CN103149274B - A kind of concrete defect detection method - Google Patents

Abstract

The present invention relates to a kind of concrete defect detection method.Method comprises: the linear FM signal in broadband when the diverse location sequential firing in space is wide; Receive echoed signal; For the echoed signal received, broad pulse linear FM signal in time domain is compressed in the shorter time period, according to locus and phase relation, relevant process of making a reduction is carried out to the echoed signal of diverse location, form the large aperture image of equivalence, based on described large aperture image recognition concrete defect.Pulse compression technique is combined with synthetic aperture imaging detection method by the present invention, improves signal to noise ratio (S/N ratio) and the resolution of detection signal, is conducive to the detection of the especially less defect of concrete defect.

Description

A kind of concrete defect detection method

Technical field

The present invention relates to Acoustic detection field, particularly relate to a kind of concrete defect detection method.

Background technology

Current Ultrasonic Detection is widely used in engineering geophysics field, is especially applied in the defects detection of the mass concretes such as dam, bridge, tunnel.The accuracy of ultrasonic testing results is directly connected to safety and the quality evaluation result of engineering.

Pulse echo method is the detection that the mode utilizing single-shot list to receive carries out defect, and ultrasound wave propagation distance in tested component is longer, energy significantly decay after echoed signal be often submerged in noise, cause flaw indication not easy to identify.Sound beam focusing to specific region, thus is strengthened the signal to noise ratio (S/N ratio) of echoed signal by ultrasonic phase array.Phased-array technique is useful in raising penetration range and signal to noise ratio (S/N ratio), but this technology needs complicated hardware and software control system, in complex dielectrics array signal wave beam control in also there is certain difficulty.Meanwhile, Site Detection condition is comparatively complicated, and the transducer of larger aperture is laid exists certain difficulty.

There is not the signal to noise ratio (S/N ratio) and resolution that can improve Ultrasonic Detection at present, again the convenient scheme implemented.

Summary of the invention

For the problems referred to above of the prior art, the invention provides a kind of concrete defect detection method, described method comprises: the linear FM signal in transmitting transducer broadband when the diverse location sequential firing of concrete surface is wide; Receiving transducer receives echoed signal, and is compressed in the shorter time period by the broad pulse linear FM signal in the time domain in the echoed signal received; Carry out coherence stack process according to locus and phase relation to corresponding to the echoed signal after the compression of described diverse location, form the large aperture image of equivalence; Based on described large aperture image recognition concrete defect.

Preferably, broad pulse linear FM signal in time domain in the echoed signal received is compressed in the shorter time period by described receiving transducer, be specially: described broad pulse linear FM signal and reference signal carry out related calculation by receiving transducer, thus described broad pulse linear FM signal was compressed in the shorter time period.

Preferably, described reference signal obtains in the following manner: transmitting transducer directly docks with receiving transducer, and launch described wide time broadband linear FM signal give described receiving transducer, the signal that receiving transducer receives is described reference signal.

Pulse compression technique is combined with synthetic aperture imaging detection method by the embodiment of the present invention, implements comparatively simple, and improves signal to noise ratio (S/N ratio) and the resolution of detection signal, be conducive to the detection of the especially less defect of concrete defect.

Accompanying drawing explanation

Be described in detail specific embodiment of the invention scheme below with reference to accompanying drawings, advantage of the present invention will highlight more accordingly.In the accompanying drawings:

Fig. 1 is the detection scene schematic diagram of the embodiment of the present invention;

Fig. 2 be the embodiment of the present invention relate to containing decaying concrete test block/test specimen schematic diagram;

Fig. 3 is the Received signal strength schematic diagram received through 29 measuring points corresponding to transmitting LFM signal of the embodiment of the present invention;

Fig. 4 is the Received signal strength schematic diagram received through 29 measuring points corresponding to transmitting short pulse signal of the embodiment of the present invention;

Fig. 5 be the embodiment of the present invention about short pulse receiving signal and LFM compressed signal, for the 18th measuring point signal to noise ratio (S/N ratio) contrast schematic diagram;

Fig. 6 is the SAFT imaging results schematic diagram about short pulse excitation of the embodiment of the present invention;

Fig. 7 is the SAFT imaging results schematic diagram about LFM excitation of the embodiment of the present invention.

Embodiment

Below by embodiment, technical scheme of the present invention is described in further detail.

In view of the defect of existing scheme, consider pulse compression technique to be combined with synthetic aperture imaging detection method.

