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 共查询到18条相似文献,搜索用时 93 毫秒
1.
The field of horizontally polarized ultrasonic shear wave radiated by a 2/2 piezoelectric composite normal probe was studied. The strictly analytic field solutions for two different surface forces were deduced and the field distribution and directivity patterns were given by numerical calculations. The vertical radiated field of shear wave was obtained theoretically and compared with experiment. The experimental result of directivity pattern conformed the theoretical prediction, which provided the theoretical basis for the engineering application of the transducer.  相似文献   

2.
The ultrasonic transient field of horizontally polarized shear wave radiated by a 2/2 piezoelectric composite normal probe was analyzed. The analytic field solutions for two different surface force sources were deduced and the transient displacement field distribution on the central cross-section was plotted by numerical calculations. Direct wave and edge wave as well as head wave were observed distinctly in the plots. The experimental results of time domain waveform conformed with the theoretical predictions, which supported the theoretical and numerical results about the transient field of the transducer.  相似文献   

3.
The characteristic of radiated sound field excitated within a non-ferromagnetic aluminum by an electromagnetic acoustic transducer consisting of circle-spiral coil and vertical bias magnetic field is studied.This article presents an improved force source model according to the principle of electromagnetic induction.Then the analytic displacement solution of sound field produced by that force source model is deduced.The tangential and normal directivities of shear and longitudinal sounds are calculated numerically and compared with experimental results.Experimental results conform well to the theoretical prediction,which not only shows that the electromagnetic acoustic transducer of this conformation has a good directivity of vertical shear-wave radiation,but also confirms the given force source model is effective to describe the actual physical behavior of the probe.Theoretical and experimental study lays a foundation for optimization design and engineering application of the electromagnetic acoustic probe.  相似文献   

4.
The radiation directivity of a complicated conformal array of underwater acoustic transducers is presented based on the boundary "element method. It includes the element directivity of each transducer, the natural beam pattern and the controlled beam pattern of the transducer array. At first, the boundary element model of the conformal array is built up, and then the boundary condition is exerted on the model according to the design and environment in which the transducer array is used, and the radiation directivity of the conformal array is calculated. An experiment has been done to measure the directivity in an anechoic water tank. The calculated and the experimental results are compared and analyzed. They are consistent to each other. It is shown that the boundary element method together with the detailed calculations is successful to simulate and predict the radiation directivity of an underwater acoustic transducer array.  相似文献   

5.
The multi-path effect of the acoustical wave in a solid plate is studied. The multireflection and wave conversion of the cylindrical compressional and shear waves, which are excited by an infinite strip on a free surface of the solid plate, are analyzed thoroughly by the far-field approximation method. The concise analytical representations of the cylindrical waves are obtained. The time reversal processing is then applied to the propagation of the cylindrical waves and analyzed theoretically and experimentally. It is shown that the waves coming from different array elements and different paths all arrive at the original place after the time reversal operation. It indicates that the time reversal can compensate automatically the wave aberration caused by the multi-path effect. The self-adaptive focusing of the time reversal field is also analyzed quantificationally by the focusing gain and the ratio of the principal to the second lobe. The effects of the focus position and the aperture of the transducer array on the focused field are also investigated. It shows that theoretical and experimental results are consistent to each other very well.  相似文献   

6.
The transient acoustic field radiated by a piezoelectric thickness-mode transducer into a solid medium is theoretically analysed.It is proved thatthe field consists of the direct wave,the longitudinal edge waves,the shear edgewaves,the head wave and the surface waves.The wavefront approximations ofall these waves are given which result in a clear physical picture which is not on-ly simple but also cotains the main features of the field.The theoretical resultwell describes the experiment.  相似文献   

7.
The focused acoustic field generated by an annular array interface are investigated theoretically and experimentally. transducer and its reflection field on a solid-liquid Theoretically, the concise analytic expressions about the radiation and reflection acoustic fields of the annular phased array are obtained by the ray approach method (saddle-point method). In experiment, an annular transducer with 8 equal-area elements is designed and fabricated, and a series of experiments about the radiation acoustic field and its reflection on the liquid-solid interface are carried out. The experimental characteristics of the transducer are in good agreement with the numerical ones. It shows the correctness of the theoretical result and the feasibility of dynamic focusing of the experiment system. With the maximum amplitude and its emergence time of the reflection wave, we can acquire the information and the imaging of the reflection interface by the annular phased array dynamic focusing.  相似文献   

8.
Acoustic scattering from the submerged fluid-filled finite cylindrical shell insonified by an incident plane wave is studied experimentally and theoretically.A monostic broadband transducer with the sharp directivity is used in the experiment.The broadband LFM signal and the single-frequency narrow pulse are used to measure the backscattering field of the cylindrical shell.The measured results have a good agreement with the theory both in time and frequency domain.The theoretical and experimental results show that the resonances of several additional waves which are caused by the internal fluid are presented in the frequency domain.And a series of ’whispering gallery’ waves produced by the waves reflected back and forth in the internal fluid filled in the cylindrical shell are added.The reason for the clustering of the bowl-shape resonance curves in the frequency-angle spectrum is explained as the superposition of the first several modes of ’whispering gallery’ waves.  相似文献   

