Chirp-based piezo-impedance measurement

Abstract

Electro-mechanical impedance and its variations, measured with piezo-sensors as a function of frequency, indicate the conditions and changes in the structures of materials and can be used for structural health monitoring. Available impedance measurement solutions have very limited features and performance or are bulky and costly and not supporting real-time monitoring of the dynamics of impedance spectra. Efficient (by various aspects) solutions using the chirp excitation signal have been described and investigated. Sine-wave chirp excitation signal together with corresponding sine and cosine reference waves have been used for calculation of the correlation in the relatively small sliding window. It enables to find real and imaginary parts of the transfer coefficient of the electrical network, including impedance of the piezo-sensor under test. From the hardware viewpoint two solutions have been proposed and tested ' one with using of the commercial connected-by-USB to PC data acquisition unit and the second with the DSP (TMS320F28335) based solution. For both cases the special analogue interface has been developed for driving the sensor-circuit with up to 60 V peak-to-peak voltage. The proposed solutions have been tested successfully. Various application fields of the proposed impedance measurement solutions are considered ' e.g. integrity-check of the piezo-sensor itself and the delamination test of the composite material.