Original embedded impedance analyzer for piezoelectric sensors

In this paper we present the design, simulation and implementation of an embedded impedance analyzer primarily intended for use with piezoelectric transducers. It is currently set to perform complex impedance measurements above 1 Ω in the range 0–5 MHz. The method does not require the current to be measured and allows grounded transducers to be analyzed in real time. It is based on feedback control of the transducer voltage using a digital resistive network RG. Real and imaginary parts of the impedance are determined from RG and the phase during a fast frequency sweeping. The entire digital architecture is implemented in an Field Programmable Gate Array (FPGA) Stratix II board with a 100 MHz frequency clock. The system is developed in a virtual environment in which the transducer is modeled by a Butterworth van Dycke structure. The duration of the analysis is optimized in real time by adjusting the sweeping speed according to changes in RG. Further, our analyzer is tested in real time and in a real situation with two 2 MHz ultrasonic transducers. The duration of the analysis is equal to 2 ms and the measurements are accurate to within 1% within the resonant zone of the transducers.