Enhancement of directional sensitivity of magnetostrictive phased array sensor using a circular comb-shaped nickel patch

In this paper, we present a magnetostrictive phased array sensor (MPAS) with a polycrystalline nickel patch of a circular comb shape in order for the use of the ultrasonic guided Lamb wave inspection technique. The MPAS was comprised of two main components of the surface-mounted nickel patch and a mobile magnetic circuit device enclosing six sensing coils and center-positioned cylindrical biasing magnets. The magnetic circuit device detects the magnetic property change induced by the elastic wave propagation through the magnetostrictive nickel patch bonded to a thin aluminum plate. The individual sensing coils were configured to have directional preferences specified along the perpendicular direction of the coil winding, and they were arranged in a hexagon with a radius of 0.5” to form a compact-sized phased array sensor. Although the magnetic circuit device contains only six physical sensing coils, the MPAS enables to increase the total numbers of sensing positions by altering the orientation of the magnetic circuit device. The enhanced directional sensing capability of the presented MPAS was achieved as a result of the combined effect on the high magnetic shape anisotropy feature along the individual comb finger directions of the nickel patch and the directional sensitivity of the hexagon magnetic circuit device itself.