JPH0436322B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an ultrasonic measuring device that measures the propagation velocity of sound waves in liquid and/or pressure such as sound pressure using a comb-shaped transducer.

BACKGROUND ART Interdigital transducers are the most important and widely used surface wave technology, and function as sound emitters or detectors into liquids at liquid-solid interfaces. The present invention provides a novel application of the interdigital transducer, and provides an ultrasonic measuring device that realizes improved sound velocity measurement in liquid and pressure measurement such as sound pressure.

(Problem to be solved by the invention) The present invention uses a blind-shaped transducer to
The purpose of the present invention is to provide an improved ultrasonic measuring device for measuring pressure such as sound velocity or sound pressure in a liquid, and its features include a container containing a liquid and having a sound wave reflecting means at the bottom, and a piezoelectric material on the surface of the piezoelectric body. a transducer having a pair of spaced-apart interdigital electrodes, the transducer being disposed in the container opposite the bottom with the electrodes in contact with the liquid; and a transducer for amplifying the electrical output of one interdigital electrode. A sound wave is reflected at the bottom of the container and propagated between the two interdigital electrodes by a frequency measuring means that measures the oscillation frequency of the circuit. The present invention relates to an ultrasonic measuring device that measures time based on changes in the frequency.

With the above configuration, by using the bottom as a rigid body or a diaphragm that is sensitive to sound pressure, pressure such as sound velocity in liquid or sound pressure can be measured. Furthermore, it is also possible to arrange a pair of transducers facing each other so as to measure the sound velocity in liquid between them.

(Structure and operation of the invention) FIG. 1 shows an example of the structure of an ultrasonic measuring device according to the invention, and illustrates measurement of sound pressure.

In FIG. 1, 10 is a container, and its bottom 14
consists of a diaphragm that is sensitive to pressure such as sound pressure. Reference numeral 16 denotes a transducer in the form of a blind, which includes a piezoelectric substrate 16a and a transducer 1 disposed at a distance on the surface of the piezoelectric substrate 16a.
Pair of interdigital electrodes (interdigital electrodes) 1
6b and 16c. A container 10 is filled with a liquid 12 and a transducer 16
is placed opposite the bottom 14 with the surface electrode in contact with the liquid. Note that 18 is a gasket, and 20 is a hole for inserting/discharging liquid.

A phase shifter 26 is connected to one electrode 16c from an amplifier 24.
When an electric signal is applied through the electrode, the electric signal is converted into a sound wave at the electrode section, the sound wave propagates through the liquid 12, is reflected by the diaphragm 14, and reaches the other electrode 16b. After converting the sound wave into an electrical signal at the electrode 16b and applying it to the input of the amplifier 24, the signal is also applied to the output terminal 28 via the phase shifter 26.

With the above configuration, a closed oscillation circuit including a liquid delay line is constructed, and the following oscillation conditions are satisfied.

ωL/V _C +φ _E =2nπ Here, ω is the oscillation angular frequency, L is the propagation path length of the sound wave in liquid, φ _E is the electrical phase delay, and n is an integer.

Since ωL/V _C ≫φ _E generally holds, the oscillation frequency is as follows.

≒nVC/L (1) Now, when the diaphragm is displaced by the sound pressure 22 etc. and the propagation length of the sound wave in the liquid changes by ΔL, the frequency deviation Δ _d will be as follows.

Δ _d = d/dLΔL=−nV _C /L ² ΔL=KΔL (2) where K is a constant. From equation (2), the oscillation frequency is centered at and undergoes frequency modulation by the sound pressure applied to the diaphragm. Therefore, sound pressure can be detected by detecting this signal, and for example, a gas pressure sensor can be realized by displacing a diaphragm with gas pressure.

Figure 2 is an example of an electric circuit used in the present invention.
It consists of an oscillation section, a mixing section, a low-pass filter section, and an FM detection section. The structure of the oscillator is shown in FIG. 1, and the liquid delay line 100 is shown in (10, 12, 14,
16, 18, 20). Since the frequency deviation is extremely small compared to the oscillation frequency of the oscillator, direct detection is difficult, so a local oscillation frequency (L ₀ .
Extract the intermediate frequency of Hz. This intermediate frequency is extracted through a low-pass filter section (removes the sum frequency component), and then the frequency -
Converts the voltage and outputs the output voltage to the output terminal.
The characteristics of the FM detection section are 6 to 13K as shown in Figure 3.
It is linear in Hz.

