Dielectric spectroscopy of fiber-reinforced epoxy materials

In this paper dielectric spectroscopy measurements on four different fiber-reinforced epoxy materials are presented. The results show that the dielectric constant and tan δ of glass, quartz, aramid (Kevlar) and poly-benzobisoxazole (Zylon) fiber-reinforced epoxy materials are in the range similar to the other commonly used insulating materials. Long-term thermal cycling from -40°C to 120°C during a period of 2500 hours has not affected the values of dielectric constant and tan δ. Surface treatment of fibers plays an important role in the values of dielectric constant and tan δ. With certain types of surface treatment unacceptable values of the dielectric constant (about 50) and tan δ (about 0.3) were obtained. The quality of fiber-reinforced materials was verified by optical and scanning electron microscopy. Neither voids nor delaminations were detected.