Liquid crystals for signal processing applications in the microwave and millimeter wave frequency ranges

Camley, R. E.; Celiński, Z.; Garbovskiy, Yuriy; Glushchenko, Anatoliy

doi:10.1080/21680396.2018.1509385

Cited by 44 publications

(28 citation statements)

References 165 publications

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“…As a result, their physical properties can be tuned in a desirable way. This fact enabled numerous applications of liquid crystals including ubiquitous liquid crystal displays (LCD) [1] and liquid crystal on silicon (LCoS) displays for virtual and augmented reality [2], tunable components of biomedical equipment (lenses, filters for hyperspectral imaging) [3,4], polarization and phase control devices (waveplates and retarders) [5,6], diffractive optical elements [7], spatial light modulators and beam-steering devices [8], light shutters [9,10], smart windows [11,12,13], various tunable signal processing devices operating at microwave and millimeter wave frequencies [14,15], and countless others.…”

Section: Introduction: Ions In Liquid Crystalsmentioning

confidence: 99%

Evaluating the concentration of ions in liquid crystal cells: hidden factors and useful techniques

Garbovskiy

2020

Proceedings of the 2nd International Online Conference on Crystals

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Many of the liquid crystal devices are driven by electric fields. Ions, typically present in molecular liquid crystal materials in minute quantities, can compromise the performance of mesogenic materials (in the simplest case, through a well-known screening effect). Even highly purified liquid crystals can be contaminated with ions during their production and handling.Therefore, measurements of the concentration of ions became an important part of the material characterization of liquid crystals. Interestingly, even a brief analysis of existing publications can reveal a quite broad variability of the values of the concentration of ions measured by different research groups for the same liquid crystals. It reflects the complexity of ion generation mechanisms in liquid crystal materials and their dependence on numerous factors. In this paper, an overview of ion generation mechanisms in liquid crystals and modern ion measurement techniques is followed by the discussion of frequently overlooked factors affecting the measured values of the ion concentration. Ion-generating and ion-capturing properties of the alignment layers (or substrates) of liquid crystal cells are considered and used to evaluate a true concentration of ions in liquid crystals. In addition, practical recommendations aimed at improving the measurements of the ion density in liquid crystals are also discussed.

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Section: Introduction: Ions In Liquid Crystalsmentioning

confidence: 99%

Evaluating the concentration of ions in liquid crystal cells: hidden factors and useful techniques

Garbovskiy

2020

Proceedings of the 2nd International Online Conference on Crystals

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“…Liquid crystal (LC) materials have become cornerstones of modern devices, with applications ranging from displays [1] to adaptive optics [2] to, more recently, radio-frequency (RF) and microwave and millimeter wave frequencies (MMW) electronics [3]. Their ability to change the orientation of molecules under the action of a biasing electric field along with an anisotropy of their properties not only revolutionized the display industry but opened a new frontier in the development of tunable and reconfigurable devices for non-display applications.…”

Section: Introductionmentioning

confidence: 99%

“…Their ability to change the orientation of molecules under the action of a biasing electric field along with an anisotropy of their properties not only revolutionized the display industry but opened a new frontier in the development of tunable and reconfigurable devices for non-display applications. For such applications, both the switching time of the LC layer and the phase shift play important roles [3]. The phase shift is proportional to the thickness of the liquid crystal layer and its birefringence according to Equation (1) [4]:…”

Section: Introductionmentioning

confidence: 99%

“…Thick liquid crystal cells are characterized by a higher phase shift according to Equation (1). At the same time, their time response is very slow because it is a quadratic function of the cell gap [1][2][3]. To simultaneously achieve both thick and fast switching liquid crystal cells, several methods have been proposed: One is a polymer-liquid crystal composite [8,9], which allows for obtainment a rapid switching of thicker liquid crystal layers, but with the loss of phase retardation.…”

Section: Introductionmentioning

confidence: 99%

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Electro-Optical Switching of Dual-Frequency Nematic Liquid Crystals: Regimes of Thin and Thick Cells

et al. 2019

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Conventional display applications of liquid crystals utilize thin layers of mesogenic materials, typically less than 10 µm. However, emerging non-display applications will require thicker, i.e., greater than 100 µm, layers of liquid crystals. Although electro-optical performance of relatively thin liquid crystal cells is well-documented, little is known about the properties of thicker liquid crystal layers. In this paper, the electro-optical response of dual-frequency nematic liquid crystals is studied using a broad range (2–200 µm) of the cell thickness. Two regimes of electro-optical switching of dual-frequency nematics are observed and analyzed.

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“…The liquid crystal (LC) based reflectarray antenna is a common reconfigurable reflectarray antenna type [1][2][3][4]. This antenna type is widely used, especially at frequencies over 60 GHz [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Tunable Liquid Crystal Based Phase Shifter with a Slot Unit Cell for Reconfigurable Reflectarrays in F-Band

et al. 2018

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An electrically tuned phase shifter based on the single slot unit cell and liquid crystal for a reconfigurable reflectarray antenna was presented. The simulation and measured results obtained at the F-band were used to demonstrate that the dielectric properties of a nematic state liquid crystal could be exploited to realize a slot unit cell phase shifter for the reconfigurable reflectarrays antennas. By reducing the inhomogeneous of the external electric field in the liquid crystal layer, a lower control voltage and improved model accuracy was obtained. In the experiments test, the achieved saturation bias voltage (10 V) was smaller than the previously reported structure, and the phase shift of the reflectarray greater than 300° was achieved in the frequency range 121.5–126 GHz. The maximum phase shift of 306° occurred at 124.5 GHz.

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Liquid crystals for signal processing applications in the microwave and millimeter wave frequency ranges

Cited by 44 publications

References 165 publications

Evaluating the concentration of ions in liquid crystal cells: hidden factors and useful techniques

Evaluating the concentration of ions in liquid crystal cells: hidden factors and useful techniques

Electro-Optical Switching of Dual-Frequency Nematic Liquid Crystals: Regimes of Thin and Thick Cells

Tunable Liquid Crystal Based Phase Shifter with a Slot Unit Cell for Reconfigurable Reflectarrays in F-Band

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