1. An electromagnetic surface acoustic wave transceiver based on time and space pulse compression, characterized by: the device comprises a pulse compression type electromagnetic ultrasonic surface wave transducer, an exciting circuit, a receiving circuit, an acquisition circuit and an upper computer; the transducer is a transmitting-receiving transducer or a transmitting-receiving integral transducer; when a transmitting transducer and a receiving transducer are adopted, the transmitting transducer is connected with the exciting circuit, and the receiving transducer is connected with the receiving circuit; when a transducer integrated with transmitting and receiving is adopted, the transducer is connected with an exciting and receiving circuit through a duplexer; the signal of the excitation circuit is a linear or non-linear frequency modulation signal or a single pulse signal matched with the coil of the transducer; the coil space arrangement of the pulse compression type electromagnetic ultrasonic surface wave transducer is matched with the excitation circuit signal, and wave packets with non-uniform wavelength distribution can be excited and received; the receiving circuit amplifies and filters the signals of the receiving transducer; the acquisition circuit carries out digital high-speed sampling on the signals processed by the receiving circuit; and the upper computer analyzes and calculates the acquired data and draws waveforms.

2. The apparatus of claim 1, wherein: the pulse compression type electromagnetic ultrasonic surface wave transducer consists of a permanent magnet and a coil, and the length and width of the permanent magnet are larger than those of the coil; the coil comprises a single-wire coil and a multi-wire zigzag coil which is distributed unevenly; the non-uniformly distributed multi-wire zigzag coil adopts linear interval change or non-linear interval change, and can be used as a signal stretcher when being used as a transmitting transducer and applying a single-pulse excitation signal; when acting as a receiving transducer and receiving electromagnetic ultrasound packets, may be used as a signal compressor.

3. The apparatus of claim 2, wherein: when a transmitting-receiving transducer is adopted, four different configuration forms can be formed, which are respectively: temporal stretching-temporal compression, spatial stretching-spatial compression, spatial stretching-temporal compression, temporal stretching-spatial compression;

(1) temporal stretching-temporal compression: the transmitting transducer applies a designed time domain excitation waveform, and the receiving transducer receives an ultrasonic signal and then completes compression by an upper computer in a digital processing process; (2) spatial broadening-spatial compression: applying sharp pulse excitation on the transmitting transducer, obtaining a sharp pulse signal on the receiving transducer, and completing the processes of widening and compressing by using a coil; (3) spatial broadening-temporal compression: applying sharp pulse excitation on the transmitting transducer, widening a coil of the transmitting transducer, receiving an ultrasonic signal by the receiving transducer, and performing digital processing by an upper computer to complete compression; (4) temporal stretching-spatial compression: the transmitting transducer is applied with a designed time domain excitation waveform, the receiving transducer coil is compressed, and the receiving transducer obtains a sharp pulse signal.

4. The apparatus of claim 2, wherein: when the receiving and transmitting integrated transducer is adopted, two different configuration forms can be formed, which are respectively: temporal stretching-temporal compression, spatial stretching-spatial compression;

(1) temporal stretching-temporal compression: the transmitting transducer applies a designed time domain excitation waveform, and the receiving transducer receives an ultrasonic signal and then completes compression by an upper computer in a digital processing process; (2) spatial broadening-spatial compression: the transmitting transducer is excited by sharp pulse, the receiving transducer obtains sharp pulse signal, and the processes of widening and compressing are completed by the coil.

5. The apparatus of claim 3 or 4, wherein: the designed time domain excitation waveform is a sine wave frequency conversion signal designed by adopting a linear frequency modulation or non-linear frequency modulation mode; the excitation circuit is divided into a sine pulse excitation circuit and a single pulse excitation circuit; the sine pulse excitation circuit is used for exciting a sine wave variable frequency signal; the single-pulse excitation circuit is used for exciting a short-time single-pulse signal.

6. The apparatus of claim 5, wherein: the sinusoidal pulse excitation circuit is connected with the single-wire coil and adopts an AB type linear power amplifier structure, typical signal indexes are that the output frequency range is 0.1-5 MHz, and the peak value is 600V; the single-pulse excitation circuit is connected to the multi-wire zigzag coils which are distributed unevenly, an H-bridge type D power amplifier structure is adopted, the typical signal pulse width is 0.1-10 mu s, and the peak-to-peak value is 600V.

