CN114216600A - L based on double-folding coil electromagnetic acoustic sensorCRWave sound beam deflection regulating and controlling method - Google Patents
L based on double-folding coil electromagnetic acoustic sensorCRWave sound beam deflection regulating and controlling method Download PDFInfo
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- CN114216600A CN114216600A CN202111540145.7A CN202111540145A CN114216600A CN 114216600 A CN114216600 A CN 114216600A CN 202111540145 A CN202111540145 A CN 202111540145A CN 114216600 A CN114216600 A CN 114216600A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
- G01L5/0047—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes measuring forces due to residual stresses
Abstract
The invention discloses an L based on a double-folding coil electromagnetic acoustic sensorCRWhen the sensor works, the rectangular neodymium-iron-boron magnet provides a static magnetic field perpendicular to the aluminum plate, the double-inflection coil carrying alternating current is arranged in the skin depth layer of the aluminum plate to induce an alternating magnetic field with the frequency consistent with the frequency of the transmitted current, and then eddy current with the direction opposite to the current direction of the coil and the frequency identical to the frequency is induced in the skin depth layer on the surface of the aluminum plate. The interaction of the static magnetic field and the induced eddy currents couples out lorentz forces, thereby exciting ultrasonic waves. By adjusting the related parameters (spacing related parameter k and time delay parameter delta t) of the double-turn coil, the sound beam deflection regulation and control capability of the electromagnetic acoustic phase control sensor is improved. The method of the invention can excite the L with smaller included angle with the surface of the plate in the metal plate structureCRAnd the wave improves the sensitivity of residual stress detection. In the aspect of ultrasonic residual stress detection, great application value and reference significance are provided.
Description
Technical Field
The invention relates to an electromagnetic acoustic sensor pair L based on a double-folding coilCRA method for regulating and controlling wave sound beam deflection belongs to the field of ultrasonic nondestructive detection, and can excite critical Refracted longitudinal waves (critical Refracted Long) with smaller included angle with the surface of a metal plate in the metal plate structureitudinal Wave,LCR) It is optimized to improve the resolution of the residual stress detection.
Background
Residual stress is a force that exists within a structural member to maintain balance when the structural member is not acted upon by an external factor. The existence of residual stress is generally harmful to the structural member, improper treatment of the residual stress may cause deformation, cracking and the like of the structural member, and the existence of the residual stress also reduces the stability of the structural member. Therefore, residual stress assessment is an important stage in the design and machining of structural members. Ultrasonic residual stress detection method based on acoustic elastic effect and using LCRThe wave evaluates the residual stress in the structural member, and is widely applied to the residual stress detection by the characteristics of no damage to the detected structural member, no damage to the human body, quick detection and the like. L isCRThe wave is a longitudinal wave propagating below the surface of the solid at a first critical angle of incidence, having the property of being sensitive to stress and insensitive to material texture, L, compared to other forms of ultrasoundCRThe wave has the highest sensitivity to stress, and is widely applied to stress detection of structural members such as steel plates, welded joints, steel rails and the like.
LCRThe principle of wave detection residual stress is based on the acoustic-elastic effect, and the surface and internal residual stress of a sample is reflected by analyzing the change of the propagation speed of ultrasonic waves, so that the residual stress in the sample is represented. L isCRThe directivity of the sound beam is an important characteristic in detection. Pair L of S.Chaki and W.KeCRThe directivity of the sound wave beam is researched, when the underwater sound coupling piezoelectric transducer is adopted for excitation and is incident at a first critical angle, refracted longitudinal waves do not completely propagate along the surface of a sample, and the included angle between the maximum amplitude position of the longitudinal sound wave beam and the surface of the sample is 25 degrees at the minimum. Analysis of the influence L by Pei and Bond et al by numerical methodsCRObtaining the incident angle and sensor aperture pair L by the key parameter of wave sound beam directivityCRThe conclusion that the wave directivity influences most. Study LCRThe optimization of the wave pointing angle has important significance for improving the resolution of residual stress detection.
Compared with the conventional piezoelectric ultrasonic sensor, the electromagnetic acoustic sensor has the advantages of non-contact and high temperature resistance. Through the adjustment to electromagnetic acoustic sensor relevant parameter, can realize controlling sound wave directive property. The invention designs a longitudinal wave electromagnetic acoustic sensor based on a double-folding coil, and achieves the purpose of regulating and controlling a longitudinal wave pointing angle by a method for adjusting related parameters (an interval related parameter k and a time delay parameter delta t) of the double-folding coil.
