JPH0560551B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ultrasonic imaging method that uses ultrasonic waves to visualize the shape and internal state of an object.

(Prior Art) A surface acoustic wave interdigital transducer effectively functions for emitting or receiving longitudinal sound waves into a liquid. Focusing on this point, various ultrasound imaging methods using interdigital transducers have been proposed. As an example, JP-A-58
-Disclosed in Publication No. 22978.

(Problems to be Solved by the Invention) However, in such conventional ultrasound imaging methods, the sound waves reflected by the subject are received by the interdigital transducer as acoustic image information of the subject. The intensity (amplitude) of the converted electrical signal was used.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic imaging method that can detect elastic changes in a subject with higher sensitivity than when the amplitude of an electrical signal is used as acoustic image information of the subject.

(Means for Solving the Problems) The present invention provides an ultrasonic device that is composed of a piezoelectric substrate and a plurality of sets of arch-shaped interdigital electrodes provided on one surface of the piezoelectric substrate, which is opposed to a subject through a liquid medium. An input electric signal is applied to a predetermined arch-shaped interdigital electrode to emit ultrasound into the liquid medium, and the ultrasound reflected by the object is received by the remaining arch-shaped interdigital electrodes. The output electrical signal obtained is extracted for the desired time through the gate circuit,
This is an ultrasound imaging method that obtains acoustic image information of a subject by determining the phase difference between the extracted output electrical signal and the input electrical signal or the phase difference between the output electrical signals.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a plan view of a configuration example of a Lamb wave device, which is one of the ultrasonic devices used in the present invention. The Lamb wave device 10 includes a piezoelectric body 12 made of a thin plate-like piezoelectric material having a polarization axis perpendicular to its surface, and four sets of arch-shaped comb-tooth electrode fingers arranged interdigitally. It is formed of interdigital electrodes 14a, 14b, 14c, and 14d. Also, 16a, 16b, 16c, 1
6d, 16e, and 16f are terminals, respectively. The thickness of the piezoelectric body 12 is within a range in which waves propagating through the thick electric body can be treated as Lamb waves having dispersion characteristics. Arch-shaped interdigital electrodes 14a, 14b, 14c, 14
d is formed by vacuum-depositing a metal such as aluminum on one surface of the piezoelectric body 12, for example.

FIG. 1 is a diagram showing the configuration of an embodiment of the ultrasound imaging method according to the present invention. In the figure, terminals 16d and 16f of the Lamb wave device 10 are connected to the input terminal 18, and the terminal 16e is grounded. Further, the terminals 16a and 16c are connected to the input terminal of the amplifier circuit 20, and the terminal 16b is grounded. The Lamb wave device 10 and the subject 22 are spaced apart from each other via a liquid layer as shown. The liquid may be anything that does not easily absorb ultrasonic waves, such as water, ether, acetone, or glycerin, and may be in the form of a gel or grease. Phase comparator 24
has a gate circuit inside. This gate circuit receives and converts electrical signals for a predetermined period of time from the ultrasonic wave 26 emitted from the input-side arch-shaped interdigital electrode, which is reflected by the subject 22 and received by the output-side arch-shaped interdigital electrode. Let it pass. and,
The phase comparator 24 receives the electrical signal (hereinafter referred to as a delayed signal) output from the gate circuit and the input terminal 1.
The phase difference with the electric signal (hereinafter referred to as a reference signal) applied to The display 28 is configured using, for example, an X-Y recorder, and displays an image of the subject 22 based on the phase difference.

In this way, between the reference signal and the delayed signal,
Since there is a phase difference that depends on the surface roughness of the object 22, internal strain, and elastic properties, the object 22 can be imaged by obtaining this phase difference. In particular, by passing a delayed signal through a gate circuit for a predetermined time,
It is possible to set a point to be imaged (for example, the surface or a point within several μm from the surface).

