CN111380963A - Omnidirectional SH wave electromagnetic ultrasonic transducer without permanent magnet and design method thereof - Google Patents
Omnidirectional SH wave electromagnetic ultrasonic transducer without permanent magnet and design method thereof Download PDFInfo
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- CN111380963A CN111380963A CN202010400305.7A CN202010400305A CN111380963A CN 111380963 A CN111380963 A CN 111380963A CN 202010400305 A CN202010400305 A CN 202010400305A CN 111380963 A CN111380963 A CN 111380963A
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/34—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
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Abstract
The invention discloses an omnidirectional SH wave electromagnetic ultrasonic transducer without a permanent magnet and a design method thereof, wherein the transducer comprises two parts of PCB coils and an insulating layer, wherein one part of the PCB coil is an electromagnetic field coil, is of an annular structure and is used for providing a bias electromagnetic field, and consists of two layers of coils which are connected end to form a closed loop; the other part of the PCB coil is a coil used for generating electric eddy current in the board, and two ends of the coil are respectively connected with an external lead; the insulating layer covers the head end and the tail end of the PCB coil and is connected with a wire connecting wire, and the wire is connected with an external power supply. The transducer can control the size of the generated magnetic field according to methods such as controlling the size of the electrified current and the like to meet the requirements of different detection conditions. Because the magnet is not needed, the volume and the weight of the transducer are minimized. The transducer can be made of a PCB circuit, can be made into a flexible circuit, and is suitable for measuring a tested piece and a tubular test piece with irregular surfaces.
Description
Technical Field
The invention relates to an ultrasonic detection technology in the field of nondestructive detection, in particular to an omnidirectional SH wave electromagnetic ultrasonic transducer without a permanent magnet and a design method thereof.
Background
In the fields of structural health monitoring, guided wave tomography, ultrasonic phased array detection and the like, the application of the transducer array to large-area plate detection has great prospect. Since transducers are the fundamental elements in array systems, much research has focused on the development of various guided wave transducers in the areas of non-destructive testing and structural health monitoring.
Compared with Lamb waves, guided waves, namely Lamb waves and SH waves propagating in a plate have non-frequency dispersion due to the fact that SH0 modes of low order have non-frequency dispersion, and are not affected by fluid loads in the propagation process, and therefore the application of the SH waves in the aspect of nondestructive testing is more advantageous. Therefore, the plate structure can be used for nondestructive detection by using SH waves in industrial application, and the plate structure has great attraction. Electromagnetic guided ultrasound waves have been widely used in recent years due to their advantages of non-contact, less environmental impact, and mobility, and have been gradually replacing magnetostrictive sheet transducers and piezoelectric transducers in some applications. However, most of the existing electromagnetic ultrasonic transducers are structured by adding a group of magnets above a coil, generating a bias magnetic field through the magnets, generating an eddy current in a metal plate after the coil is electrified, and exciting an ultrasonic guided wave by the alternating eddy current under the action of the magnetic field to realize nondestructive testing. However, the transducer has certain requirements on the magnet, and parameters such as the radius of the magnet need to be calculated when the transducer is designed, so that the required ultrasonic guided waves can be ensured to be excited, and the requirements on the magnet are different according to different detection conditions. Since the displacement of mass points within the plate when the SH wave is excited is a shear motion along the plate, an excitation load parallel to the plate surface needs to be generated within the plate. Generally, SH transducers are divided into two types, one being a single direction propagating transducer and one being an omni-directional type transducer. The SH wave excited by the transducer with the single propagation direction is similar to a plane wave, the wave front of the SH wave is a plane, and the SH wave can only propagate to one direction, so that the SH wave is suitable for unidirectional scanning of a test piece. With the development of the technology, people have higher and higher requirements on detection instruments, and hope that defects can be visually seen during detection, so that the ultrasonic detection gradually develops towards the visualization direction, and the defects are visually presented to users through signal processing and computer technology, namely ultrasonic imaging. Ultrasonic imaging has higher requirements on transducers, and the traditional single-direction SH transducer can no longer meet the imaging requirements, so that the development of a transducer capable of exciting and receiving omnidirectional SH waves is urgently needed, and in the current research, the omnidirectional SH transducer capable of exciting and receiving omnidirectional SH waves and capable of mobile detection is basically not available.
