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

Abstract

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.

Semi-analytic formulation and its experimental verification to determine the radiation patterns of ultrasonic guided waves generated on a plate by a magnetostrictive patch transducer

“…The demand for an effective approximation formulation is apparent in these respects, and the effectiveness of such a formulation given simple magnetic circuit devices is well explained by Lee et al [16,17]. Fig.…”

“…The expanded formulation includes the effect of different wave traveling lengths to consider the fact that each coil generating the actuating magnetic fields is located in different areas, in contrast to the configuration presented in Lee et al's work [16,17]. The expanded formulation is applied only to cases wherein the shape of the actuating coils can be regarded as line sources, and the biasing field is constant over a patch.…”

“…A previous review [8] summarized the up-to-date accomplishments in the area of MPT coverage not only in plate structures but also in pipe and rod structures. For example, Lee et al [16,17] reported that if the biasing and actuating magnetic fields over a magnetostrictive patch are almost constant, an approximation formulation is sufficient to estimate the radiation patterns of ultrasonic guided waves, such as S0 waves (the first branch of the symmetric Lamb wave) and SH0 waves (the first non-dispersive branch of shear horizontal waves). Directional or omnidirectional ultrasonic waves are observed based on the distribution patterns of biasing and actuating magnetic fields [16][17][18][19][20].…”

“…Two magnetic fields constitute an angle , q which is adjustable by rotating the actuating coil with the fixed biasing magnets. Assuming that the two magnetic fields are constant through the nickel patch, the radiation patterns of the generated S0 and SH0 waves can be expressed by the following relations [16,17] …”

“…In many cases, this phenomenon is named the "Joule effect" after its founder, Joule [7]. Magnetostrictive material has been developed recently in the form of patch transducers, that is, Magnetostrictive patch transducers (MPT), and has been extensively studied as a tool for structural health monitoring, as with plates and shells [8][9][10][11][12][13][14][15][16][17][18][19][20]. A previous review [8] summarized the up-to-date accomplishments in the area of MPT coverage not only in plate structures but also in pipe and rod structures.…”