MARS: Nano-Power Battery-free Wireless Interfaces for Touch, Swipe and Speech Input

TL;DR

MARS introduces a low-cost, battery-free wireless sensing system that detects touch, swipe, and speech interactions on surfaces using nanowatt power and ambient energy, enabling maintenance-free interaction sensing.

Contribution

The paper presents MARS, a novel nanowatt-powered system combining programmable oscillators and backscatter communication for battery-free interaction sensing.

Findings

Operates with less than 2 microamps current

Can be powered by ambient energy sources

Supports multiple devices in the same environment

Abstract

Augmenting everyday surfaces with interaction sensing capability that is maintenance-free, low-cost (about $1), and in an appropriate form factor is a challenge with current technologies. MARS (Multi-channel Ambiently-powered Realtime Sensing) enables battery-free sensing and wireless communication of touch, swipe, and speech interactions by combining a nanowatt programmable oscillator with frequency-shifted analog backscatter communication. A zero-threshold voltage field-effect transistor (FET) is used to create an oscillator with a low startup voltage (about 500 mV) and current (< 2uA), whose frequency can be affected through changes in inductance or capacitance from the user interactions. Multiple MARS systems can operate in the same environment by tuning each oscillator circuit to a different frequency range. The nanowatt power budget allows the system to be powered directly through ambient energy sources like photodiodes or thermoelectric generators. We differentiate MARS from previous systems based on power requirements, cost, and part count and explore different interaction and activity sensing scenarios suitable for indoor environments.