CN111307945A - Imaging method and device for detecting near-surface defects of ballastless track based on ultrasonic array - Google Patents
Imaging method and device for detecting near-surface defects of ballastless track based on ultrasonic array Download PDFInfo
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Abstract
The invention discloses an imaging method and device for detecting a near-surface defect of a ballastless track based on an ultrasonic array, wherein the imaging method comprises the steps of firstly utilizing a pulse signal to excite a receiving transducer and transmitting an ultrasonic signal with the frequency within the range of 1-2.5 MHz to the interior of the ballastless track through an ultrasonic array probe, and utilizing an ultrasonic array sensor to obtain a diffusion field signal in the ballastless track in a self-transmitting and self-receiving mode and transmitting the diffusion field signal to a computer; 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. The method 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 daily track slab damage detection of high-speed rails.
Description
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 nondestructive testing of tracks.
Background
Due to the advantages of high speed, strong transportation capacity, safety, punctuality and the like of the high-speed railway, the high-speed railway becomes one of the public transportation modes which are vigorously developed in China at the present stage, and the railway high-speed, especially the passenger railway high-speed, is a development trend in the future. With the rapid development of high-speed railways, ballastless tracks are used as a main track structure and are composed of ballastless track plates, CA mortar layers, supporting layers and beds, and the application range of the ballastless tracks is wider and wider. In recent years, however, diseases such as off-line structure separation, through cracks, and CA mortar layer collapse have been increasing in high-speed rail under-line structures. On one hand, the main reasons are that the ballastless track can be extruded and impacted in the high-speed and heavy-load running process of the train, so that various defects such as incompactness, cracks or cavities can occur in the ballastless track, and a damaged layer or a honeycomb layer is formed on the outer part of the ballastless track; on the other hand, the ballastless track has defects due to possible problems in the construction process and construction experience in the previous manufacturing; in addition, the corrosion of rain and snow, the change of environmental temperature, and other natural disasters will also cause defects. The existence of the defects seriously affects the bearing capacity and durability of the ballastless track, so that the ballastless track structure fails, the stability and smoothness of the ballastless track of the high-speed railway and the structure under the railway cannot be ensured, the stability and smoothness are the important precondition for ensuring the rapid and safe operation of the high-speed railway, and the stability and smoothness are directly related to the normal operation of the train and the personal safety of passengers.
However, at present, the detection of the near-surface defect of the ballastless track in China mainly depends on a manual static detection technology, the time of the track traffic for an effective skylight for line repair and maintenance is only 2-3 hours, and the thread of a high-speed railway is very long, so that if the existing detection means is adopted, a large amount of manpower and material resources are consumed, the efficiency is very low, the detection and maintenance cost is very high, and the requirement of track safety early warning cannot be met.
Disclosure of Invention
Aiming at the problems and requirements in the prior art, the invention aims to provide an imaging method and device for detecting the near-surface defect of the ballastless track based on an ultrasonic array, so as to realize efficient, nondestructive and real-time detection of the near-surface defect of the ballastless track, and provide timely early warning and powerful guarantee for the safe operation of a high-speed rail.
In order to achieve the purpose, the invention adopts the following technical scheme:
an imaging method for detecting near-surface defects of a ballastless track based on an ultrasonic array comprises the following steps:
a) the method comprises the following steps of 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 inside of a ballastless track through 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, wherein the specific steps are as follows: firstly, exciting an ultrasonic signal with the transmitting frequency within the range of 1-2.5 MHz by using a pulse signal, transmitting the ultrasonic signal to the interior of a ballastless track by using the transmitting end of an ultrasonic array sensor, then collecting a diffusion field signal by using a receiving end of the ultrasonic array sensor and transmitting the diffusion field signal to the receiving end of the pulse signal excitation receiving transducer, and then transmitting the received diffusion field signal to a computer by using the receiving end of the pulse signal excitation receiving transducer;
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.
In one embodiment, the step b) specifically includes the following operations:
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 ω represents the angular frequency of the transmitted signal, r is at any point in the propagation field integral confinement V, representing any defect target, and can be considered 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, Cq(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,yTi) The time of flight to P (x, y) is Ti, and the jth connection is setThe coordinates of the array elements are (x)Rj,yRj) Time of flight to P (x, y) is TjThe total time of flight T can be obtainedijComprises 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 elementijComprises 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.
