CN111307945A - Imaging method and device for detecting near-surface defects of ballastless track based on ultrasonic array - Google Patents

Abstract

The invention discloses an imaging method and device for detecting near-surface defects of ballastless track based on ultrasonic array. The ultrasonic signal inside the ballastless track is sent to the inside of the ballastless track, and the ultrasonic array sensor adopts the mode of self-sending and self-receiving to obtain the diffused field signal in the ballastless track and transmit the diffused field signal to the computer; the computer uses MATLAB software to passively measure the received signal. Extract the Green's function, perform cross-correlation on the diffuse field signal, reconstruct the Green's function between the array elements, obtain the undelayed response between the array elements, recover the early defect information submerged by noise, and then perform ballastless imaging based on the all-focus imaging algorithm. Imaging of orbital near-surface defects. The invention can clearly present the information of the near-surface defects of the track slab, and can provide timely early warning and powerful evaluation means for the daily track slab damage detection of the high-speed rail.

Description

An imaging method and device for detecting near-surface defects of ballastless track based on ultrasonic array

technical field

The invention relates to an imaging method and device for detecting near-surface defects of a ballastless track based on an ultrasonic array, and belongs to the technical field of track non-destructive testing.

Background technique

Due to the advantages of high-speed railway, such as high speed, strong transportation capacity, safety and punctuality, high-speed railway has become one of the vigorously developed public transportation modes in my country at this stage. With the rapid development of high-speed railway, ballastless track, as a main track structure, is composed of ballastless track slab, CA mortar layer, support layer and foundation bed, and its application range is getting wider and wider. However, in recent years, more and more diseases have appeared in the structure of high-speed rail lines, including the under-line structure relief, through cracks, and voids in the CA mortar layer. The main reason is that, on the one hand, during the high-speed and heavy-load operation of the train, the ballastless track will be squeezed, impacted, etc., which may cause incompactness, cracks or voids inside, and the formation of damage layers or honeycomb hemp layers on the outside. On the other hand, the ballastless track may have problems in the pre-production due to construction technology and construction experience, resulting in its own defects; in addition, natural disasters such as rain and snow erosion and changes in ambient temperature will also lead to defect. The existence of defects will seriously affect the bearing capacity and durability of the ballastless track, which will lead to the failure of the ballastless track structure. It is precisely the important prerequisite for ensuring the rapid and safe operation of high-speed rail, which will be directly related to the normal operation of the train and the personal safety of passengers.

However, at present, the near-surface defect detection of ballastless tracks in my country mainly relies on manual static detection technology. Since the effective skylight time for rail transit to be used for line maintenance is only 2 to 3 hours, and the thread of high-speed railway is very long, if The use of the existing detection methods not only consumes a lot of manpower and material resources, but also has very low efficiency, high detection and maintenance costs, and cannot meet the needs of rail safety early warning.

SUMMARY OF THE INVENTION

In view of the above problems and requirements existing in the prior art, the purpose of the present invention is to provide an imaging method and device for detecting near-surface defects of ballastless tracks based on ultrasonic arrays, so as to achieve efficient, non-destructive and real-time detection of near-surface defects of ballastless tracks Defects, provide timely early warning and strong guarantee for the safe operation of high-speed rail.

To achieve the above object, the present invention adopts the following technical solutions:

An imaging method for detecting near-surface defects of a ballastless track based on an ultrasonic array, comprising the following steps:

a) Use the pulse signal to excite the receiving transducer and transmit the ultrasonic signal with a frequency in the range of 1-2.5MHz to the inside of the ballastless track through the ultrasonic array probe. Diffuse the field signal and transmit the diffused field signal to the computer, specifically: first use the pulse signal to excite the transmitting end of the receiving transducer to transmit an ultrasonic signal with a frequency in the range of 1-2.5MHz, and transmit the ultrasonic signal from the transmitting end of the ultrasonic array sensor. To the inside of the ballastless track, the diffused field signal is collected by the receiving end of the ultrasonic array sensor and transmitted to the receiving end of the receiving transducer excited by the pulse signal, and then the receiving end of the receiving transducer is excited by the pulse signal to receive the diffused field signal. The field signal is transmitted to the computer;

b) The computer uses MATLAB software to passively extract the Green's function from the received signal, cross-correlate the diffuse field signal, reconstruct the Green's function between the array elements, obtain the undelayed response between the array elements, and recover from being submerged by noise. The early defect information of the ballastless track is then imaged based on the all-focus imaging algorithm.

