Magnetostrictive guided wave transducer and method for detecting soil covering depth in road stand column by using magnetostrictive guided wave transducer

Abstract

The invention belongs to the field of nondestructive testing, and discloses a magnetostrictive guided wave transducer and a method for detecting the soil covering depth in a road stand column through the magnetostrictive guided wave transducer. The transducer comprises a hollow cylinder framework, an annular opening coil and an annular magnetizer array, and the annular opening coil and the annular magnetizer array are embedded in the hollow cylinder framework and are coaxially arranged with the hollow cylinder framework; the hollow cylindrical framework comprises two hollow semi-cylindrical frameworks, one ends of the two hollow semi-cylindrical frameworks are connected in a turnover mode, and the other ends of the two hollow semi-cylindrical frameworks are connected in an opening and closing mode. The annular opening coil comprises a first coil located on the outer ring and a second coil located on the inner ring, the first coil and the second coil are provided with openings in the opening and closing connecting positions of the two hollow semi-cylindrical frameworks, and the opening ends of the first coil and the second coil are communicated in the radial direction to form a closed loop; the annular magnetizer array comprises a plurality of groups of magnetizer arrays, and the groups of magnetizer arrays are uniformly arranged at intervals and are positioned between the first coil and the second coil. According to the invention, the buried depth of the road column can be accurately measured in a large scale.

Description

Technical Field

[0001] The present application belongs to the field of non-destructive testing technology, and more specifically, relates to a magnetostrictive guided wave transducer and a method for detecting the depth of soil cover in a highway pillar. Background Art

[0002] There are numerous buried steel pipe columns in highway guardrail systems, which provide support for vehicles and play a vital role in buffering traffic accidents. However, unqualified construction practices may result in insufficient burial depth of these guardrail steel pipes, which weakens their protective function and endangers the safety of passing vehicles. This requires batch testing of the buried depth of the columns. Traditional methods usually use pile extraction testing and elastic wave methods for testing; but the former is a destructive and labor-intensive method that lacks efficiency, while the latter is prone to reflection overlap and significant measurement errors due to the use of long-wavelength, low-frequency elastic waves.

[0003] In recent years, waveguide technology has been increasingly widely used in the detection of various pipeline systems, but the existing column ultrasonic waveguide detection technology is not mature enough and has many problems: (1) The research on the influence of soil adhesion conditions on the waveguide propagation speed is not in-depth enough, making it difficult to accurately calculate the buried depth of the column; (2) For the detection process of the column length, the signal amplitude of the waveguide end response signal, the waveguide flight time, the soil adhesion condition and the buried length show a complex nonlinear relationship, and the length of the column cannot be accurately calculated by a single flight time. Therefore, it is necessary to provide a waveguide device and method that can realize large-scale column detection and accurately calculate the buried depth of the column, thereby providing an effective processing solution for the buried depth detection of the column. Summary of the invention

[0004] In view of the defects of the prior art, the purpose of this application is to provide a magnetostrictive guided wave transducer and a method for detecting the depth of soil cover inside a highway pillar, aiming to solve the problem of being unable to achieve large-scale and accurate detection of the buried depth of highway pillars.

[0005] To achieve the above-mentioned purpose, according to one aspect of the present application, a magnetostrictive waveguide transducer provided by the present application comprises: a hollow cylindrical skeleton, and an annular open coil and an annular magnetizer array embedded in the hollow cylindrical skeleton and coaxially arranged with the hollow cylindrical skeleton, wherein the hollow cylindrical skeleton comprises two hollow semi-cylindrical skeletons, one end of the two hollow semi-cylindrical skeletons can be flipped and connected, and the other end can be opened and closed; the annular open coil comprises a first coil located in an outer circle and a second coil located in an inner circle, the first coil and the second coil are both provided with openings at the open and closed connection of the two hollow semi-cylindrical skeletons, and the open ends of the first coil and the second coil are radially connected to form a closed loop; the annular magnetizer array comprises a plurality of groups of magnetizer arrays, each group of magnetizer arrays is evenly spaced and arranged, and is located between the first coil and the second coil.

[0006] Compared with the prior art, the above technical solution conceived by the present application greatly improves the convenience of installation and disassembly of the magnetostrictive waveguide transducer without affecting the detection effect, reduces the waste of manpower and time, and is suitable for large-scale rapid detection of the length of highway pillars because the magnetostrictive waveguide transducer can be flipped open and closed.

