JPH03272454A - Ultrasonic measuring apparatus - Google Patents

Abstract

PURPOSE:To measure an absorption coefficient in a wide frequency range at high speed by a method wherein an ultrasonic pulse is allowed to be incident on a sample and the reflected wave thereof is converted into an electric signal to extract the reflected wave components from the surface and rear of the sample and the components are respectively converted into power spectra to perform operation. CONSTITUTION:The electrical pulse signal transmitted from a pulse transmitting part 1 is subjected to electroacoustic conversion by a transducer 2 and an ultrasonic pulse is allowed to be incident on a sample 5 from an acoustic lens 3. The reflected wave from the sample 5 is again converted to an electric signal which is, in turn, inputted to a preamplifier 6 to be supplied to a gate part 7. The reflected wave component from the surface or rear of the sample 5 is extracted and recorded on the memory of a computer 10 through a sampling part 8 and an A/D converting part 9. Fast Fourier transform is applied to the reflected wave component in the computer 10 to calculate a power spectrum. By this method, the absorption coefficient of the sample in a wide frequency range can be measured at high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ultrasonic measuring device that can measure the absorption coefficient of sound waves of a measurement object in measurement using ultrasonic waves.

[Conventional technology]

Conventionally, resonance method is known as a method of measuring the absorption coefficient of sound waves of a measurement object using ultrasonic waves.

FIG. 10 shows an example of the configuration of an absorption coefficient measuring device using the above resonance method. This device includes a transmitter 10 that can vary the frequency.
The transmitted wave outputted from the ultrasonic probe 102 is manually applied to the ultrasonic probe 102, where the electroacoustic converted ultrasonic waves are incident on the sample 103. The ultrasonic waves incident on the sample 103 propagate through the sample 103 and then are converted into electrical signals by the ultrasonic probes 104 placed opposite to each other with the sample 103 in between. The electrical signal converted by the ultrasonic probe 104 (hereinafter referred to as a "received signal") is sent to the oscilloscope 1 via a preamplifier 105.
06 is input.

Here, the ultrasonic waves incident on the sample 103 are transmitted to the transmitter 101
By changing the frequency of the transmitted wave output from (
1) It resonates at the frequency f expressed by the formula.

f −n v / 2 d (n=1.2 = i
-(1) Note that V indicates the sound velocity of the sample, and d indicates the thickness of the sample.

Therefore, when the frequency is changed continuously, the strength of the received signal peaks at the frequency of equation (1), and the oscilloscope
The spectrum displayed in 6 is as shown in FIG. The frequency of one of the multiple peaks is half the intensity of the f5 peak (half width) is Δf, the wavelength of the sound wave in the sample is λ, and the absorption coefficient is α. Then, the following formula holds.

Δf/f−αλ/π...(2)(
2) From the formula, α−πΔf / v
...(3) Therefore, from equation (3), sample 103
The absorption coefficient of can be determined.

[Problem to be solved by the invention]

However, since the above-described ultrasonic absorption coefficient measuring device uses a continuous wave as a transmission wave, it is necessary to continuously change the frequency in order to find the frequency at which resonance occurs. As a result, there is a problem in that it takes time to find the frequency at which resonance occurs, and that it takes a long time to measure - times.

Further, with the above-mentioned absorption coefficient measuring device, the absorption coefficient can only be measured at frequencies that cause resonance.

However, as shown in equation (1), the resonant frequency is determined by the sound velocity and thickness of the sample, so in order to determine the absorption coefficient of various frequencies, a large number of samples with corresponding thicknesses are required. Measuring the absorption coefficient becomes an extremely complicated task.

In addition, since the ultrasonic waves incident on the sample are applied to the entire sample or a considerable area, accurate measurements cannot be performed if the sample surface is uneven, and it may be difficult to measure the absorption coefficient of a portion of the sample. Can not.

