Electromagnetic ultrasonic single coding excitation method suitable for two-phase complementary sequence

Abstract

The invention discloses an electromagnetic ultrasonic single-time coding excitation method suitable for a two-phase complementary sequence. According to the method, a decoding result during double-time coding excitation can be simulated in a single-time coding excitation mode. A reference signal and an A scanning signal corresponding to the complementary A code are obtained when the complementary A code is excited, standard signals corresponding to the complementary A code and the complementary B code are constructed, and an AB code excitation conversion factor is adopted to obtain an excitation result corresponding to the complementary B code, so that a decoding result of double encoding excitation is obtained through single excitation. According to the method, decoding errors caused by the problems of detection position change of the sensor and the sample, inconsistent system output power and the like during multiple times of measurement in the electromagnetic ultrasonic detection process are effectively avoided, meanwhile, the online detection efficiency is improved, and the application scene of the two-phase complementary sequence in the ultrasonic coding excitation technology is widened.

Description

Technical Field

[0001] The present invention relates to an electromagnetic ultrasonic single-shot coded excitation method suitable for a two-phase complementary sequence, belonging to the field of nondestructive testing and structural health testing. The method can simulate the result of double-shot coded excitation by means of single-shot coded excitation, avoiding the problems of decoding error and reduced detection efficiency caused by the two-shot transmission of a traditional two-phase complementary sequence, and is more conducive to online rapid detection of actual working conditions. Background Art

[0002] Electromagnetic ultrasound excites and receives ultrasonic waves by electromagnetic coupling. Due to its advantages of non-contact, low attenuation, and no need for coupling agents, it is suitable for detection of complex working conditions such as high temperature online and rough surfaces, such as boiler water-cooled wall tube corrosion defect detection, 450℃ high-temperature paramagnetic steel detection and other applications. However, its low transducer efficiency leads to a low signal-to-noise ratio of the received echo signal, which seriously limits its development and application. In order to improve the echo signal-to-noise ratio and distance resolution of the existing ultrasonic detection system, domestic and foreign scholars have introduced ultrasonic coded excitation and pulse compression technology to improve this situation. Specifically, pulse compression technology emits wide pulse excitation and obtains narrow pulses after matched filtering, so that the high distance resolution of narrow pulses is taken into account while ensuring the strong detection capability of wide pulses. Among the common coded signals, the phase coded signals of single and double coded excitations are represented by Barker code and Golay code, respectively. In single ultrasonic coded excitation, Zhou Zhenggan et al. (2014) from Beijing University of Aeronautics and Astronautics selected a 13-bit Barker code signal as the excitation signal and combined pulse compression with wavelet filtering to solve the problem of low signal-to-noise ratio of echo signals in defect detection of molded composite laminates using air-coupled ultrasonic signals. Unfortunately, traditional Barker codes have only a few available code lengths, and the maximum number of bits is only 13, which greatly limits the application of coded ultrasonic excitation technology. Therefore, a two-phase complementary sequence can be used as a more ideal coding signal. Its advantage is that there is no code length restriction and its theoretical compression decoding result can output a pulse compression signal without side lobes. Taking the commonly used Golay code as an example, Fan Zeng et al. (2022) proposed a hybrid coding excitation method of Barker code and Gray code convolution to improve the limitation of Barker code coding length, and applied it to ultrasonic guided wave detection. The results show that this method can effectively improve the signal-to-noise ratio of echo signals in oil and gas pipeline detection systems.

[0003] In ultrasonic coding excitation technology, traditional two-phase complementary sequences usually use double coding excitation and receiving decoding to achieve output, which will increase the error of detection results and reduce detection efficiency. In view of the above problems, the method of the present invention is based on the principle of ultrasonic coding excitation, adopts a single coding excitation method, and obtains the corresponding complementary B code by a single excitation complementary A code to achieve the effect of double excitation of A and B codes, and applies this method to electromagnetic ultrasonic detection, and verifies the feasibility of this method from theoretical and experimental perspectives. The experimental results show that this method can effectively avoid the decoding error problem caused by double coding excitation and improve the online rapid detection capability, while providing more options in the selection of ultrasonic coding excitation waveforms. Summary of the invention

[0004] In order to solve the above technical problems, the present invention aims to provide an electromagnetic ultrasonic single coded excitation method applicable to a two-phase complementary sequence, which uses a single coded excitation method to simulate the result of a double coded excitation. The method uses a single excitation method to obtain the detection result of the corresponding complementary sequence, realizes single coded excitation and decoding output, improves the online rapid detection capability, and avoids decoding errors caused by the relative scanning position change between the sensor and the sample during multiple measurements, inconsistent output power of the detection system, and other problems.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] An electromagnetic ultrasonic single-shot coding excitation method applicable to a two-phase complementary sequence, wherein the electromagnetic ultrasonic single-shot coding is a 16-bit Golay code, and the method comprises:

[0007] ① Complementary A code coded excitation;

[0008] When single coded excitation is used, 16-bit GolayA code excitation is selected to obtain the ultrasonic reference signal a r (n) and ultrasonic echo signal A e (n). In the constructed electromagnetic ultrasonic testing system, the feedback reference signal and ultrasonic echo signal can be read in real time through an oscilloscope.