FIG. 4 is a diagram showing experimental results of the present invention, in which frequency characteristics were measured in a coupler for hydrophonic calibration in order to evaluate the operating characteristics as a sound pressure sensor. This figure shows that a flat frequency response can be obtained up to 70Hz. Note that the upper limit frequency of the calibration coupler is 800Hz.

Figure 5 shows the relationship between sound pressure and output voltage at a frequency of 402Hz.
The results of actual measurements are shown, and it can be seen that excellent linearity can be obtained.

The transducer used in the experiments shown in FIGS. 4 and 5 has a piezoelectric substrate 16a made of piezoelectric ceramic 91A material (length 25 mm, width 15 mm,
The number of electrode pairs of the two electrodes 16b and 16c is 10, the period length is 210 μm, and the distance between the electrodes is
14.0 mm, the distance between the piezoelectric substrate and the diaphragm is 3.5 mm, and the center frequency is 10.0 MHz.
Also, the liquid used was water.

In FIG. 1, instead of the diaphragm 14,
If the bottom of the container is made of a rigid body, the speed of sound in the liquid can be measured. At this time, in the above equation (1), if the frequency-voltage conversion characteristic is linear (=KV _put , K is a constant), the following equation can be obtained.

ΔV _C = (KL/n)・ΔV _put (3) Here, ΔV _C is the difference between the sound velocity in liquid and the value in the reference state,
ΔV _put is the difference between the output voltage and the value in the reference state.

Figure 6 shows the actual measurement of the temperature dependence of the sound speed change in water using the above-mentioned measurement device, where K = -3.659×
10 ⁵ (Hz/V), θ=47.98°, L=20.71×10 ^-3 m, n
= 137, the reference state is 24.5°C, which agrees well with the theoretically calculated value shown by the solid line.

Figure 7 shows another experimental example of the present invention, in which the influence of changes in hydrostatic pressure on the speed of sound in water was actually measured.
It is 26.8℃. The velocity varies linearly with hydrostatic pressure, and is in good agreement with the theoretical value shown by the solid line.

In addition, in the case of measuring the sound velocity in liquid, in addition to the reflective type shown in the example, a pair of transducers having a single interdigital electrode may be arranged facing each other, and the sound velocity in liquid between them may be measured. It is also possible to do so.

In each of the above embodiments, an example was shown in which the electrode fingers were brought into contact with a liquid to excite sound waves from the electrode fingers.
It is also possible to use a thin substrate to excite so-called Lamb waves from the back side of the substrate (the surface where no electrode fingers are present).

(Effects of the Invention) The ultrasonic measuring device according to the present invention has the technical advantage of using interdigital electrodes, and has the advantage of having a relatively simple circuit configuration and high measurement accuracy.

[Brief explanation of drawings]

FIG. 1 shows an example of the configuration of an ultrasonic measuring device according to the present invention, FIG. 2 shows an electric circuit used in the device shown in FIG. 1, and FIGS. FIG. 3 is a diagram showing experimental results of the device according to the present invention. 10... Container, 12... Liquid, 14... Bottom,
16...transducer, 24...feedback amplifier.

Claims (1)

[Scope of Claims] 1. A container containing a liquid and having a sound wave reflecting means at the bottom, a pair of interdigital electrodes arranged at a distance on the surface of a piezoelectric body, and a pair of transducer-shaped electrodes arranged at a distance from each other on the surface of a piezoelectric body, and a pair of transducer-like electrodes arranged at a distance from each other on the surface of a piezoelectric body. an oscillation circuit consisting of a transducer arranged and a feedback means for amplifying the electrical output of one interdigital electrode and feeding it back to the other interdigital electrode,
An ultrasonic measuring device characterized in that a frequency measuring means for measuring the oscillation frequency of the circuit measures the time taken for a sound wave to reflect at the bottom of the container and propagate between both interdigital electrodes based on a change in the frequency. 2. The ultrasonic measuring device according to claim 1, wherein the bottom of the container is a rigid body, and the propagation velocity of sound waves in the liquid is measured by a frequency measuring means. 3. The ultrasonic measuring device according to claim 1, wherein the bottom of the container is comprised of a diaphragm that is sensitive to sound pressure, and the frequency measuring means measures the sound pressure applied to the diaphragm. 4. A container containing a liquid, a pair of transducers having interdigital electrodes on the surface of a piezoelectric body, and arranged facing each other in the container, and amplifying the electrical output of one of the transducers. an oscillation circuit comprising a feedback means for feeding back to the other transducer, and a frequency measurement means for measuring the oscillation frequency of the circuit to measure the time during which the sound wave propagates between the two transducers based on changes in the frequency; An ultrasonic measurement device characterized by: