Andy M. Morishita

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.

A Liquid-Metal Monopole Array With Tunable Frequency, Gain, and Beam Steering

A reconfigurable five-element Yagi-Uda monopole array is presented that utilizes pressure-driven liquid-metal elements. There is one centrally located driven element and six parasitic elements in the array, all of which utilize liquid metal so that their physical lengths can be varied. This allows the array to tune to different operational frequencies, vary the number of director elements, and change parasitic elements from reflectors to directors, and vice versa. The measured results show beam steering along a single axis and 1.33 dB of gain tuning at 2.4 and 3.87 GHz.

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.

A liquid-metal reconfigurable Yagi-Uda monopole array

A liquid-metal reconfigurable Yagi-Uda monopole array is presented. The three-element array consists of driven and parasitic elements whose lengths can be tuned with pressure-driven liquid metal, resulting in an array in which directors can be transformed into reflectors, and in which elements can be tuned to different frequencies. The measured radiation patterns demonstrate single-axis beam steering at multiple operational frequencies from 1.95 to 4.11 GHz.

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.

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°.

Liquid-metal reconfigurable RF components and antennas

Summary form only given. Reconfigurable RF components are attractive for changing key system parameters such as operating frequency and gain. Typical reconfigurable components use switches or solid-state devices. These methods assume that the metal elements of the circuit themselves cannot be altered. We present recent work from a different paradigm by substituting liquid metal for key metal elements to enable reconfigurability. We present an overview of recent work in this emerging field, including a liquid-metal doublestub tuner, frequency selective surface (FSS), filters, and monopole arrays as proof-of-concept demonstrations using liquid metal in RF devices. This concept can be extended to many other RF devices. In the case of a double-stub tuner, liquid metal is substituted for the two open-circuit stubs. By adjusting the lengths of the stubs, a broad range of tuning impedance is achieved. Compared to using switches for impedance matching, which only have a discrete number of states, liquid metal offers a continuous range of states because of its analog nature. An FSS was created by interspersing liquid metal with mineral oil in periodically spaced tubes. By changing both the length of the liquid metal and the mineral oil spacing, two octaves of frequency tuning from 4 GHz to 17 GHz was demonstrated. A third type of component that we describe is a tunable filter. The periodic lattices of a low-pass filter with a defected ground structure (DGS) were composed of liquid metal. Liquid metal could then either fill or evacuate a DGS lattice to achieve cutoff-frequency tuning from 1.9 GHz to 3 GHz. Finally, recent work in S-band Yagi-Uda monopole arrays is presented. Tubes of liquid metal were used as the fed, parasitic, and director elements. By adjusting the length of liquid metal inside of the elements both the operating frequency and endfire directions can be changed over an octave.