Response Improvement of Liquid Crystal-Loaded NRD Waveguide Type Terahertz Variable Phase Shifter

Abstract

Liquid crystals, which have high dielectric anisotropy even in the terahertz region and are easily controllable for dielectric permittivity by applying an electric field, have become increasingly attractive in recent years. The non-radiative dielectric (NRD) waveguide has a structure in which a dielectric line is sandwiched between two metal plates and by replacing the dielectric part with liquid crystal, a low loss liquid crystal-loaded NRD waveguide type terahertz phase shifter can be obtained. However, since the thickness of the liquid crystal layer is several hundred micrometers, it has a response time of as long as several hundred seconds when the driving voltage is removed. It is necessary to devise improvements for practical application. By inserting two polyethylene terephthalate (PET) films and reducing the thickness of the liquid crystal layer, the decay time was improved well, but the phase change was significantly reduced. In this study, we report improving both decay time and phase change with aligned nanofiber/liquid crystal complex. In addition, we demonstrate liquid crystal-load phase shifter, which has 360° phase change and the response time below one second.

Reconfigurable Liquid Crystal Dielectric Image Line Leaky Wave Antenna at W-Band

“…In order to optimize the tuning efficiency, different metallic shapes, most importantly of the connection line, can be used to achieve higher parallel alignment of the LC. The use of magnets for better perpendicular alignment could be avoided if experimental LC mixtures containing polyacrylonitrile nanofibers [43] are employed. A translation of the LC-LWA to the terahertz regime is possible, if smaller cavities can be handled, providing higher absolute bandwidths, and lowering the necessary bias voltages due to the lower DIL height.…”

Optimization of the electrospun-aligned microfiber composite with liquid crystal for terahertz wave variable phase shifters

“…A transmission line length of 5 mm and a THz wave frequency of 350 GHz were used, as in our previous study. 37) Additionally, we used polytetrafluoroethylene (e = 2.05) as the spacer material for LC cells instead of polyethylene terephthalate (e = 3.1) to ensure that the THz wave passed only through the LC and not through the spacer part under the cutoff effect of the NRD waveguide. In the application of phase shifters, the LC birefringence is known as a factor for generating the phase change of the THz wave.…”

“…27) Larger phase changes can be obtained using higher voltages, although this is not suitable for actual devices. Additionally, to induce large phase changes, a transmission line structure with low loss characteristics at a high frequency, such as a rectangular waveguide, 34,35) parallel-plate dielectric waveguide, 36) or nonradiative dielectric (NRD) waveguide, [37][38][39] must be used. These structures have the common feature of confining electromagnetic waves within metal walls, thereby impeding PSLC performance in the phase shifter because ultraviolet irradiation is required to initiate polymerizationthe most popular technique today.…”

Microwave Liquid Crystal Technology

“…The numerous subcategories of dielectric waveguides offer a high degree of freedom in designing smart millimeter wave components such as tunable phase shifters, filters and steerable antennas. A similar approach with a clear focus on response time is included in [4] for non-radiative dielectric waveguides. By the alignment of a nanofiber/liquid crystal complex, the switching time could be reduced while keeping the phase change above 360 • .…”

“…In [6] two new nematic liquid crystal mixtures are proposed by adding LC monomers to commercial LC. This and also the addition of nanofibers as in [4] are two examples for recent material development.…”