Magneto-elastic active sensors (MEAS) offer an alternative to piezoelectric wafer active sensors (PWAS) for
structural health monitoring (SHM) applications. In essence, a MEAS consists of a coil of wire carrying a timevarying
electrical current in the presence of a static magnetic field. The Lorentz-force mechanism facilitates
transduction without a mechanical bond between the sensor and the host structure, thereby circumventing some of the
shortcomings of PWAS. In this paper, the development of MEAS is briefly recounted and applications of MEAS to
SHM are presented. The miniaturization of MEAS for improved embeddability is also discussed. The ability of
MEAS to detect loose bolts by the pitch-catch method is presented. MEAS application for near-field and far-field
crack detection is also explored. Finally, the utilization of MEAS in Magneto-Mechanical Impedance (MMI) method
is discussed. The MMI technique provides a means of assessing the integrity of metallic structures through
measurement of structural dynamic response. Since structural damage affects mechanical properties, it modifies
structural dynamic characteristics reflected in MMI signature. The use of MMI to monitor fatigue damage in aluminum alloys is presented. Aluminum samples were subjected to cyclic loading in increments of 10,000 cycles until cracks appeared. The MMI responses show downward frequency shift of impedance peaks as samples deteriorate under fatigue loading, confirming the capability of MMI techniques to detect incipient fatigue damage. Thus, the applicability of MEAS to various SHM techniques is demonstrated, and the advantages and disadvantages of MEAS are explored.
One of the key issues in enabling fast and reliable deployment of space systems is structural qualification before launch.
The current qualification process is rather long and may span many months. It is envisioned that structural health
monitoring (SHM) could assist with verification of structural assembly during pre-launch procedures and enable
diagnosis of satellite components. The proposed satellite SHM system utilizes active sensors to launch and receive
elastic waves carrying elasticity information about the structural material. Sensor signatures are analyzed for variation of
the elastic behavior due to damage. Satellite structural components typically feature complex geometries involving isogrids
and bolted joints. Simple representations of complex structures are studied first, followed by investigation of elastic
wave propagation in a realistic satellite panel. The sensor network approach is utilized to detect and locate structural
damage. The acousto-elastic method is implemented for diagnosis of bolted joints in the satellite panel. Sensitivity of the
method is explored for various damage scenarios and a practical damage detection algorithm is suggested. It is shown
that the acousto-elastic method allows for assessment of the structural integrity of complex structural elements with
bolted joints.
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