A broadband orthogonal polarization shear wave electromagnetic ultrasonic thickness measuring probe

Abstract

The present invention discloses a broadband orthogonal polarization shear wave electromagnetic ultrasonic thickness measurement probe, which belongs to the field of ultrasonic thickness measurement and is mainly used for electromagnetic ultrasonic thickness measurement of non-ferromagnetic materials: it includes an orthogonal polarization shear wave coil, a BNC connector, a magnet array and a housing. The magnet array is based on a magnetically shielded orthogonal Halbach magnet array, which can obtain a stronger magnetic field with a minimum number of magnets; the orthogonal polarization shear wave coil is printed on a circuit board and is used to excite induced eddy currents on the surface of the test piece; because charged atoms are affected by the Lorentz force in the magnetic field, the surface of the test piece will excite ultrasonic waves and propagate through the thickness. After reflection, the ultrasonic waves form echoes and are then received. The electromagnetic ultrasonic thickness measurement process is completed by the excitation and reception of ultrasonic waves. Compared with traditional electromagnetic ultrasonic probes, the electromagnetic ultrasonic probe of the present invention can meet the wide frequency requirements of frequency sweeping, can be applied to anisotropic materials, can excite stronger ultrasonic shear waves, and greatly improve detection efficiency.

Description

Technical Field

[0001] The invention belongs to the field of ultrasonic thickness measurement and relates to a broadband orthogonal polarization shear wave electromagnetic ultrasonic thickness measurement probe, which is mainly used for electromagnetic ultrasonic thickness measurement of non-ferromagnetic materials. Background Art

[0002] Electromagnetic acoustic resonance (EMAR) technology uses a long-period excitation current as the transducer input signal, which makes the excited ultrasonic waves have wide time domain and long period characteristics. It can force the ultrasonic waves to resonate inside the object being measured, effectively reducing the interference of noise signals on the detection results and improving the signal-to-noise ratio. The acoustic wave resonance characteristics generated by frequency sweeping can achieve accurate measurement of areas such as metal plate thickness and pipe wall thinning. However, the frequency limitation of general ultrasonic thickness gauge probes makes it difficult to accurately obtain the acoustic time difference in the time domain. At the same time, in anisotropic materials, the acoustic wave velocity is related to the propagation direction, and its propagation characteristics are more complex. Therefore, the design of a broadband orthogonal polarization probe can meet the needs of frequency sweeping measurement and is also suitable for the measurement of anisotropic materials.

[0003] The Halbach array is a near-ideal engineering structure, designed to generate a stronger magnetic field using a minimal number of magnets. By applying a matrix magnet array, a modification of the Halbach array, to an electromagnetic ultrasonic detection probe, this improves upon the traditional permanent magnet array approach, generating a stronger magnetic field and optimizing the magnetic field direction, resulting in a more accurate and stronger vertical magnetic field. This improves the efficiency of electromagnetic ultrasonic measurements and reduces measurement errors. Therefore, the matrix magnet array, modified from the Halbach array, can produce a highly efficient and precise electromagnetic ultrasonic transducer.

[0004] In 2017, Wang Zicheng and others invented "an electromagnetic ultrasonic thickness gauge probe for measuring the thickness of workpieces" in the invention patent CN201710274314.4. They used high-temperature resistant samarium cobalt material to make permanent magnets and coils, so that the thickness gauge probe can detect equipment and workpieces in a high-temperature environment. However, the coil of the probe is placed in one direction and cannot measure anisotropic materials. In 2020, Tu Jun and others invented "an external through-type annular array electromagnetic ultrasonic thickness gauge probe" in the invention patent CN202011387932.8. The magnetization units are arranged separately from the coil in the probe, the integration is poor, and the magnetization unit needs to be manually placed at the part to be measured, which is more troublesome.

[0005] However, none of the above patents mentions a broadband orthogonal polarization shear wave electromagnetic ultrasonic thickness measuring probe. Summary of the Invention

[0006] The primary technical challenge addressed by this invention is to overcome the shortcomings of existing methods and, in response to the need for rapid and accurate workpiece thickness measurement in manufacturing environments, provide a design method for a broadband, orthogonally polarized shear-wave electromagnetic ultrasonic thickness gauge probe. This invention innovatively designs a magnetically shielded, orthogonal Halbach magnet array to produce a high-intensity vertical magnetic field. The use of orthogonally polarized shear-wave coils reduces liftoff distance and improves acoustic time-of-flight signal strength. The magnetically shielded, orthogonal Halbach magnet array and orthogonally polarized shear-wave coils are integrated into the probe, and the probe's size and structure are optimized.

