Most electromagnetic acoustic transducers (EMATs) can only excite Rayleigh waves at a specific wavelength with lower conversion efficiency. This will significantly restrict the scope of EMAT applications. Therefore, this study proposes a novel wavelength-tunable Rayleigh wave EMAT (WT-RW-EMAT) with high conversion efficiency. This transducer consists of a periodic permanent magnet (PPM) and a coil array (CA). The PPM consists of five rectangular permanent magnets arranged side by side in opposite polarity, with the CA wound separately between adjacent magnets. This configuration generates strong horizontal magnetic fields periodically at the junctions of neighboring magnets. This allows the CA to fully utilize these strong horizontal magnetic fields for exciting Rayleigh waves to improve conversion efficiency. The wavelengths of Rayleigh waves excited by WT-RW-EMAT are tunable through phase control. A finite element model of the WT-RW-EMAT is established using COMSOL Multiphysics, and the performance of the proposed WT-RW-EMAT is studied. The effectiveness is verified by experiments. The proposed EMAT configuration improves the amplitude of the Rayleigh wave by 74.2%. The simulations and experiments showed that the wavelength of Rayleigh waves excited by WT-RW-EMAT is tunable by controlling the time delay of the excitation signal of each coil. With an increase in time delay, the wavelength linearly decreases, and the center frequency nonlinearly increases. This transducer has significant potential applications in detecting gradient properties of a medium.
Zhang et al. (Thu,) studied this question.