Thomas C. Baum

Complex Dielectric Measurements of Forest Fire Ash at X-Band Frequencies

Dielectric measurements of powdered forest fire ash have been investigated and presented using the Nicholson-Ross-Weir method within a WR-90 waveguide (X-band 8-12 GHz). The dielectric measurements of five samples have been outlined and taken at a room temperature of 22.8 °C. Permittivity ε for five different species has been presented within this letter. These include Eucalypt, Bracken Fern, She Oak, Wattle, and Cypress. The Eucalypt sample was tested dry and with a 30% moisture content by weight. The dry Eucalypt sample was found to have a permittivity value of approximately 2.32 ± 0.025 with a loss tangent of 0.005 ± 0.0025.

A Complex Dielectric Mixing Law Model for Forest Fire Ash Particulates

This letter presents an empirical mixing law for forest fire ash over X-Band (8-12 GHz). Six different species of Australian flora were tested. These include eucalypt, bracken fern, she oak, wattle, cypress, and pine. The investigation highlighted the discrepancies of mixing laws based on a spherical mixing phase to those measured. By optimizing the dimensionless parameter (v) of the unified mixing law formula, a good match was achieved. An average value of v = 10 was achieved over all six samples. The effective solid complex permittivities “εi ” for all the samples were determined. These were eucalypt (6.30 + 0.06 j), bracken fern (4.85 + 0.51 j), she oak (10.05 + 1.76 j), wattle (11.44 + 0.1.71 j), cypress (8.68 + 0.85 j), and pine (16.99 + 3.51 j).

The Nature of Fire Ash Particles: Microwave Material Properties, Dynamic Behavior, and Temperature Correlation

This paper focuses on the investigation of a number of physical and electromagnetic properties of fire generated ash particles, with relation to radar observations of forest fire smoke columns. Emphasis is placed on understanding the physical properties of the ash, which have direct effects on their scattering ability. Coupled with the electromagnetic properties, these physical properties describe the scatter generated when a number of dispersed ash particles are volumetrically interacting with radar signals. Due to their planar geometry, a study of ash particles originating from the eucalyptus genus has been conducted. Particular focus is placed on this genus due to its high population and role in fueling large bushfires within the Australian continent. The fundamental scattering mechanisms required for describing the radar reflectivity in horizontal, vertical, and cross-polarization have been explored by breaking down and analyzing three distinct properties of an individual ash particle. These include its geometric, dynamic, and electromagnetic properties. Statistical distributions from all three areas have been included to aid in the development of modeling tools.

Meta-atom microfluidic sensor for measurement of dielectric properties of liquids

High sensitivity microwave frequency microfluidic sensing is gaining popularity in chemical and biosensing applications for evaluating the dielectric properties of liquid samples. Here, we show that a tiny microfluidic channel positioned in the gaps of a dual-gap meta-atom split-ring resonator can exploit the electric field sensitivity to predict the dielectric properties of liquid samples. Employing an empirical relation between resonant characteristics of the fabricated sensor and the complex permittivity of water-ethanol or water-methanol mixtures produces good congruence to standardized values from the literature. This microfluidic sensor offers a potential lab-on-chip solution for liquid dielectric characterization without external electrical connections.

Mechanically tolerant fluidic split ring resonators

Flexible resonators are crucial elements for non-planar, conformal and curved or movable surfaces in flexible high frequency electronic environments. Here, we demonstrate a stretchable, bendable, twistable and reversibly deformable split ring resonator (SRR) operating at ~3 GHz. The mechanical and electrical performance of the SRR was achieved by encapsulating liquid metal (galinstan) in a microfluidic channel of highly elastic polydimethylsiloxane. Applying mechanical deformation (bending, stretching and twisting) to the SRR results in minimal deviation of the transmission response. This offers a stable and predictable response for flexible electronic applications where mechanical deformation or conformity is inherent.

