Effect of polyimide layers on the permittivity tuning range of liquid crystals

Yaghmaee, Pouria; Kaufmann, Thomas; Bates, B.

doi:10.1109/eucap.2012.6205944

Cited by 10 publications

(4 citation statements)

References 9 publications

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“…This pre-alignment layer is particularly useful in thin planar structures with LC layer heights h LC < 150 µm, since with higher layers, more LC molecules are no longer in parallel to the surface, because of decreasing anchoring forces, reducing the orientation effectiveness. The effect of alignment layers-their thickness, orientation, and deepness of the grooves-on an LC device's tuning effectivity is analyzed in [2,74,175,185,224].…”

Section: Orientation Mechanisms and Biasing Schemesmentioning

confidence: 99%

Microwave Liquid Crystal Enabling Technology for Electronically Steerable Antennas in SATCOM and 5G Millimeter-Wave Systems

Jakoby

Gaebler²,

Weickhmann³

2020

Crystals

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Future satellite platforms and 5G millimeter wave systems require Electronically Steerable Antennas (ESAs), which can be enabled by Microwave Liquid Crystal (MLC) technology. This paper reviews some fundamentals and the progress of microwave LCs concerning its performance metric, and it also reviews the MLC technology to deploy phase shifters in different topologies, starting from well-known toward innovative concepts with the newest results. Two of these phase shifter topologies are dedicated for implementation in array antennas: (1) wideband, high-performance metallic waveguide phase shifters to plug into a waveguide horn array for a relay satellite in geostationary orbit to track low Earth orbit satellites with maximum phase change rates of 5.1°/s to 45.4°/s, depending on the applied voltages, and (2) low-profile planar delay-line phase shifter stacks with very thin integrated MLC varactors for fast tuning, which are assembled into a multi-stack, flat-panel, beam-steering phased array, being able to scan the beam from −60° to +60° in about 10 ms. The loaded-line phase shifters have an insertion loss of about 3 dB at 30 GHz for a 400° differential phase shift and a figure-of-merit (FoM) > 120°/dB over a bandwidth of about 2.5 GHz. The critical switch-off response time to change the orientation of the microwave LCs from parallel to perpendicular with respect to the RF field (worst case), which corresponds to the time for 90 to 10% decay in the differential phase shift, is in the range of 30 ms for a LC layer height of about 4 µm. These MLC phase shifter stacks are fabricated in a standard Liquid Crystal Display (LCD) process for manufacturing low-cost large-scale ESAs, featuring single- and multiple-beam steering with very low power consumption, high linearity, and high power-handling capability. With a modular concept and hybrid analog/digital architecture, these smart antennas are flexible in size to meet the specific requirements for operating in satellite ground and user terminals, but also in 5G mm-wave systems.

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Section: Orientation Mechanisms and Biasing Schemesmentioning

confidence: 99%

Microwave Liquid Crystal Enabling Technology for Electronically Steerable Antennas in SATCOM and 5G Millimeter-Wave Systems

Jakoby

Gaebler²,

Weickhmann³

2020

Crystals

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“…In a typical capacitive arrangement, where a liquid crystal cell is sandwiched between two metal electrodes and no bias voltage is applied ( = 0 V), the initial alignment of the liquid crystal molecules is achieved through coating the boundary surfaces (preferably the top and bottom layer of the cell) with a thin layer of polyimide film and then mechanically rubbing them using a velvet cloth. The rubbing creates microscopic grooves in the polyimide surfaces ( Figure 1) and enables preferred alignment for the liquid crystal molecules in the unbiased state [21,22] (Figures 2(a) and 2(b)). In electromagnetic simulations, these extremely thin polyimide layers can be neglected to a good approximation.…”

Section: Anisotropy Statesmentioning

confidence: 99%

Electrically Tuned Microwave Devices Using Liquid Crystal Technology

Yaghmaee

Karabey

Bates

et al. 2013

International Journal of Antennas and Propagation

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An overview of liquid crystal technology for microwave and millimeter-wave frequencies is presented. The potential of liquid crystals as reconfigurable materials arises from their ability for continuous tuning with low power consumption, transparency, and possible integration with printed and flexible circuit technologies. This paper describes physical theory and fundamental electrical properties arising from the anisotropy of liquid crystals and overviews selected realized liquid crystal devices, throughout four main categories: resonators and filters, phase shifters and delay lines, antennas, and, finally, frequency-selective surfaces and metamaterials.

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“…In practical designs, thin layers of rubbed polyimide coating (3-4 μm) are used to enclose the liquid crystal and define the molecule alignment in the unbiased state [7], [8].…”

Section: Properties Of Liquid Crystalmentioning

confidence: 99%

Tunable electric-LC resonators using liquid crystal

Yaghmaee

Withayachumnankul

Horestani

et al. 2013

2013 IEEE Antennas and Propagation Society International Symposium (APSURSI)

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A concept of tunable electric-LC (ELC) resonators is presented in this work. The voltage-controlled tunability is achieved by using liquid crystal in a micro-fluidic channel running through the central capacitive gaps. To attain the largest tunability, the structure is optimized through a parametric analysis using full-wave electromagnetic simulations. The simulation results predict a 6% continuous frequency tuning for this ELC resonator around the frequency of 4.5 GHz. The achieved results demonstrate the possibility of using these ELC resonators in an array to form a tunable frequency selective surfaces (FSS). The principle can be scaled for operation at higher microwave frequencies, where the dissipation of liquid crystal is low.

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Effect of polyimide layers on the permittivity tuning range of liquid crystals

Cited by 10 publications

References 9 publications

Microwave Liquid Crystal Enabling Technology for Electronically Steerable Antennas in SATCOM and 5G Millimeter-Wave Systems

Microwave Liquid Crystal Enabling Technology for Electronically Steerable Antennas in SATCOM and 5G Millimeter-Wave Systems

Electrically Tuned Microwave Devices Using Liquid Crystal Technology

Tunable electric-LC resonators using liquid crystal

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