Relentless advancements in circuits for battery-less silicon systems have recently enabled new levels of sensor node miniaturization, cost, and device lifespan, removing the limitations imposed by batteries.
The UBIGIoT project intends to develop a comprehensive and energy-autonomous sensor node able to monitor parameters (i.e. temperature, humidity, acceleration, etc.) and transfer wireless data. Multiple types of ambient energy sources can be converted to usable power. Design strategies for the electronic circuit connected to the energy harvester terminals will be developed with the aim of maximizing the energy extracted under real operating conditions. The power management circuits proposed in the literature for the maximization of the harvested energy are developed under the assumption of steady-state conditions of the ambient source (constant wind, sinusoidal accelerations, etc.), while the proposed research activity will tackle the challenge of maximizing the extracted energy under real life sporadic conditions of ambient sources.
The energy source addressed in this first part of the project is Radio Frequency (RF) energy provided by conventional Wi-Fi transmitters. The adoption of the 802.11b Wi-Fi standard is preferred to BLE, LTE, and 5G since these standards do not have widely distributed infrastructure in most of the indoor spaces (e.g. home, offices, and gyms), which makes rapid low-cost deployment quite difficult Being the available RF harvested power in the deep sub-µW/mm2 range, peak power budgets are restricted to the 1-µW range or less at millimeter-scale form factors, requiring aggressive system power reductions. At the battery-less system level, wireless transmission (e.g. Wi-Fi) generally sets the limit to further system power reductions in view of their dominant peak power. The milliwatt-range power consumption of state-of-the-art conventional Wi-Fi transmitters was recently reduced to tens of µWs through backscattering architectures. Indeed, the latter suppress gigahertz-range PLL and power amplifier by properly reflecting an incident wave from a tone generator. Complete PLL elimination has recently reduced Wi-Fi transmitter power to µWs, thanks to eventdriven temperature-compensated ring oscillator-based local oscillators.
The goal of the research activity was to enable a new class of Wi-Fi backscattering transmitters with power in the sub-µW range by removing the local oscillator power while simultaneously for the first time in the literature reusing the incoming RF signal for backscattering communications, harvesting, and sensor-less position/motion sensing.
