A Compact Wireless Passive Breath Analyzer for Health Monitoring

In this paper, a passive wireless breath analyzer is presented that utilizes capillary condensation in nano porous substrate for volatile profiling. The sensing element is an interdigitated sensor coupled to an inductor coil forming an inductor-capacitor (LC) resonant tank fabricated on a flexible porous substrate. The volatiles condense into the pores of the substrate and changes the effective dielectric constant of the substrate which in turn impedance loads the sensor and shifts the resonance frequency. The change in resonance is co-related to the concentration of volatiles condensed into the substrate. For demonstrating the capability of a practical sensing approach, a digital circuitry along with an energy harvesting module is coupled to the LC tank which converts the impedance data into digital bits. The bits are modulated and transmitted back to the receiver making it compatible with existing long-range RFID infrastructure. For proof of concept, methanol is chosen as the volatile under test. The proposed sensor is capable of detecting 5 ppm of methanol at room temperature and at atmospheric pressure. The sensor is passive and does not require a battery for operation. The rapid field-operable nature of the sensor allows it to be used as breath analyzers for identifying different health markers as well as determining blood alcohol content.