Microstrip Device for Broadband (15–65 GHz) Measurement of Dielectric Properties of Nematic Liquid Crystals

Abstract

The essential dielectric properties, the basic alignment techniques, and the common measurement methods of the nematic liquid crystal (LC) at RF are briefly reviewed. A new device for the broadband measurement of the dielectric constants and loss tangents of nematic LCs at microwave and millimeter-wave frequencies is presented. This device whose specification and fabrication are outlined is essentially a two dielectric layer microstrip structure with coplanar-waveguide terminals, which is easy to fabricate. Compared to previous structures, the proposed device is extremely broadband with 15-65-GHz bandwidth, benefits from a solid exposed ground plane for easy temperature test, and operates under bias voltage. The technique for the extraction of the dielectric parameters of the nematic LC analyzed by this device is explained and the sources imposing the frequency limits on the device performance are identified. Two different nematic LCs, MDA-00-3506 and GT3-23001, are characterized and the results are shown to compare well with those available in the literature. In the comparisons, the maximum difference found for the dielectric constants for MDA-00-3506 is 5% and for GT3-23001 is 5.3%.

Accurate modelling for the analysis and design of liquid-crystal-based microwave devices

“…2 shows a schematic diagram of the meander line phase shifter studied here. The approximate length of the meander line is 7 mm and with the material properties for GT3-23001 supplied by Merck [10] the maximum differential phase shift is approximately 40° at 60 GHz, which is obtained for a bias voltage change from 0 to 14 V. The differential phase shift as a function of voltage at…”

“…The permittivity tensor distribution 0ˆ( ) I n n ε ε ε ε ⊥ = + Δ ⊗ calculated from the liquid crystal modelling is used to calculate the microwave fields, where n is the liquid crystal director, ε ⊥ is the relative permittivity calculated in the direction perpendicular to the long axis of the liquid crystal molecules and ε Δ is the dielectric anisotropy. The desired material properties are then obtained through the comparison of the modelling and the experimental results for a simple, specially designed cell [10] within an optimisation procedure, as shown in Fig. 1.…”

Characterization of Nematic Liquid Crystals at Microwave Frequencies

“…These transmission line based methods can determine the complex permittivity of LCs within a broad frequency band, but they have a limited accuracy. We can find some examples of these techniques in the literature: in [17] a broadband coaxial line was used and in [18] an inverse microstrip line.…”

Radiation Pattern Reconfigurable Waveguide Slot Array Antenna Using Liquid Crystal

“…This motion usually concerns the rotation of the optical axis, which can tune the LC dielectric constant between ε ∥ and ε ⊥ for a certain linearly polarized electromagnetic wave. Such phenomenon is widely used for liquid crystal displays (LCDs), spatial light modulators (SLMs), and reconfigurable electromagnetic wave antennas [2][3][4][5] and devices [6][7][8][9][10].…”