Electrical- Mechanical Impedance (EMI) Method

Impedance based structural health monitoring techniques have been developed by utilizing the electro-mechanical coupling property of piezoelectric materials and form an important class of non-destructive evaluation (NDE) method. Since structural mechanical impedance measurements are difficult to obtain, impedance methods utilize the electrical impedance of the host structure, which is affected by the presence of structural damage. Through continuous monitoring of electrical impedance and comparing it with a base line measurement, one can qualitatively determine whether structural damage has occurred or is imminent. In order to ensure high sensitivity to incipient damage, the electrical impedance is measured at high frequencies (greater than 30 kHz). The basic concept of this approach is to monitor the variation in structural mechanical impedance caused by the presence of damage. At such high frequencies, the wavelength of the excitation is small and is sensitive enough to detect minor changes in the structural integrity. More importantly, high frequency signals require very low voltage (less than 1volt at microwatts) to produce a useful impedance excitation in the host structure. By integrating the impedance technique with self-sensing smart materials, it has been demonstrated that the impedance based method is suitable for use in a wide variety of structural health monitoring applications.

In the following slides a brief outline of obtaining the mechanical impedance of composite laminate using the already developed HPFE will be presented.