CN103148815A - Lamella thickness ultrasonic detecting method based on sound pressure reflection coefficient - Google Patents

Abstract

The invention discloses a lamella thickness ultrasonic detecting method based on a sound pressure reflection coefficient and belongs to the technical field of non-destructive testing. According to the lamella thickness ultrasonic detecting method based on the sound pressure reflection coefficient, an ultrasonic pulse echo technology and a sound pressure reflection coefficient self-correlation signal processing method are used for carrying out lamella thickness measuring. Firstly, an ultrasonic pulse echo system is used for collecting a reflecting echo signal of the upper surface and the lower surface of a lamella and then collecting an upper surface echo signal of a standard test block, fast Fourier transform is carried out on the collected signals, and a lamella sound pressure reflection coefficient self-correlation function is obtained. Finally, frequency which each maximum value corresponds to is read out in the self-correlation function and the lamella thickness is figured out through combination of material sound velocity. The lamella thickness ultrasonic detecting method based on the sound pressure reflection coefficient overcomes the limitation that in a traditional ultrasonic interference thickness measuring method, two resonant frequencies in a signal frequency spectrum need to be read out so as to accurately acquire the lamella thickness. The lamella thickness ultrasonic detecting method based on the sound pressure reflection coefficient has the advantages of being high in measuring accuracy, strong in operability, low in equipment cost, wide in application range and the like.

Description

Thickness of thin layer supersonic detection method based on the sound pressure reflection coefficient autocorrelation function

Technical field

The present invention relates to a kind of thickness of thin layer supersonic detection method based on the sound pressure reflection coefficient autocorrelation function, belong to technical field of nondestructive testing.

Background technology

During using ultrasound pulse echo commercial measurement thickness of thin layer, due to upper surface echo and the lower surface echoed signal generation aliasing of thin layer, traditional pulse echo signal Time Domain Analysis can't be determined thickness of thin layer.

At present, be frequency spectrum analysis method based on principle of interference for the convectional signals disposal route of using ultrasound pulse echo commercial measurement thickness of thin layer, use the 20MHz ultrasonic probe as Haines NF etc. in " The application of broadband ultrasonic spectroscopy to the study of layered media " literary composition, and use the sound pressure reflection coefficient amplitude spectrum and phase spectrum processing means obtain the epoxy resin thickness of thin layer.Xu Zhihui, Lin Li etc. in " based on the surface coating thickness supersonic damage-free detection method of power spectrumanalysis " literary composition the applied power spectral analysis technology to ZrO ₂Coating is carried out thickness measure.But above-mentioned signal processing method all needs signal spectrum two resonance frequencies to occur at least in the ultrasonic probe bandwidth range, then utilizes the relation between difference, the thin layer velocity of sound and the thickness of thin layer between these two resonance frequencies, calculates thickness of thin layer.The method is higher to the bandwidth requirement of probe, thereby the requirement of frequency probe is also improved thereupon, causes the measuring equipment cost high, and has greatly limited its application.

Sound pressure reflection coefficient have good autocorrelation performance and with the characteristics such as noise non-correlation, the situation that adopts this method can only read a resonance frequency for signal spectrum in the ultrasonic probe bandwidth range still can be carried out thin layer thickness measurement, and stands good for the signal-noise ratio signal that is low to moderate 20dB.

Summary of the invention

The purpose of this invention is to provide a kind of thickness of thin layer supersonic detection method based on the sound pressure reflection coefficient autocorrelation function.Compare with existing ultrasonic interferometry thickness of thin layer method, when measuring the material of same thickness, can reduce the requirement to ultrasonic probe frequency and frequency span, or under same ultrasonic probe condition, can the less thin layer of detect thickness.

Technical scheme of the present invention is: a kind of thickness of thin layer supersonic detection method based on the sound pressure reflection coefficient autocorrelation function adopts an impulse ultrasound water logging Echo System that comprises reflectoscope, ultrasonic pulse immersion probe, Al matter thin layer specimen, tank, digital oscilloscope and computing machine, and the step of its detection is as follows:

(1) utilize described ultrasonic pulse water logging Echo System to thin layer specimen Vertical Launch ultrasonic signal, and gather the sample signal (aliasing signal) that the boundary reflection echoed signal of a boundary reflection echoed signal that is comprised of thin layer upper surface and water and thin layer lower surface and matrix composition forms;

