THEORY AND MEASUREMENT OF THE CAPTURE OF CHARGED DUST PARTICLES BY ELECTRETS

Investigations have been carried out on the capture of charged dust particles by electrets, with a view to implementing the process in a passive dust sampler that is simple and light weight and therefore likely to be acceptable to the wearer. The electret collects dust particles at a rate that is proportional to their electrical mobility but independent of the velocity of the ambient air outside its surface provided that a critical velocity is exceeded. It is necessary to surround the electret with a metal grid during use, both to control the electric field and to give protection. The results of a laboratory evaluation are presented, in which it is shown that the collection rate of the device is in broad agreement with theoretical predictions, except at very low air velocities, where allowance must be made for the effect of the grid on the velocity of the air past the electret surface.