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1.
在线超声检测系统中螺旋线圈换能器的应用*   总被引:1,自引:1,他引:0       下载免费PDF全文
针对在线车轮超声检测系统的工程应用,研究了圆形螺旋线圈电磁超声换能器由洛伦兹力换能机制在钢中产生的辐射声场。给出了涡流、等效表面力源和辐射声场的计算方法,分析了圆形螺旋线圈换能器在钢试块上的辐射指向性。结果表明,辐射的圆周径向偏振横波为两边瓣中空指向性,对理解圆形螺旋线圈换能器的辐射声场和在重载货车车轮轮辋在线辋裂缺陷检测中的工程应用具有一定的指导意义。  相似文献   

2.
郝宽胜  黄松岭  赵伟  王珅 《中国物理 B》2011,20(6):68104-068104
This paper presents an analytical method for electromagnetic acoustic transducers (EMATs) under voltage excitation and considers the non-uniform distribution of the biased magnetic field. A complete model of EMATs including the non-uniform biased magnetic field, a pulsed eddy current field and the acoustic field is built up. The pulsed voltage excitation is transformed to the frequency domain by fast Fourier transformation (FFT). In terms of the time harmonic field equations of the EMAT system, the impedances of the coils under different frequencies are calculated according to the circuit-field coupling method and Poynting’s theorem. Then the currents under different frequencies are calculated according to Ohm’s law and the pulsed current excitation is obtained by inverse fast Fourier transformation (IFFT). Lastly, the sequentially coupled finite element method (FEM) is used to calculate the Lorentz force in the EMATs under the current excitation. An actual EMAT with a two-layer two-bundle printed circuit board (PCB) coil, a rectangular permanent magnet and an aluminium specimen is analysed. The coil impedances and the pulsed current are calculated and compared with the experimental results. Their agreement verified the validity of the proposed method. Further- more, the influences of lift-off distances and the non-uniform static magnetic field on the Lorentz force under pulsed voltage excitation are studied.  相似文献   

3.
The ultrasonic wave propagation in sinusoidally corrugated waveguides is studied in this paper. Periodically corrugated waveguides are gaining popularity in the field of vibration control and for designing structures with desired acoustic band gaps. Currently only numerical method (Boundary Element Method or Finite Element Method) based packages (e.g., PZFlex) are in principle capable of modeling ultrasonic fields in complex structures with rapid change of curvatures at the interfaces and boundaries but no analyses have been reported. However, the packages are very CPU intensive; it requires a huge amount of computation memory and time for its execution. In this paper a new semi-analytical technique called Distributed Point Source Method (DPSM) is used to model the ultrasonic field in sinusoidally corrugated waveguides immersed in water where the interface curvature changes rapidly. DPSM results are compared with analytical solutions. It is found that when a narrow ultrasonic beam hits the corrugation peaks at an angle, the wave propagates in the backward direction in waveguides with high corrugation depth. However, in waveguides with small corrugation the wave propagates in the forward direction. The forward and backward propagation phenomenon is found to be independent of the signal frequency and depends on the degree of corrugation.  相似文献   

4.
Numerical modelling of the ultrasonic wave propagation is important for Structural Heath Monitoring and System Prognosis problems. In order to develop intelligent and adaptive structures with embedded damage detector and classifier mechanisms, detailed understanding of scattered wave fields due to anomaly in the structure is inevitably required. A detailed understanding of the problem demands a good modelling of the wave propagation in the problem geometry in virtual form. Therefore, efficient analytical, semi-analytical or numerical modelling techniques are required. In recent years a semi-analytical mesh-free technique called Distributed Point Source Method (DPSM) is being used for modelling various ultrasonic, electrostatic and electromagnetic wave field problems. In the conventional DPSM approach point sources are placed along the transducer faces, problem boundaries and interfaces to model incident and scattered fields. Every point source emits energy in all directions uniformly. Source strengths of these 360° radiation sources are obtained by satisfying interface and boundary conditions of the problem. In conventional DPSM modelling approach it is assumed that the shadow zone does not require any special consideration. 360° Radiation point sources should be capable of properly modelling shadow zones because all boundary and interface conditions are satisfied. In this paper it is investigated how good this assumption is by introducing the ‘shadow zone’ concept at the point source level and comparing the results generated by the conventional DPSM and by this modified approach where the conventional 360° radiation point sources are replaced by the Controlled Space Radiation (CSR) sources.  相似文献   

5.
The analysis of adhesive bonds using electromagnetic acoustic transducers   总被引:1,自引:0,他引:1  
The paper presented here outlines a technique for examining aerospace adhesive bonds using electromagnetic acoustic transducers (EMAT). The main restriction on the use of bonded structures is the lack of a reliable, applicable non-destructive test. Simple acoustic theory shows that a shear wave at normal incidence to an interface should be a more sensitive probe of interfacing coupling than a longitudinal wave. Conventional piezoelectric shear transducers require a very viscous couplant which makes scanning problematic. The EMAT described here consists of a pancake coil, and a permanent magnet behind the coil provides a static magnetic field normal to the surface of the sample and the plane of the coil. The EMATs used have the advantage of generating broadband radially polarized shear waves, while requiring no acoustic couplant. They are also comparable in size to typical piezoelectric transducers. The broadband nature of the transducer gives it a high spatial resolution in the direction of wave propagation. Experiments performed on plate-like samples have successfully detected deliberately constructed defects, while monitoring the adhesive thickness. Defects have been identified using a C-scan technique using a single EMAT in send-receive mode from either side of the bond.  相似文献   

