中文摘要：

电磁超声换能器（Electromagnetic acoustic transducer,EMAT）灵敏度低,其静态偏置磁场是影响EMAT灵敏度的关键因素。为提高EMAT的灵敏度,利用有限元软件ANSYS计算EMAT中永磁体产生的磁感应强度,得到磁感应强度的分布规律,并结合试验方法获得永磁体的优化结构参数,以指导EMAT结构的优化设计。研究结果表明,当永磁体与线圈的间距减小时,超声振动回波幅值增大,但对线圈干扰加大,在两者之间取折中能够得到较高信噪比的回波信号;永磁体厚度对换能器灵敏度产生严重影响,当厚度增大,磁感应强度增强,但趋势逐渐变缓。聚磁板的应用有利于集中磁感应强度,提高回波信号的信噪比。

英文摘要：

Static bias magnetic field is the main factor which affects the electro-acoustic converting efficiency of electromagnetic acoustic transducer（EMAT）.To improve the sensitivity of the transducer,magnetic induction intensity produced from permanent magnet in EMAT is calculated by ANSYS and the distribution of eddy current density on the permanent magnet surface is obtained to guide the optimization of EMAT with experimentation.The results show that the received signal amplitude increases,as well as the disturbance of coil when the space between permanent magnet and coil decreases;an optimum value is obtained when the space has a proper value.The sensitivity of EMAT is affected by the thickness of permanent magnet,with the increasing of thickness,the magnetic induction intensity increases as well but the gradient gradually becomes small.The application of poly magnetic plate contributes to concentrating the magnetic induction intensity and improving the signal-to-noise ratio of echo signal.