[0007] Furthermore, the axial width of the annular open coil is half of the waveguide wavelength, so that the spatial arrangement of the annular coil can match the waveguide wavelength, and the excitation intensity of the transducer array can be maximized. If the width of the annular coil is further increased, the waveguide generated by the excitation will further destructively interfere, causing the excitation intensity to decrease.

[0008] Furthermore, the axial width of the annular open coil is 20 mm to 40 mm, so that the open annular coil can produce the best excitation intensity.

[0009] Furthermore, the number of the magnetizer arrays is at least 8 groups.

[0010] Furthermore, the magnetizer array includes a plurality of permanent magnets stacked along the axial direction of the hollow cylindrical skeleton, which can ensure the uniform excitation of the waveguide in all directions. If the number is less than this, the axial magnetic field intensity is small and unevenly distributed, which is not suitable for the excitation of magnetostrictive waveguide.

[0011] Furthermore, the magnetizer array is made of neodymium iron boron material, and the residual magnetic flux density is greater than 1 T. This can achieve the effect of making the magnetizer array have the best magnetic performance.

[0012] Furthermore, the number of the permanent magnets is 4 to 6, the length is 30 mm to 60 mm, the height is 20 mm to 25 mm, and the thickness is 8 mm to 10 mm. The thickness of the magnetizer array can be adjusted along the axial direction of the hollow skeleton according to the number of permanent magnets, thereby achieving the best space utilization and having the best magnetic performance.

[0013] Furthermore, the wire diameter of the annular open coil is 0.1 mm to 0.3 mm, and the lifting distance thereof does not exceed 3 mm, so as to improve the sensitivity of the coil and obtain a more optimized effect of magnetic field uniformity and intensity.

[0014] Furthermore, a plurality of layers of foam copper are arranged on the surface of the magnetizer array close to the annular open coil, and the thickness of the plurality of layers of foam copper is not less than 1 mm, so that the magnetizer array is not affected by the external magnetic field and its magnetic properties are kept stable.

[0015] According to another aspect of the present application, there is also provided a method for detecting the depth of soil cover in a highway column using a magnetostrictive ultrasonic guided wave transducer as described in any of the above items, comprising the following steps:

[0016] S1: setting the magnetostrictive ultrasonic guided wave transducer at the exposed sections of a plurality of known columns to obtain the flight time of the corresponding echo of the top surface of the outer covering soil of each known column, the flight time of the corresponding echo of the top surface of the inner covering soil, and the flight time of the corresponding echo of the bottom surface of each known column;

[0017] S2 uses a data fitting method to fit the calculation formula for the buried depth of the inner covering soil of each column based on the height difference between the top surface of the outer covering soil and the inner covering soil surface of each known column, the buried depth of the inner covering soil, the distance between the top surface of the outer covering soil and the magnetostrictive ultrasonic guided wave transducer, and the multiple sets of flight times obtained in step S1:

[0018]

[0019] Wherein, k is the coefficient of variation of guided wave velocity obtained by fitting, T1 is the flight time of the corresponding echo of the top surface of the outer covering soil of the column, T2 is the flight time of the corresponding echo of the top surface of the inner covering soil, T3 is the flight time of the corresponding echo of the bottom surface of the column, L1 is the height difference L1 between the top surface of the outer covering soil and the surface of the inner covering soil, L2 is the burial depth of the inner covering soil, and L3 is the distance between the top surface of the outer covering soil and the magnetostrictive ultrasonic guided wave transducer;

[0020] S3: installing the magnetostrictive ultrasonic guided wave transducer at the exposed section of the column to be tested, and obtaining the flight time of the corresponding echo of the top surface of the outer covering soil of the column to be tested, the flight time of the corresponding echo of the top surface of the inner covering soil, and the flight time of the corresponding echo of the bottom surface of the column to be tested;

[0021] S4 obtains the buried depth of the inner covering soil of the column to be measured by using the calculation formula based on the height difference between the top surface of the outer covering soil and the inner covering soil surface of the column to be measured, the distance between the top surface of the outer covering soil of the column to be measured and the magnetostrictive ultrasonic guided wave transducer, and the three flight times obtained in step S3.

[0022] The method provided in the present application for detecting the soil cover depth inside a highway pillar using a magnetostrictive waveguide transducer establishes a functional relationship between the length of the soil cover section inside the pillar and the flight time of each cross section, thereby solving the technical problem in the prior art that the signal amplitude and flight time of the response signal at the waveguide end present a complex nonlinear relationship with the soil adhesion and the buried length, making it difficult to accurately calculate the soil cover depth of the pillar.

