Issue 37 Unmanned Systems Technology April/May 2021 Einride next-gen Pod l Battery technology l Dive Technologies AUV-Kit l UGVs insight l Vanguard EFI/ETC vee twins l Icarus Swarms l Transponders l Sonobot 5 l IDEX 2021 report

10 Platform one Researchers at Imperial College, London, have developed a low-power design for wirelessly charging sensors by UAVs (writes Nick Flaherty). The UAVs can fly to a sensor board, recharge it and collect the data from the sensor. The design uses ultra-wideband (UWB) wireless technology to achieve accurate positioning over the sensor board and to provide high data throughput. Using UWB protocols in a frequency band at 6 GHz improves the accuracy by about two orders of magnitude over existing systems, to 10 cm with respect to GNSS, and achieves a 6 Mbit/s throughput. The researchers developed both the charging system on the UAV and the sensor nodes with 150 W instantaneous WPT (Wireless Power Transfer) and real- time feedback for the UAV’s precision- landing algorithm. The WPT module delivers energy via a power circuit and transmitting coil, which are directly connected to the main battery. A module from UAV maker DJI manages the UAV attitude during all flight manoeuvres, including take-off, hovering, cruise and landing. The application layer includes the onboard computer, sensor data storage and flight sensors. The UWB transceiver on the sensor node reports the inductive voltage generated at the receiving coil. The UAV then makes decisions to fly to the location where the inductive voltage reaches a maximum to get the fastest energy transfer. This requires a custom design for the sensor board, which the researchers have made open source so that anyone else can make them. The 70 x 70 mm general-purpose sensor board uses a multi-protocol radio front end with an external 30 x 40 mm UWB antenna and sensors that can be used for industrial and agricultural applications. The board uses an STM32WB55RGV dual-core microcontroller from STMicroelectronics that manages all the stacks and sensors. An ARM Cortex M4 core is used for the main processing tasks, while an ARM Cortex-M0 is the radio comms protocols engine. The board integrates temperature (TMP117), humidity (HDC2080) and digital pressure (BMP280) sensors. External analogue and digital sensors can be added through a 16-pin connector. The board also includes audio recording via a low-power digital microphone (IMP34DT05) from STMicroelectronics combined with an ultra-low-power wake-up audio sub-circuit that activates the microcontroller to trigger events when the ambient sound levels are above a predetermined threshold. The open source design includes a DW1000 UWB transceiver from Decawave and the coil voltage measurement circuit, but it can be used as a reference to develop and test new localisation methods or to improve overall system performance. The researchers modelled the performance of the sensor board to work out how often a UAV has to travel to the sensor to recharge it and pick up the data, which is around 30 days. Wireless sensor charging Airborne vehicles April/May 2021 | Unmanned Systems Technology The system allows a UAV to fly to a sensor board, recharge it and collect its data wirelessly