7. The apparatus of claim 6, wherein: the space arrangement design method of the coil of the pulse compression type electromagnetic ultrasonic surface wave transducer comprises four steps of establishing a space-time transformation relation, determining a conversion function, determining coil distribution characteristic parameters and selecting a configuration type;

step 1), constructing a space-time transformation relation:

L＝cT (1)

K＝B/c (2)

in the formula: c is the wave speed of the electromagnetic ultrasonic surface wave, B is the frequency bandwidth, T is the time width, L is the wavelength bandwidth, and K is the wave number bandwidth;

step 2), determining a conversion function, wherein for the multi-lead zigzag coil with non-uniform distribution, the specific design of the spatial arrangement of the leads has two different distribution modes:

(1) coil distribution mode 1: the linear wavelength modulation mode corresponds to a linear frequency modulation method in time pulse compression, and the linear frequency modulation signal and the spatial distribution function expression are as follows:

in the formula: s (t) is a linear frequency modulation signal, f₀Is the initial frequency; s (x) is a spatial distribution function, k₀Is the initial wavenumber; t represents time;

(2) coil distribution mode 2: the nonlinear wavelength modulation mode corresponds to a nonlinear frequency modulation method in time pulse compression, and the frequency modulation function and the spatial distribution function expression of the used nonlinear frequency modulation signal are as follows:

in the formula: w (f) is the frequency domain modulation window function, f is frequency; w (λ) is the spatial distribution function, λ is the wavelength;

step 3), determining coil distribution characteristic parameters: the method mainly comprises the steps of determining parameters L and K, wherein L determines the space length of a coil and can be selected according to the space size required in practice; k determines the number of wires under a specific L and also determines the compression ratio, the main side lobe ratio and the side lobe level index after pulse compression; after L and K are determined, drawing a curve of a spatial distribution function, selecting coordinates of points with the value of +/-1 as the position coordinates of the coil wire, placing the wire, and enabling current directions at +1 and-1 positions to be opposite;

step 4), selecting a configuration type: in both transducers, a suitable configuration is selected according to the actual use requirements.

8. The apparatus of claim 7, wherein: after the coil structure is determined, the pulse compression type electromagnetic ultrasonic surface wave transducer can receive the ultrasonic surface wave unidirectional signals, and if bidirectional receiving is required, the length of a receiving coil can be doubled and mirror symmetry type spatial arrangement can be performed.

9. The apparatus of claim 7, wherein: the coil adopts a single coil structure and a linear or nonlinear wavelength modulation structure, and the manufacturing mode of the coil comprises but is not limited to a framework winding type and a PCB type; the coordinates of each wire are calculated from the spatial distribution function, and when a linear wavelength modulation structure is adopted, the coordinates are obtained from characteristic parameters L, K and k₀And determining that when a nonlinear wavelength modulation structure is adopted, the coordinate of each wire is determined by the characteristic parameters L and K.

Background

In the fields of aerospace, petrochemical, automotive manufacturing, material processing, and the like, there are a large number of metal tubular and plate-like structures. In the using process, under the action of factors such as surface oxidation, stress concentration and the like, some weak parts on the surfaces of the pipe and the plate can generate defects such as cracks, corrosion and the like, so that partial failure of the structure is caused. Therefore, the method for detecting the pipeline and the plate efficiently, quickly and accurately by adopting a certain nondestructive detection technology is an effective method for ensuring industrial safety.

The ultrasonic surface wave is mainly concentrated on the surface and the near surface of the test piece, can effectively detect defects in the areas, is slow in attenuation and single in wave mode, and is widely used for ultrasonic nondestructive detection. The electromagnetic ultrasonic transducer can effectively excite surface waves, has the characteristics of no need of coupling and surface treatment compared with the traditional piezoelectric transducer, and is suitable for occasions such as high-speed, high-temperature and on-line detection. At present, the method has been applied to the fields of petrochemical industry, processing and manufacturing and the like to a certain extent, and has great development potential. The electromagnetic ultrasonic transducer consists of a coil and a permanent magnet, and can excite surface waves by using the electromagnetic ultrasonic transducer with a zigzag coil structure. Because the energy conversion efficiency of the electromagnetic ultrasonic transducer is low, the received signal is weak and the signal-to-noise ratio is low. Generally, after the power performance of the excitation device reaches the upper limit, the conventional way to improve the strength of the echo signal is to increase the frequency of the excitation signal or the number of coil turns, but this increases the time width of the signal and loses the time resolution. By adopting the pulse compression technology, the signal strength and the signal to noise ratio can be improved, and the signal resolution can be ensured. Conventional pulse compression is a signal processing technique using the matched filtering principle in the time domain. In electromagnetic ultrasonic surface waves, there are technical possibilities to achieve spatial pulse compression in combination with the special spatial distribution of the coils.