The present invention has been developed in view of the above-mentioned circumstances, and allows for high-speed measurement of absorption coefficients over a wide range of frequencies. It is an object of the present invention to provide an ultrasonic measuring device that can measure the absorption coefficient of the ultrasonic waves.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention includes an ultrasonic transmitter/receiver that makes an ultrasonic pulse enter a sample, receives a reflected wave from the sample, and converts it into an electric signal, and an ultrasonic wave that is converted by the ultrasonic transmitter/receiver. A means for extracting a reflected wave component from the front surface and a reflected wave component from the back surface of the sample included in the electrical signal, and a power spectrum of the front reflected wave component and the back reflected wave component respectively extracted by the extracting means. and a calculation means for determining the absorption coefficient of the sample from each of the power spectrum components determined by this means.

In addition, in order to solve the above problem, an ultrasonic pulse focused on a minute spot is made to enter the ultrasonic transmitting/receiving means on the sample, and the reference position can be set freely with the direction of incidence of the ultrasonic pulse on the sample as the Z axis. Equipped with a configurable acoustic lens,
Furthermore, a configuration is provided in which means for detecting the Z position of the acoustic lens is provided.

[Effect]

Since ultrasonic pulses with wide frequency components are incident on the sample, the absorption coefficient of the sample can be measured over a wide range of frequencies with a single incident ultrasonic pulse without changing the frequency, reducing measurement time. Ru.

In addition, since the ultrasonic pulse incident on the sample is focused by the acoustic lens, the ultrasonic pulse will be incident on one point on the sample, making it possible to improve the absorption coefficient even if the sample is uneven or a part of the sample. can be measured.

〔Example〕

Examples of the present invention will be described below.

FIG. 1 is a diagram showing an ultrasonic measuring device according to a first embodiment of the present invention.

The ultrasonic transmitting/receiving means of this device includes a pulse transmitter 1 that generates an electric pulse signal as a transmission wave, a transducer 2 that converts the electric pulse signal transmitted from the pulse transmitter 1 into an ultrasonic wave, and a transducer 2 that converts the electric pulse signal transmitted from the pulse transmitter 1 into an ultrasonic wave. It is comprised of an acoustic lens 3 that focuses the ultrasonic pulses electroacoustically converted by the transducer 2 onto a minute spot. acoustic lens 3
A sample 5 is placed near the focus of the ultrasound output from the
The space between the sample 5 and the acoustic lens 3 is filled with Kabra liquid 4 so that ultrasonic waves can propagate. The reflected wave from the sample 5 passes through the acoustic lens 3 again, is converted into an electric signal (received signal) by the transducer 2, and is input to the preamplifier 6. The output of the preamplifier 6 is supplied to a gate section 7, where a reflected wave component from the front or back surface of the sample 5 is extracted.

The extracted reflected wave component is sampled by a sampling section 8 and inputted to an A/D conversion section 9. The A/D converter converts the input signal into a digital signal and records it in the memory in the computer 10. The computer 10 is
A display 11 is connected which has a calculation function to be described later and displays calculation results.

The pulse control section 12 transmits a transmission trigger signal to the pulse transmission section 1 and also transmits a gate trigger signal to the gate section 7, thereby extracting a reflected wave component from the front or back surface of the sample 5 from the received signal. Further, the pulse control section 12 sends an operation signal to the sampling section 8 and the A/D conversion section 9. The Z scanning unit 13 has the function of moving the acoustic lens 3 up and down in two directions, and detects the relative movement distance of the acoustic lens 5 from the reference position in the Z-axis direction, when the incident direction of the ultrasonic wave is the Z-axis. Has a function.

This reference position can be freely set, and Z
The Z position information detected by the scanning unit 13 is sent to the computer 1.
Sent to 0.

Next, the absorption coefficient measuring operation of the embodiment configured as above will be explained.

When measuring the absorption coefficient, the acoustic lens 3 is placed in the Z scanning section 1.
3 to move it up and down to the position where the reflected signal from the surface of sample 5 has the maximum amplitude (the state in which the surface is in focus).
is detected, and the detected position is set as the reference position of the Z scanning unit 13.

Next, the power spectrum of the surface reflected wave of the sample 5 is measured. When a transmission trigger signal is manually input from the pulse control section 12, the pulse transmission section 1 generates a single pulse. This pulse wave is electroacoustic converted by transducer 2,
The light passes through the acoustic lens 3 and enters the sample 5. The reflected wave from the sample 5 passes through the acoustic lens 3 again and is converted into a received signal by the transducer 2. This received signal is shown in Fig. 2(a).
The waveform will be as shown in the figure below, resulting in transmission leakage and reflection within the lens.

