Electromagnetic Shielding Characteristics Research Articles

Estimation of electrical conductivity and electromagnetic shielding characteristics of graphite/epoxy laminates

Estimation of electrical conductivity and electromagnetic shielding characteristics of graphite/epoxy laminates

Estimation of Electrical Conductivity and Electromagnetic Shielding Characteristics of Graphite/Epoxy Laminates

The low electrical conductivity of advanced composites relative to metals presents the design engineer with potential problems when utilizing composites in the construction of primary aircraft components. This con ductivity is the key material property that governs the vulnerability of sensitive circuitry inside an aircraft when exposed to electromagnetic inter ference due to lightning, nuclear detonations or powerful transmitters. This paper presents experimentally verified analytical expression to esti mate the basic electrical conductivity and electromagnetic shielding charac teristics of bare and protected graphite/epoxy laminates. These expressions can be used to compare the electrical performance of various configura tions of graphite/epoxy laminates and candidate protective coatings that will improve the shielding characteristics.

Transfer impedance of braided coaxial cables under applied longitudinal torsion

The surface transfer impedance ZT of several braided coaxial cables was measured under applied longitudinal torsion to determine the electromagnetic shielding characteristics of the cables under such conditions. The results cover the frequency range 100 kHz to 150 MHz with torsion angles varying between 0°, +360° m−1 and −180°m−1. It was found that ZT increases with torsion angle and depending on the degree of optimisation in the braid, increases of up to 800% can occur at a torsion angle of 360° m−1. Further, when a cable is returned to its original position, after being subjected to torsion, the resulting value of ZT is higher than the original value.

Temperature Stress and Nuclear Radiation Effects on Electromagnetic Shielding

Military specifications, such as MIL-STD-810 and similar environmental specifications for airborne electronic equipments, delineate the extremes within which such equipment must function properly. Emphasis is usually on physical parameters such as vibration, shock, heat, cold, salt-spray, and corrosive atmospheres. Limits have usually been dictated by practical considerations of terrestrial, operational, and environmental conditions. Great strides have been taken toward lunar and interplanetary exploration, but the possible effects of known adverse environments upon the electromagnetic shielding effectiveness of electronic equipment enclosures are relatively unknown. Prior to conducting this study, opinions were solicited as to whether physical environments would affect the electromagnetic shielding characteristics of metal equipment enclosures. The consensus of educated guesses was that there would be no effect on electrical characteristics of the enclosures, provided of course that no physical damage accrued to the enclosures. The authors are not aware of any literature which purports to be a study or record of the effects of such environmental extremes upon the electromagnetic shielding effectiveness of electronic equipment enclosures. The effects of repeated temperature shock and of exposure to nuclear radiation on the shielding effectiveness S of enclosures fabricated from several common metals, incorporating several types of seam construction, are explored. This investigation results from a Boeing-sponsored companion study to work performed for the U. S. Army Electronics Command. It in no way purports to supply all the answers, but is presented in the hope that it may arouse sufficient interest so that unresolved questions will be thoroughly investigated.