Guided wave transduction experiment using a circular magnetostrictive patch and a figure-of-eight coil in nonferromagnetic plates

When an alternating magnetic field by a figure-of-eight coil is applied to a circular magnetostrictive patch bonded to a plate, ultrasonic guided waves can be effectively generated and measured. Wave experiments with two transducers consisting of the coil and the patch show that the magnitude and type of the measured waves depend on the magnetic field directions of the wave transmitting and receiving coils; a first-order theory was derived to explain the direction-dependent phenomena. The relation between the patch size and the frequency of the maximum signal output was also investigated.