Sub- μ W Battery-Less and Oscillator-Less Wi-Fi Backscattering Transmitter Reusing RF Signal for Harvesting, Communications, and Motion Detection

In this article, a sub-microwatt power 802.11b backscattering transmitter is presented to enable the reuse of the same incident wave for three purposes: RF harvesting, backscattering communications, and position/motion sensing. The removal of the battery and any off-chip motion sensor (e.g., MEMS) enables an unprecedented level of miniaturization and ubiquity, unrestricted device lifespan, and low fabrication and maintenance cost. The microwatt power wall for Wi-Fi transmitters is broken for the first time via local oscillator elimination, as achieved by extracting its frequency through second-order intermodulation of a two-tone incident wave. The two-tone scheme also enables a cumulative harvesting/transmission/sensing sensitivity down to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P_{\min }}~{\sim }- 19 $ </tex-math></inline-formula> dBm. Position/motion sensing is enabled by using the harvested voltage as a proxy for the received signal strength (RSS), allowing to sense the chip location with respect to the tone generator(s) shared across tags in indoor neighborhoods.