An omnidirectional SH wave electromagnetic ultrasonic transducer

Abstract

The invention discloses an omnidirectional SH wave electromagnetic ultrasonic transducer, comprising a PCB coil, a permanent magnet, an insulating layer, a wire and a shell, wherein the permanent magnet is placed on the PCB coil, the two ends of the PCB coil are respectively connected to the wire, the insulating layer covers the connection between the two ends of the PCB coil and the wire, the shell is sleeved outside the PCB coil and the permanent magnet, the wire is led out from a hole on the shell and connected to an external power supply. The transducer can generate a circumferential Lorentz force in a plate, thereby exciting a circumferential SH wave, and also serves as a receiving end of an omnidirectional SH wave, and simultaneously excites and receives to perform non-destructive testing on the plate.

Description

Technical Field

[0001] The invention relates to ultrasonic testing technology in the field of non-destructive testing, in particular to an omnidirectional SH wave electromagnetic ultrasonic transducer. Background Art

[0002] In the fields of structural health monitoring, guided wave tomography and ultrasonic phased array testing, the application of transducer arrays in large-area plate testing has great prospects. Since transducers are the basic components in array systems, a lot of research in the fields of non-destructive testing and structural health monitoring has focused on the development of various guided wave transducers.

[0003] Guided waves, namely Lamb waves and SH waves propagating in the plate, have more advantages in the application of nondestructive testing than Lamb waves because the low-order SH0 mode is non-dispersive and is not affected by fluid loads during propagation. Therefore, it is very attractive to use SH waves for nondestructive testing of plate-like structures in industrial applications. Omnidirectional SH wave transducers are important key components in SH guided wave tomography systems. Research on omnidirectional SH wave transducers has only been discovered in recent years, but none of these transducers directly excite SH waves in the plate. These transducers are all based on magnetostrictive sheet transducer (MPT) technology. SH waves are first generated in a piece of material with high magnetostrictive properties (such as nickel sheet), and then the transducer is bonded to the test piece with epoxy resin. The SH waves in the magnetostrictive sheet are coupled to the test piece through the epoxy resin. Since adhesives are required during use and cannot be moved, the existing omnidirectional MPT-SH transducers are difficult to be applied in practice. At present, there is no omnidirectional SH wave transducer that can achieve non-contact measurement. Summary of the invention

[0004] In response to the problems pointed out in the above-mentioned prior art, the present invention provides an omnidirectional SH wave electromagnetic ultrasonic transducer, which can generate circumferential Lorentz force in the plate, thereby exciting circumferential SH waves, and also serves as the receiving end of the omnidirectional SH wave, simultaneously exciting and receiving for non-destructive testing of the plate.

[0005] The technical solution for achieving the purpose of the present invention is:

[0006] An omnidirectional SH wave electromagnetic ultrasonic transducer comprises a PCB coil, a permanent magnet, an insulating layer, a wire and a shell. The difference from the prior art is that the permanent magnet is placed on the PCB coil, the two ends of the PCB coil are respectively connected to the wire, the insulating layer covers the connection between the two ends of the PCB coil and the wire, the shell is sleeved outside the PCB coil and the permanent magnet, the wire is led out from the hole on the shell and connected to an external power supply.

[0007] The PCB coil is a coil in a planar fan-shaped ray structure, with the wires printed on the PCB circuit board in the form of extending from the center to the radial direction. The PCB coil is a two-layer or multi-layer structure, and the layers are connected by vias; the coil is divided into an upper and lower part, wherein:

[0008] In the upper part of the coil, the top layer of the coil is wound from the outside to the inside, connected to the bottom layer through a via at the innermost circle, and then wound from the bottom layer from the inside to the outside;

[0009] In the lower part of the coil, the wire extending from the bottom layer is wound from the outside to the inside, connected to the top layer through a via in the innermost circle, and then wound from the inside of the top layer coil to the outside;

[0010] The upper and lower parts of the coil are intertwined to form a fan-shaped spiral coil. When current is passed through the coil, the current in the wire in the left half of the entire coil flows from the outside to the center of the fan, and then flows out from the right half.

