CN117949936A - Electromagnetic ultrasonic thickness measurement method and system with improved matched filtering - Google Patents
Electromagnetic ultrasonic thickness measurement method and system with improved matched filtering Download PDFInfo
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Abstract
The application provides an electromagnetic ultrasonic thickness measurement method and system for improving matched filtering, wherein the method comprises the following steps: generating a transmitting signal through the excitation signal, then reflecting the transmitting signal through a target test piece to obtain an echo signal, and intercepting the echo signal to obtain an intercepted signal; respectively obtaining a first impulse response, a second impulse response and a third impulse response according to the excitation signal, the interception signal and the echo signal, obtaining time domain interception compression according to the first impulse response and the interception signal, obtaining time domain self-compression according to the second impulse response and the interception signal, and obtaining echo self-compression according to the third impulse response and the interception signal; the pulse pressure signal with the highest comprehensive score is selected by using a preset value selection method through time domain interception compression, time domain self-compression and echo self-compression, and the final thickness value is determined by using the flight time of the pulse pressure signal and combining a time difference thickness measurement method. The method can remarkably improve the accuracy of the thickness measurement of the test piece.
Description
Technical Field
The application relates to the field of electromagnetic ultrasonic thickness measurement, in particular to an electromagnetic ultrasonic thickness measurement method and system with improved matched filtering.
Background
In recent years, metal sheets are widely used in aerospace, railway, marine and other industries. The metal plate can be thinned under the disqualified working condition for a long time, so that the mechanical property is reduced, the danger is caused to equipment and operators, and even serious accidents are caused. Therefore, accurate measurement of the thickness of the metal plate in time and accurately has important significance for ensuring safe and reliable operation of the mechanical structure.
Electromagnetic ultrasonic transducers (EMAT) have the advantages of non-contact, no need of coupling agent and easy excitation of multimode ultrasonic waves, so that the electromagnetic ultrasonic transducers (EMAT) are widely applied under severe working conditions such as high temperature, high speed and the like. However, its transduction efficiency is low, and is extremely susceptible to noise interference such that the time of flight of the ultrasonic echo is difficult to accurately extract. In order to solve the problem, the EMAT is combined with the Chirp signal, and a Pulse Compression Technology (PCT) is used for reducing noise interference so as to improve the signal-to-noise ratio of ultrasonic waves, and the method can quickly obtain the flight time between ultrasonic echoes and further measure the thickness of the metal plate.
However, no pulse compression filter has been designed or studied in depth in the prior art. In the existing pulse compression technology, after an echo signal is formed by reflection propagation of a transmitting signal in a metal test piece, only an excitation signal is used as a reference signal to carry out matched filtering processing, an output signal is used as a final pulse pressure signal, in practical application, the signal propagation is affected by environment and material characteristics, only the excitation signal is used as the reference signal, and the condition of low matching degree exists in the pulse pressure process of the actual echo signal, so that the pulse pressure signal is distorted, and the identification and analysis of the pulse pressure signal are affected.
Disclosure of Invention
Based on the above, the application provides an electromagnetic ultrasonic thickness measuring method and system with improved matched filtering, which aim to solve the problem that the prior art has difficulty in extracting the flight time when the single reference signal is used for matched filtering treatment, so that the thickness measuring error of a test piece is increased.
A first aspect of the embodiments provides an electromagnetic ultrasonic thickness measurement method that improves matched filtering, comprising:
Obtaining an excitation signal, generating a transmitting signal according to the excitation signal, obtaining an echo signal after the transmitting signal is reflected and transmitted by a target test piece, and intercepting the echo signal to obtain an intercepted signal;
obtaining a first impulse response according to the excitation signal, and carrying out matched filtering processing on the first impulse response and the interception signal to obtain time domain interception compression;
Obtaining a second impulse response according to the intercepted signal, and performing matched filtering processing on the second impulse response and the intercepted signal to obtain time domain self-compression;
obtaining a third impulse response according to the echo signal, and performing matched filtering processing on the third impulse response and the intercepted signal to obtain echo self-compression;
And selecting pulse pressure signals with highest comprehensive scores by using a preset numerical value selection method for the time domain interception compression, the time domain self-compression and the echo self-compression, and determining a final thickness value by using the flight time under the pulse pressure signals and combining a time difference thickness measurement method.
