JPH0472558A - Sound wave measuring device - Google Patents

Abstract

PURPOSE:To directly measure the sound wave of a couplant interposed between a probe and a sample by exciting an ultrasonic probe to transmit ultrasonic wave, and then receiving this signal while shifting the ultrasonic probe, and calculating the peak frequency of the high frequency signal. CONSTITUTION:A peak frequency fmax corresponds to the cycle DELTAZo of the high frequency components Vh(z) of a V(z) curve indicating the (z) position of a probe 4 and fmax = 1/DELTAZo, so DELTAZo is calculated from fmax; i.e. each time the probe 4 moves lambda/2 in the direction of Z-axis, the V(z) curve is periodically fluctuated by the influence of the interference between direct reflected wave from a sample 6 and reflected wave from the lens boundary surface of the probe 4, so DELTAZo = lambda/2. The sound velocity of ultrasonic wave within a couplant 5 is calculated from a relational expression C = 2.DELTAZo.F since a general relational expression is C = lambda.F(F is the frequency of the ultrasonic wave).

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a sound velocity measuring device for measuring the sound velocity of a liquid called a coupler which is interposed between a probe of an ultrasonic microscope and a sample.

B. Prior Art Conventionally, the sound velocity of a sample has been measured by obtaining a V (z) curve using an ultrasonic microscope. FIG. 2 is a diagram showing a schematic configuration of an ultrasonic microscope for measuring the V(z) curve. Hereinafter, the operation of observing a sample using the ultrasonic microscope will be explained with reference to this diagram. .

A medium (for example, water) 5 called a coupler is dropped onto a sample 6 placed on a sample stage 10, and an ultrasonic probe (transmission/reception type) 4 is brought into contact with the sample. A burst electrical signal is applied from a transmitter 1 to a probe 4 via a circulator 3. The probe 4 converts the electrical signal into an ultrasonic signal, focuses the ultrasonic signal with a lens provided at the end of the probe 4, and makes the ultrasonic signal enter the sample 6 via the coupler 5. The ultrasonic signals reflected and scattered by the surface layer of the sample 6 enter the same lens, are converted into electrical signals by the probe 4, and are then transmitted to the receiver 2 via the circulator 3. The electrical signal sent to the receiver 2 is suitably amplified and sent to the peak detector 7.

At this time, the directly reflected wave 14 near the center of the lens from the sample surface shown in FIG. 7 interferes with the surface acoustic wave 15, and the phase difference between the two causes a large amplitude change in the interference wave as shown in FIG. happen. This interference wave is converted into an electrical signal and transmitted to the receiver 2 via the circulator 3.

In this state, the distance between the probe 4 and the sample 6 is determined by the CPU.
Control signal (pulse) from controller 13 according to command from 9
When the peak value obtained from the peak detector 7 is measured by transmitting the wave in a fixed direction by the two-axis moving device W11, the peak value changes due to the phase change between the directly reflected wave and the surface acoustic wave described above. Therefore, this peak value is A/
When the CPU 9 takes in the data through the D converter 8 and displays it on the display 12, a curve as shown in FIG. 9 is obtained. This is called a V (z) curve, where the vertical axis is the peak value ■, and the horizontal axis is the distance 2 between the probe 4 and the sample 6. Note that the value of Z is negative in the direction from the focal position of the lens of the probe 4 toward the sample 6, and normally only negative values are measured. This V(z) curve has a shape that depends on the sound velocity of the surface acoustic wave of sample 6, and therefore, the shape of sample 6, which is the measurement target,
The sound velocity of the surface acoustic wave of the sample 6 can be measured by finding the V(z) curve. Specifically, sample 6
The sound velocity Cr of the surface acoustic wave is determined. Here, Cw is the sound speed of the coupler 5, F is the frequency of the ultrasonic wave, and Δ2 is V
(z) is the period of the curve (see Figure 9). Therefore, using accurate values of Cw, F and Δ2
This will improve the accuracy of r. Here, the value of Cw is
Measure the temperature of the couplant 5 at the time of measurement, and
It is determined from the temperature-sound velocity characteristic diagram of the coupler 5 as shown in the figure, and Cr is calculated from the above equation.

C0 Problems to be Solved by the Invention Conventionally, the temperature of the coupler 5 has been obtained by, for example, disposing a minute thermocouple on the coupler 5 and actually measuring the temperature of the coupler 5. However, although it is a minute thermocouple, there is no guarantee that it will be able to measure the temperature of the part that actually contributes to the sound velocity Cr of the sample 6. In particular, depending on the frequency used, the temperature of the part between the probe 4 and the sample 6 may be measured. In some cases, the distance becomes extremely short and it is not possible to install a thermocouple on the coupler 5. Furthermore, the composition of the coupler used is not necessarily the same as the composition of the coupler from which the calibration graph of FIG. 10 is created.