Disclosure of Invention
The invention aims to design an electromagnetic acoustic sensor pair L based on double-folding coilCRThe method for regulating and controlling the deflection of the sound wave beam solves the problems that the directivity of a longitudinal sound wave beam excited by a piezoelectric sensor is difficult to regulate and control, and the included angle between the longitudinal sound wave beam and the surface of a sample is optimized and reduced. Proposed method pair LCRThe regulation and control capability of the deflection of the wave sound beam is superior to that of the traditional piezoelectric sensor, and the wave sound beam has the advantages of non-contact and high temperature resistance.
In order to achieve the purpose, the invention adopts the following design scheme:
an electromagnetic acoustic sensor based on double-folding coils comprises a rectangular neodymium iron boron magnet 1 and a double-folding coil 2 in a flexible circuit board; the method is characterized in that: the rectangular ndfeb magnet 1 is polarized to provide a static magnetic field directed vertically downwards. The exciting current in the double-folding coil 2 in the flexible circuit board induces an alternating magnetic field with the same frequency as the exciting current in the skin depth layer of the metal plate 3, induces an induced eddy current with the same frequency and the opposite direction as the coil current in the skin depth layer of the metal plate surface, and generates Lorentz force under the interaction with the static magnetic field applied from the outside. Under the action of Lorentz force, the surface of the metal plate generates periodic elastic deformation and vibration, so that ultrasonic waves are excited. The electromagnetic acoustic sensor based on the double-folding coil is characterized in that: the cross section of the rectangular neodymium-iron-boron magnet 1 is rectangular, the polarization direction is perpendicular to the length direction, and a static magnetic field perpendicular to the metal test piece 3 is provided.
The electromagnetic acoustic sensor based on the double-folding coil is characterized in that: the distance between two adjacent wires in the same coil is equal to the half wavelength of longitudinal wave or the multiple of the half wavelength of the longitudinal wave of the double-folding coil 2 in the flexible circuit board.
The electromagnetic acoustic sensor based on the double-folding coil is characterized in that: the double-folding coil 2 in the flexible circuit board adopts an upper layer and a lower layer double-layer wiring mode. The two folding coils are respectively positioned at the upper layer and the lower layer, and currents with certain time delay are respectively led into the two coils to cause the deflection of the ultrasonic sound beam.
The invention can obtain the following beneficial effects:
1. the rectangular neodymium iron boron magnet 1 is arranged above the coil 2 and the metal plate 3 to be detected, and provides a static magnetic field which is distributed perpendicular to the metal plate 3;
2. the double-folding coil 2 in the flexible circuit board, two folding coils are in upper and lower two layers separately, the direction of current in two folding coils is the same, and lead into the electric current with certain time delay separately in two coils, in order to cause the ultrasonic sound beam to deflect;
3. compared with the traditional piezoelectric sensor, the electromagnetic acoustic sensor based on the double-inflection coil regulates and controls the deflection of the longitudinal acoustic beam by adjusting the relevant parameters of the double-inflection coil, and can excite the L with a smaller included angle with the surface of the metal plateCRWave;
4. the electromagnetic acoustic sensor based on the double-folding coil utilizes a phase control technology to realize phase time delay between the folding coils, and ultrasonic waves with a certain incident angle are coupled out through a static magnetic field and an induced eddy current, so that the regulation and control capability of an acoustic wave beam is enhanced.
Drawings
FIG. 1 is a structural schematic diagram of an electromagnetic acoustic sensor based on a double-folding coil;
FIG. 2 is a schematic view of a double-turn coil;
FIG. 3 is a schematic diagram of the working principle of an electromagnetic acoustic sensor based on a double-turn coil;
FIG. 4 θLAnd thetaTA graph of variation with k;
FIG. 5 is a diagram showing the simulation result of sound field distribution in the aluminum plate at different times;
FIG. 6 is a graph of normalized amplitude of longitudinal wave directivity;
figure 7 is a comparison graph of sound field distribution results in aluminum plates under different time delays.
In the figure: 1. rectangle neodymium iron boron magnet, 2, two inflection coils in the flexible circuit board, 3, metal sheet test piece.
Detailed Description
The present invention is further illustrated by the following examples and figures, and the following examples are illustrative and not limiting, and are not intended to limit the scope of the present invention.
