Influence of graphene quantum dot doping on Fredericks transition and phase tuning in liquid crystal-based phase shifters

This paper presents a GHz phase shifter that can be controlled electrically, utilising liquid crystals doped with graphene quantum dots (GQDs). These materials have received comparatively less attention than ferroelectric or ferromagnetic nanoparticles. The study explores the Fredericks transition and analyzes the effects of various parameters on phase shifts, including impurity dopants and applied voltage. An analytical model is developed to predict phase-shifting performance based on the concentration of GQDs, and the results are validated through CST simulations. The results demonstrate that increasing the voltage from low to high values significantly enhances the phase shift of the device. Moreover, a higher concentration of quantum dot impurities leads to a more pronounced phase shift. It was also observed that increasing the concentration of GQDs results in a decrease in the frequency at which the complete 360° phase shift occurs. The analytical results align with the simulated outcomes, confirming the reliability and accuracy of the modelling approach in predicting the device’s phase behaviour and tunable properties. These findings suggest potential applications for electronically tunable liquid crystal-based devices in the microwave range, such as phase shifters, resonators, and antennas.