6.
Shear Wave Field Radiated by an Electromagnetic Acoustic Transducer   总被引:1,自引:0,他引:1       下载免费PDF全文
The horizontally polarized ultrasonic shear wave field emitted by an electromagnetic acoustic transducer (EMAT) is studied by the surface force distribution on the EMAT approximately described as an inhomogeneous horizontal shear force. The shear wave directivity pattern is plotted by numerical calculations based on our strictly analytic solutions of the wave field we presented previously. An experimental system of EMAT generation and piezoelectric transducer reception is set up to check the predictions of the theoretical wave field by measuring the ultrasonic signals through aluminium block. The directivity pattern of the wave field obtained from the experimental results conforms the theoretical prediction, which lays a foundation for engineering applications of EMATs.  相似文献   

7.
耿袆晗 《应用声学》2019,38(3):427-427
为改善电磁超声换能器(electromagnetic acoustic transducer,EMAT)激发横波的特性,提出一种基于正交试验的优化方法,并利用有限元仿真软件COMSOL Multiphysics建立了横波EMAT的有限元模型,应用正交试验和极差分析法,分析了线圈各参数对电磁超声横波的近场长度和半扩散角的影响,比较了线圈各参数影响程度的大小。结果表明,激励电流的频率和线圈的尺寸对横波的传播特性有着明显影响,提高频率会使得横波的近场长度增大及半扩散角减小;其次,减小导线的宽度及间距,以缩小线圈尺寸能有效改善横波的传播特性。  相似文献   

8.
The ultrasonic field generated by a point focused acoustic lens placed in a fluid medium adjacent to a solid half-space, containing one or more spherical cavities, is modeled. The semi-analytical distributed point source method (DPSM) is followed for the modeling. This technique properly takes into account the interaction effect between the cavities placed in the focused ultrasonic field, fluid-solid interface and the lens surface. The approximate analytical solution that is available in the literature for the single cavity geometry is very restrictive and cannot handle multiple cavity problems. Finite element solutions for such problems are also prohibitively time consuming at high frequencies. Solution of this problem is necessary to predict when two cavities placed in close proximity inside a solid can be distinguished by an acoustic lens placed outside the solid medium and when such distinction is not possible.  相似文献   

9.
A modal expansion approach has been proposed for investigating generation of ultrasonic Lamb waves by electromagnetic acoustic transducers(EMATs).Based on the current distribution of the EMAT's meandering coil,the formal solution for the Lorentz surface stress applied on the plate surface has been derived.Then the function of the wave-number spectral density of the Lorentz surface stress for generating ultrasonic Lamb waves has been obtained using the spatial Fourier transform.On this basis,with the modal expansion approach for waveguide excitation,the mathematical expression of the Lamb wave's mode expansion coefficient has been deduced,which is closely related with the geometrical parameters of the EMAT's meandering coil.The mathematical relationship between the Lamb wave's mode expansion coefficient and the EMAT's geometrical parameters,obtained in this paper,lays a theoretical foundation for exactly analyzing generation of Lamb waves by EMATs.Further,the numerical analyses performed indicate that the Lamb wave's mode expansion coefficient can be appropriately adjusted by changing the geometrical parameters of the EMAT's coil,and thus the unwanted Lamb wave modes can be effectively restrained.This result provides a theoretical basis for generating a single and pure Lamb wave mode by the meandering coil EMAT.  相似文献   

10.
Distributed point source method (DPSM) is gradually gaining popularity in the field of non-destructive evaluation (NDE). DPSM is a semi-analytical technique that can be used to calculate the ultrasonic fields produced by transducers of finite dimension placed in homogeneous or non-homogeneous media. This technique has been already used to model ultrasonic fields in homogeneous and multi-layered fluid structures. In this paper the method is extended to model the ultrasonic fields generated in both fluid and solid media near a fluid-solid interface when the transducer is placed in the fluid half-space near the interface. Most results in this paper are generated by the newly developed DPSM technique that requires matrix inversion. This technique is identified as the matrix inversion based DPSM technique. Some of these results are compared with the results produced by the Rayleigh-Sommerfield integral based DPSM technique. Theory behind both matrix inversion based and Rayleigh-Sommerfield integral based DPSM techniques is presented in this paper. The matrix inversion based DPSM technique is found to be very efficient for computing the ultrasonic field in non-homogeneous materials. One objective of this study is to model ultrasonic fields in both solids and fluids generated by the leaky Rayleigh wave when finite size transducers are inclined at Rayleigh critical angles. This phenomenon has been correctly modelled by the technique. It should be mentioned here that techniques based on paraxial assumptions fail to model the critical reflection phenomenon. Other advantages of the DPSM technique compared to the currently available techniques for transducer radiation modelling are discussed in the paper under Introduction.  相似文献   

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