This paper investigates a study of the use of a Fe-Ga alloy (Galfenol) flake-epoxy composite patch with a circular comb shape for Magnetostrictive Phased Array Sensors (MPAS) used for Structural Health Monitoring (SHM) applications based on the ultrasonic Guided Wave (GW) inspection technique. Galfenol materials have demonstrated a variety of beneficial properties for transducer developments such as high magneto-mechanical coupling, low hysteresis loss, moderate magnetostriction and saturation magnetization, and steel-like manufacturability. However, typical Galfenol materials exhibit anisotropic magnetostrictive characteristics that are disadvantageous for a wide range of applications to the GW SHM, especially phased array technology. To overcome the limitation of the Galfenol materials for the service of the GW phased array approach, we developed the Galfenol composite patch based on the circular comb pattern to improve the directional GW sensing performance using the shape anisotropic effect of the magnetostrictive material. The GW MPAS used in this work consists of a magnetostrictive composite patch directly bonded to a waveguide structure and a non-contact and azimuthally rotatable Hexagonal Magnetic Circuit Device (HMCD) including a biasing magnet and six sensing coils with predetermined directional sensing preferences. Although the GW signals obtained from the MPAS using the Galfenol composite patch were weak, the experimental results validated that the proposed MPAS was capable of detecting GWs using the flake-epoxy composite material and exhibited the obvious directional sensing characteristics. There are only six sensing coils in the HMCD, but the MPAS can acquire additional GW signal data in the Galfenol composite patch by simply altering the rotational orientation of the HMCD, leading to effective array imaging results by suppressing unwanted shadow images induced by the side lobe effect of the directional wavenumber filtering method. (C) 2019 Author(s).
