Contact-Free Human-Machine Interfaces via Printed Thermopile Infrared Arrays

Human-machine interfaces (HMIs) are evolving as key components for advanced sensing in communication and control systems. In particular, contact-free HMIs can facilitate unique advantages in hygiene, durability, and non-destructive sensing. However, spatially resolved sensing platforms remain challenging using bulk approaches. Here, we report flexible infrared interface arrays (TIA1 and TIA2) with ≥10 pixels that exploit the photo-thermoelectric (PTE) infrared sensing properties of Bi-Te-based thermoelectric (TE) materials via a dual-stage energy conversion process: radiation-to-thermal, followed by thermal-to-electric. The p- and n-type TE materials and electrodes were printed on polyimide to fabricate TIAs. After encapsulation with a black absorber, radially patterned silver mirrors are printed on the outer part of the pixels using aerosol jet-printing to partially shield each thermocouple. This induces a localized temperature gradient, hence an output voltage via the Seebeck effect under infrared illumination. The pixels exhibit responsivities of 0.7 VW^-1 (TIA1) and 0.9 VW^-1 (TIA2), respectively, under CO₂ laser irradiation (10.6 µm), with pixel-to-pixel variation within ± 10%. The TIAs were demonstrated as non-contact handwriting and dialing interfaces, converting human gestures into digital signals. These results pave the way for a self-powered and contactless interface for future human-machine interaction technologies.