In this paper, the group velocities of electromagnetic wave for a one-dimensional coaxial photonic crystal in the stop bands with and without defect mode are studied. The results show that the group velocities exceed c (the speed of light in vac- uum) in the stop band and it tends to be very slow in the defect mode. The group velocities also are ob- tained using the method of the transmission line and transmission matrix. The simulating results agree well with the experimental.
Pressure wave propagation (PWP) method was utilized to observe the space charges packet-like behavior in sheet samples of low-density polyethylene (LDPE) under the relative low electric field. The experimental results show that space charge packets are always generated at the anode and move across the sample to the cathode regardless of the polarity of DC voltage. This paper discusses the migration of space charge packets at 30–40°C, the possible charge resource of space charge packets carriers and trap level of the space charge.
ZHENG Feihu 1 , ZHANG Yewen 1 , GONG Bin 1 , ZHU Jianwei 1 & WU Changshun 2 1. Pohl Institute of Solid State Physics, Tongji University, Shanghai 200092, China