In one embodiment, the step b) specifically comprises the following operations:

1) Data processing:

First of all, due to the interaction between the ultrasonic signal and the defect target during the propagation of the ultrasonic signal inside the ballastless track, an approximately uniform sound field will be formed after scattering and multiple reflections. This sound field is a diffuse field, and As shown in step a), the diffused field signal in the ballastless track can be obtained through the ultrasonic array sensor, and any two receiving array elements in the ultrasonic array sensor are set as r1 and r2 respectively, and the two receiving array elements r1 and r2 In a closed surface space, the integral of all sound sources of the sound field cross-spectrum at the receiving array elements r1 and r2 is equal to the difference between the frequency domain causal Green function and the non-causal Green function between r1 and r2:

G(r ₁ , r ₂ , ω)-G ^* (r ₁ , r ₂ , ω)=-2iω∫G(r ₁ ,r,ω)G(r ₂ ,r,ω)dv(1);

In formula (1), the left side of the equation is the difference between the causal and non-causal functions of the frequency domain Green's function between the two receiving elements r1 and r2, and the right side of the equation represents the sound field interaction between the receiving elements r1 and r2. The integral of all sound sources related, specifically, G(r ₁ ,r ₂ ,ω) represents the causal Green function between r1 and r2 in the frequency domain, * represents the conjugate complex number, G ^* (r ₁ ,r ₂ ,ω) ) represents the non-causal Green's function between r1 and r2 in the frequency domain, i represents the imaginary unit, i ² =-1, ω represents the angular frequency of the transmitted signal, r is the position of any point in the closed space V of diffusion field integration, Represents any defect target, which can be regarded as a noise source, G(r ₁ ,r,ω) represents the frequency domain Green’s function propagation formula between r and r1, G(r ₂ ,r,ω) represents the gap between r and r2 The frequency domain Green's function propagation formula, dV represents the differential of the closed space V;

Then, assuming that the intensity of the diffuse field noise source is uniformly distributed in space and independent of each other, the power spectral density |q(ω)| ₂ is also independent of the position of the noise source:

<q(r ₁ , ω)*q(r ₂ , ω)>=δ(r ₁ -r ₂ )|q(ω)| ² (2);

Formula (2) represents that the expected value of the cross-power spectrum of the signals at the frequency domains r1 and r2 is equal to the power spectral density of the noise source between r1 and r2. Specifically, in formula (2), <q(r ₁ , ω)*q( r ₂ ,ω)> represents the expected value of the cross-power spectrum of the signals at r1 and r2 in the frequency domain, q(r ₁ ,ω) represents the field strength at r1, q(r ₂ ,ω) represents the field strength at r2, <>represents the expected value of the statistical average, * represents the conjugate complex number, δ(r ₁ -r ₂ ) represents the cross-power spectrum of the signal between r1 and r2 is independent of the location of the noise source;

At the same time, the cross-correlation between the sound fields at the positions of the two receiving array elements r1 and r2 in the frequency domain is:

<P(r ₁ , ω)P*(r ₂ , ω)>=|q(ω)| ² ∫G(r ₁ , r)G*(r ₂ , r)dv (3);

In formula (3), p(r ₁ ,ω) represents the sound field at the receiving array element r1, p(r ₂ ,ω) represents the sound field at the receiving array element r2, <p(r ₁ ,ω)*p(r ₂ ,ω)> represents the cross-correlation function between the sound fields at the positions of the two receiving array elements r1 and r2, * represents the conjugate complex number; G(r ₁ , r) represents the propagation formula of r1 and r frequency domain Green’s function, G( r ₂ , r) represents the propagation formula of Green's function in the frequency domain of r2 and r;

Then from formulas (1) and (3) we get:

(G(r ₁ , r ₂ , ω)-G ^* (r ₁ , r ₂ , ω))|q(ω)| ² =-2iω<P(r ₁ ,ω)P ^* (r ₂ ,ω) >(4);

In formula (4), the left side of the equation is the Green's function G(r ₁ , r ₂ , ω) and its corresponding time reversal, that is, the conjugate operation in the corresponding frequency domain. Multiply these two terms by the random noise. After the power spectral density, the result is equal to the cross-correlation result of the two receiving array elements r1 and r2 in the diffuse field on the right side of the equation, * represents the conjugate complex number;

Then, the time domain expression corresponding to formula (4) is obtained. The frequency domain 2iω corresponds to the time domain 2d/dt. According to the convolution theorem, the product in the frequency domain corresponds to the convolution in the time domain, thus obtaining:

代表互相关运算，C_q(t)表示扩散场中的噪声q(t)的自相关结果，d/dt代表对t求导，p(r₁,t)代表时域中接收阵元r1处的声场，p(r₂,t)代表时域中接收阵元r2处的声场；In formula (5), G(r ₁ ,r ₂ ,t) represents the Green’s function between r1 and r2 in the time domain, and G(r ₁ ,r ₂ ,-t) represents G(r ₁ ,r ₂ ,t) ), which corresponds to the conjugation operation in the frequency domain, * represents the convolution operation,

Represents the cross-correlation operation, C _q (t) represents the autocorrelation result of the noise q(t) in the diffuse field, d/dt represents the derivation of t, p(r ₁ , t) represents the receiving array element r1 in the time domain The sound field of , p(r ₂ ,t) represents the sound field at the receiving array element r2 in the time domain;

