Materials and strategies for Terahertz humidity sensing

In many different fields, such as industrial process control, food preservation, healthcare diagnostics, and environmental monitoring, where precise and timely humidity detection is critical, humidity sensing is vital. Terahertz (THz) sensing has become a potent, label-free, high-resolution, non-contact method of detecting humidity that offers clear benefits in terms of material selectivity and sensitivity. The incorporation of sustainable and biodegradable materials, such as chitosan, cellulose, silk fibroin, and other bio-derived polymers, has been the focus of recent developments. These materials not only improve sensor performance but also meet the growing demand for disposable and environmentally friendly sensor platforms. The most recent developments in THz humidity sensors are outlined in this review, along with important sensing mechanisms (such as absorption, refractive index shift, and resonance frequency variation), material selections, device architectures, and performance metrics like durability, sensitivity, response time, and detection limit. Large-scale fabrication, long-term performance, and material stability issues are critically analyzed. The review concludes by outlining future directions for the creation of flexible, scalable, and low-impact humidity sensors made of sustainable materials. It highlights how these sensors have the potential to completely transform green sensing technologies in a variety of practical applications.