An object of the present invention is to provide a sound speed measuring device that can directly measure the sound speed of a campplant interposed between a probe and a sample.

00 Means for Solving the Problems The present invention will be explained with reference to the claim correspondence diagram in FIG. A moving unit 102 that moves the probe 101 in a direction perpendicular to the surface of the sample, a transmitting unit 103 that causes the ultrasonic probe 101 to generate ultrasonic waves, and a receiver that receives signals from the ultrasonic probe 101. Means 104;
V obtained by receiving a signal with the receiving means 104 while moving the ultrasound probe 101 with the moving means 102
(z) extraction means 105 for extracting high frequency components of the curve; peak frequency calculation means 106 for calculating the peak frequency of the high frequency signal obtained by this extraction means 105; It is composed of calculation means 107.

Further, the invention of claim 2 provides the ultrasonic probe 101, the moving means 102, the transmitting means 103, the receiving means 104, and the moving means 102, as shown in FIG. 1(b). While moving the probe 101, the receiving means 104
A frequency analysis means 201 performs frequency analysis of the V (z) curve obtained by receiving a signal at and a sound speed calculation means 203 that calculates the sound speed of the coupler from this true peak frequency.

81 Effect The V (z) curve mentioned above is affected not only by the direct reflected wave from the sample but also by the reflected wave from the interface between the probe lens surface and the coupler, and the difference between these reflected waves and the sample Interference with surface acoustic waves appears as a V(z) curve. Now, if the wavelength of the ultrasonic wave is λ and the probe is moved by λ/2 in the Z-axis direction, there will be λ between the direct reflected wave from the sample and the reflected wave from the probe lens interface. A phase difference of . On the other hand, changes in surface acoustic waves are not so sensitive to changes in This can be considered to be caused by interference. Therefore, the high frequency components of this V (z) curve are extracted by the extraction means 105, or the V (z) curve itself is frequency analyzed by the frequency analysis means 201, and these peak frequencies are calculated by the peak frequency calculation means 106 or the peak frequency determination means. It is determined by means 202. Since this peak frequency is the reciprocal of the period of the interference wave, V
(z) The period ΔZo of the curve is determined, therefore.

The sound velocity of the coupler can be determined from equation (1), which will be described later.

F. Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to one drawing.

The overall configuration of the sound speed measuring device according to the present invention is based on the second
The configuration is almost the same as that of the ultrasonic microscope shown in the figure, and therefore, the same components are given the same reference numerals and will be explained with reference to FIG.

In this embodiment, the transmitter 1 has two
It is configured to be able to send out various types of burst-like electrical signals. These two types of burst waves are
By lengthening t@ (duration time), the direct reflected wave from the sample 6 and the reflected wave from the lens boundary surface of the probe 4 can interfere with each other, and the width of the other one is shortened. This makes it difficult for the directly reflected wave from the sample 6 and the reflected wave from the lens boundary surface of the probe 4 to interfere with each other. The width of each of these burst waves is a value that depends on the physical property values of the lens material, the resonance center frequency of the probe 4, etc., and is appropriately selected and determined for each device.

Further, the CPU 9 is equipped with a memory, which is used for temporarily storing the V (z) curve, storing programs, etc., which will be described later.

Next, with reference to the flowchart shown in FIG. 3 and FIG. 4, a procedure for measuring the speed of sound using the apparatus of this embodiment will be described.

(a) When the first V (z) curve measurement program is started, the CPU 9 instructs the transmitter 1 to transmit a short burst wave, and based on this, the transmitter 1 transmits a short burst wave. A burst wave-like electrical signal is transmitted (step S1).

The burst wave electrical signal is transmitted via the circulator 3 to the probe 4, where it is converted into an ultrasonic signal and transmitted via the coupler 5 to the sample 6. The ultrasonic signals reflected and scattered by the surface layer of the sample 6 and the signals reflected by the lens interface of the probe 4 are received by the same probe 4 and converted into electrical signals, and then sent to the circulator 3.
is transmitted to receiver 2 via (step S2). The signal transmitted to the receiver 2 is stored in the memory of the CPU 9 in pairs with 2 positions via the peak detector 7 and the A/D converter 8 (step S3). Step S4) is repeated until the first V (z)
get a curve. In this first V(z) curve, since the width of the burst wave that is the transmitted signal is short, the direct reflected wave from the surface of the sample 6 and the reflected wave from the lens interface of the probe 4 do not interfere with each other. This is a curve without high frequency components as shown in FIG. 4(a).

