Ryan C. Gough

Continuous Electrowetting of Non-toxic Liquid Metal for RF Applications

Continuous electrowetting (CEW) is demonstrated to be an effective actuation mechanism for reconfigurable radio frequency (RF) devices that use non-toxic liquid-metal tuning elements. Previous research has shown CEW is an efficient means of electrically inducing motion in a liquid-metal slug, but precise control of the slugs position within fluidic channels has not been demonstrated. Here, the precise positioning of liquid-metal slugs is achieved using CEW actuation in conjunction with channels designed to minimize the liquid-metal surface energy at discrete locations. This approach leverages the high surface tension of liquid metal to control its resting position with submillimeter accuracy. The CEW actuation and fluidic channel design were optimized to create reconfigurable RF devices. In addition, solutions for the reliable actuation of a gallium-based, non-toxic liquid-metal alloy (Galinstan) are presented that mitigate the tendency of the alloy to form a surface oxide layer capable of wetting to the channel walls, inhibiting motion. A reconfigurable slot antenna utilizing these techniques to achieve a 15.2% tunable frequency bandwidth is demonstrated.

Self-Actuation of Liquid Metal via Redox Reaction

Presented here is a method for actuating a gallium-based liquid-metal alloy without the need for an external power supply. Liquid metal is used as an anode to drive a complementary oxygen reduction reaction, resulting in the spontaneous growth of hydrophilic gallium oxide on the liquid-metal surface, which induces flow of the liquid metal into a channel. The extent and duration of the actuation are controllable throughout the process, and the induced flow is both reversible and repeatable. This self-actuation technique can also be used to trigger other electrokinetic or fluidic mechanisms.

Frequency-tunable slot antenna using continuous electrowetting of liquid metal

This paper presents a frequency-tunable slot antenna which uses liquid metal to vary the electrical length of the radiating aperture. The liquid metal is driven by continuous electrowetting (CEW), a process by which motion is induced in a liquid-metal droplet through the application of a potential gradient across an electrolytic carrier fluid. The process is both fully reversible and repeatable, and the low-voltage electrical driving mechanism allows for simpler integration into electronic architectures than more common hydraulic methods. We believe this is the first instance of CEW being used to create a tunable RF device.

A tunable x-band substrate integrated waveguide cavity filter using reconfigurable liquid-metal perturbing posts

A tunable bandpass filter based on reconfigurable liquid-metal perturbing posts in a substrate integrated waveguide (SIW) cavity is demonstrated. The design consists of four reconfigurable posts in a single cavity which provide five center frequencies from 10.13 GHz to 11.31 GHz. To enable frequency tuning, nontoxic liquid-metal Galinstan is hydraulically actuated to activate and deactivate posts. The five states have an average peak insertion loss of 1.35 dB with fractional bandwidths of 0.6% to 1% and unloaded quality factors of 96 to 154.

Liquid-Metal-Based Reconfigurable Components for RF Front Ends

In June 2013, the White House identified the development of broadband wireless networks as crucial for economic growth, specifically identifying innovations in spectrum sharing as being the key to relieving an expected spectrum crunch caused by the rapidly increasing number of Internet-connected devices, currently estimated at over 500 million.

An electrically actuated liquid-metal switch with metastable switching states

An electrically actuated direct-contact RF shunt switch implemented with the nontoxic liquid metal Galinstan is presented. The Galinstan is actuated with a 5-VDC signal that induces electrocapillary action. Local surface-energy wells facilitate metastable locking of the Galinstan, thus achieving ON/OFF locking without requiring a continuous applied bias voltage. The switch operates from DC to 11.2 GHz with greater than 10 dB isolation and has less than 3 dB insertion loss from DC to 6.7 GHz.

Liquid-metal-based phase shifter with reconfigurable EBG filling factor

A phase shifter based on reconfigurable filling factors (FF) in a 1D electromagnetic bandgap (EBG) structure is presented. The device is capable of different gradations in phase shift, using liquid metal to fill or evacuate holes in the defected ground plane of a microstrip line. The design consists of three cascaded EBG lattices, each consisting of 4 circles with a FF of 0.17, 0.25, and 0.37 respectively. When actuated, a per-element phase shift of 1.8, 5.7, and 9.4 degrees at 5.6 GHz is introduced. A total of 67.2 degrees of phase shift can be achieved with an average insertion loss of 1.1 dB.

A liquid-metal reconfigurable log-periodic balun

A liquid-metal reconfigurable log-periodic balun is presented. The design consists of three sections that can be independently actuated with pressure-driven liquid metal, resulting in a planar balun that is capable of switching between three continuous bands from 1.89 to 8.45 GHz. The two output ports have a magnitude balance within 1 dB and a phase difference within 10° of 180°.

An Electrically Actuated Liquid-Metal Gain-Reconfigurable Antenna

A tunable liquid-metal antenna demonstrating gain reconfigurability is presented. This antenna uses a reconfigurable stub made with the liquid metal Galinstan. Using continuous electrowetting, a 60 Hz signal with an amplitude of 1 Vpp and 75% duty cycle can actuate the Galinstan continuously along a channel, tuning the stub length and antenna gain. Zero external power is required to maintain the position of the slug. The 5 GHz antenna offers more than 10 dB of analog gain tuning, from −5.90 to 4.43 dB.

Dual polarized active frequency selective surface for high power applications at X-band

An active frequency selective surface (AFSS) with switchable transmissive/reflective properties at X-band frequencies is introduced. This surface achieves a unique combination of maintaining a high dynamic range between active states, demonstrating an insensitivity to incoming orthogonal linear polarizations, and operating across a 10% bandwidth at X-band frequencies. This is achieved through a novel implementation of PIN diodes as short-circuit boundary conditions across a “window frame” aperture pattern that produces either constructive or destructive resonance depending on the biasing state of the diodes. The DC biasing structure maintains element symmetry while mitigating inter-element coupling, allowing adjacent FSS cells to be connected in series without distorting their resonance or limiting the polarization response of the surface. The AFSS has a measured reflective-state isolation of greater than 17 dB and transmissive-state loss of less than 1 dB across an operating band of 9 to 10 GHz. We believe this combination of performance and versatility at X-band to be unique in the literature, and is implemented here in such a way as to make this AFSS suitable for future high power applications.