JPH0440309A - Ultrasonic measuring instrument - Google Patents

Abstract

PURPOSE:To speed up the measurement of thickness of a sample by Fourier transforming, the power spectrum data, finding the period of variation in the intensity of the power spectrum, and calculating the thickness of the sample from the found frequency. CONSTITUTION:When a transmission trigger is outputted from a pulse control part 20 to a pulse transmission part 10, the transmission part 10 generates a single-shot pulse. This pulse wave is converted electracoustically by a transducer 11 into an ultrasonic wave pulse, which is passed through an acoustic lens 12, propagated in coupler liquid 15, and made incident on the sample 13. The reflected wave from the sample 13 is passed through the liquid 15 and lens 12 and converted by the transducer 11 into a reflected signal, which is amplified by a preamplification part 16. A gate part 17 gates the reflected signal and a sample reflected wave is extracted and inputted to a computer 21 through a sampling part 18 and an A/D conversion part 19. The computer 21 Fourier transforms the reflected wave from the sample to find the power spectrum, which is further Fourier transformed to calculate the thickness (d) from the found period fo and the sound velocity V.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic measuring device that can measure the thickness of a sample using ultrasonic waves.

[Conventional technology]

2. Description of the Related Art Ultrasonic thickness measuring devices that measure the thickness of a sample using ultrasonic waves are conventionally known, and FIG. 8 shows an example of the configuration of a conventional ultrasonic thickness measuring device. In this ultrasonic thickness measuring device, an output voltage from an oscillator 1 whose frequency can be varied is applied to an ultrasonic probe 2, and this applied voltage is subjected to electroacoustic conversion by the ultrasonic probe 2. Then, the ultrasonic waves acoustically converted by the ultrasonic probe 2 are incident on the sample 4 through the Kabra liquid 3. The reflected wave from the sample 4 passes through the Kabra liquid 3 and enters the ultrasonic probe 2 in reverse, and is converted into a voltage according to the intensity of the reflected wave, causing a change in the current of the oscillator 1.

Here, when the frequency f of the oscillator 1 is changed, the wavelength λ of the ultrasonic wave in the sample 4 is changed. When the thickness d of the sample 4 and the integral multiple of the half wavelength (n) are equal, that is, when the condition nλ/2-d (1) is established, a standing wave is generated in the sample 4 and resonance occurs. do. The ultrasonic 2λ wave vibration energy generated during this resonance is converted into electricity by the probe calf.

The current of the oscillator 1 increases. The current of this oscillator 1 is amplified by an amplifier 5 and displayed on an oscilloscope 6. Therefore, when the frequency of the oscillator 1 is changed, a waveform as shown in FIG. 9 is displayed on the cathode ray tube of the oscilloscope 6.

The peak part is the frequency at which resonance occurs. The frequency of the mountain part is fl+f2. ..., fffi+ ff
If expressed as fie+..., then from equation (1), d-nV/2 f,
-(2) V: The speed of sound, so if n and V are known, the thickness d of the sample 4 can be determined.

Furthermore, even if n is unknown, the thickness of the sample 4 can be found from the following equation by finding the difference with the adjacent resonance frequency.

d-V/2 (f, ya, -f,)...
・ (3) On the other hand, using a single pulse as the transmission wave, sample 4
There is also a method of extracting the reflected waves from the sample and determining the thickness of the sample from the power spectrum of the reflected waves.

As shown in FIG. 10, the power spectrum of the reflected wave from the sample produces peaks and troughs due to the interference of both reflected waves from the upper and lower surfaces of the sample. Frequency fI at this valley, f2.
fs,..., and when each frequency is an integer multiple of fl, d = V/2 f 1- (4) When it is an odd multiple, d = V/4 f s ・" (
5), and the thickness d of the sample can be calculated from equations (4) and (5).

[Problem to be solved by the invention]

However, the above-mentioned ultrasonic thickness measuring device that varies the frequency takes a long time to measure the thickness of the sample.
There is a problem that high-speed measurement cannot be performed. That is, since a continuous wave is used as the frequency, and it is necessary to continuously change the frequency in order to find the frequency at which resonance occurs, it takes a long time to measure - times.

Further, an ultrasonic thickness measuring device that uses a single pulse as a transmitted wave has a problem in that accurate measurement cannot be performed in a low frequency region due to the influence of noise. That is, since the thickness d is determined from fl by determining whether the frequency arrangement of the valleys of the power spectrum is an integer multiple or an odd multiple of fl, the thicker the sample, the lower the frequency of fl.
Since the intensity of the power spectrum is also small at low frequencies,
It becomes difficult to distinguish between valleys caused by noise and valleys caused by the intensity of the power spectrum. For example, if the transmitting frequency is 50M
In the case of Hz, the power spectrum is about 10MHz,
When the transmitting side is 10MHz, the power spectrum is 4MHz
The lower limit is about z. Therefore, it was impossible to measure the thickness of the sample when the thickness was on the order of several mm.