Compared with the prior art, the electromagnetic ultrasonic thickness measuring method with improved matched filtering provided by the application has the advantages that the transmitting signal is generated through the excitation signal, the echo signal is obtained after the transmitting signal is reflected and transmitted by the target test piece, the intercepted signal is obtained by intercepting the echo signal, and the condition that the matching degree is not high in the pulse pressure process of the echo signal by taking the excitation signal as the reference signal is considered, so that the pulse pressure signal is distorted and the identification and analysis of the pulse pressure signal are influenced, so that the intercepting signal is convenient to analyze and process the intercepted signal. Based on the characteristics of matched filtering and the problems existing in the traditional pulse compression, the application provides three novel pulse compression techniques for optimizing the traditional pulse compression techniques: the time domain interception compression is provided through the interception signal and the excitation signal, the time domain self-compression is provided through the interception signal and the self-interception signal, and the echo self-compression is provided through the interception signal and the echo signal. The pulse pressure signal with the highest comprehensive score is selected by using a preset numerical value selection method through time domain interception compression, time domain self-compression and echo self-compression, and the final thickness value is determined by using the flight time of the pulse pressure signal and combining a time difference thickness measurement method, so that the accurate thickness measurement of a test piece is realized. Therefore, the method provided by the application can solve the problems that the flight time is difficult to extract when the single reference signal is used for carrying out matched filtering processing in the prior art, and the thickness measurement error of the test piece is further increased.
As an optional implementation manner of the first aspect, the step of obtaining an excitation signal, generating a transmission signal according to the excitation signal, obtaining an echo signal after the transmission signal is reflected and propagated by a target test piece, and intercepting the echo signal to obtain an intercepted signal includes:
The Chirp signal is used as an excitation signal and expressed as:
，
Wherein, The excitation signal is represented by A, i represents an imaginary unit, f 0 represents a starting frequency, k represents a frequency modulation frequency of the Chirp signal, T represents time, and T represents a pulse width of the Chirp signal;
Under the condition that the signal pulse width T is unchanged, changing the frequency band range of the Chirp signal by changing f 0 and k;
The received echo signal r (t) is the sum of a plurality of transverse wave time domain signals s n (t), so r (t) is expressed as:
,
，
Wherein, And/>Respectively representing the amplitude and phase of the nth time domain signal,/>Representing the initial phase of an excitation signal, c represents the propagation speed of sound waves in a material, and d represents the thickness of a test piece to be tested;
performing an interception operation on the echo signal by defining an interception function F (t), namely multiplying the interception function with the echo signal to obtain an intercepted signal j (t), and using a formula as follows:
，
，
Where t 1 is the start time of the truncated signal and t 2 is the end time of the truncated signal, u is the truncated length, in practice the minimum truncated time length is equal to the excitation signal duration and the maximum truncated time length does not exceed the echo signal length, where 。
As an optional implementation manner of the first aspect, the step of obtaining a first impulse response according to the excitation signal, performing matched filtering processing on the first impulse response and the truncated signal, and obtaining time-domain truncated compression includes:
Defining the first impulse response as the excitation signal, and obtaining the expression of time domain interception compression through matched filtering processing as follows:
，
Wherein, Representing time-domain truncated compression,/>Representing convolution operations,/>Representing intercepted echo signals,/>Representing the intercepted signal at τ delay,/>Representing the first impulse response,/>Representing the mirror image of the excitation signal.
As an optional implementation manner of the first aspect, the step of obtaining a second impulse response according to the truncated signal, performing matched filtering processing on the second impulse response and the truncated signal, and obtaining time domain self-compression includes:
defining the second impulse response as the intercepted signal, and obtaining the expression of the time domain self-compression through matched filtering processing as follows:
，
Wherein, Representing time domain self-compression,/>Representing the second impulse response,/>Representing the mirror image of the intercepted signal.
As an optional implementation manner of the first aspect, the step of obtaining a third impulse response according to the echo signal, performing matched filtering processing on the third impulse response and the truncated signal, and obtaining echo self-compression includes:
defining the third impulse response as the echo signal, and obtaining the expression of echo self-compression through matched filtering processing as follows:
，
Wherein, Representing echo self-compression,/>Representing the third impulse response,/>Representing a mirror image of the echo signal.
