Piezoelectric current from shunted and shorted guard-ring quartz gauges

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Abstract
Current from quartz disks in guard-ring configurations is widely used to sense stress pulse profiles resulting from impact or explosive loading. Normally, the guard ring is loaded with a low-impedance resistive shunt selected to maintain voltage balance between electrodes. A similar configuration in which the guard ring is electrically shorted to the ground electrode with a vapor-plated metallic conductor along the periphery of the disk has also been used to sense stress pulses. An experimental investigation of the current pulses produced when these shorted guard-ring quartz gauges are subjected to impact loading has been conducted to compare the responses of shorted and shunted guard-ring quartz gauges. Gauge configurations with guard-ring widths which vary from 0.5 to 3.0 times the thickness of the disk were investigated. It is found that, unlike the behavior of the shunted gauges, shorted gauges do not exhibit a universal response characteristic, i.e., each shorted gauge configuration has a different response to impact loading. Furthermore, the input stresses at which shock-induced conductivity affects the current pulses is found to be lower for shorted gauges than for the shunted gauges and to depend upon the specific shorted gauge configuration. The effects of the width of the insulating gap which separates the guard-ring electrode from the inner electrode are shown to be detectable. Physical mechanisms responsible for the observed differences between the shunted and shorted guard-ring gauges are identified.