JPH0250422B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic measuring device for measuring changes in the velocity of ultrasonic waves propagating in a liquid.

The ultrasonic measuring device according to the present invention utilizes an ultrasonic transducer having an interdigital electrode formed by combining a pair of comb-shaped electrodes on one surface of a piezoelectric substrate. Such a transducer emits ultrasonic waves into a liquid by applying electrical signals to interdigital electrodes, and conversely receives ultrasonic waves propagating through the liquid and outputs electrical signals. It has the function of Therefore, two transducers are arranged separately from each other for input and output, and the ultrasonic waves emitted from the input transducers into the liquid are output after passing through a predetermined propagation path length. An ultrasonic delay device can be obtained by configuring the ultrasonic wave to be received by a transducer.

The present invention aims to provide an apparatus that uses such an ultrasonic delay device to measure changes in the velocity of ultrasonic waves propagating in a liquid.

To achieve this objective, the present invention features a single container containing a liquid having a reflective surface that reflects ultrasonic waves, and a pair of interdigital electrodes spaced apart from each other on one surface of a single piezoelectric substrate. a single ultrasonic element having an input ultrasonic transducer and an output ultrasonic transducer, the ultrasonic wave emitted from the input ultrasonic transducer into the liquid an ultrasonic delay device in which the ultrasonic element is attached to the container so that the wave is reflected by a reflective surface and then received by an output ultrasonic transducer; and an input signal of the input transducer of the device. The ultrasonic measurement device includes a phase difference detector that detects and outputs a phase difference between the output signal of the output transducer and the output signal, and detects a change in the speed of sound in a liquid as a phase difference.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the ultrasonic measurement apparatus according to the present invention, which includes an ultrasonic delay device 1 and a synthesizer 30 that provides an input signal of frequency f _r to the device.
and an attenuator 40 that attenuates the input signal to the output level of the device 1 and facilitates comparison with the output signal of the device 1 , and a phase difference between the output of the attenuator and the output signal of the device 1 is compared and detected. It has a phase difference detector 50. Note that the input signal may be directly applied to the phase difference detector without using the attenuator 40.

The ultrasonic delay device 1 has a container 10 and an ultrasonic element 20, as is clear from FIG. 1 and FIG. 2 showing a side cross section thereof.

The container 10 has a liquid inlet 10a and a liquid outlet 10.
b, and is configured so that the liquid 14 can be filled into the container. Ultrasonic element 2
0 is an input transducer constructed by providing two sets of electrodes 24 and 26 in which a pair of comb tooth-shaped electrodes are interdigitally combined on one surface of a single piezoelectric substrate 22 and spaced apart from each other. A and a transducer B for output. An input terminal 24a and a ground terminal 24b are drawn out from the input transducer A , and an output terminal 26a and a ground terminal 26b are drawn out from the output transducer B.
is pulled out, and the ground terminals of both transducers are grounded to the container 10. Ultrasonic element 20
The thickness of the piezoelectric substrate 22 is the thickness at which surface waves are excited, specifically, the thickness is several times or more (preferably 5 times or more) the wavelength of the sound wave excited in the substrate. As shown in FIG. 2, the ultrasonic element 20 having such a configuration has its electrode surface in contact with the liquid 14 in the container 10, and the sound waves from the input transducer A propagate through the liquid 14 to reach the bottom surface of the container. 12 and then received by the output transducer B.
It is attached to the container 10.

A synthesizer 30 is added to the device 10 with the above configuration.
When an _AC electric signal with a frequency fr is applied to the input transducer A , an ultrasonic beam is emitted in a direction forming an angle θ with the normal to the piezoelectric substrate 22, as shown in FIG. This radiation angle θ satisfies θ=sin ⁻¹ V _L /V _R (1), where V _L is the longitudinal wave velocity in the liquid and V _R is the surface wave velocity on the piezoelectric substrate. The ultrasonic beam emitted from the input transducer A into the liquid 14 at an angle θ is reflected by the container bottom 12, received by the output transducer B , and given to the output terminal 26a as a delayed output signal. . The speed of sound waves propagating in a liquid is affected by the elastic properties of the liquid depending on the type of liquid, temperature, pressure, concentration, etc., and the delay time of the output signal also varies depending on these factors. Therefore, by measuring the delay time and thus the phase difference of the output signal with respect to the input signal, changes in the elastic properties of the liquid 14 in the container can be observed.

In addition, when using a liquid in a fluid state, in this embodiment, which has an inlet and an outlet at the positions shown in Figs. 1 and 2, the liquid flows in the direction of propagation of the ultrasonic waves, so the flow rate is Depending on the situation, there may be a difference in the speed of ultrasonic propagation compared to the filled state. Therefore, in such cases, the inlet 1 should be provided on the side of the container and the It is effective to configure it so that it flows in from the right angle direction.