The results of formulas (4) and (5) show that the sound fields p(r ₁ ,t) and p(r ₂ ,t) of the receiving array elements in the diffuse field are correlated and derived, and the result is equal to the difference between the two receiving array elements. Green's function response, according to the principle of reciprocity of sound waves, on the time axis, the Green's function response between the two receiving array elements has symmetry;

2) Full focus imaging:

The ultrasonic array sensor has an independent linear array, which can not only realize B-scan and S-scan with dynamic focusing, but also has a powerful full-matrix capture function, which provides a variety of imaging methods for offline data processing;

The ultrasonic array sensor is composed of a number of ultrasonic sensors in an array. The ultrasonic sensor used for transmitting signals is called a transmitting sensor, and the ultrasonic sensor used for receiving signals is called a receiving sensor. Each transmitting sensor corresponds to a transmitting array element, and each receiving The sensor corresponds to a receiving array element. Suppose there is a defect P(x, y) on the near surface of the ballastless track. Taking a pair of transceiver sensor combinations in the ultrasonic array sensor as an example, it is assumed that the i-th array element transmits, and the If j array elements are received, then for all arrays in the ultrasonic array sensor, the time values from the array element of each transmitted signal and the array element of each received signal to P(x, y) are different, that is, there is a phase difference, Set the coordinates of the i-th transmitting array element as (x _Ti , y _Ti ), the flight time to P(x,y) as Ti, and set the coordinates of the j-th receiving array element as (x _Rj , y _Rj ) , the flight time to P(x,y) is T _j , the total flight time T _ij can be obtained as:

In formula (6), c is the constant longitudinal wave velocity of the measured ballastless track, and its value is 5900m/s;

Then the array size is an ultrasonic phased array of n*n transceiver combination pairs, and the size I _ij of a pixel value corresponding to any array element is:

Since the accumulation of pixel values at the defect is much higher than that of the normal area, different colors are displayed during imaging, so that the defect area and the size and shape of the defect can be quickly and accurately identified.

An imaging device for detecting near-surface defects of ballastless tracks based on an ultrasonic array, comprising a pulse signal to excite a receiving transducer, an ultrasonic array sensor and a computer, and the pulse signal to excite the transmitting port of the receiving transducer and the transmitting in the ultrasonic array sensor The pulse signal excites the receiving port of the receiving transducer to connect with the receiving end of the ultrasonic array sensor, and the pulse signal excites the receiving port of the receiving transducer to connect with the computer signal.

An embodiment also includes a mobile power supply unit, the mobile power supply unit includes a mobile power supply housing and a power supply body provided in the mobile power supply housing, the power supply body is respectively electrically connected with the pulse signal excitation receiving transducer and the ultrasonic array sensor , the pulse signal excitation and receiving transducer is installed in the mobile power supply casing, the side of the mobile power supply casing is evenly provided with a number of openings that are adapted to the pulse signal excitation and receiving transducer, the ultrasonic array sensor is vertical It is arranged in the casing of the mobile power supply, and the signal transmitting/receiving port of the ultrasonic array sensor passes through the casing of the mobile power supply and is located under the casing of the mobile power supply.

In a preferred solution, handles are provided at both ends of the mobile power supply housing.

An embodiment further includes a mobile communication control unit in signal connection with the pulse signal excitation receiving transducer.

A preferred solution, the mobile communication control unit includes a communication unit and a control unit, the communication unit has a wireless connection function, the control unit is signal-connected with the communication unit, and the control unit is excited by a pulse signal to receive a transducer signal connected, the communication unit is wirelessly connected to the computer.

In a preferred solution, the mobile communication control unit is arranged on the top of the mobile power supply housing.

Compared with the prior art, the present invention has the following beneficial technical effects:

1) The ultrasonic array sensor used in the present invention has the advantages of high energy and small attenuation, the ultrasonic energy hardly leaks, and is better incident on the inside of the material to be tested and interacts with the defects, forming a scattering signal favorable for detection, and Each array element in the ultrasonic array sensor can be excited individually or in combination, can realize focusing and deflection functions, and can better collect diffuse field signals, so that the present invention can use the diffuse field signals to detect slab ballastless tracks, Due to the characteristics of the diffusion field, the signal annihilated in the noise at the early stage can be reconstructed, which is convenient for the processing and analysis of the near-surface defects of the track plate, and effectively improves the detection efficiency;

2) When the present invention processes and images the signal, the computer first uses the principle of the cross-correlation operation between the diffused field signals of the receiving array elements to reconstruct the Green's function, obtains the undelayed response between the array elements, and extracts the noise submerged. Early defect scattering information, and then using frequency-domain synthetic aperture focusing imaging technology and time-domain all-focusing imaging method to superimpose signal amplitudes at defects, realize the visualization of slab ballastless track defects, and improve the accuracy and clarity of imaging. It can not only ensure the ability of high resolution, but also effectively reduce the calculation time of imaging, with high speed and high precision;

To sum up, the present invention can realize efficient, non-destructive, accurate and real-time detection of near-surface defects of ballastless tracks, can provide timely early warning and strong guarantee for the safe operation of high-speed rail, and can provide strong support for subsequent track maintenance work; Compared with the existing technology, the invention has significant progress and application value.