[0011] The PCB coil has an even number of layers.

[0012] The pads at both ends of the PCB coil are welded to the wires.

[0013] The permanent magnet is composed of two semi-annular magnets, which are placed on the PCB coil in opposite polarization directions, one of which is placed above the coil into which current flows, and the other is placed above the coil from which current flows.

[0014] The inner and outer radius of the magnet is determined by the wavelength. In order to maximize the output, the wavelength must satisfy λ = 2r m (1), and the outer radius of the magnet r o With the inner radius r of the magnet i The relationship between o -r i =λ / 2(2), the inner and outer radii of the magnet are determined according to the above formula.

[0015] The maximum diameter of the housing matches the diameter of the PCB coil, and the height of the housing can accommodate the magnet and the PCB board.

[0016] The transducer generates a circumferential Lorentz force in the test piece in a non-contact manner, and generates an omnidirectional SH wave through the Lorentz force.

[0017] Compared with the traditional SH wave ultrasonic transducer, the SH wave electromagnetic ultrasonic transducer of the present invention has the following advantages in practical applications:

[0018] 1. No coupling agent is required to stimulate SH waves in the workpiece to be detected through the transducer. By moving the transducer, SH waves can be excited and received at different positions of the workpiece to be detected, so as to achieve different detection purposes and requirements and realize non-contact detection;

[0019] 2. By changing the center frequency and the inner and outer radii of the permanent magnet, different metal plates can be detected. The phase velocity of the waveguide in different metal plates is different. In order to achieve the maximum conversion efficiency and output, the center frequency needs to be determined according to the dispersion curve. After determining the center frequency and phase velocity, the wavelength is determined. The inner and outer radii of the magnet are determined according to formula (1) (2), thereby realizing the omnidirectional SH wave electromagnetic ultrasonic transducer to excite and receive ultrasonic waves in different metal plates, so it has strong adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a three-dimensional schematic diagram of the transducer;

[0021] Figure 2 This is an exploded stereoscopic schematic diagram of the transducer;

[0022] Figure 3 It is a schematic diagram of the relative position of the permanent magnet and the PCB coil;

[0023] Figure 4 This is a schematic diagram of the current flow direction of the PCB coil;

[0024] Figure 5 Schematic diagram of the Lorentz force.

[0025] In the figure: 1. Permanent magnet, 2. PCB coil, 3. Insulation layer, 4. Wire, 5. Housing, 6. Magnetic field direction, 7. Eddy current direction, 8. Lorentz force direction DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the omnidirectional SH wave electromagnetic ultrasonic transducer more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings.

[0027] like Figure 1 , Figure 2 As shown, an omnidirectional SH wave electromagnetic ultrasonic transducer includes a PCB coil, a permanent magnet, an insulating layer, a wire, and a shell. The coil can be two-layer or multi-layer, but must be an even number of layers. When the number of layers is even, the coil is divided into an upper and lower part. In the upper part, the top layer coil is wound from the outside to the inside, connected to the bottom layer with a via in the innermost circle, and then wound from the bottom layer from the inside to the outside. The lower part is similar to the upper part. The wire coming out of the bottom layer is wound from the outside to the inside, connected to the top layer with a via in the innermost circle, and then wound from the inside of the top layer coil to the outside. The essence of the upper and lower parts of the coil is a spiral coil deformed into a fan shape (such as Figure 3 The layers of the coils and the winding directions of the coils described here are only for the purpose of illustrating the working principle, and the same effect can be achieved by changing the order of the layers and the direction of the coils.

[0028] There are pads at both ends of the PCB coil. The PCB coil is connected to the wire by welding. After welding, an insulating layer is covered at the welding point. The wire is connected to an external power supply (such as Figure 1 shown).

