Development of 'MONJU' reactor vessel ISI facilities. Investigation of SH wave EMAT with Halbach magnet configuration

In this paper, a horizontally polarized shear (SH) wave electromagnetic acoustic transducer (EMAT) with a Halbach magnet configuration is proposed and evaluated from numerical analyses and experiment measurements for the use of 'MONJU' fast breeder reactor vessel in service inspection. The SH wave EMAT with a Halbach magnet structure reveals a stronger magnetic flux density as well as ultrasound pressure than that of a SH wave EMAT with a periodic permanent magnet (PPM) structure. The above EMATs are used for inspection of artificial slits, and it was found that the Halbach magnetic structure has a better defect detectability than the PPM structure. In this work, the measured magnetic flux density and the ultrasound directivity distributions for both the Halbach and PPM structure SH wave EMATs are in excellent agreement with those expected from numerical simulations. The numerical analysis method should be useful in optimizing the magnet structure for SH wave EMAT. (author)