Description of drawings

1 is a schematic structural diagram of a pulse signal excitation and receiving transducer, an ultrasonic array sensor, a wireless power supply unit, and a mobile communication control unit in an imaging device for detecting near-surface defects in ballastless tracks based on an ultrasonic array provided by an embodiment;

2 is a schematic structural diagram from another perspective of the pulse signal excitation and receiving transducer, the ultrasonic array sensor, the wireless power supply unit, and the mobile communication control unit in the imaging device for detecting near-surface defects of ballastless tracks based on an ultrasonic array provided by an embodiment;

3 is a schematic structural diagram of an imaging device for detecting near-surface defects in ballastless tracks based on an ultrasonic array provided by an embodiment;

FIG. 4 is a state diagram of the imaging device according to the embodiment when it is working;

Fig. 5 is the principle diagram of all-focus imaging in the embodiment;

6 is a cross-sectional view of the detection track plate according to the embodiment;

7 is an all-focus imaging diagram of the track plate according to the embodiment;

The symbols in the figure are as follows: The symbols in the figure are as follows: 1. The pulse signal excites the receiving transducer; 2. The ultrasonic array sensor; 21. The signal transmitting/receiving port of the ultrasonic array sensor; 3. The mobile power unit; 31, The mobile power Shell; 311, opening; 312, handle; 4, mobile communication control unit; 5, no track; 6, computer.

Detailed ways

The technical solutions of the present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

1 to 4: An imaging device for detecting near-surface defects of ballastless tracks based on an ultrasonic array provided by the present invention includes a pulse signal excitation and receiving transducer 1, an ultrasonic array sensor 2 and a computer 6, and the pulse The signal excites the transmitting port of the receiving transducer 1 to be signal-connected with the transmitting end in the ultrasonic array sensor 2, and the pulse signal excites the receiving port of the receiving transducer 1 to signally connect with the receiving end in the ultrasonic array sensor 2. The receiving port of the signal excitation receiving transducer 1 is connected to the computer signal.

The ultrasonic array sensor 2 can be a commercially available product. For example, a contact ultrasonic array sensor can be used, which has the advantages of high energy and low attenuation, and the ultrasonic energy hardly leaks, so that it can better enter the interior of the material to be tested. and interact with defects to form scattering signals favorable for detection. The ultrasonic array sensor 2 is composed of several ultrasonic sensors in the form of an array. For example, in this embodiment, the ultrasonic array sensor 2 can be composed of 8 rows of 3 The column consists of 24 ultrasonic sensors. Correspondingly, the ultrasonic array sensor 2 has 24 array elements, and the array elements of each ultrasonic sensor can be excited individually or in combination to realize focusing and deflection functions. In addition, it can be seen from the above that the ultrasonic array sensor 2 in this embodiment has a transmitting end and a receiving end, and has the function of self-transmitting and self-receiving, that is, some of the ultrasonic sensors constituting the ultrasonic array sensor 2 are transmitting sensors for transmitting signals, The rest is the receiving sensor for receiving the signal. Due to the different propagation speed of ultrasonic waves in media with different densities, when it passes through the interface of two different media, reflection and scattering will occur. Because the ballastless track is a concrete component, it is composed of a mixture of sand, cement, and stones. Porous and heterogeneous composite materials, the ultrasonic pulse wave emitted by the receiving transducer 1 excited by the pulse signal will be diffracted when it encounters defects in the concrete, and will be scattered and reflected at the defect interface, resulting in the sound wave energy reaching the receiving sensor. The amplitude is significantly reduced. In this application, the ultrasonic array sensor 2 can not only collect the diffuse field signal more efficiently, but also superimpose the received diffuse field signal, so that the reflected diffuse field signal radiates energy in a certain direction. However, the total radiation energy in other directions is smaller, so as to achieve the focusing effect on the diffuse field signal, so that the useful diffuse field signal is enhanced, and the interference signal is suppressed, thereby ensuring the accuracy of signal acquisition and detection results.

In addition, the imaging device described in this embodiment further includes a mobile power supply unit 3, the mobile power supply unit 3 includes a mobile power supply housing 31 and a power supply body (not shown) disposed in the mobile power supply housing 31, the power supply body is respectively connected with The pulse signal excitation and receiving transducer 1 and the ultrasonic array sensor 2 are electrically connected, and the pulse signal excitation and receiving transducer 1 is installed in the mobile power supply housing 31, and the side of the mobile power supply housing 31 is evenly provided with several pulse signals The opening 311 adapted to the excitation and receiving transducer 2 (to facilitate the pulse signal excitation of the receiving transducer 1 to transmit and receive signals), the ultrasonic array sensor 2 is vertically arranged in the mobile power supply housing 31, and the ultrasonic array sensor 2 The signal transmitting/receiving port 21 passes through the mobile power supply housing 31 and is located below the mobile power supply housing 31 (to facilitate the track detection by the ultrasonic array sensor 2). The mobile power supply unit supplies power for the rest of the imaging device. In addition, the pulse signal excitation and receiving transducer 1 and the ultrasonic array sensor 2 are collectively integrated in the mobile power supply housing 31, which effectively simplifies the overall structure and occupation of the device. The floor area is convenient for the overall movement of the device.