Disclosure of Invention
The present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an omni-directional SH wave electromagnetic ultrasonic transducer without a permanent magnet and a method of designing the same, which abandons the conventional EMAT of providing a bias magnetic field using a permanent magnet, generates an electromagnetic field through only one coil, and uses the electromagnetic field as the bias magnetic field.
The technical scheme for realizing the purpose of the invention is as follows:
an omnidirectional SH wave electromagnetic ultrasonic transducer without permanent magnets comprises a two-part PCB coil and an insulating layer, which is different from the prior art that:
one part of the PCB coil is an electromagnetic field coil which is of an annular structure and used for providing a bias electromagnetic field, and the PCB coil consists of two layers of coils which are connected end to form a closed loop;
the other part of the PCB coil is a coil used for generating electric eddy current in the board, and two ends of the coil are respectively connected with an external lead;
the insulating layer covers the head end and the tail end of the PCB coil and is connected with a wire connecting wire, and the wire is connected with an external power supply.
The magnetic field coil is an electromagnetic field coil and consists of an upper layer of coil and a lower layer of coil, the two layers of coils are connected in series to form a whole, two magnetic fields with opposite polarities are generated after current is supplied, and the two magnetic fields with opposite polarities are respectively arranged on the coil with the current from outside to inside and the coil with the current from inside to outside.
The eddy current coil capable of generating the excitation signal is designed with a lead according to a plane fan-shaped ray structure, the lead is distributed in a PCB (printed circuit board) in a mode of radially extending from the center, the PCB coil is of a two-layer or multi-layer structure, multiple layers are connected through a hole, and the coil is divided into an upper part and a lower part, wherein:
in the upper half part of the coil, the upper layer coil is wound from outside to inside, is connected with the lower layer at the innermost ring by a via hole and is wound from inside to inside by the lower layer;
the lower half part of the coil is formed by winding a lead extending from the lower layer from outside to inside, connecting the innermost ring with the upper layer through a through hole and then winding the lead from the inside of the upper layer coil to outside;
two layers of wires of the eddy current coil are connected in series to form a fan-shaped coil, and when current is introduced into the coil, the current in the wires of the left half part of the whole coil flows into the center of the fan shape from the outside and then flows out from the right half part. The wires passing through the circular arc portion flow back from the right to the left again.
The number of layers of the PCB coil is even.
And welding pads are arranged at the head end and the tail end of the PCB coil and are used for being connected with an external lead.
The magnetic field coil is also composed of two layers, the coil is divided into a left half part and a right half part, the winding direction of the left half part is opposite to that of the right half part, the left side and the right side are connected in series, and pads are arranged at two ends of the coil and used for being connected with an external lead. When current is introduced, the left half coil and the right half coil generate bias magnetic fields in opposite directions.
The transducer generates Lorentz force in a non-ferromagnetic tested piece in a non-contact mode, and SH waves are generated through the Lorentz force. The SH wave can also be generated by generating lorentz force and magnetostrictive force in a ferromagnetic test piece in a non-contact manner.
The design method of the omnidirectional SH wave electromagnetic ultrasonic transducer comprises the following steps:
(1) determining the excitation frequency f of the coil according to the detection requirement and the material of the object to be detected;
(2) calculating the wavelength of the excited surface wave according to the excitation frequency f of the coil and the wave speed c of SH wave in the object to be measured, and then determining the pitch diameter of the magnetic field coil according to the wavelength, wherein the relationship between the pitch diameter of the magnetic field coil and the wavelength is
；
(3) Selecting the radial length of the exciting coil according to the pitch diameter of the field coil
Preferably, the length of the excitation coil is greater than
；
(4) According to radial length of exciting coil
Determining magnetic field coil width
Width of magnetic field coil
Has a size of
(ii) a The design can be changed according to the space size
And
but will have an effect on the amplitude of the excited SH wave, which will follow
And
becomes smaller;
(5) according to the excitation frequency f and the excitation coil length of the transducer to be designed
Width of electromagnetic field coil
The PCB circuit of the transducer is drawn.
