Refractive Index Engineering of 3D‐Printing Terahertz Composite Materials

Abstract Terahertz (THz) technology presents significant potential in non‐invasive imaging, spectroscopy, and high‐speed wireless communications. With the recent maturation of active THz devices, passive THz components are becoming increasingly important for enhancing system performance and broadening application scopes. However, the functionality of existing THz passive devices is constrained by materials and manufacturing limitations. To address these challenges, a 3D printable, low‐loss THz composite material with a widely controllable refractive index and sub‐wavelength manufacturing precision is developed. By incorporating rutile titanium dioxide nanopowder and increasing the UV exposure dose, a broad refractive index tuning range (1.6 to 1.9), along with an absorption coefficient of 2.48 cm⁻¹ at 325 GHz is achieved. This composite facilitates a scalable, flexible, and integrable manufacturing platform for designing and implementing multifunctional THz passive devices. The potential of the developed nanocomposite is shown by 3D printing ultra‐thin‐THz‐lenses that exhibited bit‐error‐rate performance comparable to conventional THz lens designs while being only one‐third the thickness, as demonstrated in a THz communication system testbed. This work shows the potential of tailored additive manufacturing for creating high‐performance, customizable, scalable THz passive device designs, paving the way for compact and multifunctional THz system platforms in sensing, imaging, and next‐generation communication applications.