Disclosure of Invention

The invention aims to solve the problems in the prior art and provides an electromagnetic ultrasonic surface wave transmitting and receiving device based on time and space pulse compression. The invention can utilize the zigzag coil structure of the transducer to form a spatial transverse filter, and can make the wave packet distribution of the electromagnetic ultrasonic surface wave and the spatial arrangement of the coil form a spatial matching relationship by matching with a matched excitation circuit, so as to compress a section of signal with a wider spatial domain into a spike pulse signal with a narrower temporal domain. Compared with the traditional equidistant electromagnetic ultrasonic surface wave transducer, the surface wave transducer has higher signal amplitude and stronger resolution. The device is applied to non-contact nondestructive testing of metal pipelines and plate-shaped structures, improves the signal-to-noise ratio and the resolution, and ensures the quality and the safety of test pieces.

The invention is realized by the following technical scheme, the invention provides an electromagnetic ultrasonic surface wave transceiver based on time and space pulse compression, and the device comprises a pulse compression type electromagnetic ultrasonic surface wave transducer, an excitation circuit, a receiving circuit, an acquisition circuit and an upper computer; the transducer is a transmitting-receiving transducer or a transmitting-receiving integral transducer; when a transmitting transducer and a receiving transducer are adopted, the transmitting transducer is connected with the exciting circuit, and the receiving transducer is connected with the receiving circuit; when a transducer integrated with transmitting and receiving is adopted, the transducer is connected with an exciting and receiving circuit through a duplexer; the signal of the excitation circuit is a linear or non-linear frequency modulation signal or a single pulse signal matched with the coil of the transducer; the coil space arrangement of the pulse compression type electromagnetic ultrasonic surface wave transducer is matched with the excitation circuit signal, and wave packets with non-uniform wavelength distribution can be excited and received; the receiving circuit amplifies and filters the signals of the receiving transducer; the acquisition circuit carries out digital high-speed sampling on the signals processed by the receiving circuit; and the upper computer analyzes and calculates the acquired data and draws waveforms.

Furthermore, the pulse compression type electromagnetic ultrasonic surface wave transducer consists of a permanent magnet and a coil, and the length and width of the permanent magnet are larger than those of the coil; the coil comprises a single-wire coil and a multi-wire zigzag coil which is distributed unevenly; the non-uniformly distributed multi-wire zigzag coil adopts linear interval change or non-linear interval change, and can be used as a signal stretcher when being used as a transmitting transducer and applying a single-pulse excitation signal; when acting as a receiving transducer and receiving electromagnetic ultrasound packets, may be used as a signal compressor.

Further, when a transmitting-receiving transducer is adopted, four different configuration forms can be formed, which are respectively: temporal stretching-temporal compression, spatial stretching-spatial compression, spatial stretching-temporal compression, temporal stretching-spatial compression;

(1) temporal stretching-temporal compression: the transmitting transducer applies a designed time domain excitation waveform, and the receiving transducer receives an ultrasonic signal and then completes compression by an upper computer in a digital processing process; (2) spatial broadening-spatial compression: applying sharp pulse excitation on the transmitting transducer, obtaining a sharp pulse signal on the receiving transducer, and completing the processes of widening and compressing by using a coil; (3) spatial broadening-temporal compression: applying sharp pulse excitation on the transmitting transducer, widening a coil of the transmitting transducer, receiving an ultrasonic signal by the receiving transducer, and performing digital processing by an upper computer to complete compression; (4) temporal stretching-spatial compression: the transmitting transducer is applied with a designed time domain excitation waveform, the receiving transducer coil is compressed, and the receiving transducer obtains a sharp pulse signal.

