EMI Shielding

By far the most developed and deployed cUAS strategy in today’s battlefield are those that focus around continuous or pulsed microwaves, these are referred to as “HPM’s”.

HPM’s use electromagnetic radiation to overwhelm or damage drone electronics, either by overloading components, causing shorts, or disrupting the drone’s guidance system.

Roark have invested significant resource in to developing a counter HPM stratgey and this is now incorporated in to all of our unmanned vehicles (air, ground and water).

The Roark HPM Strategy has 4 core components:

1. Pulse Entry– Pulse entry is the ability of unwanted EMS energy to penetrate the target and reach vulnerable electronics
2. Induction– is the ability of the energy to couple via front or back door channels into the system and produce a flow of energy that exceeds upset threshold.
3. Architecture effects– refer to the sum of the electronic components within the vehicle, andhow their specific combination affects performance when energy is induced by EMI

Pulse Entry

Defending against HPM pulse entry in UAS is a matter of design. Exterior shapes of our vehicles are built to mitigate or prevent pulse entry through seams or apertures. Negative index materials (NIM) are used as they have unique reflective and refractive properties, and are used to disperse energy that would otherwise enter through these apertures, while allowing areas of the EMS needed by sensors to pass through.

Methodology

Roark uses two build phase methods for hardening our vehicles against HPM entry. The first is to incorporate graphene in to our construction materials. The second involves wrapping either the fuselage or internal systems in separately-developed shielding material, specifically graphene infused composite braiding.

Science

EMI field attenuation (L) is measured in decibels (dB), and is ultimately expressed as a fraction (v) of original field strength. The relationship can be expressed as:

𝑣𝑣 = 10 − 𝐿𝐿 or inversely, L = 20 log10 (v).
20

For example, shielding that provides 20 dB of attenuation reduces EMI field strength to 0.1 times its original value, or a reduction of 90 percent. Assuming an initial field strength at the target of 15 kV/m, the widely accepted low-end damage threshold for electronics, a vehicle would need 38 dB of shielding to attenuate the field to an acceptable level of 200 V/m. At 25 kV/m, the point at which many robust electronics are damaged, the shielding requirement becomes 42 dB of attenuation.

Current military aircraft have an interpolated value of 40-50 dB may be assumed to be a general standard across such systems, due to many militaries requiring manned airborne systems be hardened against EMP resulting from nuclear detonations. Such pulses are capable of generating field strengths in excess of 50 kV/m, which would drive a minimum attenuation requirement of 48 dB.

Groups 4 and 5 UAS operating in the NAS and in combat environments may be assumed to have between 30 and 50 dB of shielding and it is this level of shielding that Roark aim to deliver for our Class 1-3 devices.

Detection & Propogation Halting

While exterior design and shielding materials can attenuate an HPM pulse, there will always be some energy that enters the system, either through apertures or from flight in very close proximity to the HPM source. Mitigating effects of EMI once they enter UAS electronics requires a robust architecture. Roark deliver this through a combination of detection and halting the propagation of unwanted energy.

Detection required the development of microwave pulse power detectors (MPPD). Roark use focused ion beam (FIB) manufactured Schottky diodes, as these diodes delivering a detection time of 100 nanoseconds in relation to microwave energy.

Propogation is delivered via electronic band gaps (EBG). The concept of EBG has been used in the manufacture of electronics to regulate energy within systems for years. Band gap engineering involves the intentional placement of EBG within systems to isolate or dissipate energy. Roark use a combination of embedding patterns of conductive, semi-conducting, or non-conductive material ot only in printed circuit boards, but also in connective internal chassis materials that hold components in place alongside optical switching which isolates components from nearby sources of coupled energy.