The wavelength of the excited surface wave in the step (2) is obtained by the following formula:
compared with the traditional SH wave ultrasonic transducer, the omnidirectional SH wave electromagnetic ultrasonic transducer has the following advantages in practical application:
1. the coupling agent is not needed, the SH wave can be generated in the workpiece to be detected in a non-contact mode, and the SH wave can be excited and received at different positions on the workpiece to be detected by moving the PCB coil, so that different detection purposes and requirements can be achieved;
2. SH waves with different wavelengths are obtained by changing the central frequency and the size of the magnetic field coil, and the realization mode is simple.
3. No magnet is needed, the volume and weight of the transducer can be minimized, and the transducer is convenient to carry and install.
4. The transducer can be made of a PCB circuit, can be made into a flexible circuit, and is suitable for measuring a tested piece and a tubular test piece with irregular surfaces;
5. the transducer can be made thin and can be embedded in a composite or laminated structure for structural health monitoring.
6. Can all-round excitation and receipt SH ripples, be convenient for constitute the array and realize the phased array, improve detection precision and detection efficiency, be applicable to large tracts of land guided wave formation of image.
Drawings
FIG. 1 is a diagram illustrating relative positions of coils of a PCB according to an embodiment;
FIG. 2 is a schematic view of an excitation coil of an embodiment;
FIG. 3 is a schematic view of an embodiment of a magnetic field coil current flow;
FIG. 4 is a schematic diagram of the current flow of the excitation coil of the embodiment;
FIG. 5 is a schematic diagram of the Lorentz force generation;
fig. 6 is a schematic diagram of the excitation coil and field coil excitation signals.
In the figure: 1. the magnetic field generator comprises a first layer of excitation coil, 2. a first layer of magnetic field coil, 3. a second layer of excitation coil, 4. a second layer of electromagnetic field coil, 5. a magnetic field direction, 6. a Lorentz force direction, 7. an eddy current direction, 8. an excitation coil bonding pad and 9. a magnetic field coil bonding pad.
Detailed Description
In order to make the purpose, technical scheme and advantages of the SH wave electromagnetic ultrasonic transducer more clear, the present invention is further described in detail below with reference to the accompanying drawings.
As shown in fig. 1, an omnidirectional SH wave electromagnetic ultrasonic transducer without permanent magnets is mainly a two-part PCB coil, including an excitation coil and an electromagnetic field coil. The exciting coil can be two layers or multiple layers, but the number of the exciting coil is even, the whole coil is divided into an upper part and a lower part, the upper part is the top coil, the top coil is wound from outside to inside, the innermost coil is connected with the bottom layer through a through hole, and then the bottom layer is wound from inside to outside. The lower half part is similar to the upper half part, a lead wire from the bottom layer winds from outside to inside, is connected with the top layer through a via hole at the innermost circle and then winds from the inside of the top layer coil to outside, and the upper and lower two parts of coils are both spiral coils (as shown in figure 2) deformed into fan shapes.
When current flows through the coil from any end of the coil, the current directions of the upper part and the lower part are consistent according to the arrangement mode of the coil, and the current of the whole coil is divided into a left part and a right part, as shown in fig. 4, the current flows from the outside to the direction of a circle center in the left half part, and the current flows from the circle center in the right half part, so that the current directions of the left wire and the right wire which are axially symmetrical are in the same direction, and the directions of the eddy currents generated by the left part and the right part in the metal plate are consistent above any cross section, as shown in fig. 5.
Four terminals are provided on the PCB coil, two of which are magnetic field coil terminals for generating a bias magnetic field and two of which are eddy current coil terminals for generating an ultrasonic excitation signal.
The electromagnetic field coil is composed of two parts of coils, namely an upper layer and a lower layer,
the magnetic field coil is also composed of two layers, the coil is divided into a left half part and a right half part, the winding direction of the left half part is opposite to that of the right half part, the left side and the right side are connected in series, and pads are arranged at two ends of the coil and used for being connected with an external lead. The current flows in from the positive electrode in the figure, and flows out from the negative electrode as shown in fig. 3, so that bias magnetic fields with opposite directions are generated in the vertical direction for exciting the SH wave, the magnitude of the magnetic field is adjusted by adjusting the magnitude of the current, and the direction of the current is adjusted by adjusting the direction of the magnetic field.