[0023] In general, the above technical solutions conceived by this application have the following technical advantages compared with the prior art:

[0024] 1. The magnetostrictive waveguide transducer provided in the present application designs the hollow cylindrical skeleton to be a flippable opening and closing design, and at the same time, multiple magnetizer arrays are evenly spaced and arranged into an annular magnetizer array, and the annular open coil is designed as a coil with inner and outer circles connected to each other to form a closed loop, one coil is located on the outside of the annular magnetization array, and the other coil is located on the inside of the annular magnetization array. The opposite ends of the two coils are radially connected at the opening and closing connection of the two hollow semi-cylindrical skeletons to form a closed loop. Since the annular open coil has an opening, it can follow the two hollow semi-cylindrical skeletons to flip and open and close relative to each other, thereby achieving the detection effect of the magnetostrictive waveguide transducer without affecting the convenience of installation and disassembly, reducing the waste of manpower and time, and is suitable for large-scale rapid detection of the length of highway pillars.

[0025] 2. In the present application, multiple permanent magnets constitute an integrated magnetizer array, and the magnetic poles of the magnetizer array are along the axial direction of the hollow cylindrical skeleton, which can provide an axial bias magnetic field. The axial AC magnetic field is generated by loading an alternating current signal on the annular open coil wrapped around the periphery of the magnetizer array, thereby realizing the enhancement and omnidirectional excitation of the longitudinal waveguide of the pipeline; at the same time, by designing the parameters of the coil and the magnetizer array in the magnetostrictive guided wave transducer, such as designing the number of magnetizer arrays in the magnetostrictive ultrasonic guided wave transducer to be no less than 8, the number of permanent magnets to be 4 to 6, the length, height and thickness of the permanent magnets, and the width of the annular coil to be half the wavelength of the waveguide, the excitation efficiency of the longitudinal waveguide can be further improved, ensuring the omnidirectional uniform excitation of the waveguide.

[0026] 3. The ultrasonic guided wave detection method for highway column length provided in the present application overcomes the problem that the flight time of the echo is difficult to accurately extract under the influence of background noise and waveform deformation through guided wave correlation analysis and wavelet transform filtering methods, reduces the difficulty of processing the received signal, and obtains the calculation equation of the buried depth of the column through data fitting; utilizes the wave velocity difference information under different covering conditions, and realizes the accurate calculation of the buried depth of the column based on the guided wave signal, solves the technical problem in the prior art that the signal amplitude and flight time of the response signal at the waveguide end, the soil adhesion condition and the buried length present a complex nonlinear relationship, and provides a practical and feasible operation plan for the accurate detection of highway guardrail columns. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the overall structure of the magnetostrictive ultrasonic guided wave transducer provided in Example 1 of the present application;

[0028] Figure 2 It is a schematic diagram of the partial structure of the magnetostrictive ultrasonic guided wave transducer provided in Example 1 of the present application after removing the upper frame;

[0029] Figure 3 It is a schematic diagram of the partial structure of the magnetostrictive ultrasonic guided wave transducer provided in Example 1 of the present application after removing the lower frame;

[0030] Figure 4 Schematic diagram of the other half of the hollow semi-cylindrical skeleton of the magnetostrictive ultrasonic guided wave transducer provided in Example 1 of the present application;

[0031] Figure 5 1 is a schematic diagram of the structure of the annular open coil of the magnetostrictive ultrasonic guided wave transducer provided in Example 1 of the present application;

[0032] Figure 6 is a schematic diagram of an excitation signal provided in Example 1 of the present application;

[0033] Figure 7 It is a schematic diagram of the circumferential magnetic field intensity and magnetic field distribution on the surface of the column when there are 10 magnetizer arrays provided in Example 1 of the present application;

[0034] Figure 8 It is a schematic diagram of the circumferential magnetic field intensity and magnetic field distribution on the surface of the pillar when there are 8 magnetizer arrays provided in Example 1 of the present application;

[0035] Fig. 9 It is a schematic diagram of the circumferential magnetic field intensity and magnetic field distribution on the surface of the pillar when there are 6 magnetizer arrays provided in Example 1 of the present application;

[0036] Fig.10 It is a schematic diagram of the magnetic field distribution of the magnetizer array composed of 6 permanent magnets provided in Example 1 of the present application in the axial direction of the column;

[0037] Fig.11 This is a schematic flow chart of a method for detecting the soil cover depth of highway pillars using a magnetostrictive ultrasonic guided wave transducer provided in Example 2 of the present application;

[0038] Fig.12 This is a schematic diagram of the echo waveform of the soil surface of the column obtained by using the magnetostrictive ultrasonic guided wave transducer provided in Example 2 of the present application;

[0039] Fig.13 This is a data diagram for detecting the depth of soil cover in a steel pipe provided in Example 2 of the present application.