Further, when the receiving and transmitting integrated transducer is adopted, two different configuration forms can be formed, which are respectively: temporal stretching-temporal compression, spatial stretching-spatial compression;

(1) temporal stretching-temporal compression: the transmitting transducer applies a designed time domain excitation waveform, and the receiving transducer receives an ultrasonic signal and then completes compression by an upper computer in a digital processing process; (2) spatial broadening-spatial compression: the transmitting transducer is excited by sharp pulse, the receiving transducer obtains sharp pulse signal, and the processes of widening and compressing are completed by the coil.

Further, the designed time domain excitation waveform is a sine wave frequency conversion signal designed by adopting a linear frequency modulation or non-linear frequency modulation mode; the excitation circuit is divided into a sine pulse excitation circuit and a single pulse excitation circuit; the sine pulse excitation circuit is used for exciting a sine wave variable frequency signal; the single-pulse excitation circuit is used for exciting a short-time single-pulse signal.

Furthermore, the sinusoidal pulse excitation circuit is connected with the single-wire coil, an AB type linear power amplifier structure is adopted, typical signal indexes are that the output frequency range is 0.1-5 MHz, and the peak value is 600V; the single-pulse excitation circuit is connected to the multi-wire zigzag coils which are distributed unevenly, an H-bridge type D power amplifier structure is adopted, the typical signal pulse width is 0.1-10 mu s, and the peak-to-peak value is 600V.

Furthermore, the space arrangement design method of the coil of the pulse compression type electromagnetic ultrasonic surface wave transducer comprises four steps of establishing a space-time transformation relation, determining a conversion function, determining coil distribution characteristic parameters and selecting a configuration type;

step 1), constructing a space-time transformation relation:

L＝cT (1)

K＝B/c (2)

in the formula: c is the wave speed of the electromagnetic ultrasonic surface wave, B is the frequency bandwidth, T is the time width, L is the wavelength bandwidth, and K is the wave number bandwidth;

step 2), determining a conversion function, wherein for the multi-lead zigzag coil with non-uniform distribution, the specific design of the spatial arrangement of the leads has two different distribution modes:

(1) coil distribution mode 1: the linear wavelength modulation mode corresponds to a linear frequency modulation method in time pulse compression, and the linear frequency modulation signal and the spatial distribution function expression are as follows:

in the formula: s (t) is a linear frequency modulation signal, f₀Is the initial frequency; s (x) is a spatial distribution function, k₀Is the initial wavenumber; t represents time;

(2) coil distribution mode 2: the nonlinear wavelength modulation mode corresponds to a nonlinear frequency modulation method in time pulse compression, and the frequency modulation function and the spatial distribution function expression of the used nonlinear frequency modulation signal are as follows:

in the formula: w (f) is the frequency domain modulation window function, f is frequency; w (λ) is the spatial distribution function, λ is the wavelength;

step 3), determining coil distribution characteristic parameters: the method mainly comprises the steps of determining parameters L and K, wherein L determines the space length of a coil and can be selected according to the space size required in practice; k determines the number of wires under a specific L and also determines the compression ratio, the main side lobe ratio and the side lobe level index after pulse compression; after L and K are determined, drawing a curve of a spatial distribution function, selecting coordinates of points with the value of +/-1 as the position coordinates of the coil wire, placing the wire, and enabling current directions at +1 and-1 positions to be opposite;

step 4), selecting a configuration type: in both transducers, a suitable configuration is selected according to the actual use requirements.

Furthermore, after the coil structure is determined, the pulse compression type electromagnetic ultrasonic surface wave transducer can receive the ultrasonic surface wave unidirectional signal, and if bidirectional receiving is required, the length of the receiving coil can be doubled and mirror symmetry type spatial arrangement can be performed.

Further, the coil adopts a single coil structure, a linear or nonlinear wavelength modulation structure, and the manufacturing method includes but is not limited to a skeleton winding type and a PCB type; the coordinates of each wire are calculated from the spatial distribution function, and when a linear wavelength modulation structure is adopted, the coordinates are obtained from characteristic parameters L, K and k₀And determining that when a nonlinear wavelength modulation structure is adopted, the coordinate of each wire is determined by the characteristic parameters L and K.