The imaging device for detecting the near-surface defects of the ballastless track based on the ultrasonic array 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 in the ultrasonic array sensor, a receiving port of the pulse signal excitation receiving transducer is in signal connection with a receiving end in the ultrasonic array sensor, and a receiving port of the pulse signal excitation receiving transducer is in signal connection with the computer.
The utility model provides an embodiment, still includes the portable power source unit, the portable power source unit includes the portable power source shell and locates the power body in the portable power source shell, the 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, the 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.
According to a preferable scheme, handles are arranged at two ends of the mobile power supply shell.
One embodiment further comprises a mobile communication control unit in signal connection with the pulse signal excitation receiving transducer.
In a preferred scheme, 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 a computer.
In a preferred scheme, the mobile communication control unit is arranged at the top of the mobile power supply shell.
Compared with the prior art, the invention has the following beneficial technical effects:
1) the ultrasonic array sensor has the advantages of high energy and small attenuation, ultrasonic energy is hardly leaked, the ultrasonic energy is better incident into a material to be detected and interacts with defects to form a scattering signal which is favorable for detection, each array element in the ultrasonic array sensor can be excited independently or in combination, the focusing and deflection functions can be realized, and the scattering field signal can be better collected, so that the plate-type ballastless track can be detected by using the scattering field signal, and the signal which is annihilated in noise at the early stage is reconstructed due to the characteristic of the scattering field, so that the near-surface defects of the track plate can be conveniently processed and analyzed, and the detection efficiency is effectively improved;
2) when the method is used for processing and imaging signals, a computer firstly uses the principle of cross-correlation operation between received array element diffusion field signals to reconstruct a Green function to obtain non-delayed response between array elements, extracts early defect scattering information submerged by noise, then uses a frequency domain synthetic aperture focusing imaging technology and adopts a time domain full focusing imaging method to superpose signal amplitudes at the defect, thereby realizing the visualization of the slab ballastless track defect, improving the imaging precision and definition, not only ensuring the high-resolution capability, but also effectively reducing the imaging calculation time, and having high speed and high precision;
in conclusion, the method can realize the high-efficiency, nondestructive, accurate and real-time detection of the near-surface defect of the ballastless track, can provide timely early warning and powerful guarantee for the safe operation of the high-speed rail, and can provide powerful support for the subsequent track maintenance work; therefore, compared with the prior art, the invention has remarkable progress and application value.
Drawings
Fig. 1 is a schematic structural diagram of a pulse signal excitation receiving transducer, an ultrasonic array sensor, a wireless power supply unit, and a mobile communication control unit in an imaging device for detecting a near-surface defect of a ballastless track based on an ultrasonic array according to an embodiment;
fig. 2 is a schematic structural diagram of another view angle of a pulse signal excitation receiving transducer, an ultrasonic array sensor, a wireless power supply unit and a mobile communication control unit part in the imaging device for detecting the near-surface defect of the ballastless track based on the ultrasonic array provided by the embodiment;
fig. 3 is a schematic structural diagram of an imaging device for detecting a near-surface defect of a ballastless track based on an ultrasonic array according to an embodiment;
FIG. 4 is a state diagram of the imaging apparatus in operation according to the embodiment;
FIG. 5 is a schematic diagram of an embodiment of a full focus imaging system;
FIG. 6 is a cross-sectional view of an exemplary embodiment of a test track board;
FIG. 7 is a diagram of a full focus imaging of the track plate according to one embodiment;
the numbers in the figures are as follows: the numbers in the figures are as follows: 1. the pulse signal excites the receiving transducer; 2. an ultrasonic array sensor; 21. a signal transmitting/receiving port of the ultrasonic array sensor; 3. a mobile power supply unit; 31. a mobile power supply housing; 311. an opening; 312. a handle; 4. a mobile communication control unit; 5. a ballastless track is provided; 6. and (4) a computer.
Detailed Description
The technical solution of the present invention is further described in detail below with reference to the accompanying drawings and examples.