[0040] In all the drawings, the same figure numbers are used to represent the same elements or structures, among which: A-outer covering soil, B-inner covering soil; 1-hollow cylindrical skeleton, 11-pin structure, 12-bolt structure, 2-magnetizer array, 21-multilayer foam copper, 3-annular open coil, 31-first coil, 32-second coil, 33-bending structure, 4-end cover, 5-double annular groove, 51-outer groove, 52-inner groove, 6-installation groove, 7-magnetostrictive ultrasonic guided wave transducer, 8-permanent magnet, 9-steel pipe. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0042] Example 1

[0043] The present application provides a magnetostrictive waveguide transducer, such as Figure 1-5 As shown, it includes: a hollow cylindrical skeleton 1, and an annular magnetizer array and an annular open coil 3 embedded in the hollow cylindrical skeleton 1. The hollow cylindrical skeleton 1 includes two hollow semi-cylindrical skeletons, one end of the two hollow semi-cylindrical skeletons can be flipped and connected, and the other end can be opened and closed. Specifically, one end of the two hollow semi-cylindrical skeletons is connected by a pin structure 11, and the two can be flipped around the pin, and the other end can be detachably connected by a bolt structure 12. When the magnetostrictive guided wave transducer needs to be removed from the highway column, it is only necessary to open the bolts and flip the two hollow semi-cylindrical skeletons around the pin until the opening between the two is larger than the diameter of the highway column, thereby realizing the function of easily removing the magnetostrictive guided wave transducer from structures such as highway columns; in other preferred embodiments, the bolt structure 12 can also be replaced by a snap-on structure.

[0044] In this embodiment, eight magnetizer arrays 2 are evenly spaced and arranged to form a ring-shaped magnetizer array, and four magnetizer arrays 2 are fixed to each hollow semi-cylindrical skeleton.

[0045] The aforementioned annular open coil 3 and annular magnetizer array are fixed in the hollow cylindrical frame 1 along the axial direction of the hollow cylindrical frame 1; specifically, as Figure 3 and 4As shown, a double annular groove 5 for embedding the annular open coil 3 is opened in the bottom surface of one side of the hollow cylindrical skeleton 1, and the double annular groove includes an outer groove 51 and an inner groove 52 that are connected to each other; specifically, the outer groove 51 and the inner groove 52 are connected at the opening and closing ends of the two hollow semi-cylindrical skeletons, and the opposite ends of the outer groove 51 and the inner groove 52 on one side are radially connected on the skeleton body of the opening and closing end of one hollow semi-cylindrical skeleton, and the opposite ends located on the other hollow semi-cylindrical skeleton are respectively passed through the end of the skeleton to form two inner and outer circles of connected grooves.

[0046] A rectangular groove 6 for mounting each permanent magnet is also provided on the bottom surface of the hollow cylindrical skeleton 1 , and the rectangular grooves 6 are evenly distributed between the outer groove 51 and the inner groove 52 .

[0047] The aforementioned annular open coil 3 is embedded in the double annular groove 5 to form a closed loop with an opening at the open and closed ends of the hollow semi-cylindrical skeleton, and the two end surfaces at the opening of the annular open coil 3 are connected to the external communication connector through wires here; when the two hollow semi-cylindrical skeletons are opened and closed, the annular open coil 3 can be flipped up and down with any half of the hollow semi-cylindrical skeleton due to the existence of the opening.

[0048] like Figure 5 As shown, the aforementioned annular open coil 3 includes a first coil 31 located outside the annular magnetization array and a second coil 32 located inside the annular magnetization array, and the first coil 31 and the second coil 32 are respectively embedded in the outer groove 51 and the inner groove 52; specifically, the first coil 31 and the second coil 32 are both provided with openings, and the opening ends (i.e. Figure 5 The opening on the left side in the middle is radially connected to the opening and closing connection of the two hollow semi-cylindrical skeletons to form a closed loop; at the flip connection of the two hollow semi-cylindrical skeletons, a bending structure 33 is provided on the second coil 32, and the spacing between the bending structure 33 and the first coil 31 is small to facilitate the opening and closing of the following hollow cylindrical skeleton; specifically, the annular open coil 3 can be wound by one coil.

[0049] The wire diameter of the aforementioned annular open coil 3 is 0.1mm~0.3mm, and its lifting distance does not exceed 3mm. The change in the distance between the coil and the workpiece will cause the magnetic lines of force reaching the workpiece to change, changing the magnetic flux in the workpiece, thereby affecting the change in the impedance of the coil. This phenomenon is called the lift-off effect, and the corresponding distance is the lift-off distance. Specifically, in this embodiment, the annular open coil 3 is selected to be wound by an enameled wire with a diameter of 0.2mm.

