Simultaneous acquisition of data from multiple EMAT coils using coded sequences


While Electromagnetic acoustic transducers (EMATs) are very versatile they are also very inefficient and conventionally require high power excitation signals (about 1000W). The author and his co-workers have previously reported on the use of low power (<10W) coded sequences which can enable fast acquisition of ultrasonic signals from EMATs. The use of coded sequences further enables the simultaneous transmission and reception of signals from multiple transducers/EMAT coils. This is a powerful feature which becomes particularly useful when using orthogonally oriented coils in EMATs. The method enables the transmission of orthogonally polarized shear waves that interact very differently with crack like defects. In this paper simulation and experimental results are presented that show how notches can be detected by scanning a dual coil EMAT probe over the specimen.