Metamaterial / pHEMT Hybrid Devices for Terahertz Sources, Modulators and Detectors
Between the optical frequencies and the microwave frequencies is a broad expanse of spectrum in the terahertz range. However, development of devices for operation in the terahertz range is hampered, to some extent, by a dearth of devices for manipulating or detecting terahertz waves.
Terahertz radiation is useful for a variety of purposes, including security systems. Because of its ability to penetrate most clothing, terahertz radiation provides a way to detect concealed weapons. Another use for terahertz radiation arises in the context of cancer treatment. Because of its ability to detect differences in water content and density of tissue, terahertz radiation can be used to reliably distinguish between normal cells and cancerous cells.
Electromagnetic metamaterials for supporting propagation of a particular wavelength consist of composites having a patterned metallic structure having dimensions on the order of the wavelength to be propagated. The interaction of these metallic structures with the surrounding medium results in a wave propagation medium that can have negative values of permittivity and/or permeability.
The invention is based in part on the recognition that the dimensions associated with terahertz structures are similar to those of features made with conventional integrated circuit fabrication techniques. It features an apparatus for controlling propagation of an electromagnetic wave. Such an apparatus includes a metamaterial having an array of cells, each cell containing a metallic structure having a resonant frequency; a plurality of devices integrated in the metamaterial, each of said devices being in electrical communication with a metallic structure in a cell in the array of cells; and a controller for electrically activating each of said plurality of devices to cause said resonant frequency to change, thereby causing at least one of a permeability and permittivity of the metamaterial to change.
The invention features a method for manipulating an electromagnetic wave passing through a metamaterial. Such a method includes causing an electromagnetic wave to propagate in said metamaterial; and at each of a plurality of locations in the metamaterial, dynamically changing at least one of a permittivity and a permeability of the metamaterial.