Investigations of Agile Nematic and Ferroelectric Liquid Crystals for Passive Tunable Microwave devices
Optik, Quantenoptik und Physik der Atome, Moleküle und Plasmen
Zusammenfassung der Projektergebnisse
The used measurement setups are used to cover the frequency range up to 110 GHz in a temperature range of about -10 °C up to at least 100 °C. They include transmission line techniques, like a rectangular waveguide at W-Band (75 GHz-110 GHz) and coaxial lines (500 MHz-23 GHz), supported by highly precise resonant measurement setups, like the cavity perturbation method at 10, 30, and 35 GHz. During this project new mixtures were developed, which have a broad nematic temperature range, high values of birefringence and good quality of optical orientation. The best developed mixtures have good quality factors in the microwave region. New FLC mixtures which are suitable for microwave investigations were studied and their electrooptical properties were investigated. In the past two years of the project, different nematic LCs have been investigated in order to broaden the knowledge of the microwave behavior of LCs. It could be shown, that the highest dielectric anisotropy at microwaves can be achieved by using mixtures based on tolane bridges and NCS end groups. The fact, that a high anisotropy of these materials is known at optics admits the conclusion that the microwave anisotropy and the optical anisotropy are correlated. Nevertheless, the microwave anisotropy is distinctly reduced compared to the optical anisotropy. Even if mixtures with additive compounds can influence the anisotropy of the base mixtures, this effect is insignificant compared to the choice of base mixture. Besides the microwave anisotropy, the dielectric losses play a dominant role at microwaves, which contributes to the material quality factor, which is defined as the ratio between the microwave anisotropy and the maximum dielectric losses of all director orientations. It could be demonstrated, that the tolane base matrices are preferable compared to all other investigated mixtures, because of high microwave anisotropy in combination with the highest material quality factor at microwaves. Furthermore, the investigation within this project revealed, that no absorption could be measured at least up 110 GHz. To demonstrate the features of LCs at microwaves, different microwave applications have been realized covering the whole frequency range up to 110 GHz. 1. The realized phase shifters are based on different transmission line geometries: Inverted MicroStrip Line (IMSL), Inverted FinLine (IFL), and Ridged WaveGuide (RWG). These geometries are in MIM (Metal- Insulator-Metal) topology to make best use of the available anisotropy. The available phase shift per insertion loss is calculated by the Figure-of-Merit (FoM), ranging between 70°/dB and 110°/dB. This is to the author’s knowledge the highest reported achievable value compared to tunable dielectrics like ferroelectrics and passive semiconductor circuits, and was awarded in 2005 at the European Microwave Conference with the “Young engineers prize” for the presenter Stefan Müller. 2. Varactors have been realized, since the layer thickness can be reduced for this topology by far more than for transmission line structures, which are suffering for thin cavity heights from the restriction of increased metallic losses. The distance of the plates of the varactors were reduced down to 5 μm with capacity values of up to 3 pF. The measured switching times ranges below 50 ms depending on the used nematic mixture. The operating frequency ranges currently up to 2 GHz, limited by the series resonance due to parasitics. 3. In the last two years, great advances could be presented in the development of reflectarrays based on LCs. The anisotropy of the LCs is used to steer the beam of the antenna array. The presented reflectarrays operated at 35 or 77 GHz and a 2-D beam steering with a gain of up to 20 dB was demonstrated. The developed results of applications and material characterization presented by the consortium, encouraged a number of other researchers and institutions worldwide of investigating and exploration of LC at microwaves. The material quality factor of LC at millimeterwaves shows distinguished values compared to other available technologies, which are suitable for the use in reconfigurable devices. Nevertheless, especially the low switching times of nematic LCs limits the applicability at microwaves. The further reduction of switching time by using alternative material classes or material combinations is one of the main focuses in the next project phase.
