Development of Prototype Light-weight, Carbon Nanotube Based, Broad Band Electromagnetic Shielded Coaxial Cables

Modern spacecraft and aircraft are subjected to broad spectrum electromagnetic interference (EMI). A component of these aerospace vehicles that is susceptible to EMI are coaxial cables. Coaxial cables are shielded from EMI by integrating metallic shielding into the cable designs. This shielding can add significant weight to aerospace systems. Weight is a critical design parameter in aerospace systems. To minimize the weight of the shielded cables carbon based shielding material was incorporated into prototype RG-316 coaxial cables. Carbon nanotube (CNT) paper from Nanocomp Technologies and a carbon nanotube material from NanoSperse LLC were evaluated. Mechanical requirements and winding trial results led to the down selection of the Nanocomp material for incorporation into the prototype cables. The prototypes were evaluated for representative EMI environment in a mode stir chamber and bulk current injection to evaluate shielding effectiveness from 100 kHz to 18 GHz. The cables were fatigued using a custom test protocol that applied a tensileload and bending over a radius to approximately 80% of the ultimate tensile strength. This produced damage that resulted in degraded EMI shielding in the cables. The results indicate that the use of multilayered carbon nanotube shielding provided sufficient shielding from 300 MHz to 18 GHz. The weight of single and double wrapped CNT cables were reduced 51% and 47%, respectively, compared to a double layered copper shielded cable. One of the key outcomes was that the CNT shielded cables suffered little or no degradation in shielding effectiveness when mechanically fatigued, which was in stark contrast to metal shielded cables in most cases. The prototypes cables proved to have a technical readiness level (TRL) of 4 having been demonstrated in a representative environment. The prototype cables were successful but had two deficiencies: the EMI shielding effectiveness was insufficient at low frequencies (\u3c300 MHz), and the manufacturing process for the connectors caused problems with the insertion loss and voltage standing wave ratio properties. Specifically, the resistance between the shield and the connector was three orders of magnitude higher than the metallic shield counterparts. The obvious cause of this resistance increase was related to a silver loaded epoxy used to bond the CNT shield to the connector. Increased performance below 300 MHz can be mitigated by further research into incorporating using magnetic lossy particles or more conductive particles into the CNT paper. The latter issue can be mitigated withan improved manufacturing process and further research on connector design