Gregory H. Huff

A Frequency Reconfigurable Dielectric Resonator Antenna Using Colloidal Dispersions

The vertical displacement of a columnar fluidic colloidal dispersion is examined as a frequency reconfigurable dielectric resonator antenna (DRA). The coaxial probe-fed structure has tunable impedance properties that are reversibly controlled by adjusting the columnar height of the dispersion. Colloidal barium strontium titanate was dispersed in hydrotreated naphthenic oil and placed at several heights into a section of polycarbonate tubing over an aluminum ground plane to demonstrate the impedance properties of this structure. Measured, simulated, and calculated results for a range of heights that corresponded to single-mode operation are provided for a design operating between 2.5 and 4.5 GHz.

Manipulating Liquid Metal Droplets in Microfluidic Channels With Minimized Skin Residues Toward Tunable RF Applications

A nontoxic liquid metal, such as eutectic gallium-indium (EGaIn) alloy, has been used to develop tunable radio frequency (RF) components, such as antennas, inductors, or capacitors, for enabling large tunable range, better linearity, and low loss, using fluidic displacement of the liquid metal. However, EGaIn residue, due to its fast oxidation, limits multiple movement of the EGaIn in the reconfigurable RF components. This paper focuses on the use of surfactants, carrier liquids, and microchannel coating materials that minimize EGaIn fragmentation and EGaIn residues on poly(dimethylsiloxane) (PDMS)-based microfluidic channels during repeated actuation of an EGaIn plug. Using a combination of carrier liquids and microchannel coating materials to minimize EGaIn from leaving residues on the PDMS microfluidic channel, a microstrip transmission line switch as a proof-of-concept reconfigurable RF application using the EGaIn plug is demonstrated. It is switched ON<;4 dB and OFF with a loss of <;18 dB over the frequency range between 4 and 15 GHz.

Performance analysis of wireless hybrid-ARQ systems with delay-sensitive traffic

The design of wireless communication schemes tailored to real-time traffic requires an analysis framework that goes beyond the traditional criterion of data throughput. This work considers an approach that relates physical system parameters to the queueing performance of wireless links. The potential benefits of multi-rate techniques such as hybrid-ARQ are assessed in the context of delay-sensitive traffic using large deviations. A continuous-time Markov channel model is employed to partition the instantaneous data-rate received at the destination into a finite number of states, each representing a mode of operation of the hybrid-ARQ scheme. The proposed methodology accounts for the correlation of the wireless channel across time, which is computed in terms of level-crossing rates. The tail asymptote governing buffer overflow probabilities at the transmitter is then used to provide a measure of overall performance. This approach leads to a characterization of the effective capacity of the system which, in turn, is applied to quantify the performance advantages of hybrid-ARQ over traditional schemes.

Microfluidically Switched Frequency-Reconfigurable Slot Antennas

This letter proposes a concept for frequency-reconfigurable slot antennas enabled by pressure-driven capacitive microfluidic switches. The switches are operated by pneumatically displacing a plug of eutectic gallium indium alloy (EGaIn) within an air-filled microchannel that traverses the slot orthogonally. Frequency reconfigurability is achieved by altering the displacement of conductive fluid within the channel, which reactively loads the slot. A transmission-line model is developed to capture the physical behavior of the fluid channel, and measurements are provided that show good agreement with the behavior of the model.

Stripline-Fed Archimedean Spiral Antenna

An inward-fed two-arm Archimedean spiral antenna is proposed, which integrates a stripline feed network into one of the spiral arms. A broadband stripline tapered impedance transformer conformal to the spirals winding provides a novel matching network between the input impedance of the spiral and the characteristic impedance of the stripline. The Dyson-style balun at the spirals center converts the guided stripline mode to the radiating spiral mode. The transformation from a gap-fed design to a stripline-fed design is provided to illustrate the design process. Measured and simulated results for a probe-fed design operating from 2 to over 20 GHz are provided to illustrate the synthesis and performance of a demonstration antenna.

A Stochastic Mathematical Framework for the Analysis of Spherically-Bound Random Arrays

Random arrays bound by a spherical volume are rigorously analyzed through a stochastic approach for uniform and Gaussian element distributions. The full mathematical derivation and process to determine the array characteristics are discussed and a key result is the form solution which describes both the sidelobe behavior and main beam characteristics. It is also shown that the proposed approach shares many conceptual similarities to the probabilistic approach applied to circular random arrays and comparisons are made. The 3-dB beamwidth, directivity, grating lobes, and sidelobe level are examined analytically and in numerical simulation for a conceptual system of isotropic wide-band radiators with a 100:1 bandwidth.

On the Applications for a Radiation Reconfigurable Antenna

In this work, applications involving a radiation reconfigurable antenna are presented and discussed. The antenna is capable of reconfiguring its radiation pattern from broadside to endfire over a common impedance bandwidth. After outlining the operation and radiation behavior of the single element its use in multiple antenna systems, such as multiple input-multiple output (MIMO) and diversity systems, is described. Recent results using the antenna in both one-dimensional and two-dimensional planar arrays setting are also included. These examples illustrate the potential benefits and impact that pattern reconfigurable antennas can have in diverse kinds of wireless communications networks.

Analysis of a Variable SIW Resonator Enabled by Dielectric Material Perturbations and Applications

This paper details the analysis of a variable substrate integrated waveguide resonator enabled by dielectric material perturbations. A circuit model and closed-form expressions are developed. Fluidic dispersions composed of low dielectric oil and high dielectric particles are utilized in a prototype resonator to provide proof-of-concept demonstrations for three applications, which are: 1) a tunable resonator; 2) a material measurement device; and 3) a fluid sensor. Theoretical values for the dielectric constant and loss tangent of the fluidic dispersion show a possible tuning range of ~ 20% across X-band. However, measurements show the materials composing the fluidic dispersion have more losses than expected and hinder performance for practical filtering applications (Q drops to 10 s). It is noted that utilizing better materials for the fluidic dispersions will greatly increase the performance as a tunable resonator. In the next application, the measurements on the prototype resonator and parametric studies from simulation are used to estimate new properties for the fluidic dispersions constituents. The final application utilizes the prototype as a fluidic sensor for measuring the volume fraction of a particulate in a fluid medium.

Colloidal microstructures, transport, and impedance properties within interfacial microelectrodes

The authors report in situ measurements of the reversible, electric field mediated assembly of colloidal gold microstructures and their associated impedance properties on surfaces between planar gold film microelectrodes. Video optical microscopy is used to monitor the assembly of wires and locally concentrated configurations having variable resistances and capacitances. A scaling analysis of dominant electrokinetic transport mechanisms at different electric field amplitudes and frequencies is consistent with the observed steady-state microstructures. Impedance spectra are fit to equivalent circuits with elements directly connected to physical characteristics of the microelectronic/fluidic device components and different particle microstructures.

A Coaxial Stub Microfluidic Impedance Transformer ( COSMIX )

This letter proposes a coaxial stub microfluidic impedance transformer and discusses its design, theory, and operation. Electrostatically-stabilized colloidal dispersions using non-aqueous fluids facilitate its electromagnetic agility by altering their effective medium properties. Theoretical, simulated, and measured results at 400 MHz, 800 MHz, and 1.6 GHz using 0%, 25%, and 50% volume fractions of colloidal barium strontium titanate dispersed in a low-loss severely hydrotreated mineral oil are included to demonstrate the operation of the device. Simulated results for non-spherical nanoparticles are included to show the potential of different material systems.