The paper cites certain results of an earlier paper 2 by the present writer in which are traced the consequences of the assumption that an electret is characterized by a state of polarization, semi-permanent in the sense that it decays very slowly with the time. The decay takes place under the influence of an ohmic conductivity.
The behavior of the dielectric in the case of an exponential decay is determined by the initial polarization Po, which may vary across the electret, the initial potential difference V0 between the surfaces of the electret, the coefficient, ~, in the exponential decay, and the quantity RC representing the product of the resistance and capacity associated with the electret.
In the present paper it is demonstrated that, in the case of an electret which shows a maximum in the curve representing potential difference between surfaces plotted against time, all of the foregoing quantities may be obtained from measurements of the initial potential difference, the maximum potential difference, the time for the potential difference to fall to zero, and the time for it to attain its maximum. The theory of the matter is extended to the case where the semi-permanent polarization is represented by a finite or infinite number of contributions, each having its own particular relaxation time.
The paper discusses the question of what determines the initial potential difference after the electret is removed from its forming plates. It is shown that a reasonable understanding of the facts can be obtained qualitatively and quantitatively by assuming that on separating the plates slightly from the surfaces of the electret the charge densities retained by the plates are limited by the condition that the resulting field in the air space is less than the breakdown field in air, at the moment of separation.