10 April 2014 Lift-off effect compensation for magnetic impedance-based damage detection
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Magnetic transducers have been applied in impedance-based damage detection recently. Owing to the magneto-mechanical coupling characteristics between a magnetic transducer and the underneath metallic structure, a magnetic transducer can excite the host structure by means of the Lorenz force, and its electrical impedance is directly related to the host structure’s mechanical impedance. Therefore, the change of electrical impedance before and after damage occurrence can be used as damage indicator. Since there is no direct contact between the magnetic transducer and the host structure, it appears that the magnetic transducer has advantage in online health monitoring of many structures with complex geometries and boundaries. However, one key issue is that the coupling between the magnetic transducer and the host structure is strongly influenced by the lift-off distance (i.e. the distance from the transducer to the host structure) which changes as the structure is inevitably subject to oscillation/movement due to environment disturbance. In this research, we propose a new approach of transformed impedance that can explicitly take the lift-off distance change into consideration to facilitate efficient and robust decision making. This algorithm takes advantage of the lift-off distance embedded in the impedance measurement, and is capable of removing the lift-off variation without explicitly measuring the lift-off variation. Numerical simulations and experimental validations are carried out to demonstrate the effectiveness.
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Q. Shuai, Q. Shuai, J. Tang, J. Tang, } "Lift-off effect compensation for magnetic impedance-based damage detection", Proc. SPIE 9061, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2014, 90610S (10 April 2014); doi: 10.1117/12.2045128; https://doi.org/10.1117/12.2045128

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