Shielding Aerospace Systems from Electromagnetic Interference
For decades, electromagnetic interference (EMI) shielding has been a consideration and concern to the aerospace and defense industries. But, with the airwaves becoming ever more crowded as devices get smarter and more prolific, EMI has also become a greater consideration for everyone from consumer products manufacturers to the burgeoning U.S. Space Force. Ensuring that on-demand signals are not interfered with or corrupted has made the need for materials that shield EMI more important than ever.
EMI, which is caused by one electronic device sending radio frequency or electromagnetic waves intentionally or unintentionally to another device, can disrupt electronic devices, equipment, and systems used in critical medical, military, aerospace, mass transit, vehicular control, and navigation systems. Shielding blocks electromagnetic fields with conductive barriers to ensure reliable system performance.
The most common reference point for the threat EMI poses would be travelers not being able to use cell phones on airplanes. Initially, phones were prohibited based on the potential threat of interfering with and compromising cockpit systems. Phones now operate at higher frequencies that suggest they will no longer interfere with critical aircraft systems, but the understanding that they can has kept the shielding of electronics systems from external threats a paramount concern.
Additionally, disparate internal systems can create interference, making the threat literally come from within. Take today’s smart home – from wireless speakers and programmable thermostats to security cameras, homes today have multiple systems that emit electromagnetic waves capable of interrupting each other’s signals. In fact, some industry research predicts the average North American home could have as many as 13 smart devices by this year.
EMI occurs two ways, either by being conducted or radiated. Conducted EMI comes through wiring or cables and will emit electromagnetic signatures that could interfere with something else, or may be susceptible to nearby signals. The second kind of EMI, radiated, will travel through air. This can be anything from a GPS device, a wireless medical device, or even an old television set. Many will remember when in early 2020, a village in Wales lost broadband every morning for 18 months. After repeated efforts to identify the cause, network professionals deduced the issue was single high-level impulse noise (SHINE), or a device emitting enough electrical interference to interfere with the broadband. Combing the town with a spectrum analyzer, they finally identified a second-hand television as the culprit.
The reality of crowded electronic content goes far beyond the comforts of home. On one hand, it is inconvenient. With us relying so heavily on on-demand news, video, directions, and communication, disruptions can feel frustrating and debilitating. But in some areas, the threats of EMI can be fatal. Take defense systems where even the slightest interference in a targeting or radar system can cause major deviations from the acceptable margin of error. If you’re trying to hit a target to within a meter, being off by 10 meters because your signal was interrupted can cause much more collateral damage.
Electromagnetic pulses (EMPs) are more intense bursts of electromagnetic energy that can damage electronics. While they can occur naturally in something like a lightning storm, EMPs can also be manmade to create radiated, electric or magnetic fields. In military applications, they can take the form of either Nuclear Electromagnetic Pulses (NEPs) or Non-nuclear Electromagnetic Pulses like Boeing’s Counter-electronics High Power Microwave Advanced Missile Project (CHAMP). The CHAMP is a directed-energy weapon that can intentionally damage electronic systems, or take out signals in an area. Since the technology is relatively simple, it is not limited to only highly developed countries and organizations like nuclear power, therefore broadening its potential threat in potentially affecting aerospace systems.
EMI shielding is such a valuable characteristic, that we were pleasantly surprised when we recently discovered EMI shielding characteristics for our flagship material HX5™. While it is not an insulator or a good conductor with a surface resistivity of 37.9 Ohm/Sq. and a volume resistivity of 2923 Ohm-cm, testing found that the lightweight aviation grade thermoplastic nanocomposite had exceptional attenuation when bare or plated with various thicknesses of nickel and copper. A highly engineered material, HX5 had already demonstrated its strength and performance for use in complex components, but the results of EMI testing made it an even more attractive material for use in electronics.
Thermoplastics usually have minimal attenuation, but high attenuation means parts made with HX5 prevent varying radio and electronic frequencies from interfering with each other. The level of attenuation relates to the amount of carbon in the system, as well as how deeply it is embedded in the material. Additionally, as a nanocomposite, the cross-linking nanofibers create a mesh that can inhibit transmission similar to a Faraday Cage, an enclosure used to block EM fields.
For radiated interference in aerospace, HX5 is ideal for electronic device enclosures to ensure they do not damage other systems. Traditional material choices have been aluminum or copper, which are used to plate, coat, or even paint other part materials that on their own would allow interference. These parts are often then coated with nickel to prevent corrosion. Cabling, which is at risk for conducted interference, is made with more flexible materials like a copper or stainless steel mesh over the outside, and with a protective jacket or even an overmold.
Two independent labs tested both coated and bare HX5 to investigate the relationship between film thickness and attenuation for a range of frequencies from 10 kHz to 40 GHz using testing specifications IEEE 299-2006 and MIL-STD-285. Results showed that HX5 can be plated for EMI shielding at a range of 12 kHZ to 40 GHz, while also securing data for electrical surface and volume resistivity for bare and plated HX5, confirming both electroless plating for EMI shielding and shielding effectiveness. In fact, test results showed comparable and even higher attenuation levels for bare HX5 versus plated samples for certain frequencies from 12 GHz to 40 GHz.
Developed over more than a decade of testing and validation by the Department of Defense with an R&D investment in excess of $50 million, HX5 was engineered to replace machined aerospace-grade aluminum at half the weight. Last year it was shown in third-party testing to retain up to 96% of its original mechanical performance when subjected to 5 million rads of gamma radiation. It has also demonstrated extreme corrosion resistance to solvents, fuels, lubricants, and chemicals, giving it the ability to withstand the most demanding applications.
Currently in use on jet fighters, high-speed helicopters, unmanned aerial vehicles, amphibious transport vehicles, rockets, and satellites, HX5 is highly adaptable without sacrificing strength or performance. The EMI testing results expanded the realm of possibilities for HX5 parts. With a high strength-to-weight ratio, thermal stability, environmental resistance, and manufacturing flexibility, HX5 allows component manufacturers to make complex shapes with a specific strength (ratio of tensile strength divided by density) twice that of aluminum on a weight to weight basis.
This customization and superior manufacturability, combined with its high tolerance and dimensional stability, make it an ideal alternative to the cost and production challenges associated with aluminum. HX5 parts start in pelletized form, which can be injection molded, extruded, or thermal formed, the most common manufacturing processes for thermoplastic, but can also be machined like aluminum for secondary operations.
HX5 differs from other thermoplastics because it is also a nanocomposite featuring additives like carbon and nano fiber, giving it a high level of strength. Carbon fibers are usually about seven microns in diameter while nano fibers are about 1/100th of that size. The additives used in HX5 are specifically designed for our materials, so it is very dimensionally stable and repeatable. With B-basis engineering design databases, processing databases, and full-scale component testing, it is used to design and manufacture high performance, lightweight, custom-engineered components that can be coated, primed, painted, adhesively bonded, and metalized.
As the airwaves become ever more crowded, the pressure to shield devices from the damage caused by other sources of EMI as well as preventing it from causing said damage means that novel materials like HX5 will be utilized more. Their ability to offer effective EMI shielding will only complement their previously known benefits, like equal strength and superior designability at lighter weights, helping to shield devices from unseen natural and man-made threats.
This article was written by Roger Raley, President, Alpine Advanced Materials (Dallas, TX). For more information, visit here .