[0009] ②Construct standard excitation signal;

[0010] At this time, construct standard excitation signals a(n) and b(n) of 16-bit Golay A code and 16-bit Golay B code of the same frequency. The standard excitation signal can be regarded as a sine pulse signal arranged in a coding sequence with a sine wave of a certain frequency as the carrier.

[0011] ③ Solve the complementary B code excitation result;

[0012] From the multiple signals obtained above, the reference signal b for 16-bit Golay B code excitation isr (n) through the standard signals a(n), b(n) and the reference signal a r (n) is obtained. Then, the echo signal B when excited by 16-bit Golay B code is e (n) Through the reference signal a r (n), b r (n) and echo signal A e (n)To obtain.

[0013] ④Pulse compression;

[0014] Based on the reference signal and echo signal excited by the 16-bit Golay (A, B) code, the reference signal and the corresponding echo signal are correlated and processed. This process involves pulse compression and outputs the decoding result.

[0015] ⑤Vector addition;

[0016] The decoded outputs of the 16-bit GolayA code and the 16-bit Golay B code are vector-added to eliminate the side lobes and increase the main lobe amplitude, and the final decoded signal is output.

[0017] The present invention can achieve the following beneficial effects:

[0018] 1. Based on the overall coding and decoding scheme of the traditional two-phase complementary sequence, the overall scheme of single-time coding excitation and decoding is realized through a series of processing processes such as single-time excitation complementary A code, AB code excitation conversion factor, pulse compression and vector addition. Compared with the traditional double-time coding excitation, this scheme can simulate the result of double excitation by means of single-time coding excitation. In addition, this scheme can avoid decoding errors caused by the relative movement of the sensor and the sample during multiple measurements, inconsistent output power of the detection system, and other problems.

[0019] 2. Compared with the traditional double-coding excitation technology, the single-coding excitation scheme can improve the online detection efficiency, broaden the detection application scenarios, and provide more options in the selection of coding signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 :Overall flow chart of electromagnetic ultrasound encoding and decoding based on two-phase complementary sequence;

[0021] Figure 2 : Schematic diagram of reference signal when 16-bit GolayA code is excited;

[0022] Figure 3 : Schematic diagram of reference signal for 16-bit Golay B code excitation;

[0023] Figure 4 :Schematic diagram of echo signal when excited by 16-bit GolayA code;

[0024] Figure 5 :Schematic diagram of echo signal when excited by 16-bit Golay B code;

[0025] Figure 6 :Schematic diagram of the decoded output signal when double-exciting 16-bit Golay code;

[0026] Figure 7 :Schematic diagram of 16-bit GolayA code standard excitation signal;

[0027] Figure 8 :Schematic diagram of 16-bit Golay B code standard excitation signal;

[0028] Fig. 9 : Schematic diagram of reference signal for solving 16-bit Golay B code excitation;

[0029] Fig.10 :Solving the echo signal diagram when 16-bit Golay B code is excited;

[0030] Fig.11 :Schematic diagram of the decoded output signal when a 16-bit Golay code is excited once;

[0031] Fig.12 : Comparison of decoded output signals when using double and single coded excitation 16-bit Golay code;

[0032] Fig.13 : Comparison of decoding output signals when double and single coded excitation 20-bit complementary code is used; DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0034] Taking 16-bit Golay code as an example, the overall flow chart of electromagnetic ultrasound encoding and decoding based on two-phase complementary sequence is as follows: Figure 1 As shown in the figure, the flow chart includes double and single coding excitation and decoding output process. The data shown in the legend is obtained by electromagnetic ultrasonic experiment. Specifically, the spiral coil EMAT is used to obtain the echo signal of the bottom surface of the sample. The tested sample is P91 steel with a size of φ165mm×55mm. The comparison of the two coding excitation methods and output results is as follows:

[0035] (1) When double coded excitation is used, the reference signal (a) obtained when 16-bit GolayA code and Golay B code are excited respectively r (n), b r (n)) Figure 2 ,3 As shown, the echo signal (A e (n), B e (n)) respectively as Figure 4 , 5 As shown. Assuming that the transfer function of the electromagnetic ultrasonic detection system is h(n), then:

[0036]