The invention has the beneficial effects that: the time and space pulse of the electromagnetic ultrasonic surface wave is realized by matching the zigzag coil structure of the transducer with an excitation circuit and by applying and combining four different configurations, a narrower delta-like function waveform is obtained at the upper computer end, the amplitude and the signal-to-noise ratio of the signal are improved, and the detection resolution is improved. The transducer coil can replace part of hardware and algorithm resources originally used for time pulse compression, and the structure of the electromagnetic ultrasonic surface wave detection system is simplified.

Drawings

Fig. 1 is a schematic structural diagram of an electromagnetic surface acoustic wave transceiver device based on temporal and spatial pulse compression according to the present invention;

FIG. 2 is a schematic diagram of a pulse compression type electromagnetic ultrasonic surface wave transducer;

FIG. 3 is a schematic diagram of four different combinations of an electromagnetic ultrasonic surface wave transducer of a pulse-on-pulse compression type;

FIG. 4 is a schematic diagram of two different combinations of the transmitting and receiving integrated pulse compression type electromagnetic ultrasonic surface wave transducers;

FIG. 5 is a flow chart of a design method of spatial arrangement of coils of a pulse compression type electromagnetic ultrasonic surface wave transducer;

FIG. 6 is a schematic view of a mirror-symmetric spatial arrangement of coils;

FIG. 7 is a graph comparing the waveform results of design cases one and two with a conventional equi-spaced coil in Transmit-receive transducer configuration 2;

fig. 8 is a graph comparing the waveform results of the first and second design cases with the conventional equi-spaced coil in the pitch-catch transducer configuration 4.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

With reference to fig. 1 to 8, the present invention provides an electromagnetic surface acoustic wave transceiver device based on time and space pulse compression, which includes a pulse compression type electromagnetic surface acoustic wave transducer, an excitation circuit, a receiving circuit, an acquisition circuit and an upper computer; the transducer is a transmitting-receiving transducer or a transmitting-receiving integral transducer; when a transmitting transducer and a receiving transducer are adopted, the transmitting transducer is connected with the exciting circuit, and the receiving transducer is connected with the receiving circuit; when a transducer integrated with transmitting and receiving is adopted, the transducer is connected with an exciting and receiving circuit through a duplexer; the signal of the excitation circuit is a linear or non-linear frequency modulation signal or a single pulse signal which is matched with the coil of the transducer, and is not a traditional equal frequency tone-burst signal; the coil space arrangement of the pulse compression type electromagnetic ultrasonic surface wave transducer is matched with the excitation circuit signal, and wave packets with non-uniform wavelength distribution can be excited and received; the receiving circuit amplifies and filters the signals of the receiving transducer; the acquisition circuit carries out digital high-speed sampling on the signals processed by the receiving circuit; and the upper computer analyzes and calculates the acquired data and draws waveforms.

The pulse compression type electromagnetic ultrasonic surface wave transducer consists of a permanent magnet and a coil, and the length and width of the permanent magnet are slightly larger than the coil; the coils comprise a single-wire coil (used for transmitting and receiving electromagnetic ultrasonic signals with full wavelength) and a multi-wire zigzag coil which is non-uniformly distributed (used for transmitting and receiving electromagnetic ultrasonic signals with specific wavelength distribution); the non-uniformly distributed multi-wire zigzag coil is a coil with linear spacing change or non-linear spacing change, and the transducer coils are arranged at non-equal spacing instead of the traditional equal spacing coil and can be used as a signal stretcher when being used as a transmitting transducer and applying a single-pulse excitation signal; when acting as a receiving transducer and receiving electromagnetic ultrasound packets, may be used as a signal compressor.

When a transmitting-receiving transducer is adopted, four different configuration forms can be formed, which are respectively: temporal stretching-temporal compression, spatial stretching-spatial compression, spatial stretching-temporal compression, temporal stretching-spatial compression;

(1) temporal stretching-temporal compression: the transmitting transducer applies a designed time domain excitation waveform, and the receiving transducer receives an ultrasonic signal and then completes compression by an upper computer in a digital processing process; (2) spatial broadening-spatial compression: applying sharp pulse excitation on the transmitting transducer, obtaining a sharp pulse signal on the receiving transducer, and completing the processes of widening and compressing by using a coil; (3) spatial broadening-temporal compression: applying sharp pulse excitation on the transmitting transducer, widening a coil of the transmitting transducer, receiving an ultrasonic signal by the receiving transducer, and performing digital processing by an upper computer to complete compression; (4) temporal stretching-spatial compression: the transmitting transducer is applied with a designed time domain excitation waveform, the receiving transducer coil is compressed, and the receiving transducer obtains a sharp pulse signal.

