A laser diagnostic for detecting internal electric field and mechanical strain in a resonant piezoelectric transformer

Piezoelectric transformers are simple devices that are used to produce high voltages for applications where portable high voltage, low current sources are required. Early evaluations of piezoelectric transformers (PTs) suggested that the very small resonance bandwidth required to achieve the desired extremely high voltage gain can be easily spoiled by resistive loading such as might occur if a resistive divider network were used to measure the output voltage. A diagnostic technique was developed that used a laser to probe the first-order electrooptic response of the resonant PT. Tests conducted with a resonantly driven PT indicated that the electrooptic response alone was insufficient to predict the measured behavior, and that a correct response could only be obtained if the elastooptic effects were considered as well. Results from the mathematical development are presented as well as experimental data collected on a resonantly driven PT. The experimental evidence indicates that as the internal electric fields climb within the PT, the response from a photodetector changes in a linearly correlated fashion.