FIG. 3 shows a specific circuit example of a phase difference detector, including a pulsing circuit 501 that pulses the output signal of each ultrasonic transducer, a frequency dividing circuit 502 that divides the frequency of each pulsed output signal, and a phase comparator circuit 503 which generates pulses corresponding to phase differences from each frequency-divided output signal and outputs them as DC voltage values via an integrating circuit.

FIG. 4 is a waveform diagram in the circuit of FIG. 3, and each of the waveforms A to I shows the signal waveforms at the locations indicated by the same reference numerals in FIG.

With the configuration shown in FIG. 3, the sine wave output signals A and B of the ultrasonic sound transmitter/receiver applied to the input terminals IN-1 and IN-2 of the phase difference detector, respectively, are as follows.
The pulse signal C is pulsed by the pulse generator 501.
and D to the frequency divider circuit 502. Pulse signals C and D are frequency-divided while real frequency components are removed (E, F) in a frequency divider circuit 502. The purpose of frequency division is to expand the measurement area of the speed difference. For example, by dividing the frequency by 1/2, the measurement area will be doubled.
is converted into a pulse signal corresponding to the phase difference applied to the phase comparator circuit 503, and then supplied to the output terminal OUT as a DC voltage value corresponding thereto. In addition,
Display elements 503a and 50 in the phase comparison circuit
3b is for determining whether the phase difference between the output signals is leading or lagging. That is, the display element 503
The “ON” state of a and 503b indicates that the phase difference Δφ _a before frequency division and the phase difference Δφ _b after frequency division are in a delayed phase state, respectively. In the case of a slow phase state, it is sufficient to switch the switch SW of the circuit 502, thereby making it possible to measure the output relationship exactly the same as in the phase leading state.

If the elastic properties of the liquid in the container change with the above configuration, the velocity of the sound wave propagating in the liquid will change, and as is clear from equation (1), the radiation direction θ of the sound wave beam will change. As a result, the propagation path length L also changes. The sound velocity before the change in the elastic properties of the liquid is V _L1 ,
If the sound speed after the change is V _L2 , then the respective phase differences with respect to the input signal are φ ₁ =ωL ₁ /V _L1 φ ₂ = ωL ₂ /V _L2 . Here, ω is the angular frequency, L ₁ and L ₂ are V _L1
and V _L2 are the propagation path lengths of the acoustic beams, respectively. The difference Δφ between φ ₁ and φ ₂ above is as follows Δφ=φ ₁ −φ ₂ =2ωD/V _L1 {1−(V _L1 /V _R ) ² } ^-1/2
−2ωD／V _L2 {1−(V _L2 /V _R ) ² } ^−1/2 =2ωD(1/V _L1 ² −1/2V _R ² −9V _L1 ² ／8V _R ⁴ )ΔV _L (2) Here where D is the distance between the surface of the piezoelectric substrate and the acoustic beam reflecting surface of the container, ΔV _L =V _L1 −V _L2 .
As is clear from equation (2), a linear relationship is established between Δφ and ΔV _L.

Phase differences φ ₁ and φ ₂ corresponding to the above V _L1 and V _L2 , respectively
are output by the phase difference detection circuit 50 as DC voltages V _put-1 and V _put-2 , respectively. Here, the output voltage of the phase difference detector 50 changes in proportion to the phase difference, and when the phase difference is π, the output voltage reaches the maximum value V _nax
If so, the above Δφ and ΔV _put = V _put-1 −
The following relationship with V _put-2 is satisfied.

Δφ=π/V _nax ΔV _put (3) Therefore, by using equations (2) and (3) above and using the sound speed V _L1 as the reference value, we can calculate the change in sound speed due to a change in the elastic properties of the liquid. It becomes possible to obtain ΔV _L via a phase difference detector.

Next, an experimental example of the ultrasonic measuring device according to the present invention will be shown below.

In this experimental example, the ultrasonic element was made of TDK piezoelectric ceramic 91A material (length 25 mm,
A pair of interdigital electrodes having an electrode period of 210 μm were provided at a distance of 14 mm from each other on one surface having a width of 15 mm and a thickness of 5 mm perpendicular to the polarization axis. The ultrasonic element has an electrode surface in contact with the liquid, and the distance between the electrode surface and the sound wave beam reflecting surface of the container is 5.94 mm.
It was attached to the container so that it was mm.