As an optional implementation manner of the first aspect, the preset numerical selection method is:
The signal-to-noise ratio, the main lobe peak value and the main lobe width after pulse pressure are defined as signal evaluation indexes, corresponding weight parameters are respectively distributed as gamma 1、γ2 and gamma 3, and a formula for calculating a comprehensive score is as follows:
w=γ1K1+γ2K2+γ3K3，
Wherein w is a comprehensive score, K 1 is a signal-to-noise ratio after pulse pressure, K 2 is a main lobe peak value, and K 3 is a main lobe width;
the pulse pressure signal with the highest comprehensive score is selected, and the final thickness value is determined by using the time of flight under the pulse pressure signal and combining a time difference thickness measurement method.
As an optional implementation manner of the first aspect, the calculation expression of the time difference thickness measurement method is:
,
where Δt represents the time difference between two adjacent echo signals, i.e. the time of flight.
A second aspect of an embodiment of the present application provides an electromagnetic ultrasonic thickness measurement system with improved matched filtering, comprising:
The signal acquisition module is used for acquiring an excitation signal, generating a transmitting signal according to the excitation signal, carrying out reflection propagation on the transmitting signal through a target test piece to obtain an echo signal, and intercepting the echo signal to obtain an intercepted signal;
The signal interception and compression module is used for obtaining a first impulse response according to the excitation signal, and carrying out matched filtering processing on the first impulse response and the interception signal to obtain time domain interception and compression; obtaining a second impulse response according to the intercepted signal, and performing matched filtering processing on the second impulse response and the intercepted signal to obtain time domain self-compression; obtaining a third impulse response according to the echo signal, and performing matched filtering processing on the third impulse response and the intercepted signal to obtain echo self-compression;
and the thickness measurement data processing module is used for selecting pulse pressure signals with highest comprehensive scores by using a preset numerical value selection method for the time domain interception compression, the time domain self-compression and the echo self-compression, and determining a final thickness value by using the flight time under the pulse pressure signals and combining a time difference thickness measurement method.
A third aspect of embodiments of the present application provides a computer apparatus comprising a memory for storing a computer program and a processor; the processor is used for realizing the electromagnetic ultrasonic thickness measuring method when executing the computer program stored in the memory.
A fourth aspect of the embodiments of the present application provides a storage medium storing a computer program which, when executed by a processor, implements the above-described electromagnetic ultrasonic thickness measurement method.
Additional aspects and advantages of the application will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the application.
Drawings
FIG. 1 is a flow chart of an electromagnetic ultrasonic thickness measurement method with improved matched filtering according to a first embodiment of the present application;
FIG. 2 is a schematic diagram of a novel pulse compression flow in an electromagnetic ultrasonic thickness measurement method with improved matched filtering according to the present application;
fig. 3 is a schematic structural diagram of an electromagnetic ultrasonic thickness measuring system with improved matched filtering according to a second embodiment of the present application.
The application will be further described in the following detailed description in conjunction with the above-described figures.
Detailed Description
In order that the application may be readily understood, a more complete description of the application will be rendered by reference to the appended drawings. Several embodiments of the application are shown in the drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.
In order to illustrate the technical scheme of the application, the following description is made by specific examples.
Referring to fig. 1, a flowchart of an electromagnetic ultrasonic thickness measurement method with improved matched filtering according to a first embodiment of the present application is shown, and the details are as follows:
And S01, obtaining an excitation signal, generating a transmitting signal according to the excitation signal, carrying out reflection and propagation on the transmitting signal through a target test piece to obtain an echo signal, and intercepting the echo signal to obtain an intercepted signal.
It should be noted that pulse compression is a signal processing scheme commonly adopted in radar systems, and is located at a relatively front end in the whole received signal processing system, and is mainly used for mixing different target echoes in a time domain together, and after processing, the different target echoes can be resolved in the time domain, and a relatively high signal-to-noise ratio is output. In the pulse compression technology, the speed measurement precision and the speed resolution of signals are improved by transmitting large time-width and bandwidth signals at a transmitting end, and the wide pulse signals are compressed into narrow pulses at a receiving end, so that the distance resolution precision of targets is improved. The essence of signal pulse compression is the process of matched filtering the transmitted signal (i.e., the reference signal in matched filtering) with the received signal.
