Magnetic-free radio frequency circulator based on spatiotemporal commutation of MEMS resonators

This paper reports on the first demonstration of a magnetic-free radio-frequency (RF) Microelectromechanical Resonant Circulator (MIRC). For the first time, magnetic-free non-reciprocity is achieved by imparting an effective angular momentum bias to a MEMS resonant circuit. The angular momentum is efficiently realized through spatiotemporal modulation of three strongly coupled high-Q (>1000) Aluminum Nitride (AlN) Contour Mode MEMS Resonators (CMRs) with signals of the same magnitude and phase difference of 1200. Differently from previous demonstrations based on varactor-based frequency modulation of low-Q LC networks, in this work the spatiotemporal modulation of the high-Q MEMS resonators is implemented by means of switched capacitors which minimizes the complexity of the modulation network, increases the modulation efficiency and mitigates the fundamental linearity limitations associated with solid-state varactors. Furthermore, due to the high Q of the MEMS resonators employed, strong non-reciprocity is achieved with an ultra-low modulation frequency of ∼120 kHz (∼0.08% of the RF frequency, orders of magnitude lower than previous demonstrations) which directly enables a total power consumption of only ∼38 μW which, to the best of our knowledge, is the lowest ever reported for magnetic-free RF circulators based on temporally modulated circuits.