FIG. 3 is a circuit diagram of the amplifier circuit 12 and phase comparator 24 shown in FIG. 1. The phase comparator 24 includes a gate circuit 30, a flip-flop circuit 32, a phase comparison circuit 34, and an integration circuit 36. Specifically, the gate circuit 30 is configured as shown in FIG. The gate circuit 30 includes an analog switch circuit 38 whose purpose is to input a delayed signal of a desired time to the phase comparison circuit 34 by opening the gate for an arbitrary time. The operating principle of this circuit is as follows.

1A is always kept at a high level. When a trigger is input to 1B and becomes a high level, the AND circuit outputs a high level and the first stage pulse rises. When the pulse falls and becomes a low level, a high level is input to 2A via the inverter. Since a high level is always input to 2B, the second stage pulse rises when the first stage pulse falls. The second stage pulse is input to the relay circuit, and the gate is opened by the width of the pulse, allowing the input signal to pass (see Figure 6). The pulse widths of the first and second stages are given by the following equations.

T = 0.82RC (1 + 0.2/R) R: kΩ, C: pF, T: ns Returning to Figure 3, if a reference signal from an oscillator (not shown) is input to CH1 and a delayed signal is applied to CH2, the integrator circuit A DC signal corresponding to the phase difference between the two signals is detected from the output of 36. FIG. 4 is an operation timing diagram of the circuit shown in FIG. 3. Third
A to H in the figure correspond to A to H in FIG. 4. 2
The two signals are amplified to a logic level by an amplifier circuit 20, passed through a gate circuit 30, then shaped into a rectangular wave, and frequency-divided by a flip-flop circuit 32. The two signals output from the flip-flop circuit 32 are phase-compared by a phase comparison circuit 34,
It is output as a pulse corresponding to the phase difference. This pulse is integrated by an integrating circuit 36, and finally a DC output voltage corresponding to the phase difference between the signals applied to the two channels can be obtained from the output of the integrating circuit 36. A linear relationship exists between this phase difference and the output voltage. In this case, since the frequency is divided by 1/2 in the circuit shown in FIG. 3, the output voltage is maximum when the phase difference is 360 degrees.

Next, the operation will be explained. The electrical signal applied to the input arch-shaped interdigital electrode via the input terminal 18 is converted into an ultrasonic wave (longitudinal wave), which is then radiated into the liquid according to the equation.

θ ₁ = sin ^-1 (V _C /V _L ) Here, θ ₁ is the angle between the normal to the solid-liquid interface and the radiation direction of the sound wave, and V _C is the speed of the ultrasonic wave 26 propagating in the liquid. , and V _L are the propagation speeds of the leakage Lamb waves propagating through the piezoelectric body 12 . The ultrasonic waves 26 thus emitted are reflected on the surface or inside of the subject 22, received by the arch-shaped interdigital electrode on the output side, and converted into electrical signals. Among the delayed signals thus obtained, the phase comparison circuit 34 detects the phase difference between the delayed signal and the reference signal after a predetermined period of time has elapsed from the time when the reference signal was applied due to the action of the gate circuit. An output voltage corresponding to the phase difference is obtained. The display 28 images the subject 22 based on this output voltage. Note that scanning of the subject 22 is performed by moving the subject 22 parallel to the boundary surface of the piezoelectric body 12. Further, since the Lamb wave device 10 has the velocity dispersion property of a Lamb wave, the radiation direction θ ₁ of the ultrasonic wave can be changed by changing the frequency of the reference signal.

One embodiment of the present invention has been described above. As another embodiment, instead of connecting two sets of arch-shaped interdigital electrodes in parallel as output side electrodes in the Lamb wave device 10 as in the above embodiment, they are used separately to generate two delayed signals. It can be configured to detect. In this case, in FIG. 1, consider the phase difference when a longitudinal wave propagating through the subject 22 at a radiation angle θ ₂ is reflected by planes A and B, which differ by height δH. Assuming that the phases φ _A and φ _B of the two reflected waves are the velocity V _B of the transverse wave in the object 22 and the strokes L _A and L _B , φ _A = ω (t ₀ − L _A /V _B ) φ _B = ω (t ₀ −L _B /V _B ), so the phase difference δφ is δφ=φ _A −φ _B ω/V _B (L _B −L _A ) (0≦δφ≦2π) .

