrode 3 is formed as shown in dotted lines on other side of the substrate 1 and connected to ground. Moreover, the face of the substrate 1 in contact with water is packed by a packing member made of an acrylic resin whose thickness is 2mm and whose acoustic impedance is close to water. Thus, the ultrasonic wave transducer in liquid is excited by applying a high frequency voltage between the parallel stripe form electrode and the opposed electrode while being arranged in a liquid and a longitudinal ultrasonic wave is radiated into the liquid. Thus, the efficient in-liquid ultrasonic wave transducer is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an ultrasonic transducer that transmits ultrasonic waves into a liquid.

(Prior Art) Some conventional liquid ultrasonic transducers have interdigital electrodes formed on a substrate made of a hard piezoelectric material such as ceramic.

Recently, polyvinylidene fluoride (PVDF) has been attracting attention as a piezoelectric polymer film with properties such as acoustic impedance that are similar to those of water and living organisms, and it is possible to create efficient ultrasonic transducers using it. This is being considered. However, in order to improve convergence, measures such as a lens-shaped backing material were required, and electronic scanning was not possible.

(Problems to be Solved by the Invention) The present invention focuses on these points and aims to provide an efficient submerged ultrasonic transducer that eliminates the above-mentioned conventional drawbacks.

(Means for Solving the Problems) A submerged ultrasonic transducer according to the present invention includes a polymer film substrate, an interdigital electrode formed on one surface of the substrate, and an interdigital electrode formed on the other surface of the substrate. The invention is characterized in that it is equipped with a counter electrode.

(Operation) According to the present invention, a submerged ultrasonic transducer is excited by applying a high frequency voltage between the interdigital electrode and the counter electrode disposed in the liquid, and longitudinal waves are generated in the liquid. Emits ultrasonic waves.

(Embodiment) FIG. 1 is a perspective view showing the structure of a submerged ultrasonic transducer according to an embodiment of the present invention.

The piezoelectric substrate 1 is made of a piezoelectric polymer film (LAZ material manufactured by Mitsubishi Yuka Co., Ltd.). On one surface of the substrate 1, electrode index N-20, electrode finger pitch p"100 Atrn, electrode finger width a-80 μm, electrode cross length b-6 mm, f-
An interdigital electrode 2 excited by 12 Ml (z) is formed.

A counter electrode 3 is formed on the other surface of the substrate 1 as shown by a dotted line and is grounded.

The surface of the substrate 1 in contact with water is backed by a backing material (not shown) made of acrylic resin (ρC1=0.321) with a thickness of 2 mm and whose acoustic impedance is close to that of water. Methylene dichloride (not shown), which is an adhesive for acrylic, is used to bond the substrate 1 and the backing material. The properties of the backing material have a significant impact on its acoustic properties. However, since the backing material in this case is made of thin and flexible acrylic resin, it is necessary to give it rigidity and protect the surface on which the counter electrode 3 is formed on the substrate 1. is used.

FIG. 2 shows an ultrasonic transmission/reception system using the ultrasonic transducer shown in FIG. In FIG. 2, a function generator 4 generates an output signal 4a having a frequency of f-12 MHz to drive a submerged ultrasonic transducer 5 of the present invention. The submerged ultrasonic transducer 5 is disposed in a liquid filled in a water tank 6, that is, water 7, so as to be rotatable about the Y axis.

In the water 7, a submerged ultrasonic transducer 8 having a structure similar to that of the submerged ultrasonic transducer 5 is arranged to transmit longitudinal ultrasonic waves 5a emitted from the submerged ultrasonic transducer 5.
is arranged to receive the water via water 7. A detection device 9 is connected to the submerged ultrasonic transducer 8, and its detection output 8a is inputted as an electrical signal obtained by delaying the output signal 4a, and this is displayed in synchronization with the output signal 4a of the function generator 4. I try to do that.

In operation, the submerged ultrasonic transducer 5 is excited by the output signal 4a of the function generator 4, the ultrasonic wave 5a emitted from this is detected by the submerged ultrasonic transducer 8, and the detected output 8a is sent to the detection device 9. When you enter
The following relational expression holds true. That is, assuming that the sound source constituted by the interdigital electrodes 2 is equivalent to a rectangular sound source group as shown in Fig. 1, the directivity R(θ) in the X-1 plane can be expressed by the following equation. .

the angle between the wave transducer 5, λ1 is the wavelength of the longitudinal wave in the water 3, k is the wave number (2π/λw), p/λ, -
It is 0.8.

