A patent (US 7,826,504 B2) describes active terahertz metamaterial devices that modulate terahertz frequency signals. The devices use arrays of metamaterial elements, each containing multiple loops and at least one gap. These elements can be conductive loops with insulated gaps or insulated loops with conductive gaps, enabling transmissive control. The metamaterial elements are fabricated on a semiconductor substrate, which enhances or depletes electrons near the gaps. This approach achieves a 50% on-off transmissivity ratio. The devices can be integrated into quantum cascade lasers (QCLs) to provide surface emitting properties. The invention offers efficient real-time control and manipulation of terahertz radiation, with applications in imaging, communication, and laser devices. The devices operate at room temperature and can be modulated by external signals. The patent includes 20 claims and 25 drawings, detailing various embodiments and configurations of the metamaterial devices. The invention addresses the need for practical terahertz modulation and control, overcoming limitations of existing devices.A patent (US 7,826,504 B2) describes active terahertz metamaterial devices that modulate terahertz frequency signals. The devices use arrays of metamaterial elements, each containing multiple loops and at least one gap. These elements can be conductive loops with insulated gaps or insulated loops with conductive gaps, enabling transmissive control. The metamaterial elements are fabricated on a semiconductor substrate, which enhances or depletes electrons near the gaps. This approach achieves a 50% on-off transmissivity ratio. The devices can be integrated into quantum cascade lasers (QCLs) to provide surface emitting properties. The invention offers efficient real-time control and manipulation of terahertz radiation, with applications in imaging, communication, and laser devices. The devices operate at room temperature and can be modulated by external signals. The patent includes 20 claims and 25 drawings, detailing various embodiments and configurations of the metamaterial devices. The invention addresses the need for practical terahertz modulation and control, overcoming limitations of existing devices.