High-Frequency Impedance Measurements for Microsecond State Detection

Abstract

This work investigates the use of the electromechanical impedance (EMI) method at high frequencies for application in state detection in highly dynamic systems; a key aspect of which is the excitation and measurement of PZT impedance at higher frequency bands than those typically used in structural health monitoring, in ranges greater than 1 MHz. The use of impedance analyzers, which are typically used in EMI measurements, are not considered for this work due to their slow measurement speeds, large size, heavy weight, and high cost. Instead, an alternative impedance measurement approach from the literature will be leveraged. The alternative method, which allows impedance measurements to be made using standard data acquisition devices, was originally developed to present a low-cost solution to impedance measurement. The focus of this work, however, is the adaptation of the alternative measurement approach to allow accurate impedance measurements at frequency ranges in excess of 1 MHz. The accuracy of the alternative system’s impedance measurements will be verified by comparison with theoretical models. First, the impedance response of a simple RLC circuit with well understood dynamics will be experimentally tested and then the resulting measurements will be compared to analytical solutions of the circuit impedance to validate the measurement system. This alternative measurement system is then used to perform high frequency impedance measurements on a piezoelectric wafer embedded in a structure in order to detect structural damage. The long-term goal of this research is the deployment of an impedance measurement system using high-speed real-time hardware, such as field-programmable gate array technology which has significantly higher sampling rates and calculation speeds compared to traditional data acquisition systems, to enable microsecond state detection of structures operating in highly dynamic environments using the EMI method. Microsecond state detection has a number of potential applications, such as in aerospace technology, the mining industry, and civil architecture.