With the above specifications, when using a container containing distilled water, the wavelength number of the acoustic beam at 20°C is 118.30, and in this case θ = 47.4°, L ₁ = 17.54mm, f _r =
It was 10.0MHz and V _L1 =1482.7m/s. The speed difference ΔV _L with respect to V _L1 is 12.54 m/s at Δφ=180°,
Also, the maximum output voltage of the phase difference detection circuit is Δφ=π
The voltage was 3.92V.

In order to show that such experimental results are reliable data, experimental results using this apparatus are shown below for comparison with data presented in the authoritative documents listed below.

Figure 5 shows the actual measured value of the speed difference with respect to temperature based on the sound speed in distilled water at 20°C, which is based on the published calculated value (M. Greenspan, C.
E. Tschiegg, and F. Breckenridge, The
Journal of The Acoustical Society of
America: Journal of the Acoustical Society of America, Vol. 28 (1956), No.
500 pages). Note that the points shown in the figure are actually measured values using this device, and the solid lines are calculated values from the above literature. In addition, in the characteristic diagram shown in the figure, changes in phase difference are replaced with speed differences. Therefore, it can be seen that this device can accurately measure changes in speed difference due to changes in temperature.

Figure 6 shows the measured value of the velocity difference between the sound velocity and the hydrostatic pressure in distilled water at 18°C. In this experiment, the ultrasonic delay device was placed inside a circular pressure vessel with a depth of 51 cm and an inner diameter of 16 cm. This result is based on published calculations (WD Wilson, The
Journal of the Acoustical Society of
America: Journal of the Acoustical Society of America, Vol. 31 (1959), No.
(page 1067). Note that the characteristic diagram of the measured values shown in the same figure is obtained by adjusting the temperature of distilled water to the various conditions of the above-mentioned literature. Therefore, it can be seen that this device can accurately measure changes in speed difference due to changes in hydrostatic pressure.

In the above-described embodiments, an ultrasonic delay device in which the thickness of the piezoelectric substrate is sufficiently thick compared to the period of the electrodes and the electrode surface is in contact with the filling liquid has been described as an example. Therefore, a photoresist film is applied to protect the electrodes. On the other hand, the thickness is less than λ (λ:
It is also possible to use an ultrasonic element that has poles on a thin plate piezoelectric material (the wavelength of ultrasonic waves on a piezoelectric substrate). According to this, it is possible to utilize the presence of vibrations on both sides of the piezoelectric material, so it is possible to fill the electrode surface. It has the advantage that it does not need to come into contact with liquid and there is no need to protect the electrodes. Note that in the case of a thin plate piezoelectric material, V _R in each of the above-mentioned equations must be replaced with the Lamb wave velocity.

The ultrasonic measuring device described above can be used, for example, as a temperature sensor. In this case, at least a portion of the container 10 shown in FIG. 1, preferably the acoustic beam reflecting surface of the container, is made of acrylic resin or the like to be transparent to the external heat source, and the amount of heat generated by the heat source is adjusted accordingly. It is desirable that the temperature change be applied to the liquid inside the container. Such a temperature sensor can be used as a laser power meter or a microwave oven temperature sensor. In addition, the present invention can be used for various purposes such as measuring the concentration of liquid.

As explained above, according to the present invention, an ultrasonic device is capable of measuring speed changes of ultrasonic waves propagating in a liquid with high precision using an ultrasonic transducer equipped with interdigital electrodes. Moreover, since a single ultrasonic delay device is used, the configuration of the apparatus is simplified.

[Brief explanation of drawings]

FIG. 1 is an embodiment of the ultrasonic measuring device according to the present invention, FIG. 2 is a side sectional view of an ultrasonic delay device, FIG. 3 is a specific example of a phase difference detector, and FIG. 4 is the same as that shown in FIG. The signal waveform diagrams of the circuit, FIGS. 5 and 6, are experimental examples based on the ultrasonic measuring device according to the present invention. 1; Ultrasonic delay device, A; Input transducer, B; Output transducer, 10;
Container, 14; Liquid, 20; Ultrasonic element, 22; Piezoelectric substrate, 24, 26; Interdigital electrode,
50; Phase difference detector.

Claims (1)

[Claims] 1 For input and output, consisting of a single container containing a liquid and having a reflective surface that reflects ultrasonic waves, and a pair of interdigital electrodes spaced apart from each other on one surface of a single piezoelectric substrate. a single ultrasonic element having an ultrasonic transducer of an ultrasonic delay device in which the ultrasonic element is attached to the container so as to be received by a ducer; an input signal of an input ultrasonic transducer of the device; and an output signal of an output ultrasonic transducer of the device; An ultrasonic measurement device characterized by having a phase difference detector that detects and outputs a phase difference between the two.