The diverse location sequential firing of described Synthetic Aperture Focussing Imaging (SAFT) in space also receives echoed signal, carries out coherence stack process according to locus and phase relation to the echoed signal of diverse location, thus forms the large aperture of equivalence.The method effectively can improve the signal to noise ratio (S/N ratio) of Ultrasonic Detection.

Described pulse compression technique is the linear FM signal in the broadband when transmitting terminal is launched wide, thus increase the energy transmitted, by the principle of correlation reception, the broad pulse linear FM signal in time domain is compressed within the very short time period at receiving end, both ensure that the resolution of compressed signal, improve again energy and the signal to noise ratio (S/N ratio) of signal largely, investigation depth is increased greatly.At present, pulse compression technique concentrates on underwater sound field and medical research field, and in engineering geophysics field, application is less.

Generally, technical scheme of the present invention realizes in the following manner:

1) choose applicable Site Detection condition and the transmitting transducer that resonance frequency band is wider and receiving transducer.

2) formula (1) is utilized to edit linear frequency modulation coded signal S _code, f ₀for FM signal centre frequency, sampling time interval is Δ t, and amplitude is A, and time width is T, and modulating bandwidth is B, and signal chirp rate is coded signal length (sampling number) is M ₀, the centre frequency f of signal ₀should be consistent with the centre frequency of transducer, the bandwidth of linear FM signal should be selected in transducer-6dB bandwidth range.

For ensureing that signal possesses good pulse compression characteristics, the pulse width T of linear FM signal and the product of bandwidth B should be greater than 10, and are less than 100.

$S_{\mathrm{code}}\left(\mathrm{i\Δt}\right)=A\cos [2\mathrm{\π}(f_0-\frac{B}{2})\mathrm{i\Δt}+\frac{\mathrm{\μ}{\left(\mathrm{i\Δt}\right)}^2}{2}],---\left(1\right)$

0≤i Δ t≤T, i are positive integer, and Δ t is sampling interval.

3) by coded signal S _code(i Δ t) lead-in signal generator is used for excitation, and transmitting transducer directly docks with receiving transducer, record Received signal strength S _ref, S _refas with reference to function, consider the delay of transducer, S _refsampling length M ₁be greater than M ₀.

4) according to ultrasonic field technical norms for measurement, adopt reflectometry to detect, adopt the transducer apparatus of bistatic, T-R transducer distance is less than 2cm, in the position of the N number of equally spaced measuring point of concrete surface mark, and S _codet () lead-in signal generator excitation transducer detects, record the echoed signal e of N number of measuring point _i(t) (1≤i≤N), and record measuring point coordinate (x _i, y _i).For ensure launch wide time band signal be all received, Received signal strength length (sampling number) M ₂should meet: M ₂be greater than M ₁with Δ Lsample_rate/V _estimatesum.Wherein, Δ L is detected concrete thickness, and sample_rate is sample frequency, V _estimatefor wave velocity estimation value, wherein coded signal should be consistent with the sample frequency sample_rate of collection signal.

5) formula (2) is utilized, reference function S _refwith Received signal strength e _icarry out related calculation, obtain N number of compressed signal if M ₃=M ₂+ M ₁,

$S_{c_i}\left(m\right)=\underset{k=1}{\overset{M_1}{\mathrm{\Σ}}}{S}_{\mathrm{ref}}\left(k\right)e_i(k+m),1\≤m\≤M_3,1\≤i\≤N,---\left(2\right)$

If (k+m) is greater than M in computation process ₂, get e _i(k+m)=0.

6) do not consider the effect of distance of sending and receiving transducer, the Gridding length of employing two-dimensional imaging is

Δ l=v _p/ sample_rate, if concrete long l ₁, high l ₂, then transverse grid adds up to h _number=l ₁/ Δ l, longitudinal grid number is v _number=l ₂/ Δ l, obtains the image array I that initial value is 0 _i(m, n), 1≤m≤h _number, 1≤n≤V _number.

Adopt cycle calculations, n1 is increased to M from 1 ₃, step-length is 1, if space networks lattice point (m, n) meets [(m Δ l-Δ l) ²+ (n Δ l-Δ l) ²] ^1/2=k Δ t/2v _p, (3)

Then, image array $I_i(m,n)=I_i(m,n)+S_{c_i}\left(\mathrm{nl}\right),1\≤i\≤N---\left(4\right)$

M, nl, n are integer, 1≤nl≤M ₃, v _pfor concrete velocity of longitudinal wave.

