Unmanned Systems Technology 036

42 Focus | IMUs, gyros and accelerometers 24 or so IMUs on a single PCB, overall performance could be 25% higher than that of a singular triple-axis IMU while still probably being a lighter and less expensive option than conventional optical gyroscope IMUs. Naturally, a multi-IMU MEMS array of this kind would also have far better redundancy than any other navigation system available, which could make it safety-imperative for UAVs that conduct deliveries or surveys over civilians. While multi-IMU arrays and photonic gyros look set to proliferate over the next few years, entirely new technologies are being researched. These fall under the umbrella term of ‘quantum sensors’, and could present magnitude- level improvements in inertial sensing products in 10 years or so from now. For example, the past few years have seen numerous experiments with optomechanical accelerometers. These vary in configuration but typically use a laser interferometer with some type of cavity that holds a fixed mirror and a moveable mirror. As accelerations induce oscillations in the mirror, changes in the measured radiation pressure force (the force from mechanical pressure inflicted upon an object’s surface by the momentum exchanged between it and the electromagnetic field) in the cavity, the displacement of the mirror or the cavity resonance frequency – depending on the experiment and chosen approach – can be used to calculate the rate of acceleration with extremely high sensitivity. The components can also be designed with MEMS form factors, meaning potentially revolutionary performance-to- SWaP ratios. Cold atom interferometry (CAI) represents another highly relevant area of quantum sensing, experiments with it having also demonstrated considerable potential advantages that IMUs incorporating CAI-based accelerometers and gyroscopes could yield. Such systems use lasers to first ‘cool’ atoms – that is, reduce their thermal velocity to make their quantum properties accessible and measurable – and then split the atomic wave function into two parts that travel along two paths of an interferometer. The two halves of the atomic wave function build up a phase difference, which varies depending on inertial and gravimetric interactions, much like the two beams used in the Sagnac effect. Both the phase differences and their variances can then be measured at the output of the interferometer to gauge acceleration, angular rate and gravity. CAI-based accelerometers could not only enable phenomenally sensitive inertial navigation measurements, they could also guarantee near-infinite repeatability of performance over time, given that their only moving parts are cold atoms whose inertial properties do not alter on a fundamental level with time, heat or shock. Like optomechanical sensors though, CAI sensors constructed at a chip-level scale are far from commercial availability, and still require many years of r&d to mature their underlying technology. That said, a European Commission report last year suggests that space and defence organisations – being in markets where investing in long-endurance, highly sensitive autonomous navigation is a strategic imperative – might seek to exploit such systems in roughly the next 10 years. Acknowledgements The author thanks Xavier Orr at Advanced Navigation, Jakub Maslikowski at VectorNav, KK Wong, Sergey Zotov, Martin Williams and David Blumenfeld at EMCORE, Gary Ballas and Lee Dunbar at Gladiator Technologies, Jamie Marraccini and Anton Barabashov at Inertial Labs, Yves Paturel at iXblue, Jan Khan, Jeff Brunner, Roger Ward and Sean McCormack at KVH Industries, Aviram Feingold and Lisa Koenigsberg at Physical-Logic, Matthieu Noko at SBG Systems, and Miguel Angel de Frutos of UAV Navigation for their help in researching this article. February/March 2021 | Unmanned Systems Technology Future inertial systems might use dozens of IMUs arranged in an array for higher-than-ever accuracy and integrity (Courtesy of UAV Navigation) Experiments in CAI demonstrate considerable advantages for IMUs with CAI-based accelerometers and gyroscopes