Advances in LC characterization with application to development of mm-wave devices

Nematic liquid crystals (LCs), largely used in display technology, are liquid anisotropic materials that exhibit a variation of relative dielectric permittivity when subjected to an external electric or magnetic field. The local LC molecular ordering is described by a vector called director. The relative dielectric permittivity of the LC can be described in terms of this tensor, normally by a uniaxial tensor with nonzero principal components  and corresponding to the relative dielectric permittivities in the normal and parallel directions of the director with respect to the applied bias field. LCs have already found some uses in the design of mm-wave devices such as phase shifter, variable delay lines and voltage tuned antennas. A number of different factors influence the choice of an LC material for a particular mm-wave application. These include its mm-wave dielectric anisotropy, nematic-isotropic transition temperature and switching voltage threshold. The value of the dielectric anisotropy ( Δε ) is of paramount importance as it directly determines the ability to control an LC-based device. 

The aim of this paper is twofold. First, it presents our work on two different methods for the characterization of dielectric properties of LCs at mm-waves (broadband and spot frequency) as described in [1] and [2] and, second, it covers a summary of the development of two novel LC-based mm-wave devices (reconfigurable phase shifter and resonator) in our labs, using the characterization data as described in [3] and [4]. 

 

[1] S. Bulja, D. Mirshekar-Syahkal, M. Yazdanpanahi, R. James, F. A. Fernandez and S. E. Day, “Measurement of dielectric properties of nematic liquid crystals at milimeter wavelength”, IEEE Trans. Microwave Theory and Tech., vol. 58, issue 12, 3493-3501, 2010. 

[2] M. Yazdanpanahi, S. Bulja, D. Mirshekar-Syahkal, R. James, S. E. Day and F. A. Fernandez, “Measurement of dielectric constants of nematic liquid crystals at mm-wave frequencies using a patch resonator”, IEEE Trans. Instrum. Meas., vol. 59, issue 12, pp. 3079-3085, 2010. 

[3] S. Bulja, D. Mirshekar-Syahkal, M. Yazdanpanahi, R. James, F. A. Fernandez and S. E. Day, “60 GHz Reflection Type Phase Shifter Based On Liquid Crystal”, Proc. IEEE RWS 2010, New Orleans, USA, pp. 697- 699, 10-14 Jan. 2010.

[4] M. Yazdanpanahi, S. Bulja, D. Mirshekar-Syahkal, R. James, S. E. Day and F. A. Fernandez, “Liquid-crystal-based mm-wave tunable resonator”, Proc. EuMC 2010 Paris, France, 12331236, Oct. 2010.