CN102607479B - Method for measuring round-trip time of ultrasound in thin layered medium based on sound pressure reflection coefficient power spectrum - Google Patents

Abstract

The invention provides a method for measuring round-trip time of ultrasound in a thin layered medium based on a sound pressure reflection coefficient power spectrum the technical field of ultrasonic nondestructive test and evaluation of materials. According to the method, a pulse ultrasonic water immersion echo acquisition system is adopted to acquire a aliasing signal consisting of a reflection echo signal of an interface composed of water and a thin layered upper surface and a reflection echo signal of an interface composed of water and a thin layered lower surface, as well as an upper surface echo signal of a standard test block; and then the acquired signals are respectively subjected to FFT (Fast Fourier Transform) and further processed to obtain a sound pressure reflection coefficient power spectrum; then the horizontal ordinate of delta pulse corresponding to each cosine component is read out from a magnitude spectrum in the power spectrum, and the horizontal ordinate is round-trip time of ultrasound in a thin layered medium each time. The method is used for solving the problem that round-trip time of ultrasound in a thin layered medium cannot be determined because the bandwidth of ultrasonic echo signals cannot cover two adjacent minimal values in the sound pressure reflection coefficient magnitude spectrum of the thin layered medium. Used devices are simple, operability is strong, the measurement accuracy is high and repeatability is good.

Description

Based on sound pressure reflection coefficient power spectrum measurement ultrasonic in thin-layered medium the method for two-way time

Technical field

The present invention relates to a kind of based on sound pressure reflection coefficient power spectrum measurement ultrasonic in thin-layered medium the method for two-way time.It belongs to material Ultrasonic NDT and assessment technique field.

Background technology

The thickness of using ultrasound commercial measurement thin-layered medium, the most important thing is to measure a ultrasonic two-way time in thin-layered medium.Due to surface echo and the Bottom echo signal generation aliasing of thin layer, traditional pulse echo signal Time Domain Analysis cannot be determined two-way time.At present, for measure ultrasonic in thin layer the convectional signals disposal route of two-way time be sound pressure reflection coefficient amplitude spectrum and phase spectrum, as foreign scholar Haines NF etc. is used 20MHz ultrasonic probe in " The application of broadband ultrasonic spectroscopy to the study of layered media " literary composition, and apply sound pressure reflection coefficient spectrum and phase spectrum signal processing means has obtained hyperacoustic two-way time in epoxy resin thin layer, and then determined the thickness of epoxy resin thin layer.But in the time of can not covering in thin layer sound pressure reflection coefficient amplitude spectrum adjacent two minimal values for ultrasound echo signal bandwidth, we cannot determine ultrasonic two-way time in thin layer conventionally.

Summary of the invention

The object of this invention is to provide a kind of based on sound pressure reflection coefficient power spectrum measurement ultrasonic in thin layer the method for two-way time.The method, under same experimental provision condition, can be determined the ultrasonic two-way time at thin layer for the less thin layer of thickness, has expanded scope, the intuitive measurement results of thin-layered medium thickness measure, and anti-noise jamming ability is strong.

Technical scheme of the present invention is: a kind of based on sound pressure reflection coefficient power spectrum measurement ultrasonic in thin layer the method for two-way time, it adopts an impulse ultrasound water logging Echo System that comprises reflectoscope, ultrasonic pulse immersion probe, thin layer specimen, tank, digital oscilloscope and computing machine.The measuring process that it adopts is as follows:

(1) utilize described impulse ultrasound water logging Echo System to thin layer specimen Vertical Launch ultrasonic signal and gather one and form by water and thin layer upper surface the aliasing signal (sample signal) that reflection echo signal that the reflection echo signal at interface and water and thin layer lower surface form interface forms;

(2) utilize described impulse ultrasound water logging Echo System to gather the upper surface echoed signal (reference signal) of a reference block;

(3) sample signal and the reference signal that described step (1) and (2) are collected are carried out respectively FFT, then use the frequency domain data of sample signal divided by the frequency domain data of reference signal, finally obtain corresponding real part and imaginary data;

(4) real part and the imaginary data of step (3) being tried to achieve are updated in formula 1, obtain the sound pressure reflection coefficient power spectrum of thin layer, formula 1:

${\left|V\left(f\right)\right|}^2=\mathrm{Im}{\left[S\left(f\right)\right]}^2+\mathrm{Re}{\left[S\left(f\right)\right]}^2={\mathrm{\&alpha;}}_1^2+{\mathrm{\&alpha;}}_2^2+L+{\mathrm{\&alpha;}}_{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA0000139693440000011.png"\; state="\{\{state\}\}">n</figure-callout>}}^2+2({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_2+{\mathrm{\&alpha;}}_2{\mathrm{\&alpha;}}_3+L+{\mathrm{\&alpha;}}_{n-1}{\mathrm{\&alpha;}}_n)\cos \mathrm{\&Delta;<figure-callout\; id="2"\; label="t"\; filenames="HDA0000139693440000011.png"\; state="\{\{state\}\}">t</figure-callout>}2\mathrm{\&pi;f}$

