【作者】 周佳伟；

【导师】 高松巍；

【作者基本信息】 沈阳工业大学 ， 测试计量技术及仪器， 2011， 硕士

【摘要】 区别于传统压电超声检测技术,电磁超声检测技术具有无需耦合剂、更易激发出不同模式的超声波等特点,优势逐渐凸显。由于电磁超声换能器的复杂性和多样性,本文在对国内外电磁超声检测技术对其机理的研究和认识的基础上,着重利用有限元仿真分析的方法对电磁超声的检测机理进行深入的研究。本文针对电磁超声换能器工作的三个过程：电磁场、电磁超声耦合以及声场传播理论,分析其相应的换能原理,进行详细的数学描述和理论推导。根据产生波型的不同,分析了电磁超声换能器的各组成部分中高频激励线圈和磁铁的不同配置情况,以及对应不同配置激发波形的种类和其声波传播形式。采用ANSYS有限元仿真软件对电磁超声换能器的进行电磁场仿真分析,得到被测试件中涡流和洛伦兹力的分布。同时,将电磁场得到的结果与结构场耦合,得到被测试件内部质点的应力、应变和位移情况,从而达到对电磁超声换能器辐射声场进行仿真分析的目的。电磁超声换能器的缺点是换能效率低,信号微弱。因此,为了提高换能效率,对其模型进行了优化,针对EMAT优化的主要对象,对线圈与被测试件之间的提离距离、线圈和永磁体的各参数对换能效率的影响做了分析,最终确定了激励线圈参数的优化组合。通过电磁结构耦合得到被测试件内部质点的应力、应变和位移情况。仿真分析得到电磁超声换能器被测试件内部辐射声场的分布以及被测试件表面上的指向角,通过实验验证了指向角仿真结果的正确性。并通过改变被测试件的厚度、激励电流频率得到相应辐射声场的变化。最后分析了三种配置的换能器的辐射声场分布的各自指向性特点。更多还原

【Abstract】 Distinguished from Piezoelectric ultrasonic testing technology, electromagnetic acoustic technology has many advantages, such as inspection without coupling agent, stimulated different mode wave easily and so on, attracts attention highly in Nondestructive Testing field. Because of complexity and diversity of the electromagnetic acoustic transducer, apply ANSYS to simulate and analyze it based on study and understanding of electromagnetic acoustic transducer mechanism at home and abroad.Analyze electromagnetic acoustic transducer mechanism divided into three intercoupling fields as electromagnetic field, kinetic field and ultrasonic field with detailed mathematical description. Based on various configuration of magnet and winding coil in electromagnetic acoustic transducer, analyze different mode wave stimulated by them correspondingly and sound transmission in sample.Apply ANSYS to simulate and analyze electromagnetic field of the electromagnetic acoustic transducer. Based on the established three-dimensional finite element model of electromagnetic acoustic transducer, acquisition eddy current, Lorentz force on the surface of the sample. At the same time, by means of which electromagnetic field intercoupling with structure force field, acquisition stress, strain and displacement distribution in the sample to analyze further acoustic field of the electromagnetic acoustic transducer in the sample. The weakness of electromagnetic acoustic transducer is low transduction efficiency resulting in weak signal. In order to improving transduction efficiency, optimize it including Lift-off distance between coil and sample, parameter of magnet and coil.By means of which electromagnetic field intercoupling with structure force field, obtain the orientation of radiated sound field of electromagnetic ultrasonic surface wave, its variation with thickness of sample and stimulated current frequency. Orientation result is verified by experiments. At last, compared radiated sound fields of three configuration of magnet and winding coil in electromagnetic acoustic transducer with each other.更多还原