Development of DSP-based Electromechanical (E/M) Impedance Analyzer for Active Structural Health Monitoring

The electromechanical (E/M) impedance method is a powerful technique in active structural health monitoring (SHM). E/M impedance method utilizes as its main apparatus an impedance analyzer that reads the in-situ E/M impedance of piezoelectric wafer active sensors (PWAS) attached to the monitored structure. Present-day impedance analyzer equipments (e.g.HP4194) are bulky, heavy and expensive laboratory equipment that cannot be carried into the field for on-site structural health monitoring. This paper presented the development of a compact and low-cost impedance analyzer system. First, two types of impedance measurement approaches were evaluated in a PC-based simplified impedance analyzer system. It was found that the first approach, which measures impedance frequency by frequency, is very accurate but is not timeefficient and needs more efforts to be implemented. As for the second approach, which measures impedance using broad-band excitation and transfer function method, provides a good compromise among the measurement timeefficient, accuracy and implementation efforts. Experimental results show that this approach can be used for E/M impedance method for structural health monitoring. Second, to eliminate the PC in the measurement system, a DSPbased impedance analyzer system is proposed for further miniaturization. The system hardware configuration and design, software state flow for impedance measurement, and preliminary testing were presented in details. Keyword: piezoelectric wafer active sensors, structural health monitoring, DSP, impedance analyzer, impedance measurement, PWAS