Dual-frequency liquid crystals

Dual-frequency liquid crystal (DFLC) [41,42] exhibits a unique feamre that its Ae changes from positive at low frequencies to negative as the frequency passes the crossover frequency (fc), as Figure 6.7 shows. The frequency that Ae = 0 is called the crossover frequency. The major attraction of the DFLC device is fast response time. During the tum-on and turn-off processes, AC voltage bursts, with low and high frequencies, are applied. As a result, fast rise and decay times can be achieved [43]. 

C. H. Wen and S. T. Wu, Dielectric heating effects of dual-frequency liquid crystals, Appl Phys. Lett. 86, 231104 (2005). 

Y. H. Lin, H. Ren, S. Gauza, et al.. Reflective direct-view displays using dye-doped dual-frequency liquid crystal gel, J. Display Technology, 1, 230 (2005). 

ITO electrode and then flattened by a polymer film. For phase-only modulation, homogeneous LC alignment should be used. Thus, the polymer surface and the bottom ITO glass substrate with a thin polyimide alignment layer are rubbed in anti-parallel directions. The cell gap is controlled at 18 pm by Mylar spacers and hermetically sealed using ultraviolet-curable glue. To achieve a fast response time, a dual-frequency liquid crystal (DFLC) is used. The physical properties of the DFLC mixture are summarized as follows crossover frequency /<, 5 kHz, An 0.285 (at X=633nmand T=22°C), and dielectric anisotropy Ae = 4.73 at/= 1 kHz, and Ae = -3.93 at 50 kHz. 

Figure 12.17 Voltage-dependent average refractive index of dual-frequency liquid crystal used in the experiment. Solid line and open circles represent the experimental and simulation results, respectively, X = 633 nm. Fan 2005. Reproduced with permission from IEEE.

The response time of a conventional varifocal lens is relatively slow [88], To improve the response time, a Fresnel lens with a dual frequency liquid crystal [89,90] can be used. Thus, the response time of the LC lens is sufficient for 60 Hz operation to avoid flicker. 

Director Axis Reorientation in Homeotropic and Planar Cells Dual-Frequency Liquid Crystals... 

Kirby, Andrew K., and Gordon D. Love. 2004. Fast, large and controllable phase modulation using dual frequency liquid crystals. Opt Express. 12 1470-1475. 

Katoh [1] prepared a liquid crystal composition for use as electronic paper consisting of one dual-frequency switchable smectic liquid crystal, (1), and at least one dichroic dye. 

Y. Lu, X. Liang, Y. H. Wu, et al.. Dual-frequency addressed hybrid-aligned nematic liquid crystal, Appl Phys. Lett. 85, 3354 (2004). 

As a specific example of this invention, even at a low temperature of 0 °C, an AC frequency of 60 Hz can drive the liquid crystals that contain 0.05 wt% of para-aminobenzoic acid ammonium salt. Furthermore, a value of more than 10,000 h was predicted for its lifetime. Based on this discovery, liquid crystal materials for more practical DSM-LCDs were developed in about November 1971. Thus, the dual achievement of good display characteristics and device lifetime could be demonstrated to the electronic calculator division, and the adoption of LCD was decided. 

Acoustic Wave Sensors. Another emerging physical transduction technique involves the use of acoustic waves to detect the accumulation of species in or on a chemically sensitive film. This technique originated with the use of quartz resonators excited into thickness-shear resonance to monitor vacuum deposition of metals (11). The device is operated in an oscillator configuration. Changes in resonant frequency are simply related to the areal mass density accumulated on the crystal face. These sensors, often referred to as quartz crystal microbalances (QCMs), have been coated with chemically sensitive films to produce gas and vapor detectors (12), and have been operated in solution as liquid-phase microbalances (13). A dual QCM that has one smooth surface and one textured surface can be used to measure both the density and viscosity of many liquids in real time (14). 

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