BioScatter: Low-Power Sweat Sensing with Backscatter.

Sweat contains a wealth of physiologically relevant information and has been used to detect underlying diseases or the sub-health state. However, existing sweat sensors suffer from high energy consumption due to the need for energy-hungry components (i.e., ADC and DAC) and active radio front-ends, making them unable to support continuous and long-term monitoring. This paper introduces BioScatter, a backscatter-based accurate and ultra-low-power sweat sensing wearable sensor that does not need any energy-hungry ADC, DAC, and active radios. The key to eliminating DAC is a novel low-power voltage sweeping circuit design that can perform as well as a 12-bit DAC. To eliminate the ADC, we borrow backscatter technology that can directly transmit the measured analog sensing values to the reader, thus avoiding digital sampling. Extensive results show that BioScatter has a low-power consumption of 313.5 μW and achieves more than 98.5% sensing accuracy for detecting five concentration levels of three types of important bio-fluid in sweat.