Furthermore, it was impossible to measure the thickness of a portion of the sample or the thickness of a sample with unevenness on the top or bottom surface.

The present invention was made in view of the above circumstances, and
The purpose of the present invention is to provide an ultrasonic measuring device that can speed up the measurement of the thickness of a sample and expand the measurable range.

Another object of the present invention is to provide an ultrasonic measuring device that can speed up sample thickness measurement and expand the measurable range, as well as measure the thickness of a sample with irregularities or a portion of the sample. It's about doing.

[Means to solve the problem]

A first aspect of the present invention provides an ultrasonic measuring device including an ultrasonic transmitting/receiving means for making an ultrasonic pulse enter a sample, receiving a reflected wave from the sample and converting it into a received signal, and converting the received signal to a reflected wave from the sample. means for extracting a component, means for calculating a power spectrum by Fourier transforming the waveform data of the reflected wave component extracted by this means, and means for calculating a power spectrum by Fourier transforming the power spectrum data calculated by this means again. A second aspect of the present invention provides an ultrasonic measuring device comprising: means for determining the cycle of intensity of the power spectrum; and means for calculating the thickness of the sample based on the frequency determined by the means; The ultrasonic transmitting/receiving means includes an acoustic lens that focuses ultrasonic pulses onto a minute spot on the sample.

[Effect]

According to the first invention, since a single pulse is used as the transmission wave, there is no need to continuously change the frequency, making it possible to measure at very high speed.Moreover, since the period of strength and weakness of the power spectrum is determined by Fourier transform, Samples can also be measured.

According to the second invention, by using an acoustic lens that focuses ultrasonic waves, it is possible to focus ultrasonic pulses on a minute spot on a sample, and the thickness of a sample with unevenness or a part of the sample can be measured. It becomes possible.

〔Example〕

Examples of the present invention will be described below.

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

The ultrasonic transmitting/receiving means of this device includes a pulse transmitter 10 that generates a transmit pulse, a transducer 11 that converts the transmit pulse generated by the pulse transmitter 10 into an ultrasonic wave, and a transducer 11 that focuses the ultrasonic pulse generated by the transducer 11 into a minute spot. The acoustic lens 12 is composed of an acoustic lens 12. A sample 13 is located near the focus of the ultrasonic waves transmitted from the acoustic lens 12.
is placed in the sample holding container 14. A coupler liquid 15 is placed in the sample mounting container 14 and fills the space between the acoustic lens 12 and the sample 13.

The ultrasonic waves incident on the sample 13 are reflected from the upper and lower surfaces of the sample 13, pass through the acoustic lens 12 again, are converted into electrical signals (hereinafter referred to as "reflected wave signals") by the transducer 11, and are sent to the preamplifier 16. is input. A gate section 17 is connected to the output side of the preamplifier 16, and the gate section 1
In step 7, reflected waves from the front and back surfaces of the sample 13 (hereinafter referred to as "sample reflected waves") are extracted. A sampling section 18 is connected to the output of the gate section 17, and samples the extracted reflected wave. This sampled reflected wave is converted into a digital signal by an A/D converter 19. Pulse transmitter 10. Gate part 17. Sampling section 18. Each A/D converter 19 has a pulse controller 2.
The pulse controller 20 outputs a transmission trigger signal, which is the transmission timing, to the pulse transmitter 10 and outputs a gate trigger signal to the gate 17. Further, a sampling timing signal is output to the sampling section 18 and the A/D converting section 19 to control the sampling frequency.

The digital signal output from the A/D converter 19 is stored in a memory in the computer 21. computer 2
1 determines the thickness of the sample through thickness calculation processing, which will be described later, and displays the calculation result on the connected display 22.

Next, the operation of this embodiment will be explained.

In the operation during thickness measurement, when the pulse controller 20 outputs a transmission trigger to the pulse transmitter 10, the pulse transmitter 10 generates a single pulse.

This pulse wave is electroacoustically converted by the transducer 11 to become an ultrasonic pulse, which passes through the acoustic lens 12, propagates through the Kabra liquid 15, and enters the sample 13. Sample 13
The reflected wave propagates through the Kabra liquid 15 again, passes through the acoustic lens 12, and is converted into a reflected wave signal by the transducer 11. This reflected wave signal is amplified by a preamplifier 16. As shown in FIG. 2(a), the reflected wave signal amplified by the preamplifier 16 includes sample reflected waves such as transmission leakage, reflection inside the lens, and reflection from the top surface of the sample and reflection from the bottom surface of the sample. There is. The gate section 17 receives the reflected wave signal as shown in FIG. 2(b).
A gate is applied at the timing shown in , and the sample reflected wave is extracted. The sample reflected wave extracted by the gate section 17 is converted into a digital signal by a sampling section 18 whose sampling frequency is adjusted to be at least twice the frequency included in the reflected wave, and an A/D conversion section 19, and is input to the computer 21.