[0007] The technical solution adopted in the present invention is:

[0008] A broadband orthogonal polarization shear wave electromagnetic ultrasonic thickness measuring probe, comprising an orthogonal polarization shear wave coil, a BNC connector, a magnet array and a housing;

[0009] The orthogonally polarized shear wave coil and magnet array are encapsulated inside a housing, and a threaded hole is provided on the upper surface of the housing; the BNC connector is mounted on the housing through the threaded hole; a wire is provided inside the housing for connecting the two orthogonally arranged coils of the orthogonally polarized shear wave coil in series, and simultaneously connecting the ends of the series-connected coils to the inner conductor and outer conductor of the BNC connector, respectively.

[0010] The magnet array is an orthogonal Halbach magnet array based on magnetic shielding, which adopts two linear magnet arrays arranged orthogonally, and then vertically stacks the three layers of orthogonally arranged magnet arrays. Pure iron sheets are respectively set at both ends of the two linear magnet arrays and above the magnet arrays as magnetic shielding.

[0011] The orthogonal polarization shear wave coil is composed of two polarization coils arranged orthogonally and printed on the front and back sides of the same circuit board; the circuit board is located directly below the magnet array, the orthogonal polarization shear wave coil coincides with the center of the magnet array, and the orthogonal polarization shear wave coil completely covers the vertical area of ​​the magnet array.

[0012] The material of the shell is aluminum alloy.

[0013] The magnet array is composed of a plurality of cubic permanent magnets, which are glued together with epoxy resin; the material of the cubic permanent magnets is N52 NdFeB.

[0014] The beneficial effects of the present invention are:

[0015] The broadband orthogonally polarized shear-wave electromagnetic ultrasonic thickness gauge probe of this invention solves the problems of measurement efficiency and accuracy during thickness measurement. The innovative design of a magnetically shielded orthogonal Halbach magnet array produces a high-intensity perpendicular magnetic field, enabling broadband transmission. The optimized orthogonal polarized shear-wave coil structure produces a high signal-to-noise ratio acoustic-time signal. The integration of the magnetically shielded orthogonal Halbach magnet array and the orthogonal polarized shear-wave coil into the probe meets the requirements for rapid and accurate thickness measurement in manufacturing environments.

[0016] Compared with traditional electromagnetic ultrasonic probes, the electromagnetic ultrasonic probe of the present invention can meet the wide frequency required for frequency sweeping, can be applied to anisotropic materials, can excite stronger ultrasonic shear waves, and greatly improve detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a design flow chart of the present invention.

[0018] Figure 2 It is a magnetically shielded orthogonal Halbach magnet array.

[0019] Figure 3 This is a schematic diagram of an orthogonally polarized shear wave coil.

[0020] Figure 4 This is a schematic diagram of the structure of a broadband orthogonal polarization shear wave electromagnetic ultrasonic thickness measurement probe. In the figure, A-BNC connector; B-housing; C-magnet array; D-orthogonal polarization shear wave coil.

[0021] Figure 5 It is a schematic diagram of the magnetic flux density of a magnetically shielded orthogonal magnet array.

[0022] Figure 6 It is a schematic diagram of the probe echo signal.

[0023] Figure 7 Schematic diagram of aluminum alloy detection signal in the embodiment. DETAILED DESCRIPTION

[0024] The specific implementation of the present invention is further explained with reference to the accompanying drawings and technical solutions.

[0025] like Figure 1 As shown in the figure, the design process of a broadband orthogonal polarization shear wave electromagnetic ultrasonic thickness measurement probe of the present invention is as follows: First, design and manufacture a magnetically shielded orthogonal Halbach magnet array and analyze its magnetic field distribution. Second, based on the characteristics of the magnet array, design orthogonal polarization shear wave coils. Finally, integrate and assemble the probe, such as designing and processing the housing, fixing the BNC connector, and optimizing the coil distribution. The details are as follows:

[0026] The first step is to design a magnetically shielded orthogonal Halbach magnet array.

