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

39 high surface area-to-volume ratio, so nearly every atom interacts with its environment. That allows a highly sensitive sensor to be produced in a thin layer, which can provide far more detail for engineers about the operating environment and highlight problems before they become critical, allowing preventive maintenance. Strain gauges can even be included in the layers of a composite material, for example the spar of a UAV or the suspension of a driverless vehicle. The advantage with printing is that it includes the signal lines from the sensor, connecting to an exterior antenna printed using a variant of the material. The antenna is passive, meaning it can receive a signal from an RFID reader to take a measurement from the sensor, eliminating the need for a battery or RF front end. The RFID reader can operate at distances of several metres, allowing the sensor to be monitored at the end of a mission to determine the condition of the component or even during a mission via an onboard RFID reader. The painting approach also means it will work with foam-based or elastomeric structures that are also lightweight but difficult to monitor. Monitoring composite materials The graphene material has been used to make a wireless, remotely readable strain and temperature sensor to monitor stresses in the manufacturing and transport of composite structures. That reduces the need for destructive testing of the quality of a composite, reducing costs and waste throughout the manufacturing process. The strain sensor in the composite material can also potentially be linked to an external antenna to provide data in operation. EMI shielding EMI can interfere with sensors with low output signals, such as strain gauges and temperature sensors, with an output of millivolts. This interference reduces the signal-to-noise ratio and can have a major impact on measurement performance. This is often compensated for with electronic filters and digital signal processing, but that adds weight and power consumption. Instead, using a coating 33 microns thick reduces the interference by up to 50 dB across a frequency range from 300 MHz to tens of gigahertz. As the material weighs 2 g/cm 3 , the layer weighs 66 g/m 2 . It has a conductivity of more than 500,000 S/m, approaching that of copper- or silver-based coatings. A comparable aluminium shielding enclosure would have to be 100 microns thick, and would weigh 270 g/m 2 . Frequency window Graphene platelets also act as a meta- surface, an artificially crafted structure that derives its properties from an internal microstructure rather than its chemical composition. This meta-surface uses the geometry of the microstructure and the printing process to tune the RF properties to be active in only certain windows of the spectrum. This provides the ability to print antenna structures where all the background radiation is absorbed, but there is a filter for a 30 or 40 MHz window for example. This can be used to block harmonics from other electrical systems as well as stray 5G or 4G signals, but still provide access for the RFID signals. The filtering can even change during operation. For instance, a system could use a coating that modifies its transmission of RF energy as a Performance monitoring | Focus Printing sensors allows signal lines from them to be included, and they will work with lightweight structures that are difficult to monitor Uncrewed Systems Technology | August/September 2022 Linking to an embedded sensor via RFID (Courtesy of Advanced Material Development)