(b) After returning the two positions of the second V (z) curve measurement probe 4 to the original initial position, the CPU
9 instructs the transmitter 1 to transmit a burst wave with a long width, and based on this, the transmitter 1 transmits a burst wave with a long width (step S5). The burst wave is transmitted and received by the probe 4 through a process similar to that described above,
After being converted into an electrical signal, it is transmitted to the receiver 2 via the circulator 3 (step S6). The signal transmitted to the receiver 2 is transmitted to the peak detector 7 and the A/D as described above.
The data is stored in pairs in two positions in the memory of the CPU 9 via the converter 8 (step S7). This process is repeated until 2 reaches a predetermined distance (step S8).

Obtain a second V(z) curve. This second V(z) curve is different from sample 6 because the width of the burst wave, which is the transmitted signal, is long.
The influence of interference between the direct reflected wave from the surface and the reflected wave from the lens interface of the probe 4 is large, and the curve has high frequency components as shown in FIG. 4(b).

(c) High frequency component extraction Next, the CPU 9 extracts the first V(z) curve from the second V(z) curve.
By subtracting the value of the V(z) curve, the high frequency component Vh (z) of the V(7,) curve as shown in FIG. 4(c) is extracted (step S9). Naturally, a similar result can be obtained by sampling only the second V (Z) curve and passing it through a bypass (high-pass) filter without performing such subtraction.

(d) Frequency analysis By performing an FFT (fast Fourier transform) operation on the high frequency component Vh (z) of the V (z) curve, frequency analysis of this high frequency component is performed (Step S] ○).

As a result, a frequency analysis result Fh (f) as shown in FIG. 4(d) is obtained. At this time, the value f on the horizontal axis is 1
/ΔZo.

(e) Peak frequency calculation, sound velocity calculation The result of frequency analysis Fh (f
), its peak frequency f wax is determined (step 511). The peak frequency can be determined in any way,
There are no limitations whatsoever. As mentioned above, the peak frequency f a+ax is the high frequency component Vh (z) of the V (z) curve.
), and more precisely, from the above relationship, f
Since n+ax=1/ΔZo, ΔZo is calculated conversely from f wax (step 511).

As already mentioned, the direct reflected wave from the sample 6 and the probe 4
Due to the interference with the reflected wave from the lens boundary surface, the V(z) curve periodically changes every time the probe 4 moves by λ/2 in the Z-axis direction. That is, −ΔZo=λ/2,
The sound speed of the ultrasonic wave in the coupler 5 is expressed by the general relation C=λ
・F (F is the frequency of the ultrasonic wave), so the sound speed of the couplant 5 can be calculated from the relational expression: C=2・ΔZo・F − (1) (step 512).

The sound velocity of the coupler 5 can be determined by the procedure described above. Therefore, according to the device of this embodiment, unlike the conventional sound speed measurement, the sound speed of the coupler 5 can be directly measured. As a result, when measuring the sound velocity of a surface acoustic wave of a sample using an ultrasonic microscope, there is no need to insert a thermocouple, and the sound velocity of the coupler 5 can be measured accurately and reliably under any conditions.

In particular, in this embodiment, the equipment of an ultrasound microscope is used, and there is almost no need for additional equipment, so it is easy to apply to ultrasound microscopes that are actually used. , it also has great cost advantages.

Next, FIG. 5 is a diagram showing a processing procedure of a sound speed measuring device according to a second embodiment of the present invention. The only difference between the apparatus according to this embodiment and the apparatus according to the first embodiment is the procedure for measuring the speed of sound.

This will be explained with reference to the flowchart shown in FIG. 5 and FIG. 6.

(b) Temporary peak frequency input As mentioned above, the sound speed of the coupler 5 is C=2・ΔZO・F
The following relational expression holds true, and the sound speed of the coupler 5 can be roughly estimated using the above-mentioned calibration curve. Therefore, using this, a temporary peak frequency (more precisely, the period ΔZO' of the high frequency component of the temporary V (z) curve) is calculated in advance, inputted as the temporary period ΔZo', and read in in step S21. It is stored in the memory within the CPU 9.

(b) Measurement of V (Z) curve The CPU 9 instructs the transmitter 1 to transmit a burst wave with a long width, and based on this, the transmitter 1 transmits a burst wave with a long width (step 522 ), the burst wave is transmitted to the probe 4 via the circulator 3,
Here, it is converted into an ultrasonic signal and transmitted to the sample 6 via the coupler 5. The ultrasonic signals reflected and scattered by the surface layer of the sample 6 and the signals reflected by the interface of the probe 4 are received by the same probe 4, converted into electrical signals, and then sent through the circulator 3. and is transmitted to receiver 2 (step 523). The signal transmitted to the receiver 2 is stored in pairs with two positions in the memory of the CPU 9 via the peak detector 7 and the A/D converter 8 (step 524). Step 52 of repeating this until 2 reaches a predetermined distance.
5) Obtain the V(z) curve. This V (z) curve is affected by the interference between the direct reflected wave from the surface of the sample 6 and the reflected wave from the interface of the probe 4, as mentioned above, because the width of the burst wave that is the transmitted signal is long. This is a curve in which there is a large high frequency component as shown in FIG. 6(a).

