The Research On Transduction Efficiency Of Surface Wave Emat

The transmitting process of EMAT is that transducer emits electromagnetic wave and induces Lorentz force, magnetizing force and magnetostrictive force, those forces induce vibration of particle in the sample and finally generate ultrasonic. Such working mechanism leads EMAT to poor transduction efficiency. In order to solve this problem, the paper studies the method to increase the EMAT transduction efficiency.At the beginning of the passage, we analyze the mechanism of EMAT and deduce the equation of Lorentz force, magnetizing force and magnetostrictive force. Lorentz force and magnetizing force can be calculated immediately from those equation. But magnetostrictive force equation is so complex that it cannot be calculated directly. Therefore, we design a method using magnetostrictive curve and the result of magnetic field achieved by numerical method to calculate magnetostrictive force. After that, we use theoretical acoustic to build the mathematical model of EMAT.We use finite element method to analyze the relationship between EMAT transduction efficiency and structure parameters which includes liftoff, coil conductor length, coil conductor width, magnet square and magnet thickness. And then we use orthogonal method and curve fitting method to obtain the relationship and show how to increase the transduction efficiency.As a result of long time consuming of finite element method, we design a fast method to calculate the electromagnetic parameters. The whole time we need is only 10 minutes, which is far from the finite element method. The difference between finite element method and fast method in calculation result of eddy current and Lorentz force is no more 20%. And static magnetic field is no more than 10%. Such method can sharply decrease the computing time.In order to prove the result of simulation, we designed an experiment setup to verify the relationship between transduction efficiency and structure parameters. The difference between experiment and simulation is no more than 20%, this result proves the accuracy of this paper.