With reference to fig. 1 to 4: the invention provides an imaging device for detecting the near-surface defect of a ballastless track based on an ultrasonic array, which comprises a pulse signal excitation receiving transducer 1, an ultrasonic array sensor 2 and a computer 6, wherein a transmitting port of the pulse signal excitation receiving transducer 1 is in signal connection with a transmitting end in the ultrasonic array sensor 2, a receiving port of the pulse signal excitation receiving transducer 1 is in signal connection with a receiving end in the ultrasonic array sensor 2, and a receiving port of the pulse signal excitation receiving transducer 1 is in signal connection with the computer.
The ultrasonic array sensor 2 may be a commercially available product, for example, a contact type ultrasonic array sensor may be used, which has the advantages of high energy and small attenuation, the ultrasonic energy is hardly leaked, and is better incident into the material to be detected and interacts with a defect to form a scattering signal beneficial to detection, the ultrasonic array sensor 2 is composed of a plurality of ultrasonic sensors in an array form, for example, in this embodiment, the ultrasonic array sensor 2 may be composed of 24 ultrasonic sensors in 8 rows and 3 columns, correspondingly, the ultrasonic array sensor 2 has 24 array elements, and the array elements of each ultrasonic sensor may be individually excited or may be excited in combination, so as to implement focusing and deflecting functions. Further, as can be seen from the above description, the ultrasonic array transducer 2 in the present embodiment has a transmitting end and a receiving end, and has a function of transmitting and receiving, that is, in the ultrasonic transducers constituting the ultrasonic array transducer 2, part of the transducers is transmitting transducers for transmitting signals, and the rest is receiving transducers for receiving signals. Because the ultrasonic waves have different propagation speeds in media with different densities and can generate phenomena of reflection and scattering when passing through a boundary surface of two different media, because a ballastless track belongs to a concrete member and is a porous non-uniform composite material formed by mixing sand, cement, stones and the like, when ultrasonic pulse waves emitted by a pulse signal excitation receiving transducer 1 are propagated in the concrete, defects can be diffracted, scattering and reflection can be generated at a defect interface, so that the amplitude of sound wave energy is obviously reduced when the ultrasonic pulse waves reach a receiving transducer, in the application, the ultrasonic array transducer 2 is adopted, not only can the diffusion field signals be more effectively collected, but also the diffusion field signals received by the ultrasonic array transducer can be superposed, so that the radiation energy of the reflected diffusion field signals in a certain direction is maximum, and the total radiation energy in other directions is smaller, thereby realizing the focusing effect on the diffusion field signals, useful diffusion field signals are enhanced, interference signals are restrained, and therefore accuracy of signal acquisition and detection results is guaranteed.
In addition, the imaging device of the 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 body is respectively electrically connected with the pulse signal excitation receiving transducer 1 and the ultrasonic array sensor 2, the pulse signal excitation receiving transducer 1 is arranged in the mobile power supply shell 31, a plurality of openings 311 (which are convenient for the pulse signal excitation receiving transducer 1 to emit and receive signals) matched with the pulse signal excitation receiving transducer 2 are uniformly arranged on the side part of the mobile power supply shell 31, the ultrasonic array sensor 2 is vertically arranged in the mobile power supply shell 31, and the signal transmitting/receiving port 21 of the ultrasonic array sensor 2 passes through the mobile power supply housing 31 and is positioned below the mobile power supply housing 31 (so as to facilitate the detection of the rail by the ultrasonic array sensor 2). The mobile power supply unit supplies power for the rest components in the imaging device in a mobile mode, and in addition, the pulse signal excitation receiving transducer 1 and the ultrasonic array sensor 2 are integrated in the mobile power supply shell 31, so that the whole structure and the occupied area of the device are effectively simplified, and the whole device is convenient to move.
In addition, handles 312 are provided at both ends of the portable power source housing 31, so that the portable power source unit 3 and the entire device can be transported and mounted by the handles 312.
In addition, the imaging device according to the present embodiment further includes a mobile communication control unit 4, and the mobile communication control unit 4 is in signal connection with the pulse signal excitation receiving transducer 1. Specifically, the mobile communication control unit 4 includes a communication unit having a wireless connection function (e.g., a bluetooth connection function, which can be bluetooth connected to the computer 6) to realize a wireless communication connection with a remote terminal (not shown in the figure), and a control unit (which can be a commercially available single chip microcomputer, a controller, etc.) in signal connection with the communication unit, and the control unit in signal connection with the pulse signal excitation receiving transducer 1 to automatically control the pulse signal excitation receiving transducer 1 to be switched on and off.