In addition, both ends of the mobile power supply housing 31 are provided with handles 312 , so that the mobile power supply unit 3 and the device as a whole can be transported and installed through the handles 312 .

In addition, the imaging device described in this embodiment further includes a mobile communication control unit 4 , and the mobile communication control unit 4 is signal-connected to the pulse signal excitation and reception transducer 1 . Specifically, the mobile communication control unit 4 includes a communication unit and a control unit, the communication unit has a wireless connection function (for example, a Bluetooth connection function, which can be connected with the computer 6 via Bluetooth), so as to realize communication with a remote terminal (not shown in the figure). out) for wireless communication connection, the control unit (which can be a commercially available single-chip microcomputer, a controller, etc.) is signal-connected with the communication unit, and the control unit is signal-connected with the pulse signal excitation receiving transducer 1 to automatically control the pulse signal Activate the switch of the receiving transducer 1.

In addition, the mobile communication control unit 4 is arranged on the top of the mobile power supply housing 31 , and can be fixedly installed on the top of the mobile power supply housing 31 , that is, the components of the imaging device except the computer 6 can be integrated into the mobile power supply housing 31 . Here, the overall structure of the device is simplified.

The imaging method for detecting near-surface defects of ballastless tracks using the imaging device of the present invention is as follows:

a) Place the imaging device on the free track 5 (as shown in Figure 4), adjust the position, and first use the pulse signal to excite the transmitting end of the receiving transducer 1 to transmit ultrasonic waves with a frequency in the range of 1 to 2.5 MHz The signal is transmitted to the inside of the ballastless track 5 by the transmitting end of the ultrasonic array sensor 2, and then the diffused field signal is collected by the receiving end of the ultrasonic array sensor 2 and transmitted to the receiving end of the pulse signal excitation receiving transducer 1, and then The receiving end of the receiving transducer 1 is excited by the pulse signal to transmit the received diffuse field signal to the computer 6;

b) The computer 6 uses MATLAB software to passively extract the Green's function from the received signal, perform cross-correlation on the diffuse field signal, reconstruct the Green's function between the array elements, obtain the undelayed response between the array elements, and restore the noise The submerged early defect information, and then the ballastless track near-surface defect imaging is performed according to the all-focus imaging algorithm, which includes the following operations:

1) Data processing:

First, due to the interaction between the ultrasonic signal and the defect target (see Figure 6) during the propagation of the ultrasonic signal inside the ballastless track, an approximately uniform sound field will be formed after scattering and multiple reflections. The sound field is the diffuse field, and as shown in step a), the diffuse field signal in the ballastless track can be obtained through the ultrasonic array sensor, and any two receiving array elements in the ultrasonic array sensor are set as r1 and r2, respectively. The receiver elements r1 and r2 are in a closed surface space, then the integral of all sound sources of the sound field cross-spectrum at the receiver elements r1 and r2 is equal to the difference between the frequency domain causal Green function and the non-causal Green function between r1 and r2:

G(r ₁ , r ₂ , ω)-G ^* (r ₁ , r ₂ , ω)=-2iω∫G(r ₁ ,r,ω)G(r ₂ ,r,ω)dv(1);

In formula (1), the left side of the equation is the difference between the causal and non-causal functions of the frequency domain Green's function between the two receiving elements r1 and r2, and the right side of the equation represents the sound field interaction between the receiving elements r1 and r2. The integral of all sound sources related, specifically, G(r ₁ ,r ₂ ,ω) represents the causal Green function between r1 and r2 in the frequency domain, * represents the conjugate complex number, G ^* (r ₁ ,r ₂ ,ω) ) represents the non-causal Green's function between r1 and r2 in the frequency domain, i represents the imaginary unit, i ² =-1, ω represents the angular frequency of the transmitted signal, r is the position of any point in the closed space V of diffusion field integration, Represents any defect target, which can be regarded as a noise source, G(r ₁ ,r,ω) represents the frequency domain Green’s function propagation formula between r and r1, G(r ₂ ,r,ω) represents the gap between r and r2 The frequency domain Green's function propagation formula, dV represents the differential of the closed space V;

Then, assuming that the intensity of the diffuse field noise source is uniformly distributed in space and independent of each other, the power spectral density |q(ω)| ₂ is also independent of the position of the noise source:

<q(R ₁ , ω)*q(r ₂ , ω)>=δ(r ₁ −r ₂ )|q(ω)| ² (2);

