Study of sensitivity and repeatability of piezoelectric sensors

The sensitivity and repeatability of stress measurements obtained using commercially available piezoelectric probes have been studied for impact velocities ranging from $\sim $2 m s$^{-1}$ to $\sim $1600 m s$^{-1}$. The probes used were \textit{Dynasen} piezoelectric probes, in which the sensor element is a small ((0.4$\pm $0.05) mm thick, (1.2$\pm $0.1) mm diameter) PZT disc. The probe gives an output voltage $V(t)$ proportional to the time derivative of the force normal to the z-axis of the PZT. The stress level is obtained using the time-integrated voltage. The research presented focuses on the probe's suitability for a wide range of stress levels and pulse lengths. The pressures measured by the probe are compared directly with theoretically estimated or independently measured pressures for a range of impact velocities. The lowest velocity impact experiments were achieved using a Hopkinson Bar, intermediate velocities were performed using a SIJA (Single Impact Jet Apparatus), and highest velocity impact experiments were achieved using laser-driven aluminum flyers. The experiments found that whilst the probes' pressure measurements were often close to the estimated values, the probes demonstrated a gradual drop in sensitivity for higher velocity impacts.