Polarized polymer films as electronic pulse detectors of cosmic dust particles

A dust particle detector based on a new physical principle of detection is described. The basic detecting element requires no bias voltage and consists of a thin film of the polarized polymer polyvinylidene fluoride (PVDF) having conducting electrodes on each of its surfaces. A high velocity (～10 km/s range) dust particle entering the detector removes dipoles along its trajectory. This produces a local depolarization, which results in a fast (ns range) charge pulse signal in the external circuit which is detected using pulse electronics. A theory has been developed for this new mechanism of pulse detection. The dependence of signal amplitude on particle mass and velocity has been measured for several PVDF detectors having thickness in the range 2–28 μm and area in the range 4–150 cm² using iron particles with velocity in the range ～1–12 km/s and mass in the range ～ 10^?13–10^?10 g. In addition, measurements carried out using a two-detector arrangement show that time of flight information may be obtained. Experimental results are presented which show, for example, that PVDF detectors have mass detection thresholds in the range ～10^?14–10^?12 g, at an impact velocity of 10 km/s, which compare favorably with mass thresholds reported for current dust detectors based on other physical principles. PVDF detectors have the advantages of being inexpensively and easily fabricated, tough, flexible and radiation resistant (to at least 10⁷ rad). They exhibit long term stability, and may be operated for extended periods of time over the temperature range ?50°C to + 50°C. In addition, their fast response permits a detector-pulse electronics system to count dust impacts at event rates up to 10⁴ s^?1 with no corrections required, and they have a response to dust particle impacts which is unaffected by high background fluxes of charged particles. As an example of the application of PVDF dust detectors, a detector is described which is being carried on space probes to measure the mass and flux of dust particles from Halley's Comet in March 1986. Other important applications for experiments in space are discussed.