A structural impedance measurement method by using polyvinylidene fluoride as actuator and sensor

Polyvinylidene fluoride (PVDF) patches have extremely small Young's modulus and piezoelectric coefficients. They are usually chosen as sensors in the structural impedance measurement for health monitoring. In this paper, a novel method is demonstrated for structural impedance measurement using PVDF patches as actuators and sensors. The impedance of the host structure is decoupled from the capacitance impedance of the piezoelectric transducer by using one of the patches as the actuator and the other as the sensor. Phase sensitive detection is then adopted to recover weak impedance signals in the experimental studies. This technique enables measurement of the resonant frequencies and further identification of the health condition of the host structure. The superiority of this method is illustrated theoretically comparing to the conventional impedance-base method. A prototype consisting of a metal cantilever with two PVDF patches is fabricated and tested. Experimental results demonstrate the effectiveness of the proposed method in the detection of the resonance of the substrate precisely with respect to FEM simulation and the results under base-movement excitations. Moreover, mass change induced impedance shifting can be obtained.