CARBON NANOTUBE TECHNOLOGY MAY LEAD TO REVOLUTION IN CABLING
Handling of CNTs in the form of yarns and tapes means that manufacturing processes for building cables need refinement to optimize throughput and improve yields.
Revolution in Cabling
While carbon nanotube technology (CNT) has generated widespread interest for applications ranging from semiconductors to medical, one area that is a focus of research at TE Connectivity (TE) is high-performance electrical cables. TE has been actively developing CNT for wire and cable, including cooperative efforts with universities and industry leaders, and has prototype samples for evaluation. While there is still much progress to be made before CNT cables become main stream, we believe the technology is sufficiently advanced to meet specific niche applications such as satellites.
CNT cables are now being actively developed for MIL-STD-1553B and IEEE 1394 applications for aerospace and satellite applications—with a transition from prototypes to production happening in the next few years. Initial IEEE 1394 cables will use CNT shielding, while MIL -STD-1553B cables will likely be the first all-CNT construction.
CNT-based shields combine high shielding effectiveness with significant weight savings. A two-layer CNT tape offers roughly the same shielding as a copper braid at high frequencies—roughly 50 dB at 4 GHz—but weighs less than 2 percent of the braid it replaces.
The high resistivity of CNT shields, however, means poor shielding performance below 100 MHz and an inability to provide protection against lightning strikes. For the double-braided cables common in aerospace applications, replacing one of the braids with CNT allows the remaining braid to handle low-frequency noise and lightning, while the CNT shield handles the higher frequencies. Weight savings are 25 to 30 percent for hybrid shield constructions.
Ready for Prime Time?
As progress is made toward enabling the use of CNT materials in cables, two other issues deserve mention. The first is how to terminate CNT cables. CNT conductors are compatible with existing contacts and can be terminated with standard crimping techniques, albeit with modified crimp tool settings and dies. Testing of the mechanical strength of the crimps suggests that the CNT yarns fail before the crimp fails. Shields can be terminated to backshells with steel bands and other compression techniques. Tapes and yarns are also compatible with soldering,through the use of special alloys.
The second issue is moving from prototypes to production. CNT yarns, sheets, and tapes are available in commercial quantities, but challenges remain in volume production of long parts needed for cable. The production capabilities of CNT suppliers are rapidly increasing but the supply chain today typically has long lead times. Many applications today— such as semiconductors or composite enclosures—use CNTs measured in microns or millimeters. Cables represent a completely different scale from those applications, requiring tens of meters.
As TE works with commercial and university partners to improve the conductivity of macroscopic CNT arrangements, we have also manufactured miles of CNT, wire and cable for testing and evaluation.
TE has built a CNT pilot plant capabale of producting hundreds of miles of wires and cable per year. Handling of CNTs in the form of yarns and tapes means that manufacturing processes for building cables need refinement to optimize throughput and improve yields. TE has devloped the refinements and can supply many different wires and cables in long lengths.
With a PhD in materials science, Stefanie Harvey is a former Principal Scientist for TE Connectivity, Global Aerospace, Defense & Marine. She has expertise in nanotechnology, surface science, material interfaces and thin film processing. Stefanie has more than 17 years’ experience in high tech solutions, including semiconductor processing, biotechnology and defense. Stefanie has also been an adjunct professor at San Jose State University in the department of biomedical, chemical, and materials engineering since 1999. Stefanie left TE in 2015 to pursue other opportunities.