The thickness calculation process in the computer 21 will be described in detail below.

First, the measurement principle will be explained. Consider a case where an ultrasonic wave is incident on a material F having a thickness d existing between a material E and a material G as shown in FIG. 3 from above in FIG.

At this time, the incident ultrasonic wave has two paths: a path A in which it is reflected on the upper surface of the material F, and a path B in which it is reflected in the lower surface of the material F. If the wave on path A is CA (1), then this wave CA
(t) is expressed by the following equation.

CA (t) -RJ'a (f) e""' df
-(6) In equation (6), R represents the reflectance of the interface between substance E and substance F, a (f) represents the intensity at each frequency of the incident wave, and f represents the frequency. Also,
If the wave passing through path B is CB (t), then this wave CB
(t) has a long sound path length corresponding to the thickness d of the material F, so the phase is shifted by this amount. The attenuation coefficient of material F is α(f)
, if the transmission coefficient of the interface between substance E and substance F is expressed as S, and the reflection coefficient of the interface between substance F and substance G is expressed as R', then CB (t) becomes as shown in the following equation.

CB(t)-±RZ 5J'a(f) e-ffi+1
1-24. eII2MN -72m+... (7) Here, if the acoustic impedances of the material E1, the material F1, and the material G are respectively ZE, ZP, and Zc, the signs of equation (7) are as follows.

(a) ZE >Z, >Zc or Z, <Zp <26 (1) and e! The sign is positive (b) When Z, > Z, , z, < Zc or zE < Zp , Z, > Zo (7) The sign is negative From equations (6) and (7), the reflected waves of paths A and B The sample reflected waves generated by interference with each other are C(t)
Then... (8) becomes. If we perform Fourier transform on equation (8), we can obtain Cp (f) (assuming the Fourier transform of C(t) is CF (f)).
=a (f) (R±SR# e-all°2d
, e-17 ・(9).

From the above, the power spectrum of the reflected wave is as follows.

Cp (f)12=la (f)12 (R2+S2
R"e-"""±2RR' e-2au)a
, coS(antsu)... (10) In equation (10), 1a(f')12 is the frequency intensity of the incident ultrasonic wave, which has a waveform as shown in FIG. In other words, it is a function that has a peak at a certain frequency and gradually decreases at frequencies before and after that. Also, e-′. For °6, α(f)''1/f2 holds true, so it is a function that monotonically decreases as the frequency increases. Also, (
10) The last term in the equation is the period f. -V/2d represents an increase/decrease. From these, the power spectrum of the reflected wave generated by interference between the reflected waves of paths A and B becomes a waveform in which a periodic function is superimposed on the waveform shown in FIG. 4, as shown in FIG. .

When the power spectrum in FIG. 5 is Fourier-transformed again to obtain a spectrum, the waveform shown in FIG. 6 is obtained. In FIG. 6, let S be a period with a strong peak. Since the frequency band is always limited in digital Fourier transform, if the band during Fourier transform of the power spectrum is fm, then the frequency period f of the strength and weakness in FIG. is as follows.

fo-fm/S - (11) Also (
From formula 10), the period of strength and weakness is f. is f, -V/2d
-(12), so the thickness d of the substance F
is d-V/2 f , -(13)
becomes. Therefore, if the sound velocity V is known, the thickness d can be determined.

Therefore, the computer 21 performs Fourier transform on the sample reflected wave to obtain the power spectrum of the sample reflected wave shown in FIG. 5, and further performs Fourier transform on this power spectrum to calculate the period S shown in FIG. 6. Then, the period f in FIG. 5 is determined from the obtained period S and the band fm during Fourier transform. seek. Next, this determined period f. The thickness d is calculated from equation (13) from the previously known sound velocity ■. This calculation result is displayed on the display 22.

Note that when measuring the thickness of a thin sample, the period f of the power spectrum of the sample reflected wave. Since takes a large value, the width of the period of strength and weakness of the power spectrum also becomes large, and the period when the power spectrum is Fourier transformed becomes small. In digital Fourier transform (DFT), since only integer periods can be obtained, the accuracy becomes worse for thin samples.

Therefore, in such a case, the Gaussian function or the 5i
It is preferable to perform interpolation using an nc function to obtain the peak period, or to obtain the peak period using the maximum entropy method.

As described above, according to this embodiment, since a single pulse is used as the transmitted wave, the thickness of the sample can be measured by data sampling by - times of ultrasonic wave transmission, which speeds up the measurement of the sample thickness. can.