[0050] The axial width of the annular open coil 3 is half the wavelength of the waveguide. In a preferred embodiment, the axial width of the annular open coil 3 is 20 mm to 40 mm, such as 25 mm, 30 mm, 35 mm, 40 mm, or any width value between any two of the above values.

[0051] More specifically, the current signal used to excite the magnetostrictive waveguide transducer can be referred to as Figure 6 As shown, it is specifically a three-cycle pulse sine signal modulated by a Hanning window, with a frequency of generally 100kHz, which can realize longitudinal guided wave excitation of the L(0,2) mode inside the highway column. Therefore, the axial width of the annular open coil 3 used in this embodiment is selected to be 25mm, and the number of turns is 80 turns, which can achieve the strongest excitation intensity. If the width of the annular coil is further increased, the guided waves generated by the excitation will further cause destructive interference, causing the excitation intensity to decrease.

[0052] The number of the aforementioned magnetizer arrays 2 is at least 8, all of which are cuboids, and the number is preferably an even number, such as 8, 10, 12, etc. In this embodiment, the magnetizer arrays are selected to be 8, and the axial magnetic field strength is relatively strong and evenly distributed.

[0053] like Figure 7 As shown, it is a schematic diagram of the circumferential magnetic field intensity and magnetic field distribution on the surface of the column when 10 magnetizer arrays are used. It can be seen from the figure that the circumferential magnetic field is evenly distributed, which meets the requirement of uniform propagation of guided waves around the entire circumference of the column.

[0054] like Figure 8 As shown, it is a schematic diagram of the circumferential magnetic field intensity and magnetic field distribution on the column surface when 8 magnetizer arrays 2 are used. It can be seen from the figure that the circumferential magnetic field is evenly distributed, which also meets the requirement of uniform propagation of guided waves around the entire circumference of the column.

[0055] like Fig. 9 As shown, it is a schematic diagram of the circumferential magnetic field intensity and magnetic field distribution on the surface of the column when 6 magnetizer arrays are used. It is obviously seen that the circumferential magnetic field distribution is uneven, which does not meet the requirement of uniform propagation of guided waves around the entire circumference of the column.

[0056] The aforementioned magnetizer array 2 comprises a plurality of permanent magnets 8 stacked along the axial direction of the hollow cylindrical skeleton 1. The number of permanent magnets 8 in each magnetizer array 2 is 4 to 6. If there are less than 4 permanent magnets, the axial magnetic field strength of the magnetizer array is small and unevenly distributed, which is not suitable for the excitation of magnetostrictive guided waves. If there are more than 6 permanent magnets, the axial magnetic field strength and the magnetic field distribution change little. Considering the portability of the magnetostrictive guided wave transducer during actual use, the number of permanent magnets 8 does not need to exceed 6.

[0057] like Fig.10 As shown, it is a schematic diagram of the magnetic field distribution of the magnetizer array 2 composed of 6 permanent magnets in the axial direction of the column. It can be seen from the figure that when the number of permanent magnets 8 in the magnetizer array 2 is greater than 4, the magnetic field intensity distribution in the circumferential direction is relatively uniform, which meets the requirement of uniform propagation of guided waves around the entire circumference of the column.

[0058] The height of the magnetizer array 2 is 20 mm to 25 mm, such as 21 mm, 22 mm, 23 mm, 24 mm and 25 mm, or any value between any two of the above values; the length of the magnetizer array is 30 mm to 60 mm, such as 30 mm, 40 mm, 50 mm, 60 mm, or any value between any two of the above values; the thickness of the permanent magnet is 8 mm to 10 mm, such as 8 mm, 9 mm, 10 mm, or any value between any two of the above values.

[0059] Specifically, in this embodiment, the length of each magnetizer array 2 is consistent with the length of the permanent magnet, which is selected as 30 mm, and the height is 20 mm. The thickness of the magnetizer array composed of 6 permanent magnets is 60 mm. The NS magnetic pole direction of the magnetizer array 2 is parallel to the axial direction of the column 10 to be measured and is the same as the magnetic pole direction of the magnetizer array, so as to generate the axial bias magnetic field required for longitudinal waveguide excitation; the magnetizer array 2 is made of neodymium iron boron material, and the residual magnetic flux density is greater than 1T, and has the best magnetic properties.