In order to obtain higher signal-to-noise ratio and narrower pulse width, the electromagnetic ultrasonic transducer (EMAT) adopts a Chirp signal as an excitation signal, and is expressed as follows:
，
Wherein, The excitation signal is represented by A, i represents an imaginary unit, f 0 represents a starting frequency, k represents a frequency modulation frequency of the Chirp signal, T represents time, and T represents a pulse width of the Chirp signal;
Under the condition that the signal pulse width T is unchanged, changing the frequency band range of the Chirp signal by changing f 0 and k;
Electromagnetic ultrasonic transducers generally adopt a transceiver mode, and transverse waves generated by single excitation of the electromagnetic ultrasonic transducers can be reflected in a test piece for multiple times. The received time-domain echo waveform r (t) may thus be regarded as the sum of a plurality of transverse-wave time-domain signals s n (t) (where n=1, 2, … N). In this case r (t) can be expressed as:
,
，
Wherein, And/>Respectively representing the amplitude and phase of the nth time domain signal,/>The initial phase of the excitation signal is represented, c represents the propagation speed of sound waves in the material, and d represents the thickness of a test piece to be tested.
By defining the clipping function F (t), the clipping operation can be performed on the echo signal. I.e. the truncated function is multiplied with the echo signal to obtain the truncated signal j (t).
，
，
Where t 1 is the start time of the truncated signal and t 2 is the end time of the truncated signal. Defining u as the cut-out length, in practice, the minimum cut-out time length is equal to the excitation signal duration, while the maximum cut-out time length should not exceed the length of the echo signal, wherein,。
Specifically, fig. 2 is a schematic diagram of a novel pulse compression flow chart in an electromagnetic ultrasonic thickness measuring method with improved matched filtering according to the present application.
Step S02: and obtaining a first impulse response according to the excitation signal, and carrying out matched filtering processing on the first impulse response and the interception signal to obtain time domain interception compression.
It should be noted that the present application proposes time-domain interception compression (Time domain Interception Compression, TIC) based on the process of matched filtering, that is, the interception part of the received signal and the excitation signal are matched filtered, so as to achieve the purpose of pulse compression.
Defining the first impulse response as the excitation signal, and obtaining the expression of time domain interception compression through matched filtering processing as follows:
，
Wherein, Representing time-domain truncated compression,/>Representing a convolution operation, the integral form being the cross-correlation expression between the truncated signal and the excitation signal,/>Representing intercepted echo signals,/>Representing the intercepted signal at τ delay,/>Representing the first impulse response,/>Representing the mirror image of the excitation signal.
Step S03: and obtaining a second impulse response according to the intercepted signal, and carrying out matched filtering processing on the second impulse response and the intercepted signal to obtain time domain self-compression.
It should be noted that, considering that the intercepted part of the received signal can be used as the reference signal and the received signal in the matched filtering process at the same Time, the application provides Time domain self-compression (TSC), that is, the intercepted signal and the intercepted signal are matched filtered to achieve the purpose of pulse compression.
Defining the second impulse response as the intercepted signal, and obtaining the expression of the time domain self-compression through matched filtering processing as follows:
，
Wherein, Representing time domain self-compression,/>Representing the second impulse response,/>Representing the mirror image of the intercepted signal.
Step S04: and obtaining a third impulse response according to the echo signal, and carrying out matched filtering processing on the third impulse response and the intercepted signal to obtain echo self-compression.
It should be noted that, considering that the intercepted part of the received signal may be used as a reference signal in the matched filtering process, echo self-compression (Echo interception compression, EIC) is proposed, that is, the intercepted signal and the echo signal are matched filtered, so as to achieve the purpose of pulse compression.
Defining the third impulse response as the intercepted signal, and obtaining the expression of the time domain self-compression through matched filtering processing as follows:
，
Wherein, Representing echo self-compression,/>Representing the third impulse response,/>Representing a mirror image of the echo signal.
Step S05: and selecting pulse pressure signals with highest comprehensive scores by using a preset numerical value selection method for the time domain interception compression, the time domain self-compression and the echo self-compression, and determining a final thickness value by using the flight time under the pulse pressure signals and combining a time difference thickness measurement method.