$+2({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_3+{\mathrm{\&alpha;}}_2{\mathrm{\&alpha;}}_4+\&CenterDot;\&CenterDot;\&CenterDot;+{\mathrm{\&alpha;}}_{n-2}{\mathrm{\&alpha;}}_n)\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000139693440000011.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&Delta;<figure-callout\; id="2"\; label="t"\; filenames="HDA0000139693440000011.png"\; state="\{\{state\}\}">t</figure-callout>}2\mathrm{\&pi;f}+\&CenterDot;\&CenterDot;\&CenterDot;+2\left({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_n\right)\cos (n-1)\mathrm{\&Delta;<figure-callout\; id="2"\; label="t"\; filenames="HDA0000139693440000011.png"\; state="\{\{state\}\}">t</figure-callout>}2\mathrm{\&pi;f}$

In formula: | V (f) | ²represent sound pressure reflection coefficient power spectrum, S (f) is the business of sample signal frequency domain and reference signal frequency domain, Im[S (f)] be the real part of S (f), Re[S (f)] be the imaginary part of S (f); α ₁=V ₁₂exp (2d ₁α _water), α ₂=V ₂₁w ₁₂w ₂₁exp (2d ₁α _water) exp (2d α _{thin layer}) ...,

α _waterfor the attenuation coefficient (dB/mm) of water, α _{thin layer}for the attenuation coefficient (dB/mm) of thin layer, d ₁for the distance (mm) of probe to thin layer upper surface, the thickness that d is thin layer (mm), Δ t is a ultrasonic two-way time (ns) in thin layer, V ₁₂=(Z ₂-Z ₁)/(Z ₁+ Z ₂), V ₂₁=-V ₁₂, W ₁₂=1+V ₁₂, W ₂₁=1-V ₁₂;

(5) to power spectrum | V (f) | ²carry out FFT, according to formula 2 try to achieve ultrasonic in thin layer n Δ t two-way time (n>=1), formula 2:

$F\left[{\left|V\left(f\right)\right|}^2\right]=2\mathrm{\&pi;}({\mathrm{\&alpha;}}_1^2+{\mathrm{\&alpha;}}_2^2+...+{\mathrm{\&alpha;}}_n^2)\mathrm{\&delta;}\left(t\right)+2\mathrm{\&pi;}({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_2+{\mathrm{\&alpha;}}_2{\mathrm{\&alpha;}}_3+\&CenterDot;\&CenterDot;\&CenterDot;+{\mathrm{\&alpha;}}_{n-1}{\mathrm{\&alpha;}}_n)[\mathrm{\&delta;}(t-\mathrm{\&Delta;t})+\mathrm{\&delta;}(t+\mathrm{\&Delta;t})]$

$+2\mathrm{\&pi;}({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_3+{\mathrm{\&alpha;}}_2{\mathrm{\&alpha;}}_4+\&CenterDot;\&CenterDot;\&CenterDot;+{\mathrm{\&alpha;}}_{n-2}{\mathrm{\&alpha;}}_n)[\mathrm{\&delta;}(t-2\mathrm{\&Delta;t})+\mathrm{\&delta;}(t+2\mathrm{\&Delta;t})]$

$+\&CenterDot;\&CenterDot;\&CenterDot;+2\left({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_n\right)\left\{\mathrm{\&delta;}\right[t-(n-1)\mathrm{\&Delta;t}]+\mathrm{\&delta;}[t+(n-1)\mathrm{\&Delta;t}\left]\right\}$

Thin layer specimen is placed in tank, carries out after system connection and instrumental correction, by ultra-sonic defect detector, utilize ultrasonic pulse immersion probe, ultrasound wave is launched, received to the thin layer specimen in tank, by digital oscilloscope, observes waveform and gather Wave data.In UT (Ultrasonic Testing), with repeating said process in reference block, gather the upper surface echoed signal of a reference block.Respectively sample signal and reference signal are carried out to Fast Fourier Transform (FFT) (FFT), obtain the business of sample signal frequency domain data and reference signal frequency domain data, obtain corresponding real part and imaginary data, by the real part of trying to achieve and imaginary data substitution formula 1, obtain the sound pressure reflection coefficient power spectrum of thin layer specimen.Utilize relational expression 2 between ultrasonic n Δ t two-way time (n >=1) in thin layer set up and the frequency spectrum of sound pressure reflection coefficient power spectrum, can obtain ultrasonic n Δ t two-way time (n >=1) in thin layer.