Embroidered Active Microwave Composite Preimpregnated Electronics—Pregtronics

The rapid development of the embroidery of conductive threads into textiles and associated biomedical sensors and on-body antennas has given rise to many healthcare and emergency response applications. In this paper, we investigate the embroidery of conductive threads directly into a grade of composites called “preimpregnated” (pre-preg) materials. These pre-preg materials differ from traditional textiles in that they contain a B-staged epoxy resin that must be baked in an autoclave at temperatures greater than 170 °C, and under pressures upward of 700 kPa to achieve their maximum strength. The experimental characterization of pre-preg-realized transmission line structures embroidered with different types of threads, stitches, and sewing techniques establishes the best fabrication approaches. Unlike embroidery of conductive threads into textiles, the high processing temperatures and pressures of composite materials result in conductivity and dispersion properties similar to those found in copper. We demonstrate how to incorporate passive and active electronic circuit elements directly into this structural material and its subsequent durability during the hardening process. An embroidered pre-preg electronic (pregtronic) ultrawideband amplifier is realized numerically and confirmed experimentally. Because pre-pregs have a relatively long shelf life when stored within a freezer, as well as the capability to be conformably molded to any surface, the study of pregtronics lends itself to the development of storable, conformal electronics for aerospace, automotive, and other structural applications.

Performance analysis of distorted reflector antennas basing on interval method

The aim of this paper is to analyze pattern distortion of reflector antennas with surface deformation by means of interval arithmetic. Since a reflector surface is susceptible to generate the deformation caused by structural parameter tolerances from the manufacture process or external loads (e.g., gravity, wind and ice) under the operating conditions, a robust analytical expression is introduced to model the effect of surface errors on the radiated performance of the antenna using the interval methods. In the expression, the upper and lower bounds of power pattern intervals are derived as functions of the intervals of surface errors on the basis of distorted surface caused by external loads, where the errors are connected to pattern distortion by the variation of phase terms of the aperture fields. The power pattern intervals are given under the case of different surface errors. The results clearly demonstrate that the interval method have the potential ability of giving a robust performance analysis of distorted reflector antennas.

Investigations of a Load-Bearing Composite Electrically Small Egyptian Axe Dipole Antenna

An electrically small, metamaterial-inspired Egyptian axe dipole (EAD) antenna has been investigated for use in structural composite materials. The EAD antenna consists of a differentially fed dipole element integrated with a near-field resonant parasitic EAD element. These elements have been adapted to these materials resulting in a system that is impedance matched and radiates efficiently at 307 MHz. Three cases have been identified and investigated to ascertain the performance of the manufacturing techniques and material properties used to build these electrically small antennas, as well as their performance characteristics. Uniquely, an embroidered conductive thread and a new carbon fiber based, nonwoven mat have been investigated for use as the conducting elements. Both cases are compared with a copper variant of the EAD antenna. All three prototypes were tested. Measurements confirm that both the nonwoven mat and the embroidered versions of the EAD antennas perform similarly with maximum realized gains ranging from 1.72 to 1.90 dBi.

Multi-functional composite metamaterial-inspired EEAD antenna for structural applications

An electrically small, load-bearing Egyptian axe dipole (EAD) antenna has been sewn into a low loss, pure quartz glass composite material to investigate its performance. Previous investigations of embroidered Egyptian axe dipole antennas indicated that the dielectric losses of the associated epoxy-based composite, in conjunction with the high effective surface resistance of the conductive textile threads, significantly degrade their performance. Simulations of the EAD antenna using a composite sandwich structure based on an advanced embroidery technique and the much lower loss quartz fabric have shown that a realized gain of 0.9 dBi is possible, a dramatic improvement over previous realizations.

Quasi-Orbital Angular Momentum (Q-OAM) Generated by Quasi-Circular Array Antenna (QCA)

Orbital Angular Momentum (OAM), as a property of Electromagnetic (EM) fields has recently been proposed for Radio and Microwave communications. This paper investigates a new class of OAM radiation patterns for Radio and Microwave applications, namely, Quasi-OAM radiation patterns, induced by a proposed Quasi-Circular Array Antenna (QCA). Simulations and Experiments show that Quasi-OAM waves can be induced and preserved in the far-field using the proposed QCA apertures and configurations, demonstrating non-integer dominant OAM modes corresponding to l = +1 and l = −1 with a directional quasi intensity and rotational 2π phase profiles. The proposed method in this work significantly reduces aperture size and cost by using Quasi-Circular Arrays of NQ = 5 and NQ = 6 elements in lieu of conventional OAM circular aperture arrays with N = 8 elements.