Electromagnetic ultrasonic thickness measurement method based on low voltage excitation

Abstract

The application discloses a kind of electromagnetic ultrasonic thickness measurement methods based on low-voltage excitation, belong to nondestructive testing technical field, comprising: selecting sub-pulse signal;Generation random sequence and output sequence based on Golay code;According to the value of adjacent bit in random sequence, dynamically select the first sub-pulse without zero level or the second sub-pulse containing zero level, synthesize pulse signal;Pulse signal is multiplied with random signal to obtain output signal, after power amplification, electromagnetic ultrasonic transducer is excited;The actual receiving signal is obtained by multiplying the original signal collected by receiving end with the inverse code of pulse signal, finally, long pulse string signal is related to process to obtain thickness measurement result.The application inserts receiving interval dynamically in excitation signal, effectively avoids echo aliasing in thin-wall test piece detection, while significantly reduces the demand for excitation voltage under the premise of ensuring signal-to-noise ratio.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing technology, and particularly relates to an electromagnetic ultrasonic thickness measurement method based on low-voltage excitation. Background Technology

[0002] Electromagnetic ultrasonic testing (EUT) is an advanced non-destructive testing method that excites and receives ultrasonic waves through electromagnetic coupling. It offers advantages such as non-contact operation, no need for coupling agents, low attenuation, and ease of generating various waveforms, making it widely applicable in harsh environments or high-speed industrial testing scenarios, such as pipeline corrosion detection and high-temperature online monitoring. Compared to traditional piezoelectric ultrasonic testing, this technology is better suited to complex working conditions, improving the applicability and reliability of the testing. In recent years, pulse compression technology has been introduced into EUT to improve the signal-to-noise ratio (SNR) of the detection signal and reduce the requirements for the excitation equipment. This technology transmits a long-duration signal at the excitation end, modulated by frequency or phase, to expand the signal's time-width-bandwidth product. The receiving end then correlates the echo signal with the transmitted signal to obtain a high-resolution, narrow-pulse response. Typical modulation methods include linear frequency modulation (LFM) signals and binary phase-coded signals (such as Barker codes and Gray codes). For example, there are existing examples of using LFM signals to improve the SNR of air-coupled ultrasonic testing images, or combining pulse inversion with Golay complementary codes to suppress sidelobes and significantly improve the output SNR.

[0003] However, existing electromagnetic ultrasonic testing technologies still have significant limitations in practical applications. Due to the low transduction efficiency of electromagnetic ultrasound, its received signal strength is typically 20-40 dB lower than that of piezoelectric ultrasound. Therefore, it generally relies on high-power transmitting devices (often exceeding 5 kW) and high-voltage excitation to obtain effective echoes, resulting in complex equipment structures, high costs, and operational safety hazards. Especially in flammable and explosive environments, high voltage can easily ignite electrical sparks, threatening personnel and equipment safety. Furthermore, in thin-walled components or stress concentration areas, high-voltage excitation may induce micro-damage in the material, limiting its applicability in such scenarios. Although pulse compression technology can reduce the required excitation power and improve the signal-to-noise ratio to some extent, long-sequence excitation can easily lead to echo overlap when the sample thickness is small, affecting the correct extraction and identification of the signal, making it difficult to achieve stable and effective thickness measurement under low-voltage conditions. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes an electromagnetic ultrasonic thickness measurement method based on low-voltage excitation, thereby resolving the issues present in the prior art.

[0005] To achieve the above objectives, the present invention provides an electromagnetic ultrasonic thickness measurement method based on low-voltage excitation, comprising:

[0006] S1. Select the sub-pulse signal;

[0007] S2, the generated length is L A random sequence, wherein the elements of the random sequence consist of 0 and 1;

[0008] S3. Based on the Golay code base group, the generated length is... L The output sequence, wherein the elements of the output sequence consist of -1 and 1;

[0009] S4. According to the random sequence and the output sequence, a receiving interval is dynamically inserted into the excitation signal to generate a pulse signal. Specifically, based on the value of the current element and its next element in the random sequence, a first sub-pulse signal or a second sub-pulse signal is dynamically selected as the sub-pulse signal for the current segment. The selected sub-pulse signals are then synthesized according to the order of the output sequence to obtain the pulse signal. The first sub-pulse signal is a waveform signal without zero level, and the second sub-pulse signal is a waveform signal containing a segment of zero level.

