CN102607479A - 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 the 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 the 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.Because the surface echo of thin layer and Bottom echo signal produce aliasing, traditional pulse echo signal time-domain analysis method can't be confirmed 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; In " The application of broadband ultrasonic spectroscopy to the study of layered media " literary composition, use the 20MHz ultrasonic probe like foreign scholar Haines NF etc.; And the application sound pressure reflection coefficient composes and the phase spectrum signal processing means has obtained hyperacoustic two-way time in the epoxy resin thin layer, and then confirmed the thickness of epoxy resin thin layer.But in the time of can not covering in the thin layer sound pressure reflection coefficient amplitude spectrum adjacent two minimal values for the ultrasound echo signal bandwidth, we can't confirm ultrasonic two-way time in thin layer usually.

Summary of the invention

The purpose of this invention is to provide a kind of based on the sound pressure reflection coefficient power spectrum measurement ultrasonic in thin layer the method for two-way time.This method can be confirmed ultrasonic two-way time at thin layer for the littler thin layer of thickness under same experimental provision condition, enlarged scope, the intuitive measurement results of thin-layered medium thickness measure, and the antinoise interference performance is strong.

Technical scheme of the present invention is: a kind of based on the 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 following:

(1) utilize said impulse ultrasound water logging echo system to thin layer specimen Vertical Launch ultrasonic signal and gather one and form the aliasing signal (sample signal) that reflection echo signal and the water at interface and reflection echo signal that the thin layer lower surface is formed the interface are formed by water and thin layer upper surface;

(2) utilize the upper surface echoed signal (reference signal) of a reference block of said impulse ultrasound water logging echo system acquisition;

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

The real part and the imaginary data of (4) step (3) being tried to achieve are updated in the 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 the formula: | V (f) | ²Expression sound pressure reflection coefficient power spectrum, S (f) is the merchant of sample signal frequency domain and reference signal frequency domain, and Im [S (f)] is the real part of S (f), and Re [S (f)] is 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 _WaterBe the attenuation coefficient (dB/mm) of water, α _{Thin layer}Be the attenuation coefficient (dB/mm) of thin layer, d ₁Be the distance (mm) of the thin layer upper surface of popping one's head in, d is the thickness (mm) of thin layer, and 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 the tank, carry out that system connects and instrumental correction after, by ultra-sonic defect detector, utilize the ultrasonic pulse immersion probe, the thin layer specimen emission in tank, receive ultrasound wave, observe waveform and gather 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) (FFT); Obtain the merchant of sample signal frequency domain data and reference signal frequency domain data; Obtain corresponding real part and imaginary data; With 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 the frequency spectrum of ultrasonic n Δ t two-way time (n >=1) and the sound pressure reflection coefficient power spectrum in thin layer set up, 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 made up 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.At first utilize this system to thin layer specimen Vertical Launch ultrasonic signal and gather one and form the aliasing signal that reflected signal and the thin layer lower surface at interface and reflected signal that water is formed the interface are formed by thin layer upper surface and water; Utilize the upper surface echoed signal of a reference block of this system acquisition again; Respectively the sample signal and the reference signal that collect are carried out FFT; Obtain the merchant of sample signal frequency domain data and standard signal frequency domain data, obtain corresponding real part and imaginary part; Calculate ultrasonic two-way time in thin layer through formula at last.Utilize the ultrasonic of 12～22MHz that thin-layered medium is carried out the measurement of ultrasonic two-way time, be lower than 100ns measurable two-way time.This method does not receive the restriction of thin layer material and homogeneity degree thereof, has overcome because the ultrasound echo signal bandwidth can not cover the little value of two neighboring pole in the thin layer sound pressure reflection coefficient amplitude spectrum, is not sure of the problem of ultrasonic two-way time; Device therefor is simple, workable, cost is low; Be easy to practicability, measuring accuracy is high, and measurement range is wide; Good reproducibility has bigger economic benefit and social benefit.

Description of drawings

Below in conjunction with accompanying drawing and examples of implementation the present invention is described further.

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

Fig. 2 is that the ultrasonic pulse immersion probe of employing nominal frequency 25MHz is the Al matter thin slice sample emissions of 433 μ m and the time-domain signal figure that collects to thickness.

