JPS6196452A - Sound speed/attenuation measuring method of surface elastic wave - Google Patents

Abstract

PURPOSE:To measure the sound speed of a surface elastic wave and its attenuation highly accurately by extracting only the amplitude of a reflected ultrasonic wave reflected from a sample and averaging the amplitude. CONSTITUTION:An ultrasonic lens 1 is arranged on the upper part of a measuring point F of the sample 4, and while changing a distance (z) between the focus 0 of the lens 1 and the point F of the sample 4, a piezo-electric transducer 7 is excited by a high frequency pulse echo sounder transducer to generate an ultrasonic wave and the ultrasonic wave is irradiated to the sample 4 through the lens 1 and a coupler 5. The reflected light reflected from the sample 4 is converted into an electric signal through the coupler 5, the lens 1 and the transducer 7 and the electric signal is sent to an electric computer through said pulse transmitter/receiver to record the Vz curve data of the amplitude of the reflected wave from the sample to the distance (z). Said operation is repeated plural times to obtain N Vz curve data. Similarly, reference Vz' curve data for the smooth surface of a reference sample such as lead is obtained. Operation based upon a specific formula is executed on the basis of the Vz and Vz' curve data and the sound speed of the surface elastic wave and its attenuation can be found out from the obtained power spectrum.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for measuring the sound velocity and attenuation of surface acoustic waves suitable for inspecting and evaluating surface defects of materials.

Conventional technologyUsing an ultrasonic microscope, while changing the distance z between the focal point of the ultrasonic lens and the sample surface, the amplitude V of one reflected wave is adjusted to the above distance ftz.
The resulting V (z) is measured as a function of
A method has already been proposed in which the a-velocity and attenuation of a surface acoustic wave are measured by taking the power vector of a curve and from the wave number giving its peak and the width of the peak. Furthermore, a method has been proposed in which a linear focused beam that hits the sample with a large area is used as the ultrasonic beam that irradiates the sample, and the V (z) curve is substantially averaged in one measurement.

However, the previously proposed method averages the reflected ultrasonic waves in a form that includes not only the amplitude but also the phase. In the case of a dynamic surface, it is strongly influenced by (2) periodic fluctuations in the curve, which tend to be extremely small and irregular, which poses a problem in measurement accuracy. Furthermore, in the above method, the effect of averaging is simply obtained naturally from the size of the irradiated area.

Problems to be Solved by the Invention The present invention minimizes the influence of disturbances in the reflected wave phase due to non-uniformity of the sample surface by extracting and averaging only the amplitude of the reflected ultrasonic waves reflected from the sample. The present invention provides a method for accurately measuring the sound velocity and attenuation of surface acoustic waves.

Means and Effect for Solving the Problems In order to achieve the above object, the method of the present invention uses an ultrasonic microscope to obtain V (z) curve data at each of a large number of measurement points on a sample, and calculates the V (z )'
The feature is that the curve data is Fourier-transformed, the square of the absolute value is calculated, and then averaged to obtain averaged power spectrum data, and based on this power spectrum data, the sound speed attenuation of the surface acoustic wave is determined. That is.

In such a method of the present invention, only the amplitude of the reflected ultrasound waves from the sample is extracted and averaged.

As a result, the influence of disturbances in the phase of reflected waves due to inhomogeneity in the sample is relatively small, and therefore the velocity and attenuation of surface acoustic waves can be measured with high precision.

To explain the method of the present invention in more detail, 1 the inventors:
To investigate the reflection of focused ultrasound on rough surfaces,
Impulse focused ultrasound with a center frequency of 30 MHz was incident on a soda glass placed 0.81 mm from the focal point, and the reflected waves were observed. The surface roughness when roughened with #100 SiC water-resistant abrasive paper is 5.34m Rmax
, On the other hand, the wavelength of the 1 surface acoustic wave is about 100 #L1.The 0 reflected wave is temporally separated into the directly reflected wave and the surface acoustic wave, but on a mirror surface.

These waveforms were independent of location. On the other hand, for a rough surface, the amplitude of one surface acoustic wave component was only slightly smaller than that for a mirror surface, and there was almost no variation depending on the location, but the amplitude of the directly reflected wave varied greatly depending on the location. this is,
As shown schematically in Figure 2, directly reflected waves are generated by scattering at one point on the sample surface, and reflect the heterogeneity of the surface as they are, whereas surface acoustic waves propagate over a fixed distance. This is thought to be due to the fact that local variations are averaged out.

From the above considerations, even in the V(z) curve method that uses burst signals instead of impulses, if the wavelength of the surface acoustic wave is sufficiently larger than the surface roughness, V(z) It was found that even when the shape of the curve is disordered, it is possible to measure the sound velocity attenuation of a single surface acoustic wave by removing irregularities in the directly reflected waves by averaging at different locations.

FIG. 1 shows an apparatus used for carrying out the measurement method of the present invention as described above, in which 1 is an ultrasonic lens in an ultrasonic microscope, and the tip surface of a cylindrical part 2 made of single crystal alumina, fused silica, etc. is a concave spherical surface 3, a coupler 5 made of liquid such as water is interposed between this concave spherical surface 3 and the sample 4, and a thin focused beam-shaped superwave is provided on the proximal end surface 8 on the opposite side to the concave spherical surface 3. A pressure core transducer 7 is attached to generate pressure, a high frequency pulse transducer is connected to this transducer 7, and the piezoelectric transducer 7 is connected from the transducer to the transducer 7.
The transducer is configured to transmit an electrical pulse signal to the piezoelectric transducer 7 and to receive an electrical pulse signal from the piezoelectric transducer 7.

