  We have compared measurements of a set of polyethylene terephthalate (PET)
electret samples by means of pulsed electroacoustic method (PEA) and thermally
stimulated depolarization current (TSDC) techniques. Experimental parameters
such as the combined thermal and electrical history and the electrode type have
been selected in order to correlate the polarization mechanisms revealed by
TSDC with the charge profile measured by PEA in five different cases. Existing
deconvolution procedures for PEA have been improved as a means to enhance the
calibration of PEA signals in the case of thin samples. Samples where the
$\alpha$ dipolar relaxation or the $\rho$ space charge relaxation is activated
show a uniform polarization that manifests itself as image charge at the
electrodes. In the experiments where external charge carriers are injected into
the sample, the same poling procedure has been tested under different electrode
configurations. Charge profiles are qualitatively similar in all of them but
the depolarization currents show clearly different behavior. These differences
are explained, on the one hand, by the different blocking behavior of
vacuum-deposited aluminum electrodes with regards to electrodes with a thin air
gap and, on the other hand, by the distinct behavior of electrodes with an air
gap for both directions of the charge carriers. Numerical analysis of the
polarization of TSDC peaks and charge per unit area of charge profiles supports
this interpretation and confirms the relationship between both measurement
techniques. All in all, PEA in combination with TSDC turns out to be a useful
technique in the study of thermally poled electrets, either in the study of
relaxations or of external charge.