[0027] Based on the characteristics of the Halbach magnet array, the magnetic field strength is divided into strong and weak sides. The vertical magnetic field is mainly distributed in the central area of ​​the strong side, and the horizontal magnetic field is distributed in its adjacent area. The present invention innovatively designs a magnetically shielded orthogonal Halbach magnet array, using two linear magnet arrays arranged orthogonally to increase the distribution area of ​​the vertical magnetic field in the central area. The three layers of magnet arrays are vertically stacked to increase the magnetic field strength, and pure iron sheets are placed at both ends of the two linear magnet arrays and above the magnet arrays as magnetic shields to form a magnetically shielded orthogonal Halbach magnet array.

[0028] The magnetic field strength of this magnet array is divided into strong and weak sides. On the strong side of the magnetic field, first, the central area has a high-intensity magnetic field and the direction is vertical; then, as it gradually moves away from the central area, the direction of the magnetic field in its adjacent area becomes horizontal; and when the magnetic field reaches the edge, due to the addition of pure iron sheets, the magnetic shielding takes effect and the magnetic field strength is almost zero.

[0029] Step 2: Design orthogonal polarization shear wave coils

[0030] According to the shear wave generation mechanism, a square coil occupies the perpendicular magnetic field region of the Halbach magnet array, which excites shear waves. Therefore, the coil area needs to be larger than the Halbach magnet array, ensuring that the coil completely covers the perpendicular region of the Halbach magnet array to meet the shear wave excitation conditions. Furthermore, the coils are arranged orthogonally, on the front and back sides of the same printed circuit board, to achieve orthogonal polarization, enabling the probe to measure anisotropic materials.

[0031] Step 3: Integrate and assemble the probe

[0032] The probe consists of an orthogonally polarized shear wave coil, a BNC connector, a magnet array, and a housing. The magnet array is placed on the coil, and the BNC connector is fixed to the housing, which covers the magnet array and coil from top to bottom. The housing can be made of aluminum alloy to ensure the high magnetic flux density of the magnetically shielded orthogonal Halbach magnet array. The BNC connector body is fixed to the aluminum alloy housing with threads to ensure that the connection does not loosen due to gravity or other factors during measurement. A wire is welded to the internal connection port, and the other end of the wire is welded to the coil. After the external current passes through the BNC connector, it is passed through the wire to the coil. Resin glue is used to bond the housing, magnet array, and coil together.

[0033] like Figure 4 As shown, a broadband orthogonal polarization shear wave electromagnetic ultrasonic thickness measuring probe of the present invention includes an orthogonal polarization shear wave coil D, a BNC connector A, a magnet array C and an aluminum alloy shell B.

[0034] The orthogonally polarized shear wave coil D is printed on a circuit board. The coil requires a BNC connector A, and its body is fixed to the housing B via threads. Housing B is equipped with wires for connecting the two orthogonally arranged coils of the orthogonally polarized shear wave coil D in series. The ends of the series-connected coils are connected to the inner and outer conductors of BNC connector A, respectively. This allows an applied current to pass through BNC connector A and then to the coils via the wires. Due to the Lorentz force on charged atoms in a magnetic field, ultrasonic waves are excited on the surface of the specimen and propagate through the thickness. After reflection, the ultrasonic waves form echoes, which are then received. Through the excitation and reception of ultrasonic waves, the electromagnetic ultrasonic thickness measurement process is completed.

[0035] Magnet array C is an orthogonal Halbach magnet array based on magnetic shielding, which increases the distribution area of ​​the vertical magnetic field in the central area and can obtain a stronger magnetic field with a minimum number of magnets.

[0036] Among them, the main design parameters and assembly of the magnetically shielded orthogonal Halbach magnet array probe of this embodiment are as follows: the magnet array uses a single layer of 9, three layers of 27 N52 NdFeB cubic permanent magnets bonded together by resin glue. The size of a single permanent magnet is 5mm×5mm×5mm, and the overall size is 25mm×25mm×25mm. In the orthogonal polarization shear wave coil structure, the coil size is 36mm×36mm, and the coil thickness is 0.2mm.

[0037] The assembled magnetically shielded orthogonal Halbach magnet array is as follows Figure 2 As shown in the figure, three layers of the same orthogonal Halbach magnet arrays are stacked vertically, and pure iron sheets are placed around and on top. The magnetic flux density distribution is as follows Figure 5 As shown in the figure, in the main distribution area of ​​the vertical magnetic field, the maximum magnetic flux density is about 1T, while the magnetic flux density at the edge is close to 0.

[0038] Orthogonal polarization shear wave coils such as Figure 3 As shown, transverse wave coils with orthogonal polarization directions are printed on the front and back sides of a circuit board, and the pads at both ends of the two coils are arranged at diagonal positions.

