Modeling electroluminescence in insulating polymers under ac stress: effect of excitation waveform

Abstract

A charge transport model allowing the description of electroluminescence in polyethylene films under AC stress is proposed. The fluid model incorporates bi-polar charge injection/extraction, transport and recombination. The physics is based on hopping-mobility of electronic carriers between traps with an exponential distribution in which trap-filling controls the mobility. The computation mesh is very tight close to the electrodes-of the order of 0.4 nm allowing mapping the density of positive and negative carriers during sinusoidal, triangular and square 50 Hz voltage waveforms. Experiment and simulation fit nicely and the time-dependence of the electroluminescence intensity is accounted for by the charge behaviour. Light emission scales with the injection current. It is shown that space charge affects a layer of 10 nm away from the electrode where the mobility is increased as compared to the bulk mobility due to the high density of charge. The approach is very encouraging and opens the way to model space charge under timevarying voltages.

Fluorine gas treatment improves surface degradation inhibiting property of alumina-filled epoxy composite

“…5 The photon counting technique can detect the photo emission from surface layers under electric stresses and it is used to investigate the storage and transporting of trapped charges, as well as the structure transformation and molecular motion of polymers. 6,7 During trapping and recombining process, the energy released in form of luminescence is between 5 eV and 10 eV, which is higher than the bond dissociation energy (usually less than 5 eV) in most polymers.…”

The detection of the early stages of ageing in an LDPE+graphite composite by comparison of dielectric responses induced by sinusoidal and triangular signals

“…It should be noted that the methodology presented here may be used to also study other physical properties of polymers. For example, it has been shown that electroluminescence of polymers induced by AC electrical signals exhibits a time shift, depending on the waveform signal applied [13].…”

“…The application of the sine wave electrical test signal in the investigation of the dielectric properties of polymers is a standard procedure in polymer science [10][11][12]. The other waveforms of a test signal are rarely used in the analysis of the electrical properties of polymers [13,14], but they are used for the testing of energy transformers as well as for various electronic and mechanical tests [15][16][17][18]. It is well known that the dielectric relaxations in polymers occur over broad intervals of frequencies and/or temperatures, which sometimes makes difficult to precisely establish the dielectric parameters and the exact position of the processes (they are simply too broad to be noticed).…”

Modelling electroluminescence in insulating polymers under sinusoidal stress: Effect of applied voltage, frequency and offset

“…Physical model, equations and numerical resolution are described in [3] and only a brief description is given here. Two kinds of carriers are considered (trapped electrons, n e,t and trapped holes, n h,t ) that are provided by injection at the electrodes according to:…”

“…Less effort has been done on modelling EL on the basis of the charge exchange process. We have recently [3] proposed a model accounting for the EL phenomena by recombination of charge carriers in LDPE under AC stress (hot carrier effects are not taken into account). The model incorporates injection/extraction as well as transport and recombination of charges.…”