Tuned double-coil EMATs for omnidirectional symmetric mode lamb wave generation

This paper investigates a method to generate only symmetric omnidirectional Lamb waves and proposes specially-tuned double-coil EMATs. While methods to generate omnidirectional Lamb waves have been reported, the symmetric mode is typically accompanied by unwanted antisymmetric modes. The double spiral coil works as a wavelength filter but the relation between the coil geometries and the wavelength of the symmetric mode that minimizes the unwanted antisymmetric mode has not been established. Axisymmetric analysis was performed to find the relation. Excellent rejection of antisymmetric modes with successful symmetric mode generation was confirmed by experimental results that favorably agree with the theoretical results.