Electrical- Mechanical Impedance (EMI) Method

Chung has observed that electrical impedance of the PZT bonded onto a structure is directly related to the mechanical impedance of the host structure. The variation in the PZT electrical impedance over a range of frequencies is analogous to Frequency Response Function (FRF) of a structure, which contains vital information regarding the health of the structure. Damage to a structure causes direct changes in the structural stiffness and /or damping and alters the local dynamic characteristics. In other words, the mechanical impedance is modified by damages to the structure. Since, all other properties of PZT remain invariable; it is the structural impedance that uniquely determines the overall admittance. Hence, any change in electrical impedance is an indicator of modification in the structural integrity.