Terahertz Coding Metasurface with Low-Switch-Ratio for Rapid 1-bit Phase Modulation and Beam Steering

With the advent of 6G terahertz technology, the demand for high-performance beam steering devices for terahertz waves is growing increasingly urgent. Terahertz reconfigurable intelligent surfaces (RIS) offer advantages such as low cost, high integration, extensive scalability, and flexible manipulation, making them a critical technology for enabling ultralow latency, high reliability, and dynamic adaptation in integrated terahertz wireless communication and sensing paradigms. A significant challenge hindering the widespread deployment of terahertz RIS is the limited performance of binary phase modulation, particularly the inadequate switch ratio and slow response speed of terahertz switches. This study presents a novel high-electron-mobility transistor (HEMT)-based coding metasurface operating under a low switch ratio for rapid 1-bit phase modulation and beam steering. Unlike traditional metasurface phase-shift schemes, the proposed meta-element facilitates frequency-agile phase modulation through HEMT-controlled LC-dipolar resonance shifts with a low on-off switch ratio. Verified through electromagnetic simulations, surface admittance analysis, and experimental results, the 32 x 32 prototype demonstrated a continuous 360 degrees phase shift in the 0.32-0.40 THz range and 1-bit coding dual-beam steering at -39 degrees/+37 degrees and -30 degrees/+28 degrees. Thanks to its sensitive phase modulation characteristics, the meta-device operates with a switch ratio of 2 (ON/OFF 2-dimensional electron gas density ratio), achieving a 180 degrees phase jump at 0.358 THz with an average reflectance of -8.5 dB and a response speed of 100 MHz. This low-switch-ratio design can potentially enhance terahertz RIS performance in terms of power efficiency, compact integration, and real-time adjustment capabilities.