Toward 5G Wearables: An Additively Manufactured, ThermoelectricPowered mmID and Integrated Microfluidic pH Sensor

This work presents the first additively manufactured millimeter-wave identification (mmID) platform for wearable sensing that is fully self-powered and orientation agnostic. A multilayer inkjet-printed circularly polarized retrodirective architecture is implemented, and the RF, sensing, and interconnect layers are realized through a unified additive workflow. The module integrates a thermoelectric generator with a printed mmID and microfluidic pH sensor, forming a mmWave backscatter system with biochemical sensing capability. The mmID achieves a peak differential radar cross section of −23 dBsm with ±42.5◦ angular coverage and supports 70 m interrogation under emulated on-body conditions. The thermoelectric harvester meets power needs from an emulated skin–air temperature gradient. The printed PEDOT:PSS-based pH sensor exhibits 150 Ω/pH sensitivity across pH 4–10, enabling hydration monitoring and diagnostics. Together, these advances enable long-range health monitoring in 5G-connected wearables and highlight the potential of thermoelectric, additively manufactured mmWave backscatter modules for future health and environmental sensing.