The invention has the beneficial effects as follows: this based on the ultrasonic impulse ultrasound water logging Echo System that the method use of two-way time is comprised of reflectoscope, ultrasonic pulse immersion probe, thin layer specimen, tank, digital oscilloscope and computing machine in thin layer of sound pressure reflection coefficient power spectrum measurement.First utilize this system to thin layer specimen Vertical Launch ultrasonic signal and gather one and form by thin layer upper surface and water the aliasing signal that reflected signal that the reflected signal at interface and thin layer lower surface and water form interface forms, recycle the upper surface echoed signal of a reference block of this system acquisition, respectively the sample signal collecting and reference signal are carried out to FFT, the business who obtains sample signal frequency domain data and standard signal frequency domain data, obtains corresponding real part and imaginary part; Finally by formula, calculate ultrasonic two-way time in thin layer.Utilize the ultrasonic measurement of thin-layered medium being carried out to ultrasonic two-way time of 12～22MHz, measurable two-way time is lower than 100ns.This method is not subject to the restriction of thin layer material and homogeneity degree thereof, overcome because ultrasound echo signal bandwidth can not cover the little value of two neighboring pole in thin layer sound pressure reflection coefficient amplitude spectrum, can not determine the problem of ultrasonic two-way time, device therefor is simple, workable, cost is low, be easy to practically, measuring accuracy is high, and measurement range is wide, reproducible, there is larger economic benefit and social benefit.

Accompanying drawing explanation

Below in conjunction with drawings and Examples, the invention will be further described.

Fig. 1 be a kind of based on sound pressure reflection coefficient power spectrum measurement ultrasonic in thin layer two-way time device systematic schematic diagram.

Fig. 2 is the time-domain signal figure that adopts Al matter sheet metal specimens that the ultrasonic pulse immersion probe of nominal frequency 25MHz is 433 μ m to thickness to launch and collect.

Fig. 3 is the acoustic pressure reflective power spectrogram of Al matter sheet metal specimens.

Fig. 4 is the amplitude spectrogram of the acoustic pressure reflective power spectrum of Al matter sheet metal specimens.

In figure: 1, ultra-sonic defect detector, 2, ultrasonic pulse immersion probe (nominal frequency 25MHz, centre frequency 16MHz, frequency span (6dB) 12～22MHz), 3, thin layer specimen, 4, tank, 5, digital oscilloscope, 6, computing machine.

Embodiment

Measurement mechanism shown in Fig. 1 carries out after system connection and instrumental correction, first by ultra-sonic defect detector 1, adopt wafer diameter 11.4mm, ultrasonic pulse immersion probe 2 (the centre frequency 16MHz of nominal frequency 25MHz, frequency span (6dB) 12～22MHz) to tested Al matter sheet metal specimens 3, (using miking thickness is 433 μ m, because its velocity of sound is 6320m/s, according to t=2d/c, show that be 137ns a two-way time) transmit and receive ultrasound wave (Al matter sheet metal specimens 3 as for tank 4 in), by DPO4032 digital oscilloscope 5, complete observation and the collection of Al matter sheet metal specimens Wave data.Then in UT (Ultrasonic Testing) with repeating said process in reference block, gather the upper surface echoed signal of a reference block, Figure 2 shows that Al matter sheet metal specimens echoed signal.Utilize computing machine 6 respectively sample signal and reference signal to be carried out to FFT, obtain the business of sample signal frequency domain data and reference signal frequency domain data, obtain corresponding real part and imaginary data; The real part of trying to achieve and imaginary data are updated to formula 1, obtain the sound pressure reflection coefficient power spectrum of Al matter sheet metal specimens 3, as shown in Figure 2.Then sound pressure reflection coefficient power spectrum is made to FFT, ask for its amplitude spectrum, as shown in Figure 3.Finally read the horizontal ordinate that each peak value is corresponding, be n (n >=1) the inferior two-way time of ultrasound wave in thin layer.From the amplitude spectrum of power spectrum, read respectively Δ t=128ns, 2 Δ t=284ns, 3 Δ t=440ns, Δ t=(128+284/2+440/3)/3=138.7ns.Utilizing this method to record ultrasonic two-way time in thin layer is 1.24% with the relative error of a two-way time of thickness conversion through miking.

