Piezoelectric Charger CD V-751X Final Report

摘要

The design, development and fabrication of a radiological dosimeter charger, which uses piezoelectric ceramic crystals to generate the electrical energy and a lens system for external ambient light only, is described This charger, presently designated OCD Item No. CD V-751X, has been developed as a possible replacement for the transistorized charger, OCD Item No. CD V-750, at requires no batteries; therefore, it has long shelf life. The effects of static stress on the piezoelectric properties of different ceramic materials were studied and basic formulas derived. Studies showed that the charge generated by the application of force to the piezoelectric material was directly proportional to force and to the material constant but was not dependent on the size. The material "constants" varied with stress, however, particularly at high stress values, so the size and shape affects the charge output indirectly. In the final design, force was applied to the ceramic crystals' by a spring loaded screw arrangement. Two lead-zirconate-titanate ceramic crystals were arranged in tandem mechanically, but in parallel electrically. A swamping capacitor provided fine adjustment of the low range dosimeter; a neon lamp was used to protect the dosimeter against over-voltage. A special shorting switch was designed and incorporated to prevent reversal of polarity. An optical system in the charger transmitted light from an external source to illuminate the dosimeter scale and fiber The charger is capable of using either natural sunlight or concentrated sources of light such as room light fixtures, flashlights or candles. All performance and environmental test requirements were passed on the prototype chargers except that for humidity. Modifications to the prototypes are suggested which should correct this humidity problem.