9.
Study of self—focusing in underwater waveguide by time reversal method   总被引:1,自引:0,他引:1  
Acoustic wave time reversal self-focusing in underwater waveguide is studied.The acoustic wave time reversal is theoretically and experimentally investigated in a half-infinitefluid medium and a shallow fluid layer placed on a hard half-infinite solid medium,respectively,The ray approach method is adopted to study the far field of the acoustic field in theory,and the ultrasonic experiments have been carried out in laboratory to model the underwater waveguide.It is shown by theoretical and experimental results that the focusing gain can be improved by 12dB or more.  相似文献   

10.
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   

11.
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   

12.
针对在线车轮超声探伤系统的工程应用,研究了跑道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。根据外磁场和线圈配置,将表面力源近似为非均匀的水平剪切力源,数值计算得到了此力源的辐射声场指向性图,并与实验结果进行比对,结果表明辐射的水平偏振横波具有中间强两侧弱的指向性,对理解跑道形电磁线圈超声换能器的辐射声场和在重载货车车轮辋裂缺陷探伤中的工程应用具有一定的指导意义。  相似文献   

13.
The use of non-contact laser techniques for the generation of ultrasound has extended the limits of the application of traditional ultrasonic techniques. This paper focusses on the use of one such non-contact laser technique, known as ‘optical fibre array’, to generate shear and surface waves. The shear wave experimental directivity pattern results are presented and compared with the theoretical results of a single source and an array source. The experimental directivity results for the surface wave are also presented, and compared with the theoretical results. The data show that the array enhances signal generation in the forward direction for both shear and surface waves. The array gain is also discussed. The receiver for the directivity measurements was a contact piezoelectric transducer.  相似文献   

14.
Modeling the ultrasound generated by a laser source is critical for using noncontact laser-generated ultrasonic systems for the characterization of material properties. In this work, a laser line source was modeled and verified experimentally by measuring the ultrasonic shear wave signal generated in aluminum with a broadband laser generation/electromagnetic acoustic transducer (EMAT)-detection system. Results of calculations and experiments show that the amplitude directivity of a laser line source is identical to that of a point source in the plane perpendicular to the line axis while the temporal dependence differs.  相似文献   

15.
为研究微烧蚀状态下圆形光斑斜入射时激光超声声场的指向性,使用脉冲激光辐照半圆柱形铝质工件表面,并使用压电探头和电磁超声探头分别接收纵波和横波信号。根据速度参数确定了超声信号的类型,提取了信号的峰-峰值,并绘制出声场指向性曲线。通过分析获得以下结论:激光斜入射角度在0~60°范围内变化时,纵波声场的声束轴线方向保持不变,且与工件内法线平行;另外,横波声场的峰-峰值仍然在±35°的方向上取最大值,但是横波指向图形的主瓣易受激光入射方向的影响,当倾斜角度大于等于45°时,横波主瓣的范围变得较宽。  相似文献   

16.
A theoretical model was suggested for qualitative evaluation of a sound pressure field in fruit tissue, as affected by ultrasonic probe dimensions and fruit properties. The classic directivity pattern of an ideal fluid model, expressed by Bessel function of the first kind, was extended to include energy dissipation of a real material. The directional characteristics of wave propagation, as influenced by transmitter frequency and diameter, and by fruit properties, were discussed. The model indicates how to select the parameters of the ultrasonic transducer (transducer diameter, frequency and excitation power) to control the magnitude and directivity of the ultrasonic waves in the fruit tissue. The suggested theoretical model represented fairly well the experimental sound wave distribution over the half-cut surface of potato and avocado (R2 > 0.862 and 0.977, respectively); the same theoretical model could not represent the sound wave distribution over a half-cut melon. Results of the study were applied in a new probe design for ultrasonic testing of whole fruit.  相似文献   

17.
A method is proposed to measure the stress on a tightened bolt using an electromagnetic acoustic transducer (EMAT). A shear wave is generated by the EMAT, and a longitudinal wave is obtained from the reflection of the shear wave due to the mode conversion. The ray paths of the longitudinal and the shear wave are analyzed, and the relationship between the bolt axial stress and the ratio of time of flight between two mode waves is then formulated. Based on the above outcomes, an EMAT is developed to measure the bolt axial stress without loosening the bolt, which is required in the conventional EMAT test method. The experimental results from the measurement of the bolt tension show that the shear and the mode-converted longitudinal waves can be received successfully, and the ratio of the times of flight of the shear and the mode-converted longitudinal waves is linearly proportional to the bolt axial tension. The non-contact characteristic of EMAT eliminates the effect of the couplant and also makes the measurement more convenient than the measurement performed using the piezoelectric transducer. This method provides a promising way to measure the stress on tightened bolts.  相似文献   

18.
利用理论推导及实验验证的方法研究了激光倾斜入射支持燃烧波时纵波声场的指向性。根据激光超声的产生机理, 在喷溅物质垂直作用于工件表面的前提条件下, 推导了椭圆形声源作用时远场质点的法向位移。获得了纵波声场的指向性函数, 分析了影响纵波声场指向性的因素, 并进行了实验验证。利用功率密度低于爆轰波点燃阈值的激光烧蚀工件, 使用峰值频率为5 MHz压电探头接收纵波, 进而获得纵波声场的指向性实验数据, 结果表明, 实验数据与理论数据能够较好地进行吻合。在光斑短轴长度恒定时, 与激光垂直入射相比, 各倾斜入射角度下纵波声场的声束轴线指向均保持不变, 并且指向性图形随倾斜角度的增加而变得细窄, 纵波声场的能量也更加集中。  相似文献   

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