In addition, since the sample reflected wave is subjected to Fourier transformation twice, the period S of the power spectrum of the sample reflected wave is
can be determined extremely easily and quickly, and it has also become possible to measure sample thicknesses that could not be measured due to the influence of noise using conventional thickness measurements using single pulses.

Furthermore, by using the acoustic lens 12, it is possible to focus the ultrasonic pulses on any point on the sample 13, thereby making it possible to measure the thickness of an uneven sample or the thickness of a portion of the sample. Further, since the required part of the sample reflection is extracted by the gate part 17 using ultrasonic waves, it is also possible to measure the thickness of the substance inside the sample.

In the above embodiment, the sample reflected wave is extracted at the gate section 17, but the waveform in a wide range is converted into a digital signal and input to the computer 21, and then the computer 21
If the sample reflection is extracted within the gate, it is possible to create a configuration in which the gate section 17 is omitted.

FIG. 7 shows a second embodiment of the present invention.

This second embodiment has a configuration in which a spectrum analyzer 30 is inserted between the gate section 17 and the sampling section 18 of the ultrasonic measuring device shown in FIG.

The sample reflected wave extracted by the gate section 17 is input to the spectrum analyzer 30. The spectrum analyzer 30 obtains a spectrum of the input sample reflected wave by waveform analysis such as Fourier transform, and outputs the obtained spectrum. The output spectrum is converted into a digital signal by a sampling section 18 and an A/D conversion section 19, and is input to a computer 21. In the computer 21, the input spectrum is Fourier-transformed again and the first
The thickness of the sample is calculated by the same thickness calculation process as in the example. Note that in this embodiment, since the input to the computer 2 is already spectral data, Fourier transformation in the thickness calculation process only needs to be performed once.

According to the second embodiment, it is possible to obtain the same effects as the first embodiment, and furthermore, in the thickness calculation process in the computer 21, the Fourier transform is more uniform than in the first embodiment. Since the number of times can be reduced, even faster thickness measurement is possible.

In the first and second embodiments described above, the acoustic lens 12 is used to focus the ultrasonic waves onto a minute spot.
For purposes other than measuring the thickness of a portion of a sample or an uneven portion, it is conceivable to use a non-focusing type ultrasonic probe. Even in this case, since pulse waves are used, the thickness can be measured very quickly, and it is also possible to measure the thickness of thick samples that were previously impossible to measure.

Alternatively, the waveform or power spectrum may be measured a plurality of times, and the data may be imported into the computer 21 to calculate an average value, and this average value may be used to perform the thickness calculation process. By doing so, it is possible to remove the influence of noise, and the measurement accuracy can be improved.

In addition, the present invention attaches a digital storage oscilloscope and FFT analyzer to a single-pulse ultrasonic microscope and ultrasonic flaw detector, which have been conventionally used for deep observation of samples, and implants software related to thickness calculation processing. Can easily measure thickness.

〔Effect of the invention〕

As detailed above, according to the first invention, it is possible to provide an ultrasonic measuring device that can speed up the measurement of the thickness of a sample and expand the measurable range. In addition to speeding up thickness measurement and expanding the measurable range, it is also possible to provide an ultrasonic measuring device that can measure the thickness of a sample with irregularities or a portion of the sample.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the ultrasonic measuring device according to the first embodiment, Fig. 2 is a diagram for explaining the sample reflected wave extraction operation of the same embodiment, and Fig. 3 is an ultrasonic wave on a material having a thickness of d. FIG. 4 to FIG. 6 are diagrams for explaining the thickness calculation process of the same embodiment. FIG. 7 is a configuration diagram of the ultrasonic measuring device according to the second embodiment. The figure is a diagram showing the configuration of a conventional ultrasonic thickness measuring device, Figure 9 is a diagram showing the relationship between the voltage change due to ultrasound resonance within the sample and the resonant frequency, and Figure 10 is a diagram showing the power spectrum of reflected waves. It is. DESCRIPTION OF SYMBOLS 10... Pulse transmission part, 11... Transducer, 2... Acoustic lens, 13... Sample, 17... Gate part, 8... Sampling part, 19... A/D conversion part , 0... Pulse control unit, 21... Computer, 0... Spectrum analyzer.

Claims (2)

[Claims] (1) an ultrasonic transmitting/receiving means that makes an ultrasonic pulse enter a sample, receives a reflected wave from the sample, and converts it into a received signal;
means for extracting a reflected wave component from the sample from the received signal; means for calculating a power spectrum by Fourier transforming the waveform data of the reflected wave component extracted by this means; and the power calculated by this means. means for determining the period of intensity of the power spectrum by Fourier transforming the spectral data again;
An ultrasonic measuring device characterized by comprising means for calculating the thickness of the sample based on the frequency determined by this means. (2) The ultrasonic measuring device is characterized in that the ultrasonic transmitting/receiving means includes an acoustic lens that focuses ultrasonic pulses onto a minute spot on the sample.