[0060] The surface of the magnetizer array 2 near the annular open coil 3 is provided with multiple layers of foam copper 21, and the thickness of the multiple layers of foam copper 21 is not less than 1 mm, so as to shield the interference of the external magnetic field, protect the permanent magnet from the influence of the external magnetic field, and maintain the stability of its magnetic properties.

[0061] The magnetostrictive ultrasonic guided wave transducer provided in this embodiment also includes an end cover 4, which is connected to the bottom surface of the hollow cylindrical skeleton 1 to fix the annular open coil 3 and the annular magnetizer array inside the hollow cylindrical skeleton 1; specifically, the end cover 4 and the bottom surface of the hollow cylindrical skeleton 1 are provided with bolt holes that match each other, and are fixedly connected by bolt connection.

[0062] Example 2

[0063] This embodiment provides a method for detecting the depth of soil cover in a highway column by using the magnetostrictive ultrasonic guided wave transducer provided in Embodiment 1. Fig.11 As shown, the following steps are included:

[0064] S1 sets a magnetostrictive ultrasonic guided wave transducer on the exposed sections of multiple known columns to obtain the flight time T1 of the corresponding echo of the top surface of the outer covering soil of each known column, the flight time T2 of the corresponding echo of the top surface of the inner covering soil, and the flight time T3 of the corresponding echo of the bottom surface of each known column.

[0065] The measurement principle is as follows: an alternating current signal is loaded into the annular coil (i.e., the annular open coil 3) of the magnetostrictive ultrasonic guided wave transducer, thereby generating an alternating magnetic field of the same frequency parallel to the axial direction of the column on the upper and lower end surfaces of the column; due to the magnetostrictive effect, based on a certain DC bias magnetic field, the alternating magnetic field generated by the excitation of the annular coil causes the internal material of the column to produce the same frequency strain as the axial direction, thereby driving the column particle vibration to form longitudinal guided waves; then, through a magnetizer array composed of evenly arranged permanent magnets, the enhancement of the longitudinal guided waves of the pipeline and the full circumferential excitation are achieved.

[0066] like Fig.12 As shown in the figure, it is a schematic diagram of the corresponding echo waveform of a known column. In the figure, from left to right, a is the reflected wave in the exposed section of the column close to the magnetostrictive ultrasonic guided wave transducer, b is the reflected wave on the outer covering surface, c is the reflected wave on the inner covering surface, and d is the reflected wave at the bottom end of the column far away from the magnetostrictive ultrasonic guided wave transducer. The method of obtaining the corresponding flight time according to the echo waveform is: filter the received echo and extract the envelope of the guided wave signal, and take the time point corresponding to the peak of each waveform envelope as the time point corresponding to the echo; for the convenience of subsequent derivation and calculation process, the time point corresponding to the echo is divided by 2 to obtain the flight time corresponding to the echo. In the figure, the flight time corresponding to the b echo is T1, the flight time corresponding to the c echo is T2, and the flight time corresponding to the d echo is T3.

[0067] The current signal used for excitation is Figure 6 The three-cycle pulsed sine signal modulated by the Hanning window has a frequency of 100kHz, thereby realizing the longitudinal guided wave excitation of the L(0,2) mode inside the column.

[0068] S2 uses a data fitting method to fit a calculation formula for the buried depth of the inner covering soil of each known column based on the height difference between the top surface of the outer covering soil and the surface of the inner covering soil of each known column, the buried depth of the inner covering soil, the distance between the bottom surface of the known column and the magnetostrictive ultrasonic guided wave transducer 7, and the multiple sets of flight times obtained in step S1.

[0069] Through research, it is found that the average wave velocity of the guided wave in the column changes with the change of the covering soil condition, which means that the propagation wave velocity of the guided wave in the covering soil section changes. Therefore, the corresponding mathematical formula can be fitted by the following fitting method.

[0070] First, the mathematical relationship between the height difference between the top surface of the outer covering soil and the inner covering soil surface of multiple sets of columns, the buried depth of the inner covering soil, the distance between the bottom surface of the column and the guided wave transducer, and the corresponding flight time is fitted by the data fitting method:

[0071]

[0072] In formula (1), v1, v2 and v3 are the propagation wave velocities of the guided wave in the exposed section, the external soil section and the internal soil section of the column respectively, k is the coefficient of variation of the guided wave velocity obtained by fitting, T1 is the flight time of the corresponding echo of the top surface of the external soil of the column, T2 is the flight time of the corresponding echo of the top surface of the internal soil, T3 is the flight time of the corresponding echo of the bottom surface of the column, L1 is the height difference between the top surface of the external soil and the surface of the internal soil, L2 is the buried depth of the internal soil, and L3 is the distance between the top surface of the external soil and the magnetostrictive ultrasonic guided wave transducer;

[0073] By inverting equation (1), we can obtain the calculation equation for the buried depth of the column:

[0074]

[0075] Wherein, k is the coefficient of variation of the guided wave velocity. This embodiment focuses on explaining the derivation idea of ​​obtaining the calculation equation, and therefore the specific numerical value of the k value obtained by fitting is not disclosed.