[0039] The aluminum alloy housing is optimized for design and manufacturing, ensuring sufficient space for the magnet array and coil while ensuring a compact structure. The orthogonally polarized shear wave coil is placed directly below the magnet array, ensuring that their centers coincide and that insulation is maintained between the coil and the surrounding environment. The BNC connector is threaded onto the housing, and its internal connection port is welded to the orthogonal polarized shear wave coil via wires and bonded and insulated with resin glue to ensure that the connection does not loosen due to gravity or other factors during measurement. Figure 4 The wires and resin glue are not shown.

[0040] In this embodiment, the main parameters of the material being tested are: the material is 7075 aluminum alloy, the density is 2796.84 kg / m 3 , dimensions are 100.78mm×201.03mm×0.404mm.

[0041] The principle for measuring and calculating workpiece thickness is as follows: The probe operates in "self-emission, self-reception" mode. In this mode, a coil excites ultrasonic waves, which, after reflecting from the workpiece, are received by the same coil (a single coil refers to a single coil consisting of two orthogonally polarized shear wave coils connected in series). The workpiece is measured using the EMAR method. EMAR uses a long-period excitation current as the probe input signal, imparting a wide time domain and long period to the excited ultrasonic waves. This forces the ultrasonic waves to resonate within the workpiece, ultimately determining the workpiece thickness based on the frequency of this resonance.

[0042] Figure 6 The echo signal obtained by measuring the 7075 aluminum alloy workpiece using this probe is estimated to be the signal-to-noise ratio (SNR) of 18.6 dB.

[0043] First, a single frequency is excited to obtain a time domain signal, which is then Fourier transformed to obtain a frequency domain signal. This process is then repeated until the desired frequency range is excited. The thickness value d is calculated based on the spectrum using the following formula:

[0044]

[0045] Where v is the sound velocity of the workpiece, and Δf is the frequency difference between the first and second harmonics of the ultrasonic wave.

[0046] 7075 aluminum alloy detection signal such as Figure 7 As shown in Figure 1, the thickness of the 7075 aluminum alloy workpiece is calculated using the first and second harmonics of the 7075 aluminum alloy detection signal. The measured frequency difference between the first and second harmonics, Δf, is 7.648-3.854=3.794MHz. Given that the propagation velocity of shear waves in 7075 aluminum alloy is 3063.63m / s, the thickness of the 7075 aluminum alloy workpiece can be calculated as 0.404mm according to Formula (1). This calculated thickness value is the actual thickness of the aluminum alloy workpiece, demonstrating the high detection accuracy of the probe designed in this invention.

Claims

1. A broadband orthogonal polarization shear wave electromagnetic ultrasonic thickness measuring probe, characterized in that: The broadband orthogonal polarization shear wave electromagnetic ultrasonic thickness measuring probe comprises an orthogonal polarization shear wave coil, a BNC connector, a magnet array and a housing; The orthogonally polarized shear wave coil and magnet array are encapsulated within a housing, the upper surface of which is provided with a threaded hole; the BNC connector is mounted on the housing through the threaded hole; a conductor is provided within the housing for connecting the two orthogonally arranged coils of the orthogonally polarized shear wave coil in series, and simultaneously connecting the ends of the series-connected coils to the inner conductor and outer conductor of the BNC connector, respectively; The magnet array is an orthogonal Halbach magnet array based on magnetic shielding, which adopts two linear magnet arrays arranged orthogonally, and then vertically stacked with three layers of orthogonal magnet arrays. Pure iron sheets are respectively placed at both ends of the two linear magnet arrays and above the magnet arrays as magnetic shielding. The orthogonal polarization shear wave coil is composed of two polarization coils arranged orthogonally and printed on the front and back sides of the same circuit board; the circuit board is located directly below the magnet array, the orthogonal polarization shear wave coil coincides with the center of the magnet array, and the orthogonal polarization shear wave coil completely covers the vertical area of ​​the magnet array.

2. The broadband orthogonal polarization shear wave electromagnetic ultrasonic thickness measuring probe according to claim 1, characterized in that: The material of the shell is aluminum alloy.

3. A broadband orthogonal polarization shear wave electromagnetic ultrasonic thickness measuring probe according to claim 1 or 2, characterized in that: The magnet array is composed of a plurality of cubic permanent magnets, which are glued together with epoxy resin; the material of the cubic permanent magnets is N52 NdFeB.

Images