Fig. 3 is the acoustic pressure reflective power spectrogram of Al matter thin slice sample.

Fig. 4 is the amplitude spectrogram of the acoustic pressure reflective power spectrum of Al matter thin slice sample.

Among the figure: 1, ultra-sonic defect detector, 2, the 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

After measurement mechanism shown in Figure 1 carries out system's connection and instrumental correction; At first by ultra-sonic defect detector 1; Adopt ultrasonic pulse immersion probe 2 (the centre frequency 16MHz of wafer diameter 11.4mm, nominal frequency 25MHz; Frequency span (6dB) 12～22MHz) to tested Al matter thin slice sample 3 (using miking thickness is 433 μ m; Because its velocity of sound is 6320m/s, drawing a two-way time according to t=2d/c is 137ns) transmit and receive ultrasound wave (Al matter thin slice sample 3 is as in the tank 4), accomplish the observation and the collection of Al matter thin slice sample Wave data by DPO4032 digital oscilloscope 5.Repeat said process in UT (Ultrasonic Testing) on reference block then, gather the upper surface echoed signal of a reference block, shown in Figure 2 is Al matter thin slice sample echoed signal.Utilize computing machine 6 respectively sample signal and reference signal to be carried out FFT, obtain the merchant of sample signal frequency domain data and reference signal frequency domain data, obtain corresponding real part and imaginary data; 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 thin slice sample 3, as shown in Figure 2.Then the sound pressure reflection coefficient power spectrum is made FFT, ask for its amplitude spectrum, as shown in Figure 3.Read the corresponding horizontal ordinate of each peak value at last, be n (n >=1) the inferior two-way time of ultrasound wave in thin layer.From the amplitude spectrum of power spectrum, read Δ t=128ns respectively, 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 relative error through two-way time of the thickness conversion of miking.

Claims (1)

1. One kind based on the 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), and the measuring process that it adopts is following:

   (1) utilize said impulse ultrasound water logging echo system to thin layer specimen Vertical Launch ultrasonic signal and gather one and form the sample signal that reflection echo signal and the water at interface and reflection echo signal that the thin layer lower surface is formed the interface are formed by water and thin layer upper surface;

   (2) utilize the reference signal of a reference block of said impulse ultrasound water logging echo system acquisition;

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

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

   ${\left|V\left(f\right)\right|}^2=\mathrm{Im}{\left[S\left(f\right)\right]}^2+\mathrm{Re}{\left[S\left(f\right)\right]}^2={\mathrm{\&alpha;}}_1^2+{\mathrm{\&alpha;}}_2^2+L+{\mathrm{\&alpha;}}_n^2+2({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_2+{\mathrm{\&alpha;}}_2{\mathrm{\&alpha;}}_3+L+{\mathrm{\&alpha;}}_{n-1}{\mathrm{\&alpha;}}_n)\cos \mathrm{\&Delta;t}2\mathrm{\&pi;f}$

   $+2({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_3+{\mathrm{\&alpha;}}_2{\mathrm{\&alpha;}}_4+\&CenterDot;\&CenterDot;\&CenterDot;+{\mathrm{\&alpha;}}_{n-2}{\mathrm{\&alpha;}}_n)\cos 2\mathrm{\&Delta;t}2\mathrm{\&pi;f}+\&CenterDot;\&CenterDot;\&CenterDot;+2\left({\mathrm{\&alpha;}}_1{\mathrm{\&alpha;}}_n\right)\cos (n-1)\mathrm{\&Delta;t}2\mathrm{\&pi;f}$

   In the formula: | V (f) | ²Expression sound pressure reflection coefficient power spectrum, S (f) is the merchant of sample signal frequency domain and reference signal frequency domain, and Im [S (f)] is the real part of S (f), and Re [S (f)] is 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 _WaterBe the attenuation coefficient (dB/mm) of water, α _{Thin layer}Be the attenuation coefficient (dB/mm) of thin layer, d ₁Be the distance (mm) of the thin layer upper surface of popping one's head in, d is the thickness (mm) of thin layer, and 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:

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

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

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

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