With reference to fig. 3, the transceiver transducer can be configured in four different configurations: (1) configuration mode 1: time stretching-time compression, wherein an exciting circuit 1 is connected with a coil form 1 (single-wire coil), and a receiving circuit is connected with the coil form 1 (single-wire coil); (2) configuration mode 2: the method comprises the following steps of (1) spatial widening-spatial compression, wherein an excitation circuit 2 is connected with a coil form 2 (a multi-wire zigzag coil which is distributed non-uniformly), and a receiving circuit is connected with the coil form 2 (the multi-wire zigzag coil which is distributed non-uniformly); (3) configuration mode 3: spatial broadening-time compression, wherein an excitation circuit 2 is connected with a coil form 2 (a multi-wire zigzag coil which is non-uniformly distributed), and a receiving circuit is connected with a coil form 1 (a single-wire coil); (4) configuration mode 4: time stretching-space compression, the excitation circuit 1 is connected with the coil form 1 (single-wire coil), and the receiving circuit is connected with the coil form 2 (non-uniformly distributed multi-wire zigzag coil).

When the receiving and transmitting integrated transducer is adopted, two different configuration forms can be formed, which are respectively: temporal stretching-temporal compression, spatial stretching-spatial compression;

(1) temporal stretching-temporal compression: the transmitting transducer applies a designed time domain excitation waveform, and the receiving transducer receives an ultrasonic signal and then completes compression by an upper computer in a digital processing process; (2) spatial broadening-spatial compression: the transmitting transducer is excited by sharp pulse, the receiving transducer obtains sharp pulse signal, and the processes of widening and compressing are completed by the coil.

With reference to fig. 4, the transceiver transducer can be configured in two different forms: (1) temporal stretching-temporal compression: the exciting circuit 1 is connected with the coil form 1 (single-wire coil), and the receiving circuit is connected with the coil form 1 (single-wire coil);

(2) spatial broadening-spatial compression: the excitation circuit 2 is connected to the coil form 2 (unevenly distributed multi-wire meander coil), and the reception circuit is connected to the coil form 2 (unevenly distributed multi-wire meander coil).

The designed time domain excitation waveform is a sine wave frequency conversion signal designed by adopting a linear frequency modulation or non-linear frequency modulation mode, and is an equal frequency tone-burst signal adopted by non-traditional electromagnetic ultrasound; the excitation circuit is divided into a sine pulse excitation circuit and a single pulse excitation circuit; the sine pulse excitation circuit is used for exciting a sine wave variable frequency signal; the single-pulse excitation circuit is used for exciting a short-time single-pulse signal.

The sinusoidal pulse excitation circuit is connected with the single-wire coil, adopts an AB type linear power amplifier structure, has typical signal indexes of 0.1-5 MHz of output frequency range and 600V of peak value, and is used for exciting the single-wire structure transducer; the single-pulse excitation circuit is connected to the multi-wire zigzag coils which are distributed unevenly, adopts an H-bridge type D power amplifier structure, has a typical signal pulse width of 0.1-10 mu s and a peak-to-peak value of 600V, and is used for exciting a linear or nonlinear wavelength modulation structure transducer. Both excitation circuits can be used to excite electromagnetic ultrasound signals with a particular wavelength distribution.

With reference to fig. 5, the spatial arrangement design method of the coil of the pulse compression type electromagnetic ultrasonic surface wave transducer includes four steps of establishing a space-time transformation relationship, determining a conversion function, determining coil distribution characteristic parameters, and selecting a configuration type;

step 1), constructing a space-time transformation relation:

L＝cT (1)

K＝B/c (2)

in the formula: c is the wave speed of the electromagnetic ultrasonic surface wave, B is the frequency bandwidth, T is the time width, L is the wavelength bandwidth, and K is the wave number bandwidth;

step 2), determining a conversion function, wherein for the multi-lead zigzag coil with non-uniform distribution, the specific design of the spatial arrangement of the leads has two different distribution modes:

