Issue 45 | Uncrewed Systems Technology Aug/Sept 2022 Tidewie USV Tupan | Performance monitoring | Bayonet 350 | UAVs insight | Xponential 2022 | ULPower UL350i and UL350iHPS | Elroy Air Chaparral | Gimbals | Clogworks Dark Matter

40 Focus | Performance monitoring function of mechanical deformation or stress. So, if a component stretches by say 5 or 10%, the transmission in a specific window can change by 80%. This would provide an emergency signal on a different frequency to highlight a problem. As a built-in component measuring structural health, the coating can transmit as it deforms, measuring localised stress and communicating the mechanical integrity of the part to other systems. That could provide real- time measurement of health in a tiny window unaffected by all the other RF components on the platform. Testing performance The graphene platelet material has demonstrated a shielding performance of about 50 dB, and shown to provide shielding at higher frequency applications for the same amount of shielding from 10 to 80-plus GHz. In contrast, silver coatings shield EMI in the low gigahertz window with an attenuation of the order of 35- 60 dB depending on the thickness of the spray coating, which can be hundreds of microns. The next generation of graphene coatings will potentially be able to give as much as 90 dB attenuation from a layer of around 20 microns. The graphene material can be sprayed directly onto complicated, corrugated, non-planar structures, and works extremely well across a range of temperature windows for high-performance cars, for example. It can also be applied as a coating or a laminate with an adhesive layer on the back to put down as tape on a UAV. Battery monitoring The material is well-suited for monitoring the performance of battery packs. Strain gauges can provide data on the swelling of cells with silicon anodes during charging, while temperature sensors can provide key data to control fast charging, preventing thermal runaway in lithium-ion cells. Current monitors can also provide key data on the performance of the cells, and using printed antennas to connect up all these sensors avoids the weight of a wireless battery management system. The next generation of materials will combine carbon graphene with silicone for even more efficient monitoring, and will have a heat conductivity of up to 25 W/m.K. These can be deployed directly against cells for heat transfer when aluminium enclosures are replaced with composite materials, as well as providing EMI shielding. Fuel level sensors Every gasoline-powered UAV has to measure how much fuel it has, and the more accurately that is measured the further the UAV can fly. The latest solid-state capacitive level sensors are adding additional processing to output not only the fuel level but also various temperatures, such as the tank temperature or the fuel temperature directly from the bottom of the tank. With more processing, a key requirement is the ability to pass stringent EMC tests. Many level sensors are tested to industrial standards, but military- spec testing to Mil-Std 461F and RTCA DO160F Section 25 can be 10 to 15 times more aggressive than industrial tests. These test against conducted susceptibility as well as testing for EMI that might occur through the cable and power leads. They also test the protection against radiated emissions and voltage spikes as well as electrostatic discharges, which can disable the electronics in the sensor. These tests ensure that the level sensor with its integrated electronics will remain reliable in harsh EMI environments. August/September 2022 | Uncrewed Systems Technology Capacitive fuel sensors for UAVs are tested to stringent EMI standards (Courtesy of Reventec) Graphene platelets have demonstrated a shielding performance of about 50 dB; silver coatings have an attenuation of the order of 35-60 dB