7) to the compressed signal of all measuring points carry out the computing of (4) formula, and superpose, final image matrix can be obtained $I_{\mathrm{sum}}(m,n)={\mathrm{\Σ}}_{i=1}^N{I}_i(m,n)---\left(5\right).$

According to the cross-sectional sizes of defect, set up image array I _sumthe brightness of each grid (m, n) of (m, n) is by compressed signal ? the amplitude of moment ripple determines. that theoretic ripple is from focus to the travel-time of defect impact point.The compressed signal peak value of all measuring points is all by grid (m corresponding to defect impact point _aim, n _aim) carry out amplitude superposition, result is (m _aim, n _aim) place's amplitude maximum, on the contrary, zero defect grid place amplitude is less.The amplitude of all image lattices is by with different look chi imagings, and defect will show with bright band region.

Below in conjunction with accompanying drawing, the embodiment of the present invention is described in more details, so that those skilled in the art understand its principle and implementation detail better.

Fig. 1 is for detecting schematic diagram.For implementing described detection, make the concrete test block as Fig. 2, the long 35cm of this test block, high 29cm, thick 10cm.There is the rectangle defect of a long 10cm, high 3cm centre.Linear FM signal encourage, time wide 20 μ s, bandwidth range 250kHz-750kHz.

Particularly, following steps are carried out:

(1) according to test block size, test block is divided into transverse direction 176, vertical direction 145 grids.Tested by reality, test block longitudinal wave velocity is 3970m/s.Select transducer centre frequency 500kHz ,-6dB bandwidth 500kHz.

(2) 3 in technical scheme is utilized) obtain reference signal.

(3) sending and receiving Distance Between Transducers is 1cm, the left hand edge 3cm of first measuring point distance test block, successively the transducer of synchronizing moving transmitting-receiving to the right, and adjacent measuring point distance 1cm, detect 29 measuring points altogether, detection signal is as Fig. 3.

(4) after carrying out same-amplitude compacting to direct-path signal, utilize formula (2) to obtain the pulse compression signal of 29 measuring points, as Fig. 4, the signal to noise ratio (S/N ratio) of compressed signal improves degree in table 1.

(5) utilize detection scheme 6) and 7) obtain the imaging results shown in Fig. 5, by Fig. 5, imaging results and actual defects position comparatively identical.

For encouraging Detection results to contrast with short pulse, be the excitation of 500kHz short pulse by the frequency in 2 cycles, test mode is identical with impulse compression method test mode.Received signal strength is as Fig. 4.After the signal compression of the 18th measuring point that contrast LFM detects, comparatively short pulse detection signal-to-noise ratio improves about 8dB, as Fig. 5.

For contrast SAFT image effect, the signal amplitude within 12dB is only calculated during SAFT imaging, Fig. 6 and Fig. 7 is respectively the Received signal strength of short pulse excitation and the SAFT imaging results of LFM excitation compressed signal, two kinds of methods all can carry out imaging to the defective locations of inside concrete, the defect imaging position of Fig. 6 is a little less than the defective locations of Fig. 7, and the bright band re-imaging length of two figure all can show the lateral length of defect.Noise spot in Fig. 6 apparently higher than noise spot in Fig. 7, will show that impulse compression method can significantly improve the signal to noise ratio (S/N ratio) of defects detection.

To sum up, visible key point of the present invention and advantage as follows:

1) launch linear FM signal when having wide, broadband character, have good compression property, after compression, the signal to noise ratio (S/N ratio) of signal is higher.

2) transmit wide time, broadband character determines that the energy of signal is comparatively large, can penetrate the tested component of long distance.

3) basic waveform of linear FM signal is sinusoidal wave, and the length of signal does not have anything to limit,

Its pulse compression ratio can manual control, is is easily transmitted and received by existing sonac.

4) the detected image noise point calculated is few, easily to the identification of defect.

Those skilled in the art should recognize further, the software unit that the method step in conjunction with embodiment disclosed herein description can use hardware, processor to perform, or the combination of the two is implemented.Software unit can be placed in the storage medium of other form any known in random access memory (RAM), internal memory, ROM (read-only memory) (ROM), electrically programmable ROM, electrically erasable ROM, register, hard disk, moveable magnetic disc, CD-ROM or technical field.