Formula (2) represents that the expected value of the cross-power spectrum of the signals in the frequency domain r1 and r2 is equal to the power spectral density of the noise source between r1 and r2. Specifically, in formula (2), <q(r ₁ , ω)*q( r ₂ ,ω)>represents the expected value of the cross-power spectrum of the signals at r1 and r2 in the frequency domain, q(r ₁ ,ω) represents the field strength at r1, q(r ₂ ,ω) represents the field strength at r2,<>represents the expected value of the statistical average, * represents the conjugate complex number, δ(r ₁ -r ₂ ) represents the cross-power spectrum of the signal between r1 and r2 is independent of the location of the noise source;

At the same time, the cross-correlation between the sound fields at the positions of the two receiving array elements r1 and r2 in the frequency domain is:

<P(r ₁ , ω)P ^* (r ₂ , ω)>=|q(ω)| ² ∫G(r ₁ , r)G ^* (r ₂ , r)dv (3);

In formula (3), p(r ₁ ,ω) represents the sound field at the receiving array element r1, p(r ₂ ,ω) represents the sound field at the receiving array element r2, <p(r ₁ ,ω)*p(r ₂ ,ω)> represents the cross-correlation function between the sound fields at the positions of the two receiving array elements r1 and r2, * represents the conjugate complex number; G(r ₁ , r) represents the propagation formula of r1 and r frequency domain Green’s function, G( r ₂ , r) represents the propagation formula of Green's function in the frequency domain of r2 and r;

Then from formulas (1) and (3) we get:

(G(r ₁ , r ₂ , ω)-G ^* (r ₁ , r ₂ , ω))|q(ω)| ² =-2iω<P(r ₁ ,ω)P ^* (r ₂ ,ω) >(4);

In formula (4), the left side of the equation is the Green's function G(r ₁ , r ₂ , ω) and its corresponding time reversal, that is, the conjugate operation in the corresponding frequency domain. Multiply these two terms by the random noise. After the power spectral density, the result is equal to the cross-correlation result of the two receiving array elements r1 and r2 in the diffuse field on the right side of the equation, * represents the conjugate complex number;

Then, the time domain expression corresponding to formula (4) is obtained. The frequency domain 2iω corresponds to the time domain 2d/dt. According to the convolution theorem, the product in the frequency domain corresponds to the convolution in the time domain, thus obtaining:

代表互相关运算，Cq(t)表示扩散场中的噪声q(t)的自相关结果，d/dt代表对t求导，p(r₁,t)代表时域中接收阵元r1处的声场，p(r₂,t)代表时域中接收阵元r2处的声场；In formula (5), G(r ₁ ,r ₂ ,t) represents the Green’s function between r1 and r2 in the time domain, and G(r ₁ ,r ₂ ,-t) represents G(r ₁ ,r ₂ ,t) ), which corresponds to the conjugation operation in the frequency domain, * represents the convolution operation,

Represents the cross-correlation operation, Cq(t) represents the autocorrelation result of the noise q(t) in the diffuse field, d/dt represents the derivation of t, and p(r ₁ ,t) represents the receiving array element r1 in the time domain. Sound field, p(r ₂ ,t) represents the sound field at the receiving array element r2 in the time domain;

The results of formulas (4) and (5) show that the sound fields p(r ₁ ,t) and p(r ₂ ,t) of the receiving array elements in the diffuse field are correlated and derived, and the result is equal to the difference between the two receiving array elements. Green's function response, according to the principle of reciprocity of sound waves, on the time axis, the Green's function response between the two receiving array elements has symmetry;

2) Full focus imaging:

The ultrasonic array sensor has an independent linear array, which can not only realize B-scan and S-scan with dynamic focusing, but also has a powerful full-matrix capture function, which provides a variety of imaging methods for offline data processing;

The ultrasonic array sensor is composed of a number of ultrasonic sensors in an array. The ultrasonic sensor used for transmitting signals is called a transmitting sensor, and the ultrasonic sensor used for receiving signals is called a receiving sensor. Each transmitting sensor corresponds to a transmitting array element, and each receiving The sensor corresponds to a receiving array element, as shown in Figure 5, assuming that the ballastless track has a defect P(x, y) on the near surface, taking a pair of transceiver sensor combinations in the ultrasonic array sensor as an example, it is assumed that it is the i-th For all arrays in the ultrasonic array sensor, the time values from the array element of each transmitted signal and the array element of each received signal to P(x, y) are different , that is, there is a phase difference, set the coordinates of the i-th transmitting array element as (x _Ti , y _Ti ), the flight time to P(x, y) as Ti, and set the coordinates of the j-th receiving array element as ( x _Rj , y _Rj ), the flight time to P(x,y) is T _j , and the total flight time T _ij can be obtained as:

In formula (6), c is the constant longitudinal wave velocity of the measured ballastless track, and its value is 5900m/s;

Then the array size is an ultrasonic phased array of n*n transceiver combination pairs, and the size I _ij of a pixel value corresponding to any array element is:

Since the accumulation of pixel values at the defect is much higher than that of the normal area, different colors are displayed during imaging, so that the defect area and the size and shape of the defect can be quickly and accurately identified (as shown in Figure 7).

