System and method for nondestructive detection of structural irregularities using a directional magnetostrictive phased array sensor with a comb-shaped magnetostrictive patch

A system for structural health monitoring, using a directional magnetostrictive phased array sensor (MPAS), comprising:

• an annularly-contoured comb-shaped patch member, formed of a magnetostrictive material and configured with a first plurality of comb finger members extending radially along the periphery of said patch member;
• a magnetic circuit unit removably attached to said patch member along a central axis thereof and angularly displaceable relative thereto about a rotational axis of said magnetic circuit unit, said rotational axis of said magnetic circuit unit coinciding with said central axis of said patch member,
• wherein said magnetic circuit unit is configured with a second plurality of sensing coils extending radially along a respective longitudinal axis thereof in a spaced apart angular relationship one with another in said magnetic circuit unit, each of said second plurality of sensing coils having a sensing direction coinciding with said longitudinal axis thereof, and
• at least a pair of biasing cylindrically-shaped magnets installed in said magnetic circuit unit along said rotational axis thereof, said biasing magnets generating a static biasing magnetic field in said patch member;
• a source of ultrasonic excitation;
• and
• a signal data acquisition sub-system operatively coupled to said magnetic circuit unit to obtain signals generated thereat;
• wherein, for the structural health monitoring, said comb-shaped patch member is attached to a structure under study with said sensing coils controllably positioned in at least two predetermined angularly spaced apart sensing directions, and
• wherein said source of ultrasonic excitation is operatively coupled to the structure under study to generate guided Lamb waves (GLWs) propagating in said structure under study, said GLWs causing a deformation in said patch member attached thereto, resulting in generation of a respective strain-induced dynamic magnetic field in said patch member at each of said at least two predetermined sensing directions, and coupling of said generated dynamic magnetic field to said sensing coils;
• and
• wherein said signal data acquisition sub-system measures said strain-induced dynamic magnetic field generated at each of said at least two predetermined directions as an output on respective ones of said sensing coils, and indicates the presence of an irregularity in the structure under study if a change of the dynamic magnetic field between said at least two sensing directions is detected.

A method for structural health monitoring using a magnetostrictive phased array sensor (MPAS), comprising the steps of:

• (a) establishing a MPAS configured with a circular comb-shaped patch member manufactured from a magnetostrictive material and formed with a first plurality of comb fingers extending radially along the periphery of said patch member, and
• a magnetic circuit unit attached to said patch member along a central axis thereof and rotationally displaceable relative thereto about a rotational axis of said magnetic circuit unit, said rotational axis of said magnetic circuit unit coinciding with said central axis of said patch member,
• wherein said magnetic circuit unit is configured with a second plurality of sensing coils extending radially in said magnetic circuit unit in a predetermined spaced apart angular relationship one with another, each of said second plurality of sensing coils having a sensing direction coinciding with the longitudinal axis thereof, and
• at least a pair of biasing cylindrically shaped magnets installed in said magnetic circuit unit along said rotational axis thereof, said biasing magnets generating a static biasing magnetic field induced in said sensing coils;
• (b) coupling a source of ultrasonic excitation to a structure under study;
• (c) attaching said comb-shaped patch member of said MPAS to the structure under study;
• (d) operatively coupling a signal data acquisition sub-system to said magnetic circuit unit;
• (e) subsequently positioning said magnetic circuit unit in at least first and second measuring directions with said sensing direction of a respective sensing coil in each of said at least first and second measuring directions being angularly displaced one from another;
• (f) activating said source of ultrasonic excitation to generate guided Lamb waves (GLWs) propagating in the structure under study, thus causing a deformation in said patch member attached thereto and generating a respective strain-induced dynamic magnetic field on said patch member coupled to said respective sensing coil;
• (g) measuring, at each of said at least first and second measuring directions, said strain-induced dynamic magnetic field coupled to said respective sensing coil;
• and
• (h) indicating the presence of an irregularity in the structure under study if a change of the dynamic magnetic field between said at least first and second measuring directions has been detected.