Contains reflection components such as sample surface reflection and sample back reflection. In order to extract the sample surface reflected wave from this received signal, the received signal output from the preamplifier 6 is gated by a gate signal shown in FIG. 2(b) in the gate section 7. The sample surface reflected wave extracted in this way is converted into a digital signal via the sampling section 8 and the A/D conversion section 9, and is input to the computer 10. The sampling frequency at this time is set to be at least twice the frequency included in the reflected wave. The computer 10 performs fast Fourier transform on the reflected wave to obtain a power spectrum. The obtained power spectrum of the sample surface reflected wave is recorded in the memory within the computer 10, the external storage device 14, or the like.

Next, the acoustic lens 3 is moved in the Z-axis direction by the Z scanning unit 13 and set to a position where the reflected wave from the back surface of the sample 5 has the maximum amplitude, and the distance of that position from the reference position is detected by the Z scanning unit 13. and record it in the memory of the computer]1. Thereafter, the same operation as above is performed to obtain the power spectrum of the wave reflected from the back surface of the sample of sample 5. At this time, the gate signal of the gate section 7 is set so that the back reflected wave can be extracted as shown in FIG. 2(c).

Next, the computer 10 calculates the absorption coefficient of the sample 5 using the front surface reflected wave and the back surface reflected wave extracted as described above.

Since the transmitted wave is a single pulse, the ultrasonic waves emitted from the acoustic lens 3 have frequency components in a very wide range as shown in FIG. This power spectrum will be expressed as A (f).

Further, as shown in FIG. 4(a), the relative distance between the acoustic lens 3 and the sample 5 when focused on the sample surface is Z.

far. Furthermore, when the reflectance of the surface of the sample 5 is R5 and the absorption coefficient of the coupler liquid 4 is aL (f), the power spectrum As (f) of the wave reflected from the sample surface is expressed by the following equation.

As(f)”Rs A(f) e Lo-(4) 4th
As shown in Figure (b), the distance between the acoustic lens 3 and the front surface of the sample 5 when focusing on the back surface of the sample 5 is Z l
+ The thickness of the sample is d, the transmittance from coupler liquid 4 to sample 5 is Ts, and the transmittance from sample 5 to coupler liquid 4 is T
When the reflectance of the back surface of L + sample 5 is RB, and the absorption coefficient of sample 5 is αs (f), the power spectrum AB(f) of the back surface reflected wave can be expressed by the following equation.

AB (f) -TL T5 RB A(f) e-”
””“22.+a5f/)-2d) ,,,(5゜(
5) By dividing the equation by the equation (4) and taking the logarithm, the third term on the right side of the equation (6) is a constant, so that part is set as C.

Here, since absorption in liquids and solids is proportional to the square of the frequency f, the proportional coefficients α5(r) and α,(f) are expressed as αs(f')-a s f 2. a L(f')-a
When t f 2-(8) and Z2-(Zo Z+) are set, equation (7) is obtained. From this, when the power spectrum of the back surface reflected wave is divided by the power spectrum of the front surface reflected wave and the logarithm thereof is plotted against frequency, a quadratic curve as shown in FIG. 5 is obtained. The coefficient of f2 in equation (9) can be found by finding the slope of f2 using the least squares method for the measured values. Generally, water is often used for Kabra liquid 4,
Since this absorption coefficient is often measured, aL is known. Moreover, Z2 can be measured by the above means, and if the thickness d of the sample is known, the absorption coefficient of sample 5 is (9)
It can be easily calculated using Eq. On the other hand, when the absorption coefficient of the sample is not proportional to the square of the frequency, such as in a living body, a 5(f) −a s f x, a L(f) −a can be used instead of equation (8).
By substituting Lf x into equation (7), and taking the logarithm of − degrees (C is a constant, so ignore it)
, becomes. Since a I- and Z2 are known, the left side can be calculated from the measured power spectrum, and when the values are plotted with respect to log and f, they show a constant slope as shown in FIG. Since X can be found from this slope, a5 can be found from equation (11) by the least squares method.