[0010] S5. Multiply the pulse signal with a random signal of equal length to obtain the output signal;

[0011] S6. After the output signal is generated and amplified, a long pulse train signal is generated to excite the electromagnetic ultrasonic transducer.

[0012] S7. The ultrasonic signal reflected by the test piece is received through the electromagnetic ultrasonic transducer and converted into an electrical signal. After filtering and amplification, the original received signal is obtained.

[0013] S8. Multiply the original received signal by the inverse code of the random signal to obtain the actual received signal;

[0014] S9. Perform correlation processing on the actual received signal and the long pulse train signal to obtain the final thickness measurement result.

[0015] Preferably, in step S1, the waveform of the sub-pulse signal is a periodic sine wave, square wave, or triangular wave.

[0016] Preferably, in step S1, the waveform of the sub-pulse signal is a frequency-modulated signal or a phase-modulated signal.

[0017] Preferably, in step S4, the dynamic selection specifically means: when the current element in the random sequence is 1 and the value of the next element is 1, the first sub-pulse signal is selected; otherwise, the second sub-pulse signal is selected.

[0018] Preferably, in step S3, the output sequence is generated by extending the basic code group of the Golay code using a general term recursion method or a cross interpolation method.

[0019] Preferably, in step S6, the signal generation is achieved collaboratively by the host computer and the FPGA.

[0020] Preferably, in step S7, the received and filtered amplified signal is acquired by a data acquisition card and transmitted to a host computer.

[0021] Preferably, in step S9, the correlation processing is matched filtering processing.

[0022] Preferably, the zero-level duration contained in the second sub-pulse signal corresponds to the receiving interval, in order to avoid overlap of the echo signals in the time domain.

[0023] Preferably, the method is applicable to electromagnetic ultrasonic thickness measurement of thin-walled specimens.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] This invention employs a technique that dynamically selects either a first sub-pulse signal without a zero level or a second sub-pulse signal containing a zero level based on a random sequence during pulse signal generation. This technique actively embeds a receiving interval into the long sequence of excitation signals. This allows for the complete reception of reflected echoes from the thin-walled specimen interface during the excitation interval, fundamentally solving the information confusion problem caused by the time-domain overlap of the excitation and echo signals. This significantly improves the reliability and accuracy of pulse compression technology in the thickness measurement of thin-walled specimens.

[0026] This invention constructs a complete low-voltage encoding excitation and decoding system by employing techniques such as multiplying a pulse signal with a random signal to generate an output signal, and multiplying the original received signal with the inverse code of the random signal at the receiving end followed by correlation processing. This scheme utilizes pulse compression technology to extend the signal bandwidth to reduce instantaneous power and leverages synchronous modulation and demodulation processing to effectively extract weak signals. This allows the system to achieve a signal-to-noise ratio that meets thickness measurement requirements without the high-voltage, high-power excitation relied upon by traditional techniques, thus reducing equipment complexity and operational risks.