Electromagnetic acoustic sensor pair L based on double-folding coil is designed based on Lorentz force mechanismCRA method for regulating and controlling deflection of a sound beam. On an aluminum plate, the sensor is used for exciting L with a smaller included angle with the surface of the plateCRAnd the electromagnetic acoustic sensor based on the double-inflection coil is proved to improve the sound beam regulation and control capability compared with the traditional piezoelectric sensor. FIG. 1 is a schematic structural diagram of an electromagnetic acoustic sensor based on a double-turn coil according to the present invention; the flexible printed circuit board comprises a rectangular neodymium iron boron magnet 1 and a double-folding coil 2 in the flexible printed circuit board; the ultrasonic wave is generated at the position of the aluminum plate 3 and has a specification of 100X 50 (unit: mm). The double-folding coil 2 in the flexible circuit board is arranged between the rectangular neodymium iron boron magnet 1 and the aluminum plate 3 and is in close contact with the rectangular neodymium iron boron magnet 1 and the aluminum plate 3.
The double-folding coil 2 in the flexible circuit board is shown in fig. 2, and the central distance d between two adjacent wires in the same coil is equal to the half wavelength of the longitudinal wave in the aluminum plate. The total number of individual wires is 12. Adopt upper and lower double-deck wiring, upper and lower two-layer totally 12 wires, single wire length is 32mm, and the width is 0.2 mm.
Usually, the permanent magnet of the longitudinal wave electromagnetic acoustic sensor provides a static magnetic field parallel to the surface of the test piece, and the excited longitudinal wave is vertical to the surface of the test piece and propagates along the depth direction of the test piece. The permanent magnet provides a static magnetic field vertical to the surface of the test piece, and the excited longitudinal wave theoretically propagates along the direction parallel to the surface of the test piece, and the energy amplitude is small. On the basis, parameters of the double-folding coil are adjusted, amplitude of longitudinal waves which are approximately propagated along the direction parallel to the surface of the sample is increased, and the requirement of regulating and controlling the directivity of the longitudinal waves in residual stress detection is met. The rectangular neodymium-iron-boron magnet 1 is shown in figure 1, and has the following dimensions: 34mm long, 22mm wide and 22mm high.
On the basis of the sensor, parameters such as excitation signal frequency f, adjacent wire spacing d and array element time delay delta t are determined and adjusted to analyze and research sound field distribution characteristics and control longitudinal sound beam directivity.
The longitudinal wave and transverse wave velocity in the metal structure can be obtained by the following formula,
wherein c isLIs the velocity of longitudinal wave, cTThe transverse wave velocity, E, Young's modulus, σ, Poisson's ratio, and ρ, the density.
When phase matching of a bulk wave is satisfied, the following relationship is obtained according to snell's law
nλ＝2L sinθ#(3)
Where n is an odd integer, typically the ground state n is 1; λ is the target acoustic wavelength; l is the coil spacing; theta is the included angle between the propagation direction of the target sound wave and the normal line. Due to the fact that
Setting L ═ k λTThen, θ is plottedLAnd thetaTThe theoretical variation with k is shown in fig. 4.
With the increase of k and the increase of the coil spacing, the space width of the generated acoustic wave beam is increased, and grating lobes can be generated, influence on the detection precision of the phased array is caused, and meanwhile, the acoustic wave pointing angle theta is reducedLAnd thetaT. When the pointing angle is large (greater than 80 °), the position of the peak becomes difficult to determine, and it is not easy to perform explicit measurement. Therefore, it is not desirable to make the k value too large, but too small a k value (close to the cut-off k value, too large pointing angle) is not favorable for measurement.
The longitudinal wave in the aluminum plate is about 30 ° to the surface and the transverse wave is about 60 ° to the surface. Here, Δ T is set to 0.25T, and T is the excitation signal period. The normalized simulation results of the sound field amplitude at different times in the aluminum plate at f-0.5 MHz and k-1.0 are shown in fig. 5. The time delay set by each channel of the electromagnetic acoustic sensor enables various acoustic waves to deflect. The double-fold electromagnetic acoustic sensor has higher energy at one side of the deflection direction of longitudinal waves excited in the aluminum plate and transmits along the near surface. The change of the coil spacing can affect the directivity of the longitudinal wave, thereby affecting the detection sensitivity of the longitudinal wave electromagnetic acoustic phase control sensor.
TABLE 1 electromagnetic acoustic sensor parameter table
The received signal is sampled at a point on a circular arc with a radius of 40mm, and a normalized curve of the amplitude of the longitudinal wave directivity is drawn as shown in fig. 6. The results of the directivity-related parameters are in table 1. Along with the increase of the distance between adjacent wires, the longitudinal wave pointing angle is firstly reduced and then increased, the bandwidth is firstly reduced and then increased, and the amplitude is also changed, which shows that the longitudinal wave electromagnetic acoustic phased array acoustic beam pointing angle can be effectively reduced and the energy concentration can be improved by properly increasing the distance between the wires. However, the change of the amplitude value is comprehensively considered, and the k value is recommended to adopt 0.8-1.0 to design longitudinal wave electromagnetic acoustic phase control.