Therefore, data such as the thickness of the sample 5 necessary for calculation of the absorption coefficient, which is known in advance, is manually entered into the computer 10, and data regarding the surface reflected wave, the back surface reflected wave, and the Z of the acoustic lens 3 are inputted by the above operation. The position information is input, and the calculation of equation (9) or equation (12) is executed by the computer 10, and the absorption coefficient of the sample 5 at a predetermined frequency is measured.

As described above, according to this embodiment, a single pulse containing a wide frequency component is focused by the acoustic lens 3 and made incident on the sample 5, and from the reflected wave, the sample surface reflected wave and the sample back surface reflected wave are transmitted to the gate section 7. Both reflected wave components are input to the computer 10, and the positions of the acoustic beam 3 in two directions are input to the computer 10, where the absorption coefficient of the sample 5 is determined by the above calculation. It is possible to measure absorption coefficients over a wide range of frequencies by measuring -degrees, and the time required to measure absorption coefficients can be significantly reduced.

In addition, the ultrasonic pulse can be applied to any one point on the sample 5, and if the unevenness existing on the sample 5 is approximately 1 mm or less, the ultrasonic pulse can be successfully applied without being affected by the unevenness. Absorption coefficient measurements can be made, and
It is also possible to perform measurements on only a portion of the sample 5.

In the above embodiment, the acoustic lens 3 is focused separately to measure the reflected wave from the front surface of the sample and the reflected wave from the back surface of the sample. It is also possible to input both reflected wave components into the computer 10 at the same time by applying a signal. A computer 10 calculates the power spectrum by dividing the waves into front-surface reflected waves and back-surface reflected waves.

In this method, since the position of the acoustic lens 3 in the Z direction is the same when measuring the surface reflected wave and the back surface reflected wave, (Zo Zl) becomes 0 in equation (7), and the absorption coefficient term of the Kabra liquid 4 is eliminated, making calculations easier.

Next, a second embodiment of the present invention will be described with reference to FIG.

This embodiment is an example in which the pulse transmitting/receiving section of the first embodiment is replaced with a non-focusing type ultrasonic probe 71, and the other parts are the first embodiment.
This is the configuration of the device shown in the figure and the road.

In this embodiment, a single pulse transmitted by the pulse transmitter 1 is converted into an ultrasonic wave by the ultrasonic probe 71 and is incident on the sample 5. The space between the ultrasonic probe 7] and the sample 5 is filled with Kabra liquid 4. The reflected wave from the sample 5 is converted into a received signal by the ultrasonic probe 71 and input to the preamplifier 6. The output of the preamplifier 6 is gated in a gate section 7.

The received signal output from the preamplifier 6 is shown in FIG. 8(a).
As shown in , there is transmission leakage and reflected waves from the sample surface.

Contains waves reflected from the back of the sample. The gate part 7 is shown in Fig. 8 (
A wave reflected from the front surface and a wave reflected from the back surface of the sample are extracted using the gate signal shown in b). The extracted reflected wave components are input to the computer 10 in the same manner as in the first embodiment. The computer 10 divides the input reflected wave component into a front surface reflected wave and a back surface reflected wave and obtains a power spectrum.

Hereinafter, the absorption coefficient is measured in the same manner as in the case where (Zo Zl)-0 is set in the first example.

As described above, according to the second embodiment, since a non-focusing type ultrasonic probe is used, in the case of a flat sample, the focusing operation of the acoustic lens, which was necessary in the first embodiment, can be omitted. This allows for faster measurements.

Next, a third embodiment of the present invention will be described.

FIG. 9 is a diagram showing a partial configuration of the third embodiment, and the configuration before the manual stage of the gate section 7 is omitted because it is the same as that in FIG. 1.

This embodiment has a configuration in which a spectrum analyzer 91 is inserted between the gate section 7 and the sampling section 8 of the apparatus shown in FIG.

In this embodiment, the reflected wave of the sample 5 extracted by the gate section 7 is input to the spectrum analyzer 91. The spectrum analyzer 91 outputs the spectrum of the manually input signal. The output of the spectrum analyzer 91 is converted into a digital signal via the sampling section 8 and the A/D conversion section 9, and then input to the computer 10. The computer 10 calculates the absorption coefficient in the same manner as in the first embodiment.