(2) utilize the upper surface reference signal (echoed signal) of a reference block of described ultrasonic pulse-echo system acquisition;

(3) sample signal and the reference signal that described (1) and (2) are collected are carried out respectively Fast Fourier Transform (FFT), then use the frequency domain data of sample signal divided by the frequency domain data of reference signal, obtain complex function S (f);

(4) the complex function S (f) that (3) is tried to achieve is updated in formula 1, obtains thin layer sound pressure reflection coefficient autocorrelation function R _S(φ):

$R_S\left(\mathrm{\φ}\right)-\underset{F\→\∞}{\lim }\underset{0}{\overset{F}{\∫}}S{\left(f\right)S}^{*}(f+\mathrm{\φ})\mathrm{df}---\left(1\right)$

In formula: R _S(φ) expression thin layer sound pressure reflection coefficient autocorrelation function, S (f) is the business of sample signal frequency domain and reference signal frequency domain;

(5) R that asks in (4) _SRead n the frequency φ that maximum value is corresponding (φ) _i, i=0,1,2 ... n is with φ _i, i=0,1,2 ... n and thin layer velocity of sound c substitution formula (2) just can be tried to achieve thickness of thin layer:

$d=\frac{\underset{i=0}{\overset{i=n}{\mathrm{\Σ}}}i*c/\left({2\mathrm{\φ}}_i\right)}{n}---\left(2\right)$

In formula, c is the thin layer velocity of sound (mm/s), and d is thickness of thin layer (mm).

Thin layer specimen is placed in tank, after carrying out system's connection and instrumental correction, by ultra-sonic defect detector, utilizes the ultrasonic pulse immersion probe, ultrasound wave is launched, received to the thin layer specimen in tank, observes waveform and collection Wave data by digital oscilloscope.Repeat said process in UT (Ultrasonic Testing) on reference block, gather the upper surface echoed signal of a reference block.Respectively sample signal and reference signal are carried out Fast Fourier Transform (FFT), obtain the business of sample signal frequency domain data and reference signal frequency domain data, obtain complex function S (f), with S (f) the substitution formula (1) of trying to achieve, obtain the sound pressure reflection coefficient autocorrelation function R of thin layer specimen _S(φ).Read R _Sφ corresponding to each maximum value (φ) _i, in the situation that the known thin layer velocity of sound is utilized the thickness of thin layer d and the φ that set up _iBetween relational expression (2), can obtain thickness of thin layer d.

The invention has the beneficial effects as follows: this thickness of thin layer supersonic detection method based on the sound pressure reflection coefficient autocorrelation function uses the ultrasonic pulse water logging Echo System that is comprised of reflectoscope, ultrasonic pulse immersion probe, thin layer specimen, tank, digital oscilloscope and computing machine.At first utilize this system to thin layer specimen Vertical Launch ultrasonic signal and gather the aliasing signal that the boundary reflection signal of a boundary reflection signal that is comprised of thin layer upper surface and water and thin layer lower surface and matrix composition consists of, recycle the upper surface echoed signal of a reference block of this system acquisition, respectively the sample signal and the reference signal that collect are carried out Fast Fourier Transform (FFT), obtain the business of sample signal frequency domain data and standard signal frequency domain data, obtain complex function S (f), and ask for the autocorrelation function R of complex function S (f) _S(φ); Calculate thickness of thin layer by formula at last.Utilizing bandwidth is that the ultrasonic water immersion probe of 10.3～20.5MHz carries out thickness measure to thin-layered medium, if thin layer is aluminium, this moment measurable thickness of thin layer less than 310 μ m, and signal to noise ratio (S/N ratio) still can the Measurement accuracy thickness of thin layer when being 20dB.Overcome the problem that is difficult to accurately obtain thickness of thin layer when only having a resonance frequency and low signal-to-noise ratio when signal spectrum in the ultrasonic probe bandwidth range in traditional ultrasonic interference thickness measuring method, device therefor is simple, workable, cost is low, be easy to practical, measuring accuracy is high, measurement range is wide, has larger economic benefit and social benefit.

Description of drawings

The invention will be further described below in conjunction with drawings and Examples.

Fig. 1 is a kind of systematic schematic diagram of the thickness of thin layer supersonic detection device based on the sound pressure reflection coefficient autocorrelation function.

Fig. 2 is the metallograph of aluminium matter thin layer xsect.