[0027] This invention, by comprehensively utilizing the aforementioned dynamic interval insertion technique and random signal modulation and demodulation process, successfully combines the advantages of long-sequence encoded excitation with the requirements of thin-walled, low-voltage detection scenarios. This integrated solution not only overcomes the application limitations of traditional pulse compression technology in such scenarios but also reduces the stringent requirements on the overall system hardware performance, enabling electromagnetic ultrasonic thickness measurement technology to be more conveniently applied to more industrial sites such as flammable and explosive environments, portable devices, or online rapid detection. Attached Figure Description

[0028] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0029] Figure 1 This is a flowchart of an electromagnetic ultrasonic thickness measurement method based on low-voltage excitation according to an embodiment of the present invention;

[0030] Figure 2 The first sub-pulse signal in this embodiment of the invention p 1( t ) Schematic diagram;

[0031] Figure 3 The second sub-pulse signal in this embodiment of the invention p 2( t ) Schematic diagram;

[0032] Figure 4 The pulse signal of this embodiment of the invention S ( t Partial waveform diagram;

[0033] Figure 5 Random signal in an embodiment of the present invention r 1( t Partial waveform diagram;

[0034] Figure 6 The long pulse train signal in this embodiment of the invention x ( t A partial waveform diagram;

[0035] Figure 7 The original received signal in this embodiment of the invention y 1( t A partial waveform diagram;

[0036] Figure 8 The actual received signal in this embodiment of the invention y 2( t A partial waveform diagram;

[0037] Figure 9 The thickness measurement results of this embodiment of the invention y ( t (Diagram) Detailed Implementation

[0038] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0039] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0040] Example 1

[0041] like Figure 1 As shown, this embodiment provides an electromagnetic ultrasonic thickness measurement method based on low-voltage excitation, which includes an encoding excitation and decoding output process, specifically including:

[0042] S1. Select the sub-pulse signal;

[0043] Furthermore, in step S1, the waveform of the sub-pulse signal is a periodic sine wave, square wave, or triangular wave.

[0044] Furthermore, in step S1, the waveform of the sub-pulse signal is a frequency-modulated signal or a phase-modulated signal.

[0045] Specifically, sub-pulse signal p ( t The selection of the sub-pulse waveform offers a variety of options. Basic waveforms, such as sine waves, square waves, or triangular waves of different periods, can be used; complex modulation signals, such as frequency modulation or phase modulation signals, can also be used, and their duration can be flexibly set as needed.

[0046] During testing, the overall flowchart of the low-voltage electromagnetic ultrasonic thickness measurement scheme is as follows: Figure 1 As shown, it mainly includes signal excitation and reception processing. Taking a single-frequency sinusoidal signal with several cycles as an example, the selected sub-pulse signal... p 1( t ), p 2( t ) respectively as Figure 2 , 3 As shown.

[0047] S2, the generated length is L A random sequence, wherein the elements of the random sequence consist of 0 and 1;

[0048] Specifically, random sequence R The generation length is L random sequence R The sequence consists of only two elements: "0" and "1".

[0049] S3. Based on the Golay code base group, the generated length is... L The output sequence, wherein the elements of the output sequence consist of -1 and 1;

[0050] Furthermore, in step S3, the output sequence is generated by extending the basic code group of the Golay code using the general term recursion method or the cross interpolation method.

[0051] Specifically, the output sequence S The generation of [the code] is based on the Golay code base group, and is extended and generated using methods such as general term recursion or cross interpolation to generate a code of length [length]. L long pulse train sequence S The sequence consists of only two elements: "-1" and "1".

[0052] S4. According to the random sequence and the output sequence, a receiving interval is dynamically inserted into the excitation signal to generate a pulse signal. Specifically, based on the value of the current element and its next element in the random sequence, a first sub-pulse signal or a second sub-pulse signal is dynamically selected as the sub-pulse signal for the current segment. The selected sub-pulse signals are then synthesized according to the order of the output sequence to obtain the pulse signal. The first sub-pulse signal is a waveform signal without zero level, and the second sub-pulse signal is a waveform signal containing a segment of zero level.

[0053] Further, in step S4, the dynamic selection specifically means: when the current element in the random sequence is 1 and the value of the next element is 1, the first sub-pulse signal is selected; otherwise, the second sub-pulse signal is selected.

[0054] Furthermore, the zero-level duration contained in the second sub-pulse signal corresponds to the receiving interval, which is used to avoid overlap of the echo signals in the time domain.

