Robust Damage Metric in Terms of Magnitude and Phase for Impedance-based Structural Health Monitoring

Structural health monitoring has been a research interest for its great potential for life safety and economic benefits for decades. Structural vibration impedance by way of piezoceramic patch excitation and sensoring offers a local damage detection technique and has caused a wide research interest. The commonly used damage index in this method is the rate of change of the real part of the measured electromechanical impedance. This paper studied several damage indices constructed by the real and imaginary parts or magnitude and phase. It theoretically deducted and concluded that the damage index in terms of changes in real part is in fact not a properly defined index and is physically obscure; on the other hand, indices in terms of the change in magnitude and phase were shown to be physically clear and properly defined. It further verified that a new damage index in terms of the whole complex-valued impedance turned out to be the elegant combination of the magnitude and phase damage indices in the form of their Euclidean norm. Experimental result further demonstrated that the damage index in terms of real part was largely influenced by the phase, whereas the whole complex impedance offered an optimized and robust damage metric.