Lamb waves are widely used in nondestructive testing (NDT) and structural health monitoring (SHM) for its obvious advantages, such as good directionality, longer-range propagation and lower loss etc. However, it is difficult to analysis and interpret the echo signals because of the multi-modes and dispersion of the Lamb waves. In this paper, the properties of single-mode Lamb waves which were excited by electromagnetic acoustic double transducer were studied based on the principles of multi-modes and the characteristics of wave structure. Meanwhile, the correctness of the double transducer excitation structure has been verified by experiments. Simulations and experimental results show that the double transducer excitation structure can stimulate single-mode Lamb waves and eliminate the extra modes which produced by modal conversion at ends of the specimen. The single-mode excitation of Lamb waves is beneficial to reduce the difficulty of signal processing and provide reliable information for locating the defects. The researches in this paper can be used as a theoretical basis to design double transducer excitation system.%Lamb 波因其指向性好、传播距离远、损耗小等优点而被广泛应用于构件的无损检测和健康监测中.但是,Lamb波的频散性和多模态的特点,使其在实际应用中的回波信号分析变得十分困难.该文在分析 Lamb 波多模态特性的基础上,根据 Lamb 波两种模式波结构的特点,研究电磁超声双换能器激发结构产生单模态Lamb波的特性,并对双换能器激发结构进行实验研究.仿真和实验结果表明,双换能器结构可激发单模态 Lamb 波,并且可以消除端面模态转换产生的多模态,从而减小后续信号处理的难度,为实际检测中缺陷的定位、识别提供有效信息,并为电磁超声双换能器激发结构的设计提供理论指导.
展开▼
