Electrically Controlled Liquid Metal Antennas and Periodic Structures

摘要

Reconfigurable antennas and periodic structures with frequency, polarization, or pattern agility, are multi-functional and adaptable to changing demands in wireless communications. As such they are actively researched by antenna engineers. Well-established reconfiguration techniques, such as electrical switching, structural and material change, are used to reconfigure the current distribution on the antenna structures to deliver dynamic characteristics. However, these techniques only achieve a limited number of reconfiguration states and suffer from inherent restrictions. Liquid metal (LM), particularly non-toxic alloy of gallium and indium, is a promising conductor capable of delivering a larger number of tunable states than conventional reconfigurable techniques. In most pre-existing applications, a pneumatic control dominates the actuation of LM but requires a bulky micro-pump. In this dissertation, a novel electrochemical control of the LM changes the interfacial tension of LM by removing and passivating the surface oxide skin using only electric potential. For the first time, we address the research gap by implementing the electrochemically controlled LM system into the design of reconfigurable structures.;Using this method, we first study a capillarity tuning of LM in a single direction. Tuning of the LM in capillaries can be switched on and off by only adjusting the applied potential. A reconfigurable monopole antenna using electrochemically controlled LM possesses a larger frequency tuning range and higher linearity level compared to tunable antennas using common reconfiguration techniques. The electrical actuation of LM provides a chance for autonomously tuning LM to the desired state based on a feedback control, as demonstrated in the programmable frequency control of the LM antenna developed in this dissertation. This electrical control further facilitates the integration of the LM system into a reconfigurable system without resorting to the bulky micro-bump of a pneumatic control system.;We then discuss the tradeoff associated with this novel actuation mechanism of LM, specifically the tuning speed of LM, power consumption and antenna efficiency associated with electrolyte concentration, and biasing condition. Briefly, a less concentrated electrolyte generates a fewer loss to the antenna but requires a larger biasing power to actuate the same speed with a more concentrated electrolyte. Understanding this tradeoff is integral to selecting a biasing current and electrolyte when implementing an LM system into a practical antenna system. The limitations and practical issues that arise from using electrolytes and packaging liquids are also discussed.;Finally, the single capillarity tuning of LM is developed into a multi-directional control in multi-capillaries and on open surfaces, capable of independently tuning the LM surface tension in different directions with independent biasing voltages. The multi-directional control of LM creates more flexible structure topologies that are harder to achieve through a pneumatic actuation of LM. A crossed dipole with compound frequency and polarization agility is demonstrated for multi-directional capillarity tuning of LM. The circular and linear polarization tunability is predicted from a high pass circuit model, thereby reducing the simulation efforts. Then, we apply the electrically controlled LM on 2D to a periodic structure- HIS on open surfaces. The LM is used as the conductor of a circular patch element and a split ring resonator element. Electrically tuning the LM surface tension expands or retracts the LM into a larger and smaller area. Simulation results suggest that a shifting reflection phase curve should be attained with this model, however, tunability is lost after adding the electrolyte into the elements. The likely explanation for this failure is detailed. The broad range of future directions and limitations of the electrically controlled LM are discussed at the end of this dissertation.