It is to be noted, these are only present pre-ferred embodiments, not be used for limiting practical range of the present invention, the technician with professional knowledge base can realize the present invention by above embodiment, therefore every any change according to making within the spirit and principles in the present invention, amendment and improvement, all cover by the scope of the claims of the present invention.Namely, above embodiment is only in order to illustrate technical scheme of the present invention and unrestricted, although with reference to preferred embodiment to invention has been detailed description, those of ordinary skill in the art is to be understood that, can modify to technical scheme of the present invention or equivalent replacement, and not depart from the spirit and scope of technical solution of the present invention.

Claims (3)

1. a concrete defect detection method, is characterized in that, described method comprises:

The linear FM signal in transmitting transducer broadband when the diverse location sequential firing of concrete surface is wide;

Receiving transducer receives echoed signal, and is compressed in the shorter time period by the broad pulse linear FM signal in the time domain in the echoed signal received;

Carry out coherence stack process according to locus and phase relation to corresponding to the echoed signal after the compression of described diverse location, form the large aperture image of equivalence;

Based on described large aperture image recognition concrete defect;

Described linear FM signal is determined by following formula:

$S_{\mathrm{code}}\left(\mathrm{i\Δt}\right)=A\cos [2\mathrm{\π}(f_0-\frac{B}{2})\mathrm{i\Δt}+\frac{\mathrm{\μ}{\left(\mathrm{i\Δt}\right)}^2}{2}]$

Wherein, described f ₀for described linear FM signal centre frequency, described Δ t is sampling time interval, and described A is amplitude, and described B is modulating bandwidth, and 0≤i Δ t≤T, i are positive integer, and described T is time width, and the product of T and B is greater than 10, and is less than 100, and signal chirp rate is coded signal length is M ₀;

Echoed signal after described compression is determined by following formula:

$S_{c_i}\left(m\right)=\underset{k=1}{\overset{M_1}{\mathrm{\Σ}}}{S}_{\mathrm{ref}}\left(k\right)e_i(k+m),1\≤m\≤M_3,1\≤i\≤N$

Wherein, described S _reffor Received signal strength, M ₃=M ₁+ M ₂, M ₁for signal S _refsampling length, M ₁be greater than M ₀, M ₂for Received signal strength length, N is the number of the equidistant point position at concrete surface mark, described e _ifor the broad pulse linear FM signal in the time domain in the described echoed signal received, if k+m>M in computation process ₂, then e _i(k+m)=0;

Describedly carry out coherence stack process according to locus and phase relation to the echoed signal after the compression corresponding to described diverse location, the large aperture image forming equivalence specifically comprises:

Utilize the echoed signal after described compression, obtain image array, overlap-add procedure is carried out to described image array, obtain the large aperture image of equivalence; Described image array is determined by following formula;

${I^{\mathrm{nl}}}_i(m,n)={I_i}^{\mathrm{nl}-1}(m,n)+S_{c_i}\left(\mathrm{nl}\right),$

Wherein, the Gridding length adopting two-dimensional imaging is Δ l=v _p/ sample_rate, if concrete long l ₁, high l ₂, then transverse grid adds up to h _number=l ₁/ Δ l, longitudinal grid number is v _number=l ₂/ Δ l, image array I _i(m, n) initial value is 0,1≤i≤N, 1≤m≤h _number, 1≤n≤v _number, m, nl, n are integer, 1≤nl≤M ₃, v _pfor concrete velocity of longitudinal wave; Adopt cycle calculations, n1 is increased to M from 1 ₃, step-length is 1, if space networks lattice point (m, n) meets [(m Δ l-Δ l) ²+ (n Δ l-Δ l) ²] ^1/2=k Δ t/2v _p; Then described large aperture image is determined by following formula:

$I_{\mathrm{sum}}(m,n)={\mathrm{\Σ}}_{i=1}^N{I}_i(m,n).$

2. method according to claim 1, it is characterized in that, broad pulse linear FM signal in time domain in the echoed signal received is compressed in the shorter time period by described receiving transducer, be specially: described broad pulse linear FM signal and reference signal carry out related calculation by receiving transducer, thus described broad pulse linear FM signal was compressed in the shorter time period.

3. method according to claim 2, it is characterized in that, described reference signal obtains in the following manner: transmitting transducer directly docks with receiving transducer, and launch described wide time broadband linear FM signal give described receiving transducer, the signal that receiving transducer receives is described reference signal.