Accurate Modelling of Liquid Crystal-Based Microwave Devices

Fernández, FA; Seddon, L.; James, Richard; Day, SE; Bulja, Senad; Deo, Prafulla; Mirshekar‐Syahkal, D.

doi:10.1080/15421406.2015.1087271

Cited by 5 publications

(7 citation statements)

References 19 publications

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“…Fig. 4 shows a comparison between the error of the piecewise solution (14) and the derivable analytical function (17), when comparing them with the original differential equation (2) and its no squared derivative approximation (4). As observed in Fig.…”

Section: B Analytical Functionmentioning

confidence: 96%

“…4b, the error of both analytical expressions practically overlaps each others when the applied voltage is high enough. When the potential drop is under 5 V, the error goes up strongly near the midpoint d 2 with the piecewise function, reaching almost 20 • when the polarization voltage is 3 V, which does not happen with the derivable analytical expression (17). The appendix shows an alternative manner to validate the analytical approach.…”

Section: B Analytical Functionmentioning

confidence: 99%

“…Another parameter of interest, especially when working with the liquid crystal as a tunable dielectric, is the average director tilt angle θ m . In essence, it can be calculated from (17) as which leads to a difficult expression that is function of the elastic constants and the bias voltage. In Fig.…”

Section: B Analytical Functionmentioning

confidence: 99%

“…13 presents the maximum phase shift at 20 GHz, associated to each bias voltage V , that the GT3-23001 LC mixture can provide. The analytical solution (17) has been used to obtain the permittivity tensor for each voltage value. Then, the permittivity tensor is introduced in the simulator and the phase shift is computed and compared with the results of [32].…”

Section: Electromagnetic Simulationmentioning

confidence: 99%

“…On the other hand, 2D and 3D finite element methods are used in [14] and [15], respectively, to model the non-uniform electric and director fields in the liquid crystal. More recent studies have made use of a finite-difference frequency-domain method [16] and a finite element method [17] to analyze diffraction effects and wave propagation through liquid crystal devices. Another numerical approach to solve boundary problems like this one makes use of the shooting method (depicted in section IV.C).…”

Section: Introductionmentioning

confidence: 99%

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Analytical Approach of Director Tilting in Nematic Liquid Crystals for Electronically Tunable Devices

et al. 2019

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This paper presents an analytical expression that models the tilt angle of directors in a nematic liquid crystal (LC), depending on its elastic properties, its dielectric anisotropy, and the quasi-static electric field applied. The analytical solution obtained is fast and easily computable in comparison with numerical estimations and is of special interest in radiofrequency; for instance, for the LC modeling in full-wave electromagnetic simulators in the design process of electronically tunable devices, such as microwave phase shifters or electronically steerable antennas for satellite communications. Subsequently, a comparison is made between numerical approaches (self-implemented shooting method) and the analytical formulas when varying the parameters of the LC, being demonstrated its usefulness. The average LC director is then obtained and used to form the full permittivity tensor that completely characterizes the electrical properties of the material. Finally, an electromagnetic simulation is carried out to show the capabilities of the LC as a tunable phase shifter. It is shown that only 5 cm of a commercial 200-µm LC mixture is necessary to achieve 360 • of the maximum variable phase shift at the 30-GHz band. INDEX TERMS Liquid crystal, nematic phase, analytical expression, microwave, phase shifting.

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Section: B Analytical Functionmentioning

confidence: 96%

Section: B Analytical Functionmentioning

confidence: 99%

Section: B Analytical Functionmentioning

confidence: 99%

Section: Electromagnetic Simulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Analytical Approach of Director Tilting in Nematic Liquid Crystals for Electronically Tunable Devices

et al. 2019

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Liquid‐Crystal High‐Frequency Microwave Technology: Materials and Characterization

Zografopoulos

Ferraro

Beccherelli

2018

Adv Materials Technologies

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Ever since the advent of microwave technology, tunable devices, such as phase shifters, resonators, and antennas, have been indispensable in applications requiring radiofrequency signal filtering, beam shaping, or steering. This necessity becomes even more relevant in view of a new era in high‐bandwidth wireless communications in 5G networks, satellite links, and advanced radars for sensing and safety. As the operating frequency is pushed toward the millimeter‐wave range or beyond, the performance of traditional microwave tunable elements, such as PIN diodes, micro‐electromechanical system switches, ferrites, or ferroelectric films, degrades, while their fabrication complexity and cost increases. In this respect, liquid crystals present a promising solution, as they provide continuous tuning, low dielectric constants, moderate losses, low dispersion, and potentially low cost. Here, a comprehensive overview of the available microwave liquid crystal materials is provided, including their key application‐relevant properties, and the techniques employed for their characterization, focusing on the spectrum above 1 GHz. Their performance metrics in terms of dielectric constant tunability, response speed, insertion losses are discussed and guidelines for their selection in different microwave applications are provided. Moreover, the differences observed in the experimental data regarding their characterization are highlighted and possible sources of the observed discrepancies are discussed.

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