These properties provide useful information about the insulators' performance and aging degree, which may help users to take necessary actions to prevent potential risks to the safety and stability of electric power systems.
Researchers and engineers are constantly developing novel techniques to accurately measure the electromagnetic properties of electrical insulators. This method is potentially useful for the design of 3DOW-GFRP with desired εr′ for applications such as electromagnetic shielding and electrostatic discharging structures. A comparison between the measured and calculated εr′ indicates that the proposed method is highly accurate with ≤ 2.68% maximum error, while the latter reaches 7.82% for the classic rule-of-mixture equations. As opposed to previously reported lumped circuit models, our model addresses the issue of orthogonality of fiber and considers the shape and spatial disposition of the composite with respect to the polarization direction of the THz waves for accurate determination of εr′. Simulation results are compared to those obtained from the classic rule-of-mixture equations to determine the representative equations for the three different cases of fiber orientations in the (x,y,z)-coordinate system and a new model is developed to calculate εr′ of 3DOW-GFRP composites based on electromagnetic modeling principles. The dielectric anisotropy is demonstrated through simulation by considering a single propagation direction of the THz waves and three different fiber orientations in unidirectional GFRP composites. And the cracks and voids on the surface and interior of the aged sample could provide channels for the EM wave to enter into the aged samples.Ī novel method to calculate the dielectric constant (εr′) of three-dimensional orthogonal woven glass fiber-reinforced polymer-matrix (3DOW-GFRP) composites in the terahertz (THz) frequency range is developed and experimentally verified using the THz time-domain spectroscopy (THz-TDS). The uneven surface of the aged sample could diffuse the incident EM wave. This is because of thermo-oxidative aging results in an uneven surface and numerous cracks and voids in the aged composite. The results indicate that the aged composite has better EM absorbing properties than the unaged one. In this paper, the 3D quasi-isotropic braided CF/GF bismaleimide composites were newly designed, and its EM absorbing properties were investigated under thermo-oxidative aging. However, the influence of thermo-oxidative aging on laws and mechanisms of EM absorbing properties of CF/GF-PMCs has not been reported. The electromagnetic (EM) absorbing properties are essential for the survival of the weapon systems.
The hybrid carbon/glass fibers reinforced polymer matrix composites (CF/GF-PMCs) used as structural materials of weapon systems often suffer high-temperature condition, leading performance degradation of them. From the experimental data, empirical relation between the dielectric properties of composites and test variable was suggested and verified. Complex relative permittivities of low-loss composite were measured with respect to the angle between the fiber orientation and the electric field vector of EM wave in X-band frequency range.
In the very early stage of the research on stealth techniques, many researches were mainly concentrated on the reduction of RCS and development of radar absorbing materials (RAM), but nowadays studies on investigating the radar absorbing structures (RAS) using fiber reinforced polymeric composite materials are becoming popular research field.In this study, electromagnetic characteristics of unidirectional E-glass fiber reinforced epoxy composites were tested with free space methods, which can overcome drawbacks of conventional cavity and waveguide methods.
By reducing the detectability of aircrafts or warships, of which the radar cross section (RCS) is a measure, they could evade radar detection, which affected not only the mission success rate but also survival of them in the hostile territory. The introduction of microwave radars during the second World War altered the air defense scenario significantly, and this led to the development of the “stealth” techniques.