Furthermore, an image recording and display unit and a total of 32 electronic devices are connected to the transducer.

The ultrasonic microscope described above is equipped with a lens scanning mechanism similar to that in a general-purpose ultrasonic microscope, and the lens l is placed on the sample 4.
The lens 1 is configured to be able to move toward and away from the sample 4 along an axis perpendicular to , and to be able to move in parallel along a plane parallel to the sample 4.

The measuring method of the present invention has the above configuration. This is implemented by 1tWk as follows.

First, the ag wave lens 1 is positioned above the measurement point F in the sample number, and while the ultrasonic lens l is displaced only in the vertical direction, that is, the distance between the focal point 0 of the ultrasonic lens l and the point F on the sample 4 is While changing the distance 2 between
Let it irradiate for $44 through the lens. Contrary to the above, the reflected wave reflected from the sample 4 is transmitted to the transducer 7 through the coupler 5 and the ultrasonic lens 1, and the electrical signal from the transducer 7 is transmitted to the computer through the transducer. , V (Z) curve data representing the dependence of the amplitude of the reflected wave from the sample 4 on the distance z is recorded.

Furthermore, the ultrasonic lens 1 is moved to another measurement location on the sample 4, the above measurement operation is performed, and a new V (z)
get a curve. By repeating this several times, 1, for example, N
V (z) curve data are obtained.

In addition, the same measurement operation as above was performed on the smooth surface of a standard sample such as lead, in which surface acoustic waves are difficult to be excited, in place of sample 4, and as a result, l(
l! Obtain standard V(z) curve data for I.

N v(2) in the sample reef thus obtained
From the curve data, subtract the standard V(z) curve data in the standard sample as the background.
N(11)Vi(z) (i ! l , 2 , @
・, N) Obtain curve data, and calculate the averaged power spectrum F (k) from the data using the following equation (1).

here.

k: wave number z+: This is the measurement range of the V(z) curve.

The calculation using equation (1) above is performed for each V (z
) represents signal processing in which a power spectrum is obtained by Fourier transforming each curve data and then averaged.

Then obtained in this way. With the fri k layer on wave 1 giving the maximum f11 of the peak of the power spectrum I.

The background at the hem of the peak has no effect! Select a value of T that is as large as possible from the above, and find the radiation Δk where the power spectrum F becomes one-half of the maximum value. Using these values, the sound velocity vμ attenuation α of one surface acoustic wave can be obtained from the following equation.

COjθ, xt−, vohatcr (
2) V, x Vo/5inO, (3) a-Δ”k/2(T-1j' (4)
α = Enter, /2tc tan O, (a/2+
ay/cos θ, ) (5) where, θ, critical angle of two-surface acoustic wave excitation vo: +1 speed f in coupler: T74 wave number of a sound wave, wavelength of two-surface acoustic wave αw: reduction R in coupler It is a constant.

Examples Two types of samples with non-uniform surfaces were used: a soda glass surface polished with No. 320 SiC abrasive paper to give Rmax of 2.5 GBm and Ra O of 27p, and a polypropylene surface. , by sliding it with copper and applying F! to its surface. A sample with I scratches formed thereon was used. For these samples, 20 ($9 V (z)
The curve was measured. Figure 3 A, H
As can be seen in Figure 0, the V(z) curve fluctuates irregularly depending on the location, reflecting the inhomogeneity near the sample surface, and as it is, the measured value of the surface acoustic wave sound velocity Mg is not reliable. You can't ask for it.

Figure A shows the results of calculating the averaged power spectrum using equation (1) above using 5, 10, or 20 of the 20 V (z) curve data obtained for each sample. , H. From these figures, a single peak is obtained regardless of whether soda glass or polypropylene is used as the sample, and the shape of the peak is also the same when a homogeneous material is used as the sample. It is understood that the shape is close to that of the obtained peak.

Effects of the Invention As described above, according to the present invention, a power spectrum with clear peaks can be obtained even when the sample is highly heterogeneous. Therefore, according to the present invention, it is possible to evaluate the elastic properties of the surface of a heterogeneous material such as a porous ceramic, a processed surface having roughness or defects near the surface, or a sliding surface.

[Brief explanation of drawings]

Fig. 1 is an overall configuration diagram of the apparatus used to implement the present invention, Fig. 2 is a schematic explanatory diagram of reflected waves on a rough sample surface,
fiIJ3 diagrams A and B are diagrams showing V (z) curves measured in different samples, respectively, and WS4 diagrams A and B are diagrams showing power spectra calculated based on the above V (z) curves. 4Φ・Sample. IFJ Figure 2 OC Figure 3 Distance #Z (fml Distance Z (/””)

Claims (1)

[Claims] 1. Using an ultrasound microscope, determine the amplitude of reflected ultrasound at a number of measurement points on the sample as V(z) curve data, which is a function of the distance z between the ultrasound lens and the sample, and calculate those V(z) curves. The feature is that the data is Fourier transformed, the square of the absolute value is calculated, and then averaged to obtain averaged power spectrum data, and based on this power spectrum data, the sound speed attenuation of the surface acoustic wave is determined. A method for measuring the sound velocity and attenuation of surface acoustic waves.