Metamaterials have been gaining attention recently for their capabilities in tuning high-frequency circuits. For extremely high-frequency/optical applications, flexible metamaterials have enabled tuning at frequencies from 0.1 to 10.0 THz. Researchers from Boston University—including Kebin Fan, Xiaoguang Zhao, H.R. Seren, Jingdi Zhang, Xin Zhang, and G. Keiser from Boston University, along with Grace Metcalfe and Michael Wraback from the U.S. Army Research Laboratory in Adelphi, Md.—explain how to develop flexible optically tunable metamaterials for use at THz frequencies.
The responses of flexible tunable metamaterials were characterized with the aid of optical-pump terahertz-probe (OPTP) spectroscopy. Scans were performed with air as the reference, and terahertz frequency pulses were measured. Transmissions were studied at 0.98 THz and at 1.25 THz, using commercial Computer Simulation Technology software. The metamaterials are mounted on a semi-insulating GaAs layer which is modeled as a simple lossy dielectric material with high dielectric constant of 12.9 for the top layer and with a second layer of GaAs as the bottom portion of the two-layer substrate.
The research showed that the flexible metamaterials on GaAs substrates could achieve the high resonant frequencies well through 1.25 THz, with outstanding modulation depth over a broad frequency range from 1.1 to 1.8 THz. The computer modeling made it possible to determine the effective permittivities of the different metamaterials used with the GaAs substrates and show how these tuning circuits can help create multilayer nonplanar tunable electromagnetic composite materials for nonlinear and multiple-function applications, including signal sensing, modulation, and energy harvesting systems. See “Optically Tunable Terahertz Metamaterials on Highly Flexible Substrates,” IEEE Transactions on Terahertz Science and Technology, November 2013, p. 702.