Abstract
The use of nematic liquid crystal (LC) mixtures for microwave frequency applications presents a fundamental drawback: many of these mixtures have not been properly characterized at these frequencies, and researchers do not have an a priori clear idea of which behavior they can expect. This work is focused on developing a new procedure for the extraction of the main parameters of a nematic liquid crystal: dielectric permittivity and loss tangent at 11 GHz under different polarization voltages; splay elastic constant K11, which allows calculation of the threshold voltage (Vth); and rotational viscosity γ11, which allows calculating the response time of any arbitrary device. These properties will be calculated by using a resonator-based method, which is implemented with a new topology of substrate integrated transmission line. The LC molecules should be rotated (polarized) by applying an electric field in order to extract the characteristic parameters; thus, the transmission line needs to have two conductors and low electric losses in order to preserve the integrity of the measurements. This method was applied to a well-known liquid crystal mixture (GT3-23002 from MERCK) obtaining the permittivity and loss tangent versus bias voltage curves, the splay elastic constant, and the rotational viscosity of the mixture. The results validate the viability of the proposed method.
Highlights
Current wireless communication systems are driven by a growing demand for greater capability and data rate, more functionality, and improved mobility
The objective of this work is to develop a practical procedure for the extraction of the main parameters of a nematic liquid crystal: dielectric permittivity and loss tangent at microwave frequencies related to the polarization voltage, splay elastic constant K11, and rotational viscosity γ11
The resonator was designed on a new topology of substrate integrated transmission line, which presents less radiation loss and better quality factors than other planar resonators, such as the ones implemented on inverted microstrip lines
Summary
Current wireless communication systems are driven by a growing demand for greater capability and data rate, more functionality, and improved mobility. This, along with the scarcity of frequency spectrum, leads to the development of more flexible and adaptable RF front ends [1,2]. Reconfigurability can be implemented through three main different technologies: mechanical actuators, integrated devices, and tunable materials. Mechanical actuators as microelectromechanical systems (MEMS) and integrated devices as PIN diodes or field-effect transistors (FETs) have been traditionally used due to their easy integration in planar structures. These technologies only achieve a discrete reconfigurability and have high transmission losses, especially at higher frequencies [3]
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