[0076] S3: a magnetostrictive ultrasonic guided wave transducer is arranged at the exposed section of the column to be tested, and the flight time of the corresponding echo of the top surface of the outer covering soil of the column to be tested, the flight time of the corresponding echo of the top surface of the inner covering soil, and the flight time of the corresponding echo of the bottom surface of the column to be tested are obtained;

[0077] Specifically, this embodiment uses a 1.8m long 45 steel seamless industrial steel pipe as the column to be tested to verify the accuracy of the above calculation formula. Fig.13 As shown in FIG. 1 , it is a data schematic diagram for detecting the depth of the soil covering the steel pipe 9. In the figure, the steel pipe 9 is horizontal, A is the outer soil covering, B is the inner soil covering, the left side is actually the top surface, and the right side is actually the bottom surface. The outer diameter of the steel pipe 9 is 140 mm, and the wall thickness is 4.5 mm. Among them, the height difference l1 between the top surface of the outer soil covering A and the inner soil covering B of the steel pipe 9 is 17 cm, the actual depth l2 of the inner soil covering section is 70 cm, and the distance l3 from the top surface of the outer soil covering to the magnetostrictive ultrasonic guided wave transducer 7 is 80 cm.

[0078] The same method as step S1 is used to obtain the flight time of the echo corresponding to the external covering surface of the steel pipe to be tested, the flight time of the echo corresponding to the top surface of the internal covering soil, and the flight time of the echo corresponding to the bottom surface of the steel pipe to be tested (i.e., the end face of the steel pipe on the right end of the figure). The specific values ​​are T1=0.152ms, T2=0.185ms, and T3=0.326ms.

[0079] S4 obtains the buried depth of the inner soil of the column to be measured by using calculation formula (2) based on the three flight times obtained in step S3, the height difference between the top surface of the outer soil and the inner soil of the column to be measured, and the distance between the outer soil surface of the column to be measured and the magnetostrictive ultrasonic guided wave transducer.

[0080] Combining the above values, the inner cover depth is calculated using formula (2), and the calculated inner cover depth L2 = 71.29 cm is obtained. The relative error with the actual depth of 70 cm is 1.84%, which is small and the calculation accuracy is high.

[0081] The above analysis process is sufficient to prove that the ultrasonic guided wave detection method for highway pillar length provided in the present application establishes an accurate functional relationship between the length of the soil covering section inside the pillar and the corresponding echo flight time on its surface, thereby solving the technical problem in the prior art of a complex nonlinear relationship between the signal amplitude, flight time, soil adhesion and buried length of the response signal at the waveguide end.

[0082] In summary, the magnetostrictive waveguide transducer provided in the present application is structurally optimized for installation convenience, and realizes the opening and closing installation and disassembly of the magnetostrictive waveguide transducer, which greatly improves the installation convenience without affecting the detection effect, reduces the waste of manpower and time, and is suitable for large-scale rapid detection of the length of highway pillars.

[0083] In addition, the method provided in the present application for ultrasonic guided wave detection of the length of highway pillars using the aforementioned magnetostrictive guided wave transducer overcomes the problem that the flight time of the echo is difficult to accurately extract under the influence of background noise and waveform deformation through guided wave correlation analysis and wavelet transform filtering methods, reduces the difficulty of processing the received signal, and obtains the calculation equation of the buried depth of the pillar through data fitting; utilizes the wave velocity difference information under different covering conditions, and realizes the accurate calculation of the buried depth of the pillar based on the guided wave signal, solves the technical problem in the prior art that the signal amplitude and flight time of the response signal at the waveguide end, the soil adhesion condition and the buried length present a complex nonlinear relationship, and provides a practical and feasible operation plan for the accurate detection of highway guardrail pillars.

[0084] It should be understood that expressions such as "include" and "may include" used in this application indicate the existence of the disclosed functions, operations or constituent elements, and do not limit one or more additional functions, operations and constituent elements. In this application, terms such as "include" and / or "have" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components or combinations thereof.