Specifically, the calculation formula of the time difference thickness measurement method is as follows:
,
wherein d represents the thickness of a test piece to be tested, c represents the propagation speed of sound waves in the material, and Δt represents the time difference between two adjacent echo signals, namely the flight time.
Further, the preset numerical value selecting method is as follows:
By defining three key signal evaluation indicators: signal-to-noise ratio after pulse pressure, main lobe peak value and main lobe width. Corresponding weight parameters, gamma 1、γ2 and gamma 3 respectively, are assigned to reflect their relative importance in signal performance assessment. The composite score calculation formula may be expressed as:
w=γ1K1+γ2K2+γ3K3，
Where w is the composite score, K 1 is the post-pulse-pressure signal-to-noise ratio, K 2 is the main lobe peak, and K 3 is the main lobe width. The pulse pressure signal with the highest comprehensive score is selected, and the final thickness value is determined by using the time of flight under the pulse pressure signal and combining a time difference thickness measurement method.
In one embodiment, the Chirp signal is generated by any of the waveform generators Aglient-33250A, the test piece is 7075 aluminum alloy, and the dimensions are 100mm by 10mm. The experiment adopts a SNAP-5000 high-performance nonlinear detection system. The system amplifies power of Chirp signals led in by a signal generator, excites ultrasonic waves for detection through equipment such as a duplexer, impedance matching and the like, then receives echo signals through the same transducer, and monitors and subsequently processes data by using an oscilloscope.
Further, the output excitation signal is determined by setting the start frequency, pulse width, frequency modulation rate of the Chirp signal. The initial frequency f 0 =1 MHz, the pulse width t=10μs, and the tuning frequency k is 3× 11 Hz/s.
The conventional Pulse Compression Technique (PCT) is used in detecting the echo after the excitation signal is removed, and by intercepting the echo signal of 30-70 μs as the impulse response h (t), and the signal-to-noise ratio, the main lobe peak value and the main lobe width after pulse compression, and the result of adopting the preset numerical selection method are shown in table 1 by adopting the corresponding methods of time domain interception compression (TIC), time domain self compression (TSC) and echo self compression (EIC), respectively. In this embodiment, γ 1、γ2 and γ 3 are set to 30%, 40% and 30%, respectively.
TABLE 1 post pulse compression signal to noise ratio, main valve Peak, main valve Width and Integrated score comparison for different pulse compression techniques
The data in table 1 can obtain that the signal-to-noise ratio, the main lobe peak value and the main lobe width after the EIC pulse pressure are the highest according to the score obtained by a preset numerical method, and the time difference between the first complete wave packet and the second complete wave packet in the pulse pressure signal is used as the flight time. The flight time of PCT pulse pressure results is 6.4 mu s, and the error rate of the thickness 9.867mm of the test piece and the actual thickness 10mm of the test piece is 1.33% by combining a time difference thickness measuring formula; and the flight time of EIC pulse pressure results is 6.50 mu s, and the error rate of the thickness 10.023mm of the test piece and the actual thickness 10mm of the test piece is 0.23% by combining a time difference thickness measuring formula. I.e. the EIC is lower than the PCT thickness error rate.
The EIC selected by the numerical method has more excellent anti-interference capability and stronger spatial resolution, can greatly improve the detection efficiency, and has the characteristics of high thickness measurement accuracy and stability.
In summary, the electromagnetic ultrasonic thickness measuring method with improved matched filtering provided by the application generates the transmitting signal through the excitation signal, obtains the echo signal after being reflected and transmitted by the target test piece, and then intercepts the echo signal to obtain the intercepted signal, and the step of intercepting the echo signal is convenient for further analyzing and processing the intercepted signal by considering the condition that the pulse pressure signal is distorted and the pulse pressure signal is influenced due to the fact that the matching degree is not high in the pulse pressure process of using the excitation signal as the reference signal and the actual echo signal. Based on the characteristics of matched filtering and the problems existing in the traditional pulse compression, the application provides three novel pulse compression techniques for optimizing the traditional pulse compression techniques: the time domain interception compression is provided through the interception signal and the excitation signal, the time domain self-compression is provided through the interception signal and the self-interception signal, and the echo self-compression is provided through the interception signal and the echo signal. And finally, selecting a pulse pressure signal with the highest comprehensive score by using a preset numerical value selection method through time domain interception compression, time domain self-compression and echo self-compression, and determining a final thickness value by using the flight time of the pulse pressure signal and combining a time difference thickness measurement method.
