Calculation and Analysis of Two Level Traps Model in Polymeric Materials

Space charge formation in polymeric materials can cause some serious concern for design engineers as the electric field may severely be distorted, leading to part of the material being overstressed, resulting in material degradation and possibly premature failure at the worst. It is therefore important to understand charge generation, trapping, and detrapping processes in the material. Trap depths and concentration of materials are important as they are potentially related to microstructure of the material. Changes in these parameters may reflect aging taken place in the material. In the present paper, characteristics of charge trapping and detrapping in low density polyethylene (LDPE) under dc electric field have been investigated using the pulsed electroacoustic (PEA) technique. A simple trapping and detrapping model based on two trapping levels has been used to qualitatively explain the observation. Numerical simulation based on the above model has been carried out to extract parameters related to the material. It has been found that trap depths and concentration of both shallow and deep traps show significant differences for the sample with different periods of electric field application. Besides, the trap energy levels of these shallow and deep traps are compared with the values in literature to evaluate the model. The results indicate that trap depths and concentration of both shallow and deep traps may be used as aging markers as changes in the material will certainly affect trapping characteristics (trap depth and concentration)

Modulation efficiency of LiNbO₃ waveguide electro-optic intensity modulator operating at high microwave frequency

The modulation efficiency, at high-frequency microwave modulation, of a LiNbO3 waveguide electro-optic modulator is shown to be degraded severely, especially when it is used as a frequency translator in a Brillouin-distributed fiber-sensing system. We derive an analytical expression for this attenuation regarding the phase-velocity mismatch and the impedance mismatch during the modulation process. Theoretical results are confirmed by experimental results based on a 15 Gb/s LiNbO3 optical intensity modulator