| Summary: | Implementation of low-power wireless sensing nodes (WSN) is essential to realization of the internet-of-things (IoT). Lifetime of conventional WSNs is limited by their always active radios. To extend lifetime of WSNs, we have fabricated a fully passive sleep-but-alert radio frequency (RF) receiver. This wake-up receiver (WUR) is composed of a cross-sectional Lamé-mode piezoelectric Aluminum Nitride resonator cascaded to a high-Q resonant switch (referred to as a resoswitch)
and a threshold switch. The resonator filters an amplitude-modulated (AM) RF tone of interest from the entire spectrum and amplifies it to transfer power to a resonant switch tuned to the AM frequency. When the resoswitch makes contact, a threshold switch is activated, turning on the radio. In addition, energy transfer between the micromechanical resonator and the resoswitch is increased by optimizing the modulation of the trigger signal to enhance WUR's sensitivity. It was found that
resonator goes out of tune as the resoswitch is set in motion. To ensure that resonator is always at resonance and hence outputs the maximum voltage, we first frequency modulate the carrier signal. Further, the width of the duty cycle and the phase of the AM signal are adjusted for maximum energy transfer. We report ~10 dBm improvement in sensitivity compared to previously predicted sensitivity value of -60 dBm.
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