Claims (1)

1. One kind based on sound pressure reflection coefficient power spectrum measurement ultrasonic in thin-layered medium the method for two-way time, it is characterized in that: it adopts an impulse ultrasound water logging Echo System that comprises reflectoscope (1), ultrasonic pulse immersion probe (2), thin layer specimen (3), tank (4), digital oscilloscope (5) and computing machine (6), the measuring process that it adopts is as follows:

   (1) utilize described impulse ultrasound water logging Echo System to thin layer specimen Vertical Launch ultrasonic signal and gather one and form by water and thin layer upper surface the sample signal that reflection echo signal that the reflection echo signal at interface and water and thin layer lower surface form interface forms;

   (2) utilize described impulse ultrasound water logging Echo System to gather the reference signal of a reference block;

   (3) sample signal and the reference signal that described step (1) and (2) are collected are carried out respectively FFT, then use the frequency domain data of sample signal divided by the frequency domain data of reference signal, finally obtain corresponding real part and imaginary data;

   (4) real part and the imaginary data of step (3) being tried to achieve are updated in formula 1, obtain the sound pressure reflection coefficient power spectrum of thin layer, formula 1:

   $\begin{array}{c}{\left|V\left(f\right)\right|}^2=\mathrm{Im}{\left[S\left(f\right)\right]}^2+\mathrm{RE}{\left[s\left(f\right)\right]}^2={\mathrm{\&alpha;}}_1^2+{\mathrm{\&alpha;}}_2^2+L+{\mathrm{\&alpha;}}_n^2+2({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_2+{\mathrm{\&alpha;}}_2{\mathrm{\&alpha;}}_3+L+{\mathrm{\&alpha;}}_{n-1}{\mathrm{\&alpha;}}_n)\cos \mathrm{\&Delta;t}2\mathrm{\&pi;f}\\ +2({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_3+{\mathrm{\&alpha;}}_2{\mathrm{\&alpha;}}_4+\&CenterDot;\&CenterDot;\&CenterDot;+{\mathrm{\&alpha;}}_{n-2}{\mathrm{\&alpha;}}_n)\cos 2\mathrm{\&Delta;t}2\mathrm{\&pi;f}+\&CenterDot;\&CenterDot;\&CenterDot;+2\left({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_n\right)\cos (n-1)\mathrm{\&Delta;t}2\mathrm{\&pi;f}\end{array}$ In formula: V (f) ²represent sound pressure reflection coefficient power spectrum, S (f) is the business of sample signal frequency domain and reference signal frequency domain, Im[S (f)] be the real part of S (f), Re[S (f)] be the imaginary part of S (f); α ₁=V ₁₂exp (2d ₁α _water), α ₂=V ₂₁w ₁₂w ₂₁exp (2d ₁α _water) exp (2d α _{thin layer}) ...,

   

   wherein: n>2, α _waterfor the attenuation coefficient of water, unit is dB/mm, α _{thin layer}for the attenuation coefficient of thin layer, unit is dB/mm, d ₁for the distance of probe to thin layer upper surface, unit is mm, the thickness that d is thin layer, and unit is mm, and Δ t is a ultrasonic two-way time in thin layer, and unit is ns, V ₁₂=(Z ₂-Z ₁)/(Z ₁+ Z ₂), V ₂₁=-V ₁₂, W ₁₂=1+V ₁₂, W ₂₁=1-V ₁₂; Z represents the acoustic impedance of medium, and it is numerically equal to the product of the medium velocity of sound and density;

   (5) to power spectrum V (f) ²carry out FFT, according to formula 2 try to achieve ultrasonic in thin layer n Δ t two-way time (n>=1), formula 2:

   $\begin{array}{c}F\left[\right|V\left(f\right){|}^2]=2\mathrm{\&pi;}({\mathrm{\&alpha;}}_1^2+{\mathrm{\&alpha;}}_2^2+\&CenterDot;\&CenterDot;\&CenterDot;+{\mathrm{\&alpha;}}_n^2)\mathrm{\&delta;}\left(t\right)+2\mathrm{\&pi;}({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_2+{\mathrm{\&alpha;}}_2{\mathrm{\&alpha;}}_3+\&CenterDot;\&CenterDot;\&CenterDot;+{\mathrm{\&alpha;}}_{n-1}{\mathrm{\&alpha;}}_n)[\mathrm{\&delta;}(t-\mathrm{\&Delta;t})+\mathrm{\&delta;}(t+\mathrm{\&Delta;t})]\\ +2\mathrm{\&pi;}({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_3+{\mathrm{\&alpha;}}_2{\mathrm{\&alpha;}}_4+\&CenterDot;\&CenterDot;\&CenterDot;+{\mathrm{\&alpha;}}_{n-2}{\mathrm{\&alpha;}}_n)[\mathrm{\&delta;}(t-2\mathrm{\&Delta;t})+\mathrm{\&delta;}(t+2\mathrm{\&Delta;t})]\\ +\&CenterDot;\&CenterDot;\&CenterDot;+2\left({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_n\right)\left\{\mathrm{\&delta;}\right[t-(n-1)\mathrm{\&Delta;t}]+\mathrm{\&delta;}[t+(n-1)\mathrm{\&Delta;t}\left]\right\}.\end{array}$

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