Issue 41 Unmanned Systems Technology December/January 2022 PteroDynamics X-P4 l Sense & avoid l 4Front Robotics Cricket l Autonomous transport l NWFC-1500 fuel cell l DroneX report l OceanScout I Composites I DSEI 2021 report

7 Platform one Unmanned Systems Technology | December/January 2022 Researchers at CEA-Leti have developed a gyroscope for navigation systems that measures just 1.3 mm 2 (writes Nick Flaherty). The single-axis gyroscope, developed in collaboration with a team at Politecnico di Milano, exploits a technique called nano-resistive sensing, which uses miniature piezoresistive elements as a strain gauge to measure the movement of a small silicon structure. The design allows the volume of the silicon structure to be reduced to 0.026 mm 3 , a small fraction of the size of those used in commercial MEMS gyroscopes.   Navigation-grade gyros require improved characteristics of one or two orders of magnitude compared with the best commercial MEMS gyroscopes, which typically have a bias stability well below 0.1 º /h and an angular random walk (ARW) of less than 0.01 º / √ h. “This improved performance must not come with a high cost, so the device will be priced competitively for large- volume markets, such as automotive and consumer,” said Philippe Robert, a MEMS expert at CEA-Leti. “The size of these new gyros must therefore not exceed 2 mm 2 per axis, while maintaining standard MEMS technology and using wafer-level vacuum packaging.” Combining CEA-Leti’s expertise in sensors based on piezoresistive silicon nano-gauges and Politecnico di Milano’s expertise in gyro design, the new gyro reached a performance of 0.004 º / √ h ARW and 0.02 º /h bias stability over several test samples on non-static operations. After a 9 minute navigation operation where the gyro was repeatedly tilted by 180 º constant angle rotations the residual angle error at the end of navigation corresponded to only 0.07 º . These results were achieved without the Kalman filter compensation used on larger MEMS gyroscopes to reduce errors in the measurements. Avoiding the need for a Kalman filter can reduce the processing requirement for the gyroscope and so reduce the size of a complete system. To keep manufacturing costs low, the team focused on the sensor’s size and the robustness of the fabrication process. The device is fully compatible with standard MEMS processes for high- volume markets. The two groups are now working on three-axis gyro integration, whose feasibility has already been demonstrated but where the objective will be to bring the same level of performance to the three axes. This gyro will have a resonant frequency greater than 25 kHz to withstand conventional vibration environments. The gyro is manufactured on CEA- Leti’s silicon pilot line and can be integrated with a three-axis accelerometer and barometric pressure sensors. As it is compatible with most MEMS manufacturing processes, commercial products based on the technology could be available within 2 years. Navigation Minute single-axis gyro The gyro measures only 1.3 mm 2 , yet uses standard MEMS technology The performance must not come with a high cost, so the device will be priced for large- volume markets such as automotive and consumer