Research on Diffraction Type of Millimeter-Wave Control Devices Using Liquid Crystal Materials

Although usual nematic liquid crystals (LC) have considerable large refractive index anisotropy in the millimeter-wave (MMW) region, still more large anisotropy is desired for practical MMW device applications because of the extremely long wavelength comparing with visible rays. We prepare Au-nano particle contained LC materials to improve their performance. In this stage, clear difference with the pure LCs has not been found out yet in the MMW region. However, it is usually very difficult to have uniform mixture with nano particle, then the experimental method can be expanded to other various nano particles to search excellent combinations.Extremely thick LC layer is also necessary to construct the LC devices for MMW application, and then we adopt membrane films for supporting the thick LC layer. We investigate the LC molecular orientation anisotropy induced by the film using the capacitance measurement method, because the molecular alignment effect is also very important for the LC device performance. It is found that the microscopic fine fiber in the membrane film can well align the LC molecules and this type of membrane is useful for constructing the thick LC layer without any stretching treatment.Since we are planning to adopt Fresnel structure to reduce the LC device thickness, a Fresnel test lens is fabricated by machining of plastic plate. It is found that only 4 steps of machining resolution and 3 periods of Fresnel ring are is enough to get excellent lens performance in the MMW region. Stacked electrode structure is necessary to drive the thick LC layers, then we proposed the rolling type of stacked electrode structure to fabricate large size of MMW LC lens devices. We investigated the transmission properties of the new type electrode structure and excellent focusing properties have been confirmed by combining with the plastic test lens.