Generally, in order for a sound source composed of interdigital electrodes to have the same directivity as a rectangular sound source with the same aperture length, it is necessary to satisfy the condition p/λw<l (2). It can be seen that under the condition of equation (2), the influence of the electrode fingers hardly appears, so that the sound source composed of interdigital electrodes can be treated equivalently to a line sound source.

FIG. 3 shows the output signal 4a (frequency f - 12 MHz) of the function generator 4 shown in FIG.
) shows the directivity pattern of the ultrasonic wave 5a formed in the X-2 plane when excited. In Fig. 3, the angle from the Z axis is the radiation angle of the ultrasonic wave 5a, and the distance is the radiation angle of the ultrasonic wave 4a.
It corresponds to the relative amplitude (dB) of .

Figure 4 shows the submerged ultrasonic transducer 5.8 of the present invention.
FIG. The X-axis is the frequency (MHz
), and the Y axis shows impedance.

As shown in the figure, a resonance point exists near 13 MHz.

The directivity at 12 MHz is as shown in FIG. As is clear from these, it can be understood that the vibration mode of the submerged ultrasonic transducer 5 is thickness vibration.

FIG. 5 shows the frequency characteristics of insertion loss of the submerged ultrasonic transducers 5 and 8. The X-axis shows frequency, and the Y-axis shows insertion loss. The center frequency is about 12.5 MHz, and the insertion loss at the center frequency is about 43 dB for the entire transmission and reception, which shows that the submerged ultrasonic transducers 5 and 8 of the present invention can be applied to ultrasonic imaging devices and the like. * indicates data with backing, and O indicates data without backing. As shown, the center frequency is approximately 11 MHz, and the insertion loss is 50 d.
B has an increase of about 4 dB, but the bandwidth is 5.4 MII
z to 7.5MHz. This increase in insertion loss is believed to be due to the acoustic mismatch that exists at the interface between water and acrylic.

Figure 6 shows a submerged ultrasonic transducer 5.8 of the present invention.
FIG. 4 is a pulse response characteristic diagram when a backing is provided and when a backing is not provided. In FIG. 6, the X axis is 0.
1 μs/div time axis, Y axis is 20IIIV/di
Indicates the voltage of v. Also, a is without backing and pulse width is 42 ns), b is with backing (pulse width is 47 ns)
) are shown below. As is clear from Figure 6,
It can be seen that the pulse response is improved by providing the backing.

(Effects of the Invention) As described above, according to the submerged ultrasonic transducer of the present invention, since the interdigital electrodes are arranged on one surface of the piezoelectric polymer film, the insertion loss is reduced to a level that allows signal processing. In addition, each interdigital electrode can be electronically scanned, and by dividing the interdigital electrodes into multiple groups, it is possible to transmit and receive signals with the same aperture area without using a circulator. By applying signals with different phases or amplitudes to each electrode finger, it is possible to obtain good response characteristics such as beam convergence, control of radiation direction, and suppression of side lobes. This makes it easy to apply.

Further, according to the present invention, since the transducer is lined with acrylic resin, the insertion loss of this lining increases, but the processability as a transducer is
This has the effect of improving practicality such as operability and maintainability.

[Brief Description of the Drawings] Fig. 1 is a perspective view showing the structure of a submerged ultrasonic transducer according to the present invention; Fig. 2 is an ultrasonic transmission/reception system using the submerged ultrasonic transducer shown in Fig. 1; 3 to 6 are characteristic diagrams of the submerged ultrasonic transducer shown in FIG. 1. 1... Substrate, 2... Interdigital electrode, 3...
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Claims (3)

[Claims] (1) An ultrasonic transducer that transmits ultrasonic waves into a liquid, which includes a polymer film substrate, an interdigital electrode formed on one surface of the substrate, and a counter electrode formed on the other surface of the substrate. A submerged ultrasonic transducer comprising: (2) The submerged ultrasonic transducer according to claim 1, wherein the substrate is lined with a backing material. (3) The submerged ultrasonic transducer according to claim 2, wherein the backing material is made of acrylic resin.