Graduation Year

2020

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Gokhan Mumcu, Ph.D.

Committee Member

Nathan Crane, Ph.D.

Committee Member

Jing Wang, Ph.D.

Committee Member

Thomas Weller, Ph.D.

Committee Member

Jiangfeng Zhou, Ph.D.

Keywords

integrated actuation, frequency tunability, piezoelectric actuation, microfluidics, power handling

Abstract

Microfluidic reconfiguration of microwave devices has emerged as a potentially attractive alternative to integrated semiconductor (ICs/MMICs) and microelectromechanical systems (MEMS) based technologies. On the one hand, MMICs suffer from low power handling capabilities, high IL, non-linear effects, and elevated costs; on the other hand, MEMS are limited by their complex packaging requirements, and relatively low reliability from stiction-based effects. However, microfluidic reconfiguration provides low insertion loss (IL) due to its mechanical nature and it is not limited by power saturation effects. These attributes are especially valuable for applications at mm-waves, potentially reducing costs and increasing power efficiency capabilities. Microfluidic reconfiguration of microwave devices is possible by repositioning a volume of liquid metal or a metallized plate near the component geometry. Initial research within our group introduced microfluidically reconfigurable focal plane arrays (MFPAs) to demonstrate microfluidic beam-steering applications at 30 GHz. The first concept involves a patch antenna that was microfluidically positioned along the focal plane of a lens. However, the total movement for this design is ~40 mm, providing long reconfiguration times. Moreover, available bandwidth was limited by array size due to the use of resonant transmission lines. This dissertation solves these limitations by introducing a metallized plate inside a microfluidic channel and exploiting capacitive coupling effects to produce RF short-circuit conditions. The capacitive coupling is investigated via microfluidically switched microstrip lines that demonstrate RF switching operation from 20 GHz to 40 GHz. The coupling provides low-loss (<0.2 dB) and wideband (~20 GHz) performance. Furthermore, the RF switching concept is implemented in a 30 GHz 8-element MFPA. The MFPA exhibits ~12 GHz bandwidth and reconfiguration time of ~270 ms (as compared to ~1 GHz and 5 s respectively in previous work). Nevertheless, a remaining setback of microfluidic reconfiguration was the need for external micropumps to enable fluid motion. Such pumps are bulky as compared to the microwave components, or hard to integrate within the device. Therefore, miniaturization is necessary to achieve higher reconfiguration speeds and reliable operation. To achieve these goals, this work presents a novel integrated actuation mechanism in the form of piezoelectric bending actuators, eliminating the need for pumps. With the integrated actuation a miniaturized single-pole single-throw microfluidically reconfigurable switch is demonstrated, and it is scalable to single-pole four-throw configurations. The miniaturized switch performs with low losses (i.e. ~ 0.7 dB) and wide bandwidth (i.e. >20 GHz). The integrated actuation allows for reconfiguration speed and reliability tests that were not possible before with external micropumps. Experiments demonstrated reconfiguration times of 1.1 ms and reliable operation of the device over 3 million cycles. Moreover, the switch is expected to handle up to 30 W of continuous RF power, with experimental verification performed up to 2 W at 32 GHz. Successful realization of this compact actuation mechanism provided a path for mm-wave microfluidically reconfigurable filters with improved reconfiguration speeds and integrated microfluidic actuation. Specifically, a microfluidically reconfigurable bandpass filter that exhibits relatively low loss (i.e. up to 3.1 dB), reconfiguration speeds of 285 ms/MHz, and reliable operation up to 12 million cycles is demonstrated. The filter is reconfigurable both in frequency (from 38 GHz down to 28 GHz) and bandwidth (from 7.6% up to 16.8%) and is expected to handle up to 5 W of continuous RF power.

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