Multimodal sub-terahertz fiber antenna for environmental and fiber deformation sensing

Fiber sensors are commonly used in a variety of applications, detecting signals related to environmental, physiological, optical, chemical, and biological factors. Thermally drawn fibers offer numerous advantages over other commercial products, including enhanced sensitivity, accuracy, improved functionality, and ease of manufacturing. Multimaterial, multifunctional fiber sensors are good candidates for encapsulating essential internal structures within a micro-scale fiber, as opposed to macroscale sensors that require separate electronic components. The compact size of fiber sensors enables seamless integration into existing systems, providing the desired functionality. Here, we present a multimodal, sub-THz fiber antenna that monitors, in real-time, the local deformation of the fiber and the environmental change by a foreign object in fiber proximity. An electromagnetic wave generated by Time Domain Reflectometry (TDR) propagates through the fiber, allowing for the precise determination of spatial changes along the fiber with exceptional resolution and sensitivity. The local change in impedance measures deformation on the fiber, and proximity is detected by a change in the evanescence field formed around the fiber. The fiber antenna works as a waveguide, where the symmetric and antisymmetric modes are analyzed separately to detect local deformation through the antisymmetric mode and environmental changes through the symmetric mode. The fiber sensor's multifunctionality broadens the fiber's application area from biomedical engineering to cyber-physical interfacing. In antisymmetric mode, the Sub-THz fiber antenna can sense local changes in pressure, temperature, pH, and many other physiological parameters. Furthermore, fiber operating in symmetric mode can be used in touch screens, environmental detection for security, cyber-physical interfacing, and human-robot interactions.