[0055] Specifically, the generation of the excitation output signal in the host computer mainly includes two steps: 1) the overall pulse signal S ( t The generation of sub-pulse signals p ( t It consists of two basic waveforms: one without a zero level. p 1( t ) and containing a zero level p 2( t The selection criteria are as follows: First, determine the random sequence. R Current position R ( i ) and the next one R ( i +1) value; if both are "1", then the segment pulse p ( t Select sub-pulse p 1( t In all other cases, a sub-pulse is selected. p2( t Finally, the above sub-pulses are processed according to the output sequence. S The pulse signal is synthesized by combining the following sequences in sequence. S ( t ).

[0056] This embodiment judges a random sequence. R The pulse signal is generated by taking the element values ​​of the current bit and the next bit. S ( t and random signals r 1( t Its partial waveform diagram is as follows: Figure 4 , 5 As shown.

[0057] S5. Multiply the pulse signal by a random signal of equal length to obtain the output signal;

[0058] Specifically, the length is L pulse signal S ( t ) and random signals of equal length r 1( t The output signal is obtained by performing a multiplication operation. T ( t ).

[0059] S6. After the output signal is generated and amplified, a long pulse train signal is generated to excite the electromagnetic ultrasonic transducer.

[0060] Furthermore, in step S6, the signal generation is achieved collaboratively by the host computer and the FPGA.

[0061] Specifically, the output signal generated by the host computer T ( t The signal is output to the signal generation module, which then outputs the signal to the power amplification module to generate a long pulse train signal to excite the electromagnetic ultrasonic transducer. x ( t ).

[0062] Long pulse train signal x ( t The magnetic field acts on the surface of the test specimen, inducing eddy currents within the specimen. These eddy currents interact with the applied static bias magnetic field to generate a Lorentz force, which in turn drives the grains on the surface of the test specimen to vibrate. This vibration propagates into the material in the form of elastic waves, thus generating ultrasonic waves within the specimen.

[0063] In this embodiment, the selected encoding sequence is L When a long sequence of 1000-bit Golay codes is generated, an output signal is generated in the host computer. T ( tThe signal generated by the host computer is transmitted via the signal generation module. T ( t The signal is then amplified by a power amplifier module and used to generate a long-pulse excitation signal to excite the electromagnetic ultrasonic transducer. x ( t The waveform diagram of the long pulse train signal is shown below. Figure 6 As shown.

[0064] S7. The ultrasonic signal reflected by the test piece is received through the electromagnetic ultrasonic transducer and converted into an electrical signal. After filtering and amplification, the original received signal is obtained.

[0065] Furthermore, in step S7, the received and filtered amplified signal is acquired by the data acquisition card and transmitted to the host computer.

[0066] Specifically, the reflected ultrasonic signal is converted into an electrical signal by an electromagnetic ultrasonic transducer, and the receiving end acquires and filters and amplifies the original received signal. y 1( t The signal is transmitted to the oscilloscope.

[0067] In this embodiment, the original received signal obtained after filtering and amplification of the signal collected by the receiving coil following the reflection from the sample is described. y 1( t A partial waveform diagram is shown below. Figure 7 As shown in the figure, this signal reflects the original response characteristics sensed by the system under the action of the excitation signal, and its waveform is used for further analysis and processing.

[0068] S8. Multiply the original received signal by the inverse code of the random signal to obtain the actual received signal;

[0069] Specifically, in the host computer, the received signal... y 1( t The inverse of a random signal r 2( t Perform a multiplication operation to obtain the actual received signal. y 2( t The partial waveform diagrams are as follows: Figure 8 As shown.

[0070] S9. Perform correlation processing on the actual received signal and the long pulse train signal to obtain the final thickness measurement result.

[0071] Specifically, the accompanying host computer will receive the signal. y 1( t The inverse of a random signal r 2( t Multiplying them yields the actual received signal. y 2(t ).