In such a third embodiment, since the human power of the computer 10 is a power spectrum, the fast Fourier transform that was performed in the first and second embodiments is not necessary, so that the absorption coefficient can be calculated even faster. become.

Furthermore, it is also possible to use an FFT analyzer instead of the spectrum analyzer 91.

Even with this configuration, since the FFT calculation is performed by hardware, it is possible to further speed up the calculation of the absorption coefficient.

Furthermore, by measuring the waveform or power spectrum multiple times and averaging them using a computer, the influence of noise can be reduced and measurement accuracy can be increased.

In addition, 1. In the second and third embodiments, the gate section 7
Although the necessary reflected waves are extracted in advance, the configuration is such that the gate section 7 is removed and a wide range of waveforms are input manually to the computer 10 as digital signals, and then the necessary reflected waves are extracted within the computer 10. This can also simplify the configuration.

In addition, in the first example, the power spectrum of the surface reflected wave is obtained by focusing on the sample surface, but the reflectance and transmittance of equations (4) to (7) change as the sample changes. R5, RB.

Ts and TL, and this part becomes the constant term C in equation (7) and does not affect the calculation of the absorption coefficient. Therefore, if the ultrasonic transmitter/receiver does not change the power spectrum of the sample surface, it is sufficient to obtain it once and save it, and there is no need to repeat it for each measurement.

The present invention is originally used for deep observation of samples, but by attaching a digital storage oscilloscope, FFT analyzer, etc. to a pulse mode ultrasonic microscope or ultrasonic flaw detector and implanting software, Absorption coefficient measurements can be easily made in each of these devices.

〔Effect of the invention〕

As described in detail above, according to the present invention, by using a single pulse wave as a transmitted wave, it is possible to measure the absorption coefficient of a sample at a very high speed and over a very wide range of frequencies.

Furthermore, by using an acoustic lens, the ultrasonic waves are focused and made incident on the sample, making it possible to measure the absorption coefficient of a sample with uneven surfaces or only a portion of the sample.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the first embodiment of the present invention, Fig. 2 is an explanatory diagram of the operation of the same embodiment, Fig. 3 is a diagram for explaining the frequency components of an ultrasonic pulse, and Fig. 4 is a diagram for explaining the frequency components of the ultrasonic pulse. A diagram showing the focal position of the acoustic lens and the relative relationship between the acoustic lens and the sample. Figure 5 shows the logarithm of the power spectrum of the back-reflected wave divided by the power spectrum of the front-reflected wave, plotted against frequency. Figure 6 is a characteristic diagram when the absorption coefficient of the sample is not proportional to the square of the frequency, Figure 7 is a partial configuration diagram of the second embodiment, and Figure 8 is the operation of the second embodiment. FIG. 9 is a partial configuration diagram of the third embodiment, FIG. 10 is a diagram for explaining a conventional absorption coefficient measuring method, and FIG. 11 is a diagram for explaining the resonance frequency. 1...Pulse transmitter, 2...Transducer, 3
...Acoustic lens, 4...Coupler liquid, 5...Sample, 6...Preamplifier, 7...Gate section, 8...Sampling section, 9...A/D conversion section , 10... Computer, 11... Display, 12... Pulse control unit, 13... Z scanning unit. Clear weather

Claims (2)

[Claims] (1) Ultrasonic transmitting/receiving means for making an ultrasonic pulse incident on a sample, receiving a reflected wave from the sample, and converting it into an electrical signal; and the sample included in the electrical signal converted by the ultrasonic transmitting/receiving means. a means for extracting a reflected wave component from the front surface and a reflected wave component from the back surface, a means for converting the front reflected wave component and the back reflected wave component respectively extracted by the extracting means into power spectra; An ultrasonic measuring device comprising: calculation means for determining the absorption coefficient of the sample from each of the power spectra determined by the means. (2) The ultrasonic measuring device according to claim 1, wherein an ultrasonic pulse focused on a minute spot is incident on the sample,
Further, an acoustic lens whose reference position can be freely set with the direction of incidence of the ultrasonic pulse on the sample as the Z axis is provided in the ultrasonic transmitting/receiving means, and further a means for detecting the Z position of the acoustic lens is provided, An ultrasonic measuring device characterized in that Z position information of the acoustic lens detected by a detection means is input to the calculation means.