Touchless user interfaces offer an attractive pathway toward hygienic, remote, and interactive control over devices. Exploiting the humidity generated from fingers or human speech is a viable avenue for realizing such technology. Herein, titania microspheres including solid and yolk-shell structures with varying microstructural characteristics were demonstrated as high-performance, ultrafast, and stable optical humidity sensors aimed for touchless control. When water molecules enter the microporous network of the microspheres, the effective refractive index of the microsphere increases, causing a detectable change in the light scattering behavior. The microstructural properties of the microspheres, namely, the pore characteristics, crystallinity, and particle size, were examined in relation to the humidity-sensing performance, establishing optimum structural conditions for realizing humidity-responsive wavelength shifts above 100 nm, near full-scale relative humidity (RH) responsivity, ultrashort response times below 30 ms, and prolonged lifetimes. These optimized microspheres were used to demonstrate a colorimetric touchless sensor that responds to humidity from a finger and a microcontroller-based detector that translates the moisture pattern from human speech to electrical signals in real time. These results provide practical strategies for enabling humidity-based touchless user interfaces.
Bibliographical noteFunding Information:
This research was supported by grants (NRF-2017R1A5A1015365 and NRF-2019R1C1C1002802), the Creative Materials Discovery Program (NRF-2020M3D1A1110522), the Technology Development Program to Solve Climate Changes (NRF-2016M1A2A2940914) of the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT & Future Planning, and the Korea Basic Science Institute (National Research Facilities and Equipment Center) grant funded by the Ministry of Education (2020R1A6C101B194).
© 2021 American Chemical Society
- Mie scattering
- humidity sensors
- mesoporous particles
- titania microspheres
- touchless control
- ultrashort humidity responsivity