Lightweight, ultrathin self-powered real time alcohol detector based on flexible metallized polyimide

Abstract The growing popularity of wearable electronics brings significant challenges to battery technology. The capacity of their built-in batteries tends to be limited by the size and weight, along with concerns regarding lifespan, maintenance, and potential health impacts. This paper proposes a flexible alcohol detector that offers the advantages of easy fabrication, wireless operation, cost-efficiency and battery-free. An ultra-thin, flexible self-powered alcohol detector with dimensions of 30×30×0.05 mm³is designed in this paper, exhibiting exceptional bendability and flexibility. The detector implements RF energy harvesting technology to obtain autonomous direct current (DC) power, thereby resolving the maintenance challenges and operational limitation associated with external power supplies in existing sensor system. The RF energy harvester (RFEH) efficiently transforms ambient electromagnetic energy at 2.45 GHz ISM band into electric power for device operation. The structural configuration of RFEH consists of a four-gap square ring resonator coupled with two nested square split-ring resonators and a circular split-ring resonator, which is fabricated on a polyimide (PI) substrate by enhanced in-situ metallization and cost-effective printed patterning techniques. Four Schottky barrier diodes integrated at the outermost ring's gaps enable self-rectification functionality, eliminating the requirement for the complicate rectifying circuit. Moreover, alcohol can modify the dielectric properties of the PI substrate, resulting in a measurable shift of the RFEH's resonant frequency that directly modulates energy harvesting efficiency. This shift can trigger a real-time alarm with a LED indicator. The electric power for LED indicator is supplied by RFEH. The range for alcohol concentration detection is of 0-100% with excellent linearity. A fast response time of 12 s and a recovery time of 17 s can be observed, respectively, along with good mechanical stability under repeated bending cycles. This ultra-thin, flexible self-powered real time alcohol detector shows significant potential for implementation in wearable intoxication prevention system and intelligent food quality monitoring.