From the above, it can be seen that the present invention can realize the detection and evaluation of near-surface defects of ballastless track, solve the problem of low efficiency of the current track, and can greatly reduce the manpower and work intensity, and provide the service of visualization of defects, which can improve railway safety. Maintenance provides strong support; in addition, the present invention has a simple structure and convenient use, which can greatly reduce the maintenance cost; therefore, the present invention has significant progress and application value compared with the prior art.

Finally, it is necessary to point out here: the above is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this, and any person skilled in the art is within the technical scope disclosed by the present invention. Any changes or substitutions that can be easily thought of within the scope of the present invention should be covered within the protection scope of the present invention.

Claims (7)

1. An imaging method for detecting near-surface defects of a ballastless track based on an ultrasonic array is characterized by comprising the following steps:

a) exciting a receiving transducer by using a pulse signal, transmitting an ultrasonic signal with the frequency within the range of 1-2.5 MHz to the interior of the ballastless track by using an ultrasonic array probe, acquiring a diffusion field signal in the ballastless track by using an ultrasonic array sensor in a self-transmitting and self-receiving mode, and transmitting the diffusion field signal to a computer;

b) a computer adopts MATLAB software to passively extract a Green function from the received signals, cross-correlation is carried out on the diffusion field signals, the Green function between array elements is reconstructed, non-delayed response between the array elements is obtained, early defect information submerged by noise is recovered, and then near-surface defect imaging of the ballastless track is carried out according to a full-focusing imaging algorithm.

2. The imaging method according to claim 1, characterized in that said step b) comprises in particular the operations of:

1) data processing:

firstly, in the process of propagating ultrasonic signals in the ballastless track, the ultrasonic signals and a defect target interact to form an approximately uniform sound field after scattering and multiple reflections, the sound field is a diffusion field, and as shown in step a), the diffusion field signals in the ballastless track can be obtained through an ultrasonic array sensor, any two receiving array elements in the ultrasonic array sensor are set to be r1 and r2, the two receiving array elements r1 and r2 are located in a closed curved surface space, and then all sound source integrals of sound field cross spectra at the receiving array elements r1 and r2 are equal to the difference between a frequency domain causal green function and a non-causal green function between r1 and r 2:

G(r₁，r₂，ω)-G^*(r₁，r₂，ω)＝-2iω∫G(r₁，r，ω)G(r₂，r，ω)dv (1)；

in equation (1), the left side of the equation is the difference between the causal and non-causal functions of the frequency domain green's function between the two receiving elements r1 and r2, and the right side of the equation represents all the sound source integrals of the sound field cross-correlation at the receiving elements r1 and r2, specifically, G (r 2)₁，r₂ω) represents the causal green function between r1 and r2 in the frequency domain, which represents the complex conjugate, G^*(r₁,r₂ω) represents an non-causal Green's function between r1 and r2 in the frequency domain, i represents an imaginary unit²Where-1, ω represents the angular frequency of the transmitted signal and r is in dispersionAny point position in the field integral closed space V represents any defect target and can be regarded as a noise source G (r)₁R, ω) represents the frequency domain green's function propagation equation between r and r1, G (r)₂R, ω) represents the frequency domain green's function propagation equation between r and r2, dV represents the differential of the enclosed space V;

then, assuming that the diffuse field noise source intensities are spatially uniformly distributed and uncorrelated with each other, the power spectral density | q (ω) is less dense₂Independent of the position of the noise source:

<q(r₁，ω)*q(r₂，ω)>＝δ(r₁-r₂)|q(ω)|²(2)；

equation (2) represents that the expected values of the cross-power spectra of the signals at frequency domains r1 and r2 are equal to the power spectral density of the noise source between r1 and r2, and in particular, in equation (2),<q(r₁，ω)*q(r₂，ω)>expected values, q (r) representing the cross-power spectra of the signals at frequency domains r1 and r2₁ω) represents the field strength at r1, q (r)₂ω) represents the field strength at r2,<>representing the expected value of the statistical mean, representing the complex conjugate, delta (r)₁-r₂) The cross-power spectrum representing the signal between r1 and r2 is independent of the location of the noise source;

meanwhile, the cross-correlation between the sound fields at the positions of two receiving array elements r1 and r2 in the frequency domain is:

<P(r₁，ω)P^*(r₂，ω)>＝|q(ω)|²∫ G(r₁，r)G^*(r₂，r)dv (3)；

in the formula (3), p (r)₁ω) represents the sound field at the receiving array element r1, p (r)₂ω) represents the sound field at the receiving array element r2,<P(r₁，ω)P^*(r₂，ω)>represents the cross-correlation function between the sound fields at the positions of the two receiving array elements r1 and r2, and represents the conjugate complex number; g (r)₁R) represents r1 and the r frequency domain Green function propagation formula, G (r)₂R) represents a green function propagation formula representing r2 and r frequency domain;

then, the following equations (1) and (3) are obtained:

