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The Future of Electrical Conductors and Shields for Aerospace Applications Introduction

Electrical conductors and the shields used to protect them from electromagnetic interference (EMI) have not changed fundamentally since their inception. Advanced materials, improved connectors and other changes to electrical conductors and shields have brought incremental technology advances to platforms that are subjected to increasing design challenges demanded by vehicle operators from a variety of industries. But there have been no revolutionary advances in the way that power and signal are transmitted within aerospace vehicles, with the exception of fiber-optic connections. Even “fly-by-wire” technology, while replacing mechanical linkages, use traditional conductors; and wireless applications are, and will remain, non-starters for most applications in aerospace interconnections due to unacceptable risks in this environment.

The Challenges for the Future of Aerospace Wires & Shields

As aerospace vehicles have evolved from relatively simple airframes and engines into highly complex integrated systems, the demands placed on their electrical components have begun to outpace what traditional conductors and shields can handle. These demands now include: •	High fatigue resistance due to longer vehicle life demands and harsher use in more extreme and often-changing environments

•	Better diagnostic and prognostic systems to detect and isolate faults in live wires to allow repair or replacement before they become life or mission critical to the vehicle

•	Improved interconnect systems that can withstand the rigors of removal and replacement cycles required by mission modularization and diagnostic checks (ruggedization)

•	Enhanced shielding as EMI has grown substantially due to external and vehicle-organic sources

•	Lighter weight cabling and shields to enable greater payload and range while ensuring complementary designs that maintain or enhance structural integrity with lighter weight airframe and supporting structures

•	Integrated designs that make electrical interconnect assemblies much more ergonomic and less obtrusive for the requirements of increased and inter-changeable payloads, and efficiencies in maintenance

Building the Future of Electrical Interconnect Systems

Taken together, all of the challenges mentioned herein represent a sizable technical hurdle for those tasked with engineering future aerospace vehicles and improving the “guts” of legacy systems. Electrical interconnect systems can no longer be the last design consideration, with traditional assumptions about their capabilities and limitations. They must instead be part of the overall systems engineering design from the very beginning, and industry standards must be raised across the board to meet the demands. And, these new demands require that conductors and shields move well past traditional materials such as copper and aluminum, and standard polymers for jacketing that are heavy, costly, and prone to fatigue; and beyond fault detection systems that are external to the system rather than integral to it.

There is R&D work being performed in the industry to transform what conductors and shields can and should be for air vehicles. The following is a list of capabilities that represent significantly changed products and processes for the interconnect industry, some of which are already being built into prototype systems for satellites, Unmanned Aerial Vehicles (UAVs) and manned aircraft. The revolutionary programs that are underway include: •	Prognostic Health Management (PHM) Wire: PHM wire uses two technologies that are vastly better for isolating faults “in-situ” (in live wires), including deep into and through multiple connection points:  Smart Connector, which uses Spread Spectrum Time Domain Reflectometry (SSTDR); and carbon nanotube (CNT) layering that can act as a sacrificial boundary for fault detection. The CNT process was developed with a scalable “green” process using CO2 called Rapid Expansion of Supercritical Suspension (RESS). Taken together, these methods represent not only extremely accurate fault detection for critical systems, but also the ability to predict faults before they occur (“prognostication”).

•	Fatigue Resistant Wire (FRW): FRW uses advanced materials and proprietary construction (and incorporation of CNT for PHM, described above) to produce wire that lasts far longer than normal conductors and shields. This work requires fluoro-polymer extrusion of FRW conductors, and wrap and sintering processes to perfect its shielding.

•	Non-Metallic Cables and Shields: This program is producing CNT-based conductors and shields that are extremely lightweight for airborne applications (up to 65% lighter than traditional wires), radio-translucent, corrosion-resistant, and thermally stable in extreme environments. Included with this effort are proprietary processes for extrusion and termination of CNT materials.

•	Embedded Wire: Advanced airborne vehicle designs demand radically improved interior designs, particularly to ensure more open space for added payload and onboard systems. This program is exploring novel ways to make wire and cable harness assemblies more conformal, “neat” and even completely hidden within composite structures, while ensuring improved electrical interconnection and signal integrity.

•	StretchyWire: ™ Originally developed for the U.S. Army’s Future Force Warrior Soldier vest system, StretchyWire ™ and its commercialized product iStretch ™ has been developed to make conductors elastomeric, allowing up to 100% stretch and return to original length with no loss in signal integrity and conductivity. The wire can be applied wherever there is a requirement to remove stress from interconnects due to movement of the overall system. Examples include communications headset assemblies and earphones, wired apparel such as body-metric monitoring ensembles, and medical lead wires.