[0037] Figure 6 is the pulse compression result y2(n) of Golay (A, B) code after decoding and adding output, L G is the encoding sequence length of the Golay code, δ(n) is the impulse function, and * is the convolution process. The processing process can be expressed as:

[0038]

[0039] y2(n)=y a (n)+y b (n) = h(n)*[a r (n)*a r (-n)+b r (n)*b r (-n)]=2L G ·δ(n)*h(n) (3)

[0040] (2) When single-code excitation is used, taking the 16-bit GolayA code as an example, the reference signal a can be obtained. r (n) and echo signal A e (n). Figure 7 , 8 They are the standard signals a(n) and b(n) corresponding to the 16-bit Golay (A, B) code, so the reference signal b corresponding to the 16-bit Golay B code is r (n) Fig. 9 As shown, * -1 It is deconvolution processing, and its solution process can be expressed as:

[0041] b r (n) = a r (n)* -1 a(n)*b(n) (4)

[0042] At this time, the echo signal B when excited by 16-bit Golay B code e (n) can be converted to factor b through AB code excitation r (n)* -1 a r (n) Get, then:

[0043] Be (n) = h(n)*a r (n)*b r (n)* -1 a r (n) = [h(n)*a r (n)*b r (n)]* -1 a r (n) (5)

[0044] The subsequent decoding output process is consistent with the decoding process of double coded excitation, and the acquired echo signal B e (n) and the decoding output results y1(n) are respectively as follows Fig.10 , 11 As shown. Fig.10 , 11 It can be seen that the correlation result of complementary B code excitation can be obtained through the AB code excitation conversion factor and effective decoding output can be achieved.

[0045] When using 16-bit Golay code and 20-bit complementary code excitation, the comparative decoding output results of double and single coded excitation methods are as follows: Fig.12 , 13 Compared with double coded excitation, the echo signal and decoding output results obtained by single excitation are almost the same, with only a slight increase in the sidelobe level.

[0046] The present invention proposes an electromagnetic ultrasonic single coded excitation method suitable for two-phase complementary sequences. The method adopts a single excitation complementary A code method, and obtains the result of complementary B code excitation through the AB code excitation conversion factor, thereby simulating the decoding output result of double excitation. By comparing the decoding output results of double and single coded excitation of 16-bit Golay code and 20-bit complementary code, it can be seen that both methods can achieve effective decoding output, indicating that the method can simulate the decoding result of double excitation by single excitation, which is more suitable for actual detection scenarios.

Claims

1. An electromagnetic ultrasonic single-shot coded excitation method applicable to a two-phase complementary sequence, comprising complementary A-code coded excitation, constructing a standard excitation signal, solving a complementary B-code excitation result, pulse compression and vector addition processing; characterized in that: A single excitation complementary A code obtains a reference signal and an echo signal, and the result of complementary B code excitation is obtained through the AB code excitation conversion factor; the excitation results of complementary A code and B code are pulse compressed and vector added to obtain the final decoding output result; wherein, the reference signal during complementary B code excitation is obtained by the reference signal obtained during complementary A code coding excitation and the constructed complementary A and B code standard excitation signals; subsequently, the echo signal during complementary B code excitation can be obtained by the obtained reference signal of the complementary B code, the reference signal of the complementary A code and the echo signal; the subsequent decoding output process is consistent with the single coding excitation process.

2. The electromagnetic ultrasonic single-shot coded excitation method applicable to a two-phase complementary sequence according to claim 1, characterized in that: In the constructed electromagnetic ultrasonic detection system, the corresponding reference signal and echo signal are obtained when complementary A-code excitation is used.

3. The electromagnetic ultrasonic single-shot coded excitation method applicable to a two-phase complementary sequence according to claim 1, characterized in that: A complementary A-code standard excitation signal and a complementary B-code standard excitation signal of the same frequency are constructed, and based on the reference signal and echo signal during complementary A-code excitation, the corresponding reference signal and echo signal during complementary B-code excitation are solved.

4. The electromagnetic ultrasonic single-shot coded excitation method applicable to a two-phase complementary sequence according to claim 1, characterized in that: The reference signal and echo signal during complementary A and B code excitation are pulse compressed to obtain the decoding output result; then, the decoding results of the two outputs are vector-added to eliminate the side lobes and increase the main lobe amplitude to improve the signal-to-noise ratio of the output signal.

5. The electromagnetic ultrasonic single-shot coded excitation method applicable to a two-phase complementary sequence according to claim 1, characterized in that: The results of double excitation of A and B codes are achieved by solving the results of complementary B code excitation by means of single excitation complementary A code and AB code excitation conversion factors, avoiding decoding errors caused by changes in the relative position of the sensor and the sample during multiple measurements and inconsistent output power of the detection system, while improving online detection efficiency.

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