Projektbezogene Publikationen (Auswahl)
- “Cavity Perturbation Method for Characterization of Liquid Crystals up to 35 GHz”. IEEE European Microwave Week, EuMW2004, Amsterdam, Oct. 2004
A. Penirschke, S. Mueller, P. Scheele, C. Weil, M. Wittek, C. Hook and R. Jakoby
- “Tunable Passive Phase Shifter for Microwave Applications using Highly Anisotropic Liquid Crystals”. IEEE Int. Microwave Symp., IMS2004, Fort Worth, June 2004
S. Müller, P. Scheele, C. Weil, M. Wittek, C. Hock and R. Jakoby
- Chiral liquid crystalline 3,6-disubstituted cyclohex-2-enones, their derivatives and FLC compositions based upon them. Liq. Cryst. 32 , 889- 900 (2005)
V.S. Bezborodov, V.I. Lapanik, G.M. Sasnovski, W. Haase
- New FLC compounds with high optical anisotropy and the compositions based upon them. Mol.Cryst. Liq. Cryst. 439, 1945-1950 (2005)
V. Lapanik, V. Bezborodov, A. Minko, W. Haase
- “Broad-Band Microwave Characterization of Liquid Crystals Using a Temperature-Controlled Coaxial Transmission Line“. IEEE Trans. Microwave Theory and Technique, vol. 53, no. 6, part 2, pp. 1937- 1945, June 2005
S. Mueller, A. Penirschke, C. Damm, P. Scheele, M. Wittek, C. Weil and R. Jakoby
- “Microwave phase shifter with ferroelectric liquid crystal having large tilt angle”. Mol. Cryst. Liq. Cryst. 434, 527-535, 2005
H. Moritake, K. Toda, T. Kamei, Y. Utsumi, W. Haase
- “Passive Tunable Liquid Crystal Finline Phase Shifter for Millimeterwaves”. IEEE European Microwave Week, EuMW2005, Paris, France, Oct. 2005
S. Mueller, C. Felber, P. Scheele, M. Wittek, C. Hock and R. Jakoby
- “Cavity Perturbation Method for Temperature Controlled Characterization of Liquid Crystals at 38 GHz”. GeMiC 2006 German Microwave Conference, Karlsruhe, Germany, 28.-30. March 2006
A. Penirschke, S. Mueller, F. Goelden, A. Lapanik, V. Lapanik, V. Bezborodov, W. Haase and R. Jakoby
- “Characterisation of 35 GHz Tunable Reflectarray Unit Cells Using Highly Anisotropic Liquid Crystal”. GeMiC 2006 German Microwave Conference, Karlsruhe, Germany, 28.-30. March 2006
R. Marin, A. Mössinger, J. Freese and R. Jakoby
- “IP3 Measurements of Liquid Crystals at Microwave Frequencies”. 36th European Microwave Conference (EuMC), Manchester, England, Sept. 2006
F. Goelden, S. Mueller, P. Scheele, M. Wittek and R. Jakoby
- “Passive Phase Shifter for W-Band Applications using Liquid Crystals”. 36th European Microwave Conference (EuMC), Manchester, England, Sept. 2006
S. Mueller, F. Goelden, P. Scheele, M. Wittek, C. Hock and R. Jakoby
- ”Electronically reconfigurable reflectarrays with nematic liquid crystals”. IEE ELECTRONICS LETTERS, vol. 42, pp. 899-900, Aug. 2006
A. Mössinger, R. Marin, S. Mueller, J. Freese and R. Jakoby
- ”Realization of 35 GHz Steerable Reflectarray Using Highly Anisotropic Liquid Crystal”. 2006 IEEE APS/URSI Symp. on Antennas and Propagation, Albuquerque, NM, USA, July 2006
R. Marin, A. Mössinger, J. Freese, A. Manabe and R. Jakoby
- “Grundlegende Untersuchungen steuerbarer passiver Flüssigkristall-Komponenten für die Mikrowellentechnik”. Dissertation, Shaker Verlag, ISBN 978-3-8322-6076-7, 2007
S. Mueller
- “Liquid Crystal Reflectarray with Electronic 2D-Reconfiguration Capability”. 29th ESA Antenna Workshop on Multiple Beams and Reconfigurable Antennas, pp. 67-70, April 2007
A. Moessinger, R. Marin, D. Eicher, R. Jakoby, and H. Schlaak
- “Systematic Investigation of Nematic Liquid Crystal Mixtures at 30 GHz”. IEEE LEOS Summer Topical Meeting, Portland, Oregon – USA 23-25 July 2007
F. Goelden, A. Lapanik, A. Gaebler, S. Mueller, W. Haase and R. Jakoby
- “Tunable Microwave Phase Shifter using Thin Layer Ferroelectric Liquid Crystals”. 11th International Conference on Ferroelectric Liquid Crystals, Sapporo, Hokkaido, Japan, 3-8. Sept. 2007
F. Goelden, A. Lapanik, A. Gaebler, S. Mueller, V. Lapanik, V. Bezborodov, W. Haase and R. Jakoby
- „Investigations on the Behavior of Ferroelectric Liquid Crystals at Microwave Frequencies“. European Microwave Conference, Munich, Oct. 2007
F. Goelden, A. Lapanik, S. Mueller, A. Gaebler, W. Haase and R. Jakoby