In addition, when inputting the above-mentioned temporary period ΔZo', the period ΔZo' may be directly measured by visual inspection or the like from the V (z) curve obtained in this manner, and the value may be input.

(c) Frequency analysis Frequency analysis of the V(z) curve is performed by performing FFT (fast Twolier transform) on the values of the V(z) curve (step 826). As a result, a frequency analysis result F(f) as shown in FIG. 6(b) is obtained. The value f on the horizontal axis at this time corresponds to 1/ΔZo'.

(d) Peak frequency determination, sound velocity measurement Results of frequency analysis F In (f), find the peak value of the frequency analysis near the tentative peak frequency f″wax (=1/ΔzO′) input in advance, and use this as the true value. The peak frequency is set to f wax (step 527).The range for determining the peak value can be determined in any way, but for example:
Find the valley of the frequency analysis value around the tentative peak frequency f'o+ax (see G1 and β1 in Figure 6(b)), and calculate [G
1. [G2. Preferred methods include determining the peak value within the range of β2.

Then, as in the case of the first embodiment, fmax=1/Δ
Since Zo', ΔZO is calculated conversely from fmax (step 527), and based on this, the sound velocity of the coupler 5 can be calculated from the above-mentioned relational expression (step 828).

Therefore, this embodiment can also provide the same effects as the first embodiment.

In one or more embodiments, the reflected wave from the lens boundary surface of the probe 4 and the reflected information from the sample were described as interfering with each other, but instead of the reflected wave from the lens boundary surface of the probe 4, the reference wave It is clear that it is also possible to interfere by inputting separately as . Further, the details of the sound velocity measuring device of the present invention are not limited to the above-mentioned embodiments, and various modifications are possible.

G3 Effects of the Invention As explained in detail above, the sound speed measuring device of the present invention, unlike conventional sound speed measurements, can directly measure the sound speed of Camplant, and does not require the trouble of inserting a thermocouple. At the same time, it is possible to accurately and reliably measure the sound velocity of the couplant under any conditions.

[Brief explanation of the drawing]

FIG. 1 is a complaint correspondence diagram. Fig. 2 is a schematic diagram showing the overall configuration of an ultrasonic microscope that can be used as a sound speed measuring device according to the present invention, Fig. 3 is a flowchart showing the procedure for measuring sound speed according to the same embodiment, and Fig. 4 is according to the same embodiment. A diagram for explaining the procedure for measuring the speed of sound, FIG. 5 is a flow chart showing the procedure for measuring the speed of sound by the sound speed measuring device according to the second embodiment of the present invention, and FIG. 6 is a diagram for explaining the procedure for measuring the speed of sound according to the same embodiment. Figure 7 is a diagram showing the relationship between reflected waves and surface waves in an ultrasound microscope.
FIG. 8 is a diagram for explaining the interference state between a reflected wave and a surface wave, FIG. 9 is a diagram showing a V (z) curve, and FIG. 10 is a diagram showing an example of a calibration curve of a coupler. 107.203: Sound speed calculation means 202: Peak frequency determination means 201: Frequency analysis means

Claims (1)

[Claims] 1) A device for measuring the sound velocity of a coupler interposed between an ultrasonic probe and a sample, the device comprising: an ultrasonic probe; a moving means for moving in a direction perpendicular to the surface; a transmitting means for exciting the ultrasonic probe to transmit ultrasonic waves; a receiving means for receiving a signal from the ultrasonic probe; and the moving means. an extraction means for extracting a high frequency component of a V(z) curve obtained by receiving a signal with the receiving means while moving the ultrasonic probe; and a peak frequency of the high frequency signal obtained by this extraction means. A sound speed measuring device comprising: a peak frequency calculation means for calculating the sound speed of the coupler; and a sound speed calculation means for calculating the sound speed of the coupler based on the peak frequency. 2) A device for measuring the sound velocity of a coupler interposed between an ultrasonic probe and a sample, which includes an ultrasonic probe and an ultrasonic probe placed in a direction perpendicular to the surface of the sample. a moving means for moving the ultrasonic probe; a transmitting means for exciting the ultrasonic probe to transmit ultrasonic waves; a receiving means for receiving signals from the ultrasonic probe; frequency analysis means for performing frequency analysis of a V(z) curve obtained by receiving a signal with the receiving means while moving the child; A sound speed measuring device comprising: a peak frequency determining means for determining a true peak frequency; and a sound speed calculating means for determining the sound speed of the coupler based on the true peak frequency.