Development of High Temperature Rayleigh Wave Electromagnetic Acoustic Transducer with Double Coil Structure

Rayleigh wave electromagnetic acoustic transducer (EMAT) has the advantages of non-contact and long inspection distance. It is suitable for automatic testing and can be used on rough surfaces and at elevated temperatures. The conventional Rayleigh wave EMAT using a permanent magnet has the problem of demagnetization above 300°C. So that, a double coil structure Rayleigh wave EMAT is proposed in this paper to allow continuous operation above 300°C. The newly EMAT comprises an electromagnet coil and an eddy current coil. The kA-level milliseconds-duration current passes through the electromagnet coil to provide a quasistatic bias magnetic field for the EMAT transducing process. The inspections using the proposed EMAT have been successfully performed at 400°C.