(G(r₁，r₂，ω)-G^*(r₁，r₂，ω))|q(ω)|²＝-2iω<P(r₁，ω)P^*(r₂，ω)>(4)；

in equation (4), the left side of the equation is the Green function G (r)₁,r₂ω) and its corresponding time reversal, i.e. corresponding to a conjugate operation in the frequency domain, multiplying these two terms by the power spectral density of the random noise, the result of which is equal to the cross-correlation result of the two receiving elements r1 and r2 in the right-hand side of the equation, representing the complex conjugate;

then, a time domain expression corresponding to equation (4) is obtained, and the frequency domain 2i ω corresponds to the time domain 2d/dt, and it can be known from the convolution theorem that the product in the frequency domain corresponds to the convolution in the time domain, thereby obtaining:

in the formula (5), G (r)₁,r₂T) represents the Green function between r1 and r2 in the time domain, G (r)₁,r₂And-t) represents G (r)₁,r₂T), i.e. corresponding to a conjugate operation in the frequency domain, represents a convolution operation,

representing a cross-correlation operation, C_q(t) represents the autocorrelation of the noise q (t) in the diffusion field, d/dt represents the derivative on t, p (r)₁T) represents the sound field in the time domain at the receiving array element r1, p (r)₂T) represents the sound field at the receiving array element r2 in the time domain;

the results of equations (4) and (5) show that the sound field p (r) of the receiving array element in the diffusion field₁T) and p (r)₂T) cross-correlation and derivation, the result of which is equal to the green function response between the two receiving array elements, the green function response between the two receiving array elements has symmetry on the time axis according to the reciprocity principle of sound waves;

2) full-focus imaging:

the ultrasonic array sensor has mutually independent linear arrays, not only can dynamically focus to realize B scanning and S scanning, but also has a strong full-matrix capture function, and provides various imaging methods for offline data processing;

the ultrasonic array sensor is composed of a plurality of ultrasonic sensors in an array, wherein the ultrasonic sensors for transmitting signals are called transmitting sensors, the ultrasonic sensors for receiving signals are called receiving sensors, each transmitting sensor corresponds to one transmitting array element, each receiving sensor corresponds to one receiving array element, a defect P (x, y) is assumed to exist on the near surface of the ballastless track, a pair of transceiving sensor combination pairs in the ultrasonic array sensors are taken as an example, the transmitting sensor combination pair is set to be an ith array element transmitting and a jth array element receiving, time values from each transmitting array element to P (x, y) of each receiving signal are different for all the arrays in the ultrasonic array sensor, namely, a phase difference exists, and coordinates of the ith transmitting array element are set to be (x, y)_Ti,y_Ti) The time of flight to P (x, y) is Ti, and the coordinates of the jth receiving array element are set to (x)_Rj,y_Rj) Time of flight to P (x, y) is T_jThe total time of flight T can be obtained_ijComprises the following steps:

in the formula (6), c is the constant longitudinal wave velocity of the measured ballastless track, and the value is 5900 m/s;

the array size is n × n ultrasonic phased arrays of transmit-receive combined pairs, and one pixel value size I corresponding to any array element_ijComprises the following steps:

because the pixel value accumulation at the defect position is far higher than that of the normal area, different colors are presented during imaging, and therefore the size and the shape of the defect area and the defect are quickly and accurately identified.

3. The utility model provides an image device based on near surface defect of ultrasonic array detection ballastless track which characterized in that: the ultrasonic array transducer comprises a pulse signal excitation receiving transducer, an ultrasonic array sensor and a computer, wherein a transmitting port of the pulse signal excitation receiving transducer is in signal connection with a transmitting end of the ultrasonic array sensor, a receiving port of the pulse signal excitation receiving transducer is in signal connection with a receiving end of the ultrasonic array sensor, and a receiving port of the pulse signal excitation receiving transducer is in signal connection with the computer.

4. The imaging apparatus according to claim 3, characterized in that: still include portable power source unit, portable power source unit includes the portable power source shell and locates the power body in the portable power source shell, power body arouses receiving transducer and supersound array sensor electricity with pulse signal respectively and is connected, pulse signal arouses receiving transducer to install in the portable power source shell, the lateral part of portable power source shell evenly is equipped with a plurality ofly and pulse signal arouses the opening of receiving transducer looks adaptation, supersound array sensor is vertical to be located in the portable power source shell, and supersound array sensor's signal transmission/receiving port passes the below that the portable power source shell is located the portable power source shell.

5. The imaging apparatus according to claim 4, characterized in that: handles are arranged at two ends of the mobile power supply shell.

6. The imaging apparatus according to claim 3, characterized in that: the mobile communication control unit is in signal connection with the pulse signal excitation receiving transducer.

7. The imaging apparatus according to claim 6, characterized in that: the mobile communication control unit comprises a communication unit and a control unit, the communication unit has a wireless connection function, the control unit is in signal connection with the communication unit, the control unit is in signal connection with the pulse signal excitation receiving transducer, and the communication unit is in wireless connection with the computer.

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