[0085] It should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0086] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0087] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0088] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A magnetostrictive waveguide transducer, characterized in that: The invention comprises a hollow cylindrical skeleton (1), an annular open coil (3) and an annular magnetizer array which are embedded in the hollow cylindrical skeleton (1) and arranged coaxially with the hollow cylindrical skeleton (1); the hollow cylindrical skeleton (1) comprises two hollow semi-cylindrical skeletons, one end of the two hollow semi-cylindrical skeletons can be flipped and connected, and the other end can be open and closed; the annular open coil (3) comprises a first coil (31) located in the outer circle and a second coil (32) located in the inner circle; the first coil (31) and the second coil (32) are both provided with openings at the open and closed connection of the two hollow semi-cylindrical skeletons, and the open ends of the first coil (31) and the second coil (32) are radially connected to form a closed loop; the annular magnetizer array comprises a plurality of groups of magnetizer arrays (2), each group of magnetizer arrays (2) is evenly spaced and arranged, and is located between the first coil (31) and the second coil (32).

2. The magnetostrictive waveguide transducer according to claim 1, characterized in that: The axial width of the annular open coil (3) is half the wavelength of the waveguide.

3. The magnetostrictive waveguide transducer according to claim 2, characterized in that: The axial width of the annular open coil (3) is 20 mm to 40 mm.

4. The magnetostrictive waveguide transducer according to claim 1, characterized in that: The magnetizer array (2) comprises at least 8 groups.

5. The magnetostrictive guided wave transducer according to claim 1, characterized in that: The magnetizer array (2) comprises a plurality of permanent magnets (8) stacked in an axial direction of a hollow cylindrical skeleton (1).

6. The magnetostrictive waveguide transducer according to claim 5, characterized in that: The permanent magnet (8) is made of neodymium iron boron material, and has a residual magnetic flux density greater than 1T.

7. The magnetostrictive waveguide transducer according to claim 5, characterized in that: The number of the permanent magnets (8) is 4 to 6, the length is 30 mm to 60 mm, the height is 20 mm to 25 mm, and the thickness is 8 mm to 10 mm.

8. The magnetostrictive waveguide transducer according to claim 1, characterized in that: The wire diameter of the annular open coil (3) is 0.1 mm to 0.3 mm, and its lifting distance does not exceed 3 mm.

9. The magnetostrictive guided wave transducer according to claim 1, characterized in that: A plurality of layers of foam copper (21) are arranged on the surface of the magnetizer array (2) close to the annular open coil (3), and the thickness of the plurality of layers of foam copper (21) is not less than 1 mm.

10. A method for detecting the depth of soil cover in a highway pillar using a magnetostrictive ultrasonic guided wave transducer as claimed in any one of claims 1 to 9, characterized in that: The following steps are involved: S1: setting the magnetostrictive ultrasonic guided wave transducer at the exposed sections of a plurality of known columns to obtain the flight time of the corresponding echo of the top surface of the outer covering soil of each known column, the flight time of the corresponding echo of the top surface of the inner covering soil, and the flight time of the corresponding echo of the bottom surface of each known column; S2 uses a data fitting method to fit the calculation formula for the buried depth of the inner covering soil of each column based on the height difference between the top surface of the outer covering soil and the inner covering soil surface of each known column, the buried depth of the inner covering soil, the distance between the top surface of the outer covering soil and the magnetostrictive ultrasonic guided wave transducer, and the multiple sets of flight times obtained in step S1: Wherein, k is the coefficient of variation of guided wave velocity obtained by fitting, T1 is the flight time of the corresponding echo of the top surface of the outer covering soil of the column, T2 is the flight time of the corresponding echo of the top surface of the inner covering soil, T3 is the flight time of the corresponding echo of the bottom surface of the column, L1 is the height difference L1 between the top surface of the outer covering soil and the surface of the inner covering soil, L2 is the burial depth of the inner covering soil, and L3 is the distance between the top surface of the outer covering soil and the magnetostrictive ultrasonic guided wave transducer; S3: installing the magnetostrictive ultrasonic guided wave transducer at the exposed section of the column to be tested, and obtaining the flight time of the corresponding echo of the top surface of the outer covering soil of the column to be tested, the flight time of the corresponding echo of the top surface of the inner covering soil, and the flight time of the corresponding echo of the bottom surface of the column to be tested; S4 obtains the buried depth of the inner covering soil of the column to be measured by using the calculation formula based on the height difference between the top surface of the outer covering soil and the inner covering soil surface of the column to be measured, the distance between the top surface of the outer covering soil of the column to be measured and the magnetostrictive ultrasonic guided wave transducer, and the three flight times obtained in step S3.

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