Electrical-mechanical impedance (EMI) method

In EMI technique, a PZT actuator/sensor patch is bonded to the surface of the structure whose health is monitored using high strength epoxy adhesive. The conductance signature of the patch is obtained over a high frequency range. This signature is the benchmark for assessing the health of a structure.

Figure 5.2: Interaction model of PZT patch and host structure

The signature of the bonded PZT patch is acquired using impedance analyzer. Electro-mechanical coupling between mechanical impedance Z of the host structure and electro-mechanical admittance Y is utilized in damage detection. Z is a function of the structural parameters such as stiffness, damping and the mass distribution. Any damage to the structure will lead to change in these structural parameters, hence, the mechanical impedance [Figure 5.2]. Cracks, debonding and damage in connections are the common causes that alter the structural impedance.