Self-Powered Humidity Sensing and Real-Time Respiration Monitoring Based on Nonlinear-Optical Single Crystals of Imidazolium Perchlorate

Abstract

In recent years, there has been growing interest in developing advanced devices capable of real-time monitoring for healthcare, tracking both physiological activities and environmental conditions. Despite this progress, the creation of a fully selfsustaining device remains a significant challenge. In this work, we report single crystals of imidazolium perchlorate (IMP), grown at room temperature using the slow evaporation solution growth method. A self-powered humidity sensor was fabricated using these IMP crystals, offering a wide detection range of 11−90% relative humidity, with a response time (T res ) of 75 s and a recovery time (T rec ) of 18 s. The sensor demonstrated strong potential in detecting physiological signals such as coughing and variations in breathing rates. It also proved highly effective in touchless sensing, detecting skin moisture evaporation from distances of up to 3 mm, making it particularly valuable in environments where minimizing virus transmission is critical. To improve its practicality, the sensor was made to be self-powered through piezoelectric generation (PEG), which produced a peak-to-peak output voltage of 360 mV at a tapping frequency of 20 Hz. This feature is especially advantageous for medical applications. Furthermore, the sensor's recyclability and reusability further highlight its potential to contribute to the sustainable development of our society.