Research on butterfly coil EMAT sound field characteristics

As a main coil structure of an electromagnetic ultrasonic transducer (EMAT), the butterfly coil can excite transverse waves under the action of the vertical magnetic field, which is widely used in the thickness measurement of metal plates and the detection of internal buried defects. This paper discusses the directivity of the butterfly coil in the acoustic field to facilitate the design and application of the electromagnetic ultrasonic transducer and obtain the energy distribution state of the radiated acoustic field. The acoustic field directivity of butterfly coil EMAT is discussed in this paper. Firstly, the ultrasonic excitation principle of the butterfly coil EMAT is analyzed, and the radiated acoustic field of the butterfly coil is theoretically calculated by equating the main flap of the butterfly coil to a rectangular wave source. The experimental system of acoustic field directivity measurement was constructed to measure the directivity data of the radiated acoustic field of the ultrasonic shear wave. The acoustic field was analyzed for different working frequencies and different polarization directions of the relative semicircular specimen. The experimental data matched the theoretical calculations well, and this paper provides a reference basis for the engineering application of this transducer.