Referring to fig. 3, a schematic structural diagram of an electromagnetic ultrasonic thickness measurement system with improved matched filtering according to a second embodiment of the present application is shown, where the system includes:
The signal acquisition module 10 is used for acquiring an excitation signal, generating a transmitting signal according to the excitation signal, obtaining an echo signal after the transmitting signal is reflected and transmitted by a target test piece, and intercepting the echo signal to obtain an intercepted signal;
The signal interception and compression module 20 is configured to obtain a first impulse response according to the excitation signal, and perform matched filtering processing on the first impulse response and the interception signal to obtain time domain interception and compression; obtaining a second impulse response according to the intercepted signal, and performing matched filtering processing on the second impulse response and the intercepted signal to obtain time domain self-compression; obtaining a third impulse response according to the echo signal, and performing matched filtering processing on the third impulse response and the intercepted signal to obtain echo self-compression;
The thickness measurement data processing module 30 is configured to select a pulse pressure signal with the highest comprehensive score by using a preset value selection method for the time-domain intercept compression, the time-domain self-compression and the echo self-compression, and determine a final thickness value by using a time-of-flight under the pulse pressure signal and combining a time difference thickness measurement method.
The embodiment of the application also provides computer equipment, which comprises a memory and a processor, wherein the memory is used for storing a computer program; the processor is used for realizing the electromagnetic ultrasonic thickness measuring method when executing the computer program stored in the memory.
The embodiment of the application also provides a storage medium which stores a computer program, and the computer program realizes the electromagnetic ultrasonic thickness measuring method when being executed by a processor.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The foregoing examples illustrate only a few embodiments of the application and are described in detail herein without thereby limiting the scope of the application. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the application, which are all within the scope of the application. Accordingly, the scope of protection of the present application is to be determined by the appended claims.
Claims (10)
1. An electromagnetic ultrasonic thickness measurement method for improving matched filtering, characterized in that the method comprises the following steps:
Obtaining an excitation signal, generating a transmitting signal according to the excitation signal, obtaining an echo signal after the transmitting signal is reflected and transmitted by a target test piece, and intercepting the echo signal to obtain an intercepted signal;
obtaining a first impulse response according to the excitation signal, and carrying out matched filtering processing on the first impulse response and the interception signal to obtain time domain interception compression;
Obtaining a second impulse response according to the intercepted signal, and performing matched filtering processing on the second impulse response and the intercepted signal to obtain time domain self-compression;
obtaining a third impulse response according to the echo signal, and performing matched filtering processing on the third impulse response and the intercepted signal to obtain echo self-compression;
And selecting pulse pressure signals with highest comprehensive scores by using a preset numerical value selection method for the time domain interception compression, the time domain self-compression and the echo self-compression, and determining a final thickness value by using the flight time under the pulse pressure signals and combining a time difference thickness measurement method.
2. The electromagnetic ultrasonic thickness measurement method according to claim 1, wherein the step of obtaining an excitation signal, generating a transmission signal according to the excitation signal, obtaining an echo signal after the transmission signal is reflected and propagated by a target test piece, and obtaining an interception signal by intercepting the echo signal comprises:
The Chirp signal is used as an excitation signal and expressed as:
，
Wherein, The excitation signal is represented by A, i represents an imaginary unit, f 0 represents a starting frequency, k represents a frequency modulation frequency of the Chirp signal, T represents time, and T represents a pulse width of the Chirp signal;
Under the condition that the signal pulse width T is unchanged, changing the frequency band range of the Chirp signal by changing f 0 and k;
The received echo signal r (t) is the sum of a plurality of transverse wave time domain signals s n (t), so r (t) is expressed as:
,
，
Wherein, And/>Respectively representing the amplitude and phase of the nth time domain signal,/>Representing the initial phase of an excitation signal, c represents the propagation speed of sound waves in a material, and d represents the thickness of a test piece to be tested;
performing an interception operation on the echo signal by defining an interception function F (t), namely multiplying the interception function with the echo signal to obtain an intercepted signal j (t), and using a formula as follows:
，
，
Where t 1 is the start time of the truncated signal and t 2 is the end time of the truncated signal, u is the truncated length, in practice the minimum truncated time length is equal to the excitation signal duration and the maximum truncated time length does not exceed the echo signal length, where 。
3. The method of electromagnetic ultrasonic thickness measurement according to claim 2, wherein the step of obtaining a first impulse response from the excitation signal, performing matched filtering processing on the first impulse response and the truncated signal, and obtaining time-domain truncated compression includes:
Defining the first impulse response as the excitation signal, and obtaining the expression of time domain interception compression through matched filtering processing as follows:
，
Wherein, Representing time-domain truncated compression,/>Representing convolution operations,/>Representing intercepted echo signals,/>Representing the intercepted signal at τ delay,/>Representing the first impulse response,/>Representing the mirror image of the excitation signal.