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, all components except the computer 6 in the imaging device can be integrated at the mobile power supply housing 31, and the whole structure of the device is simplified.
The imaging method for detecting the near-surface defect of the ballastless track by adopting the imaging device comprises the following steps:
a) the imaging device is placed on a ballastless track 5 (as shown in fig. 4), the position is adjusted, a pulse signal is firstly utilized to excite a transmitting end of a receiving transducer 1 to transmit an ultrasonic signal with the frequency within the range of 1-2.5 MHz, the ultrasonic signal is transmitted to the interior of the ballastless track 5 through the transmitting end of an ultrasonic array sensor 2, then a receiving end of the ultrasonic array sensor 2 collects a diffusion field signal and transmits the diffusion field signal to the receiving end of the pulse signal excitation receiving transducer 1, and then the receiving end of the pulse signal excitation receiving transducer 1 transmits the received diffusion field signal to a computer 6;
b) the computer 6 adopts MATLAB software to passively extract Green functions from the received signals, performs cross-correlation on the diffusion field signals, reconstructs the Green functions between the array elements, obtains the response without delay between the array elements, recovers the early defect information submerged by noise, and performs near-surface defect imaging of the ballastless track according to a full-focusing imaging algorithm, which specifically comprises the following operations:
1) data processing:
firstly, in the process of propagating ultrasonic signals in the ballastless track, interaction occurs between the ultrasonic signals and a defect target (shown in fig. 6), an approximately uniform sound field is formed 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 the 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 the sound field cross spectrum at the receiving array elements r1 and r2 are equal to the difference between the frequency domain causal green function and the 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 ω represents the angular frequency of the transmitted signal, r is at any point in the propagation field integral confinement V, representing any defect target, and can be considered 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 expectation of the cross-power spectra of the signals at frequency domains r1 and r2 is equal to the power spectral density of the noise source between r1 and r2, specifically, < q (r) in equation (2)1，ω)*q(r2ω) > represents the expected value of the cross-power spectrum of the signals at frequency domains r1 and r2, q (r)1ω) 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 of the conjugateNumber, 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 (r)1,ω)*p(r2ω) > represents the cross-correlation function between the sound field at the location of the two receiving array elements r1 and r2, which represents the complex conjugate; 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,r2,t) The time reversal of (a) corresponds to a conjugate operation in the frequency domain, representing a convolution operation,
representing the cross-correlation operation, Cq (t) representing the autocorrelation of the noise q (t) in the diffusion field, d/dt representing 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 sensor for transmitting signals is called a transmitting sensor, the ultrasonic sensor for receiving signals is called a receiving sensor, each transmitting sensor corresponds to a transmitting array element, each receiving sensor corresponds to a receiving array element, as shown in fig. 5, assuming that the near surface of the ballastless track has a defect P (x, y), taking a pair of transmitting and receiving sensor combination pairs in the ultrasonic array sensor as an example, it is set that the ith array element transmits, and the jth array element receives, for all arrays in the ultrasonic array sensor, the time values from the array element of each transmitting signal to P (x, y) are different, that is, there is a phase difference, and the coordinate of the ith transmitting array element is set as (x, y)Ti,yTi) The time of flight to P (x, y) is Ti, and the coordinates of the jth receiving array element are set to (x)Rj,yRj) Time of flight to P (x, y) is TjThe total time of flight T can be obtainedijComprises 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 elementijComprises the following steps:
since the pixel value accumulation at the defect is much higher than that of the normal area, different colors are presented during imaging, so that the size and shape of the defect area and the defect can be quickly and accurately identified (as shown in fig. 7).
In conclusion, the method can realize the detection and evaluation of the near-surface defect of the ballastless track, can solve the problem of low efficiency of the conventional track, can greatly reduce labor and working strength, provides visual service of the defect, and can provide powerful support for railway safety maintenance; in addition, the invention has simple structure and convenient use, and can greatly reduce the maintenance cost; therefore, compared with the prior art, the invention has remarkable progress and application value.
It is finally necessary to point out here: the above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the 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, Cq(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,yTi) The time of flight to P (x, y) is Ti, and the coordinates of the jth receiving array element are set to (x)Rj,yRj) Time of flight to P (x, y) is TjThe total time of flight T can be obtainedijComprises 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 elementijComprises 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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