A Novel Variable-Length Meander-Line-Coil EMAT for Side Lobe Suppression

Typically, meander-line-coil electromagnetic acoustic transducers (EMATs) with wires of a constant length are used to generate Rayleigh waves. However, significant side lobes are observed in this design. In this paper, a novel meander-line-coil with variable-length wires is proposed to suppress side lobes of the Rayleigh waves' beam. This novel EMAT is simulated by using a wholly analytical method, which involves the coupling of an analytical EM model and an analytical US model to generate the radiation pattern of Rayleigh waves. The Rayleigh waves' beam directivity of this novel variable-length meander-line-coil (VLMLC) is quantitatively analyzed by the half power beamwidth and the sidelobe level; the effect of the length step on the Rayleigh waves' beam directivity is discussed. A 50-mm VLMLC with a length step of 8 mm is fabricated and experimentally analyzed; experimental results showed that novel VLMLCs are capable of suppressing side lobes of the Rayleigh waves' beam, which is not achievable by the conventional meander-line-coil. To the best of our knowledge, there has been no report so far of the VLMLCs EMAT.