Therefore, by providing two amplifiers for the delayed signals received by the two sets of arch-shaped interdigital electrodes, and connecting the outputs of these amplifiers to CH1 and CH2 shown in FIG.
2 can be visualized.

In addition, although the above embodiment has a configuration using a Lamb wave device, a device using Rayleigh waves,
That is, it can be carried out in the same way even if an ultrasonic device using a thick piezoelectric material is used. Furthermore, although the case where there are four sets of arch-shaped interdigital electrodes has been described as an example, the present invention can be similarly implemented with other numbers of sets.

Note that experimental results based on the above embodiments (FIGS. 1 and 2) are shown below. Here, the device used for the experimental results was a thin plate piezoelectric ceramic (TDK 91
-A material, thickness 0.2mm), the distance between opposing electrodes is
It has four sets of arch-shaped interdigital electrodes with a diameter of 7.0 mm, an aperture angle of 60°, and an electrode period of 0.8 mm. First of all, the seventh
The figure shows a block diagram of aluminum used as the specimen. A non-through hole is provided in the center, and 30 μm thick copper foil is glued to the ends. FIGS. 8 and 9 are diagrams showing the video results according to this embodiment. A thermal pulse was applied to the copper foil in FIG. 7 by periodically discharging the electrical energy stored in the capacitor, and what kind of elastic change occurred was observed. FIG. 8 shows the heat pulse applied to the object before the heat pulse was applied, and FIG. 9 shows the heat pulse applied to the object after charging at 25.7V. In this way, it can be seen that the method of the present application makes it possible to detect minute elastic changes.

(Effects of the Invention) As explained above, according to the present invention, the ultrasonic reflecting part (the wall of the container)
The method used to measure how the propagation speed of ultrasonic waves propagating in liquid is affected by changes in temperature, concentration, etc. is not a problem, but in the present invention, it has been further improved to measure the propagation speed of ultrasonic waves in liquid. Propagation is considered to be negligible, and the resolution of the acoustic image can be greatly improved by the arm-shaped interdigital electrode structure. It is possible to visualize the acoustic image of the object by detecting the change in the reflected signal due to the difference in the elastic properties of the ultrasonic wave in the object from the phase difference.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a plan view of a Lamb wave device, FIG. 3 is a circuit diagram of the amplifier circuit and phase comparator shown in FIG. The diagram shows the operation timing of the circuit in Figure 3, Figure 5 is a circuit diagram of the gate circuit shown in Figure 3, Figure 6 is an operation time chart of the gate circuit, and Figure 7 is the aluminum block used as the test object. Figures 8 and 9 are diagrams showing video results according to this embodiment. 10... Lamb wave device, 12... Piezoelectric body, 1
4a, 14b, 14c, 14d... arch-shaped interdigital electrode, 16a, 16b, 16c, 16d, 1
6e, 16f... terminal, 18... input terminal, 20
... Amplification circuit, 22 ... Test object, 24 ... Phase comparator, 26 ... Ultrasonic wave, 28 ... Display device.

Claims (1)

[Claims] 1. An ultrasonic device consisting of a piezoelectric substrate and a plurality of sets of arch-shaped interdigital electrodes provided on one surface of the piezoelectric substrate is installed so as to face the subject through a liquid medium, and This is a delayed signal obtained by applying an input electrical signal that is a reference signal, emitting ultrasonic waves to the liquid medium, and receiving the ultrasonic waves reflected by the object with the remaining arch-shaped interdigital electrodes. Acoustic image information of the subject is obtained by extracting the output electrical signal via a gate circuit for a desired time and determining the phase difference between the extracted output electrical signal and the input electrical signal or the phase difference between the output electrical signals. An ultrasonic imaging method characterized by: