Publications

Abstract not provided.

Coupled Mode Theory (CMT) is a classic model that addresses many diverse problems in physics and electrical engineering. Although CMT is well-established in areas such as filter and directional coupler design, its significance in antenna engineering is less well-recognized. Recently, Characteristic Mode Analysis has shown how CMT quantitatively models a wide variety of broadband, multi-mode patch structures. In this paper, we review these results and discuss the similarities and differences between these radiators through the lens of CMT. With these principles in mind, multi-mode radiators may be designed in a straightforward manner and new ideas for broadband, multi-mode patches are stimulated.

It is hypothesized that dark matter is composed of particles called quark nuggets, and further that these particles have a permanent magnetic dipole moment. If this hypothesis is true, calculations predict that a magnetized quark nugget (MQN) will oscillate when encountering the Earth's magnetosphere, and emit RF radiation between 30kHz and 30MHz. To support testing this hypothesis, a loop antenna sensor was designed and developed, which is described in this report. This sensor operates between 300kHