Thin Carbon Nanotube Layers for Terahertz Wave Applications
Time: Tue 2019-04-02 15.00
Location: Q2, Malvinas väg 10
Lecturer: Dmitry Lyubchenko, Department of Micro and NanoSystems
The research and development in 0.1-1.0 THz frequency region are extremely significant for the wide range of applications, such as telecommunication and imaging systems, material spectroscopy, medical imaging and treatments, etc. In spite of the problems in technology and high prices for basic components (phase shifters, directional couplers, etc.), the THz systems offer higher date rates for telecommunication, high spatial resolution in the visualization of objects, small size of antennas and other elements. The state-of-the-art of the THz devices reveals serious problems with continuous wave semiconductor-based source, electronically tunable phase shifters, amplifiers, etc.
Dielectric rod waveguides (DRW) are the promising transmission lines, when low loss dielectric materials are used, and can be combined with semiconductor devices (oscillators, detectors, mixers, etc.) in the hybrid and/or monolithic integrated circuits. DRW offer a new opportunity for passive and active component performance, as it allows to decrease the insertion loss. Besides, DRWs have no cut-off frequency enabling broad band operation. DRW antenna was proved to operate in the frequency band of 0.1-1.1 THz.
The DRW is an open, i.e., not metal-shielded, waveguide system allowing to affect it with outside electro-magnetic fields including light. If one of the DRW walls is covered with a variable impedance layer, the propagation constant can be tuned. Carbon nanotubes (CNT) offer unique properties due to their natural small dimensions and outstanding electrical properties that makes them very attractive for future THz system applications. Integration of CNTs with the dielectric rod waveguide technology enables novel technology platform for tunable THz systems. I propose to use thin layers of optically-controlled CNTs as a novel solution. The simplicity of the CNT deposition gives an opportunity to cover a large area, which is essentially important for e.g. for reflector surface coating, sensor matrices, etc. CNT components can be integrated with DRW antenna elements for THz beam steering applications.
A novel technique for millimeter wave absorber material embedded in a metal waveguide is proposed. The absorber material is a highly-porous CNT aerogel prepared by freeze-drying technique. CNT aerogel structures are shown to be a good absorber with a low reflection coefficient, less than -12 dB at 95 GHz. Reflection coefficient of the novel absorber is 3-4 times lower than that of commercial absorbers with identical geometry.