(1) coil distribution mode 1: the linear wavelength modulation mode corresponds to a linear frequency modulation method in time pulse compression, and the linear frequency modulation signal and the spatial distribution function expression are as follows:

in the formula: s (t) is a linear frequency modulation signal, f₀Is the initial frequency; s (x) is a spatial distribution function, k₀Is the initial wavenumber; t represents time;

(2) coil distribution mode 2: the nonlinear wavelength modulation mode corresponds to a nonlinear frequency modulation method in time pulse compression, and the frequency modulation function and the spatial distribution function expression of the used nonlinear frequency modulation signal are as follows:

in the formula: w (f) is the frequency domain modulation window function, f is frequency; w (λ) is the spatial distribution function, λ is the wavelength;

step 3), determining coil distribution characteristic parameters: the method mainly comprises the steps of determining parameters L and K, wherein L determines the space length of a coil and can be selected according to the space size required in practice; k determines the number of wires under a specific L and also determines the compression ratio, the main side lobe ratio and the side lobe level index after pulse compression; in general, the basis is chosen to make K as large as possible in the case of a determination of L; after L and K are determined, drawing a curve of a spatial distribution function, selecting coordinates of points with the value of +/-1 as the position coordinates of the coil wire, placing the wire, and enabling current directions at +1 and-1 positions to be opposite;

step 4), selecting a configuration type: in both transducers, a suitable configuration is selected according to the actual use requirements.

After the coil structure is determined, the pulse compression type electromagnetic ultrasonic surface wave transducer can receive the ultrasonic surface wave unidirectional signals, and if bidirectional receiving is required, the length of a receiving coil can be doubled and mirror symmetry type spatial arrangement can be performed.

The coil adopts a single coil structure and a linear or nonlinear wavelength modulation structure, and the manufacturing mode of the coil comprises but is not limited to a skeleton winding type and a PCB type (wherein the PCB mode comprises a hard PCB mode and a flexible PCB mode); the coordinates of each wire are calculated from the spatial distribution function, and when a linear wavelength modulation structure is adopted, the coordinates are obtained from characteristic parameters L, K and k₀And determining that when a nonlinear wavelength modulation structure is adopted, the coordinate of each wire is determined by the characteristic parameters L and K.

The following gives two examples of the design of the pulse compression type electromagnetic ultrasonic surface wave transducer.

The first design case is as follows:

coil distribution 1, take k₀＝0mm^-1,K＝0.68mm^-1And L is 30 mm. The number of turns of the coil is 20 turns, and the corresponding position coordinates of the lead are (unit: mm): 4.69,8.12, 10.49, 12.42, 14.08, 15.57, 16.92, 18.18, 19.35, 20.46, 21.51, 22.51, 23.47, 24.39, 25.28, 26.14, 26.97, 27.78, 28.56, 29.32.

Design case two:

coil distribution mode 2, taking K as 2mm^-1And L is 30 mm. The number of turns of the coil is 20 turns, and the corresponding position coordinates of the lead are (unit: mm): 4.12,8.61, 11.41, 13.60, 15.48, 17.11, 18.59, 19.94, 21.17, 22.32, 23.39, 24.38, 25.32, 26.20, 27.03, 27.81, 28.55, 29.24, 29.87, 30.45.

It can be seen from fig. 7 and 8 that the two design cases are significantly better than the common coil in the case of the pitch-receive transducer configurations 2 and 4, compared with the common coil.

The device can realize time and space pulse compression of the electromagnetic ultrasonic surface wave transducer coil and circuit signals, obtain very narrow delta function-like form signals, and improve the signal amplitude and detection resolution. The transducer coil can replace part of hardware and algorithm resources originally used for time pulse compression, and the structure of the electromagnetic ultrasonic surface wave detection system is simplified. The design method of the time and space pulse compression coil can be applied to other electromagnetic ultrasonic guided wave transducer designs without obvious dispersion conditions, such as SH0 guided waves, Lamb waves with weak dispersion and the like.

The present invention provides an electromagnetic surface acoustic wave transceiver based on time and space pulse compression, which is described in detail above, and the principle and the implementation of the present invention are explained herein by using specific examples, and the description of the above examples is only used to help understand the method of the present invention and the core idea thereof; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.