Considering the influence of the time delay change on the directivity of the sound beam, because the method of theoretical derivation is very complex, the time delay parameter delta t is adjusted, and the influence of the time delay change on the directivity of the longitudinal wave is researched by utilizing a finite element analysis method, so that the aim of regulating and controlling the directivity of the longitudinal wave is fulfilled. When f is 1.5MHz, k is 1.0, and t is 6 mus, the normalized simulation result of the longitudinal wave sound field amplitude under different conditions is shown in fig. 7. The deflection effect of the sound beam caused by different time delays is different, when the delta T is 0.250T, the sound beam is deflected to one side more intensively, and no obvious side lobe is seen. The other two cases have poor single-sided deflection.
The invention designs an electromagnetic acoustic sensor pair L based on double-folding coilCRMethod for regulating and controlling deflection of wave sound beam, sensor related by method is rectangular neodymium iron boron magnetIron and a double-turn coil. When the sensor works, the rectangular neodymium-iron-boron magnet provides a static magnetic field vertical to the aluminum plate, the double-folding coil which is electrified with alternating current induces an alternating magnetic field with the same frequency as the current in the skin depth layer of the aluminum plate, and further induces an induced eddy current with the same frequency and the opposite direction as the current direction of the coil in the skin depth layer of the aluminum plate surface, the vertical static magnetic field and the induced eddy current interact, and the vertical incident Lorentz force is coupled according to the left-hand rule. The Lorentz force applied to the metal plate can excite ultrasonic wave with certain frequency. Under the action of certain parameters of the double-folding coil and phase control time delay, the sound beam deflection regulation and control capability of the double-folding coil electromagnetic sound sensor is improved. The method of the invention can excite the L with smaller included angle with the surface of the plate in the metal plate structureCRAnd the wave improves the resolution of residual stress detection. In the aspect of ultrasonic residual stress detection, great application value and reference significance are provided.
Claims (5)
1. The utility model provides an electromagnetic acoustic sensor based on two inflection coils which characterized in that: comprises a rectangular permanent magnet (1) and a double-folding coil (2) in a flexible circuit board; the method is characterized in that: the permanent magnet (1) is vertically polarized to provide a vertical static magnetic field; the double-folding coil (2) in the flexible circuit board is arranged in a skin depth layer of the metal plate (3) and induces an alternating magnetic field with the same frequency as the emission current, so that eddy currents with the opposite direction and the same frequency as the coil current are induced in the skin depth layer of the metal plate surface, and Lorentz force is generated under the interaction with a static magnetic field in the vertical direction applied by the outside; under the action of Lorentz force, periodic vibration is generated on the surface of the metal plate, and ultrasonic waves are further excited.
2. The electromagnetic-acoustic sensor based on the double-turn coil as claimed in claim 1, wherein: the cross section of the rectangular permanent magnet (1) is rectangular, the polarization direction is perpendicular to the length direction, and a static magnetic field perpendicular to the metal plate (3) is provided.
3. The electromagnetic-acoustic sensor based on the double-turn coil as claimed in claim 1, wherein: the distance between two adjacent wires in the same coil is equal to the half wavelength of longitudinal wave or the multiple of the half wavelength of the longitudinal wave.
4. The electromagnetic-acoustic sensor based on the double-turn coil as claimed in claim 1, wherein: the double-folding coil (2) in the flexible circuit board, two folding coils are respectively positioned at an upper layer and a lower layer, the current directions in the two folding coils are the same, and currents with certain time delay are respectively led into the two coils to realize the deflection of the ultrasonic sound beam.
5. The electromagnetic-acoustic sensor based on the double-turn coil as claimed in claim 1, wherein: the spacing related parameter k and the time delay parameter delta t of the double-back-folded coil (2) can be adjusted by using a finite element analysis method to determine the optimal parameters.
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| CN114858106A (en) * | 2022-03-31 | 2022-08-05 | 西安交通大学 | Longitudinal wave-transverse wave integrated electromagnetic ultrasonic probe |
| CN115014587A (en) * | 2022-05-30 | 2022-09-06 | 西安工程大学 | Magnetic effect phased array signal acquisition structure, system and method |
| CN115855333A (en) * | 2022-12-21 | 2023-03-28 | 北京工研精机股份有限公司 | Surface stress distribution cloud picture construction method based on critical refraction longitudinal wave detection |
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