4. The electromagnetic ultrasonic thickness measurement method according to claim 3, wherein the step of obtaining a second impulse response from the truncated signal, subjecting the second impulse response and the truncated signal to matched filter processing, and obtaining time-domain self-compression comprises:
defining the second impulse response as the intercepted signal, and obtaining the expression of the time domain self-compression through matched filtering processing as follows:
，
Wherein, Representing time domain self-compression,/>Representing the second impulse response,/>Representing the mirror image of the intercepted signal.
5. The method of electromagnetic ultrasonic thickness measurement according to claim 4, wherein the step of obtaining a third impulse response from the echo signal, performing matched filtering processing on the third impulse response and the truncated signal, and obtaining echo self-compression comprises:
defining the third impulse response as the echo signal, and obtaining the expression of echo self-compression through matched filtering processing as follows:
，
Wherein, Representing echo self-compression,/>Representing the third impulse response,/>Representing a mirror image of the echo signal.
6. The electromagnetic ultrasonic thickness measurement method according to claim 5, wherein the preset numerical selection method is as follows:
The signal-to-noise ratio, the main lobe peak value and the main lobe width after pulse pressure are defined as signal evaluation indexes, corresponding weight parameters are respectively distributed as gamma 1、γ2 and gamma 3, and a formula for calculating a comprehensive score is as follows:
w=γ1K1+γ2K2+γ3K3，
Wherein w is a comprehensive score, K 1 is a signal-to-noise ratio after pulse pressure, K 2 is a main lobe peak value, and K 3 is a main lobe width;
the pulse pressure signal with the highest comprehensive score is selected, and the final thickness value is determined by using the time of flight under the pulse pressure signal and combining a time difference thickness measurement method.
7. The electromagnetic ultrasonic thickness measurement method according to claim 6, wherein the time difference thickness measurement method has a calculation expression of:
，
where Δt represents the time difference between two adjacent echo signals, i.e. the time of flight.
8. An electromagnetic ultrasonic thickness measurement system with improved matched filtering, the system comprising:
The signal acquisition module is used for acquiring an excitation signal, generating a transmitting signal according to the excitation signal, carrying out reflection propagation on the transmitting signal through a target test piece to obtain an echo signal, and intercepting the echo signal to obtain an intercepted signal;
The signal interception and compression module is used for obtaining a first impulse response according to the excitation signal, and carrying out matched filtering processing on the first impulse response and the interception signal to obtain time domain interception and compression; obtaining a second impulse response according to the intercepted signal, and performing matched filtering processing on the second impulse response and the intercepted signal to obtain time domain self-compression; obtaining a third impulse response according to the echo signal, and performing matched filtering processing on the third impulse response and the intercepted signal to obtain echo self-compression;
and the thickness measurement data processing module is used for selecting pulse pressure signals with highest comprehensive scores by using a preset numerical value selection method for the time domain interception compression, the time domain self-compression and the echo self-compression, and determining a final thickness value by using the flight time under the pulse pressure signals and combining a time difference thickness measurement method.
9. A computer device comprising a memory and a processor, wherein:
the memory is used for storing a computer program;
the processor is configured to implement the electromagnetic ultrasonic thickness measurement method according to any one of claims 1 to 7 when executing the computer program stored on the memory.
10. A storage medium storing a computer program which, when executed by a processor, implements the electromagnetic ultrasonic thickness measurement method according to any one of claims 1-7.
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