[0072] Furthermore, in step S9, the correlation processing is a matched filtering process.

[0073] Specifically, the actual received signal is transmitted in the host computer. y 2( t ) and the long pulse excitation signal at the output terminal x ( t The relevant processing is performed to obtain the final thickness measurement result. y ( t The thickness measurement results are shown in the diagram below. Figure 9 As shown.

[0074] The method described in this embodiment is applicable to electromagnetic ultrasonic thickness measurement of thin-walled specimens.

[0075] The beneficial effects of this embodiment:

[0076] This embodiment proposes an electromagnetic ultrasonic thickness measurement method based on low-voltage excitation. This method effectively overcomes the information confusion caused by partial overlap of echo signals under long-sequence excitation by dynamically inserting receiving intervals into the excitation signal. This removes the limitation of sample thickness on long-sequence excitation in actual testing, significantly improving the applicability of pulse compression technology. Furthermore, compared to traditional electromagnetic ultrasonic technology, this solution significantly reduces the performance requirements of the instrument hardware, effectively expanding the application scenarios and scope of electromagnetic ultrasonic technology.

[0077] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for electromagnetic ultrasonic thickness measurement based on low-voltage excitation, characterized in that, Includes the following steps: S1. Select the sub-pulse signal; S2, the generated length is L A random sequence, wherein the elements of the random sequence consist of 0 and 1; S3. Based on the Golay code base group, the generated length is... L The output sequence, wherein the elements of the output sequence consist of -1 and 1; S4. According to the random sequence and the output sequence, a receiving interval is dynamically inserted into the excitation signal to generate a pulse signal. Specifically, based on the value of the current element and its next element in the random sequence, a first sub-pulse signal or a second sub-pulse signal is dynamically selected as the sub-pulse signal for the current segment. The selected sub-pulse signals are then synthesized according to the order of the output sequence to obtain the pulse signal. The first sub-pulse signal is a waveform signal without zero level, and the second sub-pulse signal is a waveform signal containing a segment of zero level. S5. Multiply the pulse signal with a random signal of equal length to obtain the output signal; S6. After the output signal is generated and amplified, a long pulse train signal is generated to excite the electromagnetic ultrasonic transducer. S7. The ultrasonic signal reflected by the test piece is received through the electromagnetic ultrasonic transducer and converted into an electrical signal. After filtering and amplification, the original received signal is obtained. S8. Multiply the original received signal by the inverse code of the random signal to obtain the actual received signal; S9. Perform correlation processing on the actual received signal and the long pulse train signal to obtain the final thickness measurement result.

2. The method according to claim 1, characterized in that, In step S1, the waveform of the sub-pulse signal is a periodic sine wave, square wave, or triangular wave.

3. The method according to claim 1, characterized in that, In step S1, the waveform of the sub-pulse signal is a frequency-modulated signal or a phase-modulated signal.

4. The method according to claim 1, characterized in that, In step S4, the dynamic selection specifically means: when the current element in the random sequence is 1 and the value of the next element is 1, the first sub-pulse signal is selected; otherwise, the second sub-pulse signal is selected.

5. The method according to claim 1, characterized in that, In step S3, the output sequence is generated by extending the basic code group of the Golay code using the general term recursion method or the cross interpolation method.

6. The method according to claim 1, characterized in that, In step S6, the signal generation is achieved collaboratively by the host computer and the FPGA.

7. The method according to claim 1, characterized in that, In step S7, the received and filtered amplified signal is acquired by the data acquisition card and transmitted to the host computer.

8. The method according to claim 1, characterized in that, In step S9, the correlation processing is matched filtering processing.

9. The method according to claim 1, characterized in that, The zero-level duration contained in the second sub-pulse signal corresponds to the receiving interval and is used to avoid overlap of echo signals in the time domain.

10. The method according to claim 1, characterized in that, The method is applicable to electromagnetic ultrasonic thickness measurement of thin-walled specimens.

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