When the electromagnetic field generating device is used, the electromagnet coil is electrified to generate a magnetic field, then the exciting coil is electrified with alternating current, the exciting coil can generate eddy current in the metal plate, and the eddy current generates Lorentz force under the action of the magnetic field generated by the electromagnetic field coil. As shown in fig. 5, in any section of the left half portion and the right half portion, the directions of the magnetic fields generated by the electromagnet coils are opposite from one another from outside to inside and from inside to outside, so that lorentz forces which are the same in the circumferential direction are generated, and when the current is alternating current, the alternating lorentz forces are generated, so that the inner mass point of the plate is caused to perform shearing motion in the circumferential direction, and SH waves are excited in the metal plate. The SH wave can also be generated by generating Lorentz force and magnetostriction force in a ferromagnetic tested piece in a non-contact mode.
The method comprises the following steps:
the method comprises the following steps: determining the excitation frequency f of the coil according to the detection requirement and the material of the object to be detected;
step two: calculating the wavelength of the excited surface wave according to the excitation frequency f of the coil and the wave speed c of SH wave in the object to be measured, and then determining the pitch diameter of the magnetic field coil according to the wavelength, wherein the relationship between the pitch diameter of the magnetic field coil and the wavelength is
;
Step three: selecting the radial length of the exciting coil according to the pitch diameter of the field coil
Preferably, the length of the excitation coil is greater than
；
Step four: according to radial length of exciting coil
Determining magnetic field coil width
Width of magnetic field coil
Has the optimum size of
(ii) a The design can be changed according to the space size
And
but will produce an amplitude of the excited SH waveThe amplitude of the SH wave will follow
And
becomes smaller;
step five: according to the excitation frequency f and the excitation coil length of the transducer to be designed
Electromagnetic field coil
The PCB circuit of the transducer is drawn.
An omnidirectional SH transducer was fabricated from the PCB circuit of the transducer as drawn.
In the first step of the present embodiment, the excitation frequency f is determined according to the characteristics of the object to be measured and the dispersion curve.
In step two of the present embodiment, the excited surface wave wavelength is obtained according to the following formula.
In step two of the present embodiment, the pitch diameter of the magnetic field coil is determined by the wavelength, and is obtained by the following formula:
。
when in use, the signal input of the electromagnetic field coil and the signal input of the exciting eddy current coil are carried out simultaneously, so that a magnetic field with enough strength is ensured in the exciting process of an exciting signal, Lorentz force can be generated in an object to be detected, and an ultrasonic exciting signal and a magnetic field exciting signal are shown in figure 6. The pulse width of the magnetic field excitation signal is larger than the total width of the excitation signal, and the magnetic field needs to be excited first, and then the excitation signal is fed into the excitation coil, so that the bias magnetic field has enough strength.
In the design method of the omnidirectional SH wave electromagnetic ultrasonic transducer according to this embodiment, the excitation frequency of the excitation signal is selected according to the characteristics of the object to be measured and the measurement requirement, and then the excitation frequency f of the excitation signal and the object to be measured are selectedThe wavelength lambda is calculated from the volume wave velocity c, and the width w of the exciting coil is determined according to the wavelength lambda1。
Claims (9)
1. An omnidirectional SH wave electromagnetic ultrasonic transducer without a permanent magnet comprises two coils and an insulating layer, and is characterized in that:
one part of the PCB coil is an electromagnetic field coil which is of an annular structure and used for providing a bias electromagnetic field, and the PCB coil consists of two layers of coils which are connected end to form a closed loop;
the other part of the PCB coil is a coil used for generating electric eddy current in the board, and two ends of the coil are respectively connected with an external lead;
the insulating layer covers the head end and the tail end of the PCB coil and is connected with a wire connecting wire, and the wire is connected with an external power supply.
2. The omni-directional SH wave electromagnetic ultrasonic transducer of claim 1, wherein: the electromagnetic field coil is composed of an upper layer of coil and a lower layer of coil, the two layers of coils are connected end to form a loop, two magnetic fields with opposite polarities are generated after current is supplied, and the two magnetic fields with opposite polarities are respectively arranged on the coil with the current from outside to inside and the coil with the current from inside to outside.
