Electret Surface Potential Research Articles

Study of electrets stored at pressures lower than atmospheric

20 μm thick polypropylene electrets obtained in a corona discharge were studied. Before charging, the samples were cleaned in an ultrasonic bath with alcohol for 4 min, rinsed with distilled water and dried under room conditions. After charging, the electret surface potential was measured by the vibrating electrode method with compensation. The measurement system was located in a vacuum chamber, with a gauge to measure the pressure. The surface potential vs storage time relationships for electrets stored at various pressure (20, 50, 100, 150, 200 and 300 Torr) were measured. The dependence of the electret surface potential on the time of storage at room conditions, after the samples had been taken out of the vacuum chamber, and the second evacuated effect on the electret surface potential were also studied. A desorption from the electrets is suggested to explain the results obtained. The dependence of the surface potential on time is satisfactorily described by an equation that is analogous to the equation of desorption. The results also show that if the electrets are initially held at a pressure much lower than 200 Torr for a time, their subsequent time stability under room conditions increases.

A percolation theory analysis of surface potential decay related to corona chargedpolypropylene (PP) electrets

We have studied the behaviour of20 µm thick PP corona charging electrets, stored before and after they were charged, at variousconditions of controlled relative humidity. The electret surface potential was measured for250 days using a vibrating electrode with compensation. The time dependence of the surfacepotential was analysed by the percolation model for the 2D case. We have developedcomputer software for nonlinear programming. We have compared the experimental curvesto the theoretical ones. We calculated the basic parameters that determine clusterformation and growth to an unbounded cluster, leading to a fast neutralization of electretcharges.The percolation model allowed us to analyse electret surface discharge and to reveal thesignificant influence of the humidity level at which they have been stored. This is extremelyimportant and should be taken into account in the study of the stability of electret sensorsand devices that are used at room temperature and function under real conditions atvarious humidity levels.

On the charge decay in PP electrets stored at pressures lower than atmospheric

Polypropylene electrets 20-μm thick obtained in a corona discharge were studied. After the electrets were charged, they were put into a vacuum chamber at various pressures and the electret surface potential was measured over a 1-h period. A desorption from the electrets is suggested to explain the results obtained.

An electret passive environmental 222Rn monitor based on ionization measurement.

The electret passive environmental 222Rn monitor (E-PERM) is an extension of electret dosimeters used for measurement of x and gamma radiation. An E-PERM consists of a small cup or canister, having an electret at the bottom, and a filtered inlet at the top. The 222Rn gas entering through the filter and the decay products formed inside the cup generate ions which are collected by the electret. The reduction of charge (or surface potential) on the electret is a measure of time integrated 222Rn exposure. An E-PERM of 220-mL volume with an electret of 0.23 cm thickness gave a surface potential drop of 2.5 V for 37 Bq m-3 d (1 pCi L-1 d). The electret voltage was measured with a specially built surface potential voltmeter. This sensitivity was found adequate for a 1-wk measurement of 222Rn in homes. For longer term measurements, an E-PERM of 40-mL volume and an electret of 51-micron thickness was developed which gave a surface potential drop of 2.6 V for 37 Bq m-3 y (1 pCi L-1 y). Other combinations of chamber volume and electret thicknesses gave responses between these two values. The surface potential of electrets made from Teflon FEP were shown to stay stable even under extreme conditions of relative humidity. The ion collection process in E-PERMs was also shown to be independent of humidity down to an electret surface potential of 100 V.

Investigations of the thermally stimulated change of the surface potential of FEP electrets

Investigations of the thermally stimulated change of the surface potential of FEP electrets