[0029] When the current is passed through the coil, it enters from either end. Figure 4 The direction shown is through the coil. According to this coil arrangement, the current direction of the upper and lower parts is consistent, and the entire coil current is divided into left and right parts, such as Figure 4 As shown, in the left half, the current flows in the direction close to the center of the circle, and in the right half, the current flows in the direction away from the center of the circle, so that the currents on the left and right sides are in the same direction, so that the eddy currents generated in the metal plate by the left and right parts are in the same direction on any cross section, as shown in Figure 5 shown.

[0030] The permanent magnet is composed of two semi-circular magnets. The inner and outer radius of the magnets are determined according to the wavelength. In order to maximize the output, the wavelength must satisfy λ=2r m (1), and the outer radius of the magnet r o With the inner radius r of the magnet i The relationship between o -r i =λ / 2(2). The inner and outer radii of the magnet are determined according to the above formula. Two semi-circular magnets are placed on the PCB coil in opposite directions of polarity. Figure 1 As shown, the contact surface of the two semi-circular magnets is perpendicular to the straight line parallel to the ends of the coil, that is, along the dividing line between the left and right halves of the entire coil, as shown in Figure 3 shown.

[0031] When using, first place the magnet into the housing according to the relationship between the wires to be led out from the housing hole and the relative position of the magnet and the coil, then lead the wires out through the housing hole, and then place the PCB coil into the housing. Figure 1 As shown. Connect the wire to an external power supply. When the power supply outputs AC, the PCB coil will generate eddy currents in the metal plate. The eddy currents will generate Lorentz force under the action of the magnetic field generated by two magnets with opposite polarities. Figure 5 As shown, the eddy currents are in the same direction and the magnets are in opposite polarities, thus generating Lorentz forces in opposite directions. The alternating Lorentz forces cause the particles in the plate to produce in-plane shear vibrations, thereby exciting omnidirectional SH waves in the metal plate.

Claims

1. An omnidirectional SH wave electromagnetic ultrasonic transducer, comprising a PCB coil, a permanent magnet, an insulating layer, a wire and a housing, characterized in that: The permanent magnet is placed on the PCB coil, and the two ends of the PCB coil are connected to the wires respectively. The insulation layer covers the connection between the two ends of the PCB coil and the wires. The outer shell is set outside the PCB coil and the permanent magnet. The wires are led out from the holes on the outer shell and connected to the external power supply. The PCB coil is a coil in a planar fan-shaped ray structure, with the wires printed on the PCB circuit board in the form of extending from the center to the radial direction. The PCB coil is a two-layer or multi-layer structure, and the layers are connected by holes; the coil is divided into upper and lower parts, wherein: In the upper part of the coil, the top layer of the coil is wound from the outside to the inside, connected to the bottom layer through a via at the innermost circle, and then wound from the bottom layer from the inside to the outside; In the lower part of the coil, the wire extending from the bottom layer is wound from the outside to the inside, connected to the top layer through a via in the innermost circle, and then wound from the inside of the top layer coil to the outside; The upper and lower parts of the coil are connected to each other to form a fan-shaped closed coil. When current is passed through the coil, the current in the wire of the left half of the entire coil flows from the outside to the center of the fan, and then flows out from the right half; The pads at both ends of the PCB coil are welded to the wires; The permanent magnet is composed of two semi-annular magnets, which are placed on the PCB coil in opposite polarization directions, one of which is placed above the coil into which the current flows, and the other is placed above the coil out of which the current flows; The inner and outer radius of the magnet is determined by the wavelength. In order to maximize the output efficiency, the wavelength must satisfy λ = 2r m (1), and the outer radius of the magnet r o With the inner radius r of the magnet i The relationship between o -r i =λ / 2(2), the inner and outer radii of the magnet are determined according to the above formula; The maximum diameter of the housing matches the diameter of the PCB coil, and the height of the housing can accommodate the magnet and the PCB board; The transducer can generate a circumferential Lorentz force in the test piece in a contact or non-contact manner, and generate an omnidirectional SH wave through the Lorentz force.

2. The omnidirectional SH wave electromagnetic ultrasonic transducer according to claim 1 is characterized in that: The PCB coil has an even number of layers.

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