Fig. 3 is that to adopt bandwidth be that the ultrasonic pulse immersion probe of 10.3～20.5MHz is the Al matter thin layer specimen emission ultrasonic signal of 415 μ m and the time domain waveform (signal to noise ratio (S/N ratio) is 20dB) that collects to thickness.

Fig. 4 is the sound pressure reflection coefficient autocorrelation function graph of Al matter thin layer specimen.

In figure: 1, ultra-sonic defect detector, 2, the ultrasonic pulse immersion probe (centre frequency 15.4MHz, bandwidth is 10.3～20.5MHz), 3, Al matter thin layer specimen, 4, tank, 5, digital oscilloscope, 6, computing machine.

Embodiment

After measurement mechanism shown in Figure 1 carries out system's connection and instrumental correction, at first by ultra-sonic defect detector 1, adopting the ultrasonic pulse immersion probe 2(centre frequency of wafer diameter 11.4mm is 15.4MHz, bandwidth is that 10.3～20.5MHz) to obtain its thickness to tested Al matter thin layer specimen 3(from Fig. 2 be 415 μ m, its velocity of sound is 6420m/s) transmit and receive ultrasound wave (Al matter thin layer specimen 3 is as in tank 4), complete observation and the collection of Al matter thin layer specimen Wave data by DPO4032 digital oscilloscope 5.Then repeat said process in UT (Ultrasonic Testing) on reference block, gather the upper surface echoed signal of a reference block, Figure 3 shows that Al matter thin layer specimen echoed signal (signal to noise ratio (S/N ratio) is 20dB).Utilize computing machine 6 respectively sample signal and reference signal to be carried out Fast Fourier Transform (FFT), obtain the business of sample signal frequency domain data and reference signal frequency domain data, obtain complex function S (f); The complex function S (f) that tries to achieve is updated to formula (1), obtains the sound pressure reflection coefficient autocorrelation function R of Al matter thin layer specimen 3 _S(f), as shown in Figure 4.Then read R _STwo φ that maximum value is corresponding (φ) ₁And φ ₂, be respectively 8MHz and 15.75MHz, as shown in Figure 3.With φ ₁, φ ₂Namely can calculate Al matter thickness of thin layer with material velocity of sound c substitution formula (2) is 408 μ m, and the absolute error between actual (real) thickness 415 μ m is 7 μ m, and relative error is 1.69%.

Claims (1)

1. thickness of thin layer supersonic detection method based on the sound pressure reflection coefficient autocorrelation function, it is characterized in that: adopt an impulse ultrasound water logging Echo System that comprises reflectoscope (1), ultrasonic pulse immersion probe (2), Al matter thin layer specimen (3), tank (4), digital oscilloscope (5) and computing machine (6), the step of its detection is as follows:

(1) utilize described impulse ultrasound water logging Echo System to thin layer specimen Vertical Launch ultrasonic signal, and gather the sample signal that the boundary reflection echoed signal of a boundary reflection echoed signal that is comprised of thin layer upper surface and water and thin layer lower surface and matrix composition forms;

(2) utilize the upper surface reference signal of a reference block of described ultrasonic pulse-echo system acquisition;

(3) sample signal and the reference signal that described (1) and (2) are collected are carried out respectively Fast Fourier Transform (FFT), then use the frequency domain data of sample signal divided by the frequency domain data of reference signal, obtain complex function S (f);

(4) the complex function S (f) that (3) is tried to achieve is updated in formula 1, obtains thin layer sound pressure reflection coefficient autocorrelation function R _S(φ):

$R_S\left(\mathrm{\φ}\right)-\underset{F\→\∞}{\lim }\underset{0}{\overset{F}{\∫}}S{\left(f\right)S}^{*}(f+\mathrm{\φ})\mathrm{df}---\left(1\right)$

In formula: R _S(φ) expression thin layer sound pressure reflection coefficient autocorrelation function, S (f) is the business of sample signal frequency domain and reference signal frequency domain;

(5) R that asks in (4) _SRead n the frequency φ that maximum value is corresponding (φ) _i, i=0,1,2 ... n is with φ _i, i=0,1,2 ... n and thin layer velocity of sound c substitution formula (2) just can be tried to achieve thickness of thin layer:

$d=\frac{\underset{i=0}{\overset{i=n}{\mathrm{\Σ}}}i*c/\left({2\mathrm{\φ}}_i\right)}{n}---\left(2\right)$

In formula, c is the thin layer velocity of sound (mm/s), and d is thickness of thin layer (mm).

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