3. The omni-directional SH wave electromagnetic ultrasonic transducer of claim 1, wherein: the eddy current coil capable of generating the excitation signal is designed with a lead according to a plane fan-shaped ray structure, the lead is distributed in a PCB (printed circuit board) in a mode of radially extending from the center, the PCB coil is of a two-layer or multi-layer structure, multiple layers are connected through a hole, and the coil is divided into an upper part and a lower part, wherein:
the top layer coil is wound from outside to inside, the innermost coil is connected with the bottom layer through a through hole, and then the top layer coil is wound from inside to outside through the bottom layer;
the lower half part of the coil is formed by winding a lead extending from the bottom layer from outside to inside, connecting the innermost ring with the top layer through a via hole and then winding the lead from the inside of the top layer coil to outside;
the upper part and the lower part of the winding are mutually connected to form a fan-shaped coil, and when the coil is electrified, the current in the lead of the left half part of the whole coil flows into the center of the fan shape from the outside and then flows out from the right half part; the wires passing through the circular arc portion flow back from the right to the left again.
4. The omni-directional SH wave electromagnetic ultrasonic transducer of claim 1, wherein: the number of layers of the PCB coil is even.
5. The omni-directional SH wave electromagnetic ultrasonic transducer of claim 1, wherein: and welding pads are arranged at the head end and the tail end of the PCB coil and are used for being connected with an external lead.
6. The omni-directional SH wave electromagnetic ultrasonic transducer of claim 1, wherein: the electromagnetic field coil is also composed of two layers, the coil is divided into a left half part and a right half part, the winding direction of the left half part is opposite to that of the right half part, the left side and the right side are connected in series, and pads are arranged at two ends of the coil and used for being connected with an external lead; when current is introduced, the left half coil and the right half coil generate bias magnetic fields in opposite directions.
7. The omni-directional SH wave electromagnetic ultrasonic transducer of claim 1, wherein: the transducer generates Lorentz force in a non-ferromagnetic tested piece in a non-contact mode, and SH waves are generated through the Lorentz force; the SH wave can also be generated by generating Lorentz force and magnetostriction force in a ferromagnetic tested piece in a non-contact mode.
8. The method of designing an omnidirectional SH wave electromagnetic ultrasonic transducer of claim 1, wherein: the method comprises the following steps:
(1) determining the excitation frequency f of the coil according to the detection requirement and the material of the object to be detected;
(2) calculating the wavelength of the excited surface wave according to the excitation frequency f of the coil and the wave speed c of SH wave in the object to be measured, and then determining the pitch diameter of the magnetic field coil according to the wavelength, wherein the relationship between the pitch diameter of the magnetic field coil and the wavelength is
；
(3) Selecting the radial length of the exciting coil according to the pitch diameter of the field coil
Preferably, the length of the excitation coil is greater than
；
(4) According to radial length of exciting coil
Determining magnetic field coil width
Width of magnetic field coil
Has a size of
(ii) a The design can be changed according to the space size
And
but will have an effect on the amplitude of the excited SH wave, which will follow
And
becomes smaller;
(5) according to the excitation frequency f and the excitation coil length of the transducer to be designed
Width of electromagnetic field coil
The PCB circuit of the transducer is drawn.
9. The design method as claimed in claim 8, wherein: the wavelength of the excited surface wave in the step (2) is obtained by the following formula:
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| CN202010400305.7A CN111380963A (en) | 2020-05-13 | 2020-05-13 | Omnidirectional SH wave electromagnetic ultrasonic transducer without permanent magnet and design method thereof |
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| CN202010400305.7A CN111380963A (en) | 2020-05-13 | 2020-05-13 | Omnidirectional SH wave electromagnetic ultrasonic transducer without permanent magnet and design method thereof |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112268954A (en) * | 2020-08-31 | 2021-01-26 | 北京工业大学 | L based on electromagnetic ultrasonic phased array sensorCRWave sound beam deflection regulating and controlling method |
| CN114666705A (en) * | 2022-05-25 | 2022-06-24 | 山东省科学院激光研究所 | Method for keeping sound field directivity based on transducer |
-
2020
- 2020-05-13 CN CN202010400305.7A patent/CN111380963A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112268954A (en) * | 2020-08-31 | 2021-01-26 | 北京工业大学 | L based on electromagnetic ultrasonic phased array sensorCRWave sound beam deflection regulating and controlling method |
| CN114666705A (en) * | 2022-05-25 | 2022-06-24 | 山东省科学院激光研究所 | Method for keeping sound field directivity based on transducer |
| CN114666705B (en) * | 2022-05-25 | 2022-09-02 | 山东省科学院激光研究所 | Method for keeping sound field directivity based on transducer |
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