Position: Graduate Student Researcher

Current Institution: University of California at Berkeley


The widespread expectation that autonomous sensor networks will fuel massively accessible information technology, such as the Internet of Things (IoT), comes with the daunting realization that huge numbers of sensor nodes will be required, perhaps approaching one trillion. Needless to say, besides cost, energy will likely pose a major constraint in such a vision. The wireless module in a typical sensor node consumes 30mW of power, of which half is spent on the receiver alone. The power-hungry transceiver calls for sleep/wake strategy which requires additional timing and control system that also consumes 1uW of extra power. A low-cost printed battery with 1J of energy would only last 11.5 days even when the sensor node is at sleep with only the sleep/wake control system running. On the other hand, if the receiver could consume zero quiescent power, the sensor node can listen without draining any battery at all times. The trillion-sensor wireless network would suddenly become feasible. A first-in-kind all-mechanical communication receiver front-end employing resonant micromechanical switch (i.e., resoswitch) technology has detected and demodulated frequency shift keyed (FSK) signals as low as −60dBm at a VLF frequency of 20kHz suitable for extremely long-range communications, all while consuming zero quiescent power when listening. The key to attaining high quality signal reception and demodulation with zero quiescent power consumption derives from the use of heavily nonlinear amplification, provided by mechanical impact switching of the resoswitch. This approach would be inconceivable in a conventional receiver due to performance degradation caused by nonlinearity, but becomes plausible here by virtue of the RF channel-selection provided by the resonant behavior of the mechanical circuit.

Ruonan Liu attended the Ohio State University in 2008 and received her B.S. degree in Electrical and Computer Engineering with honor in 2011. She is currently a fifth year Ph. D. student in the University of California at Berkeley. Her research focus on ultra-low power wireless communications using MEMS resonators. MEMS device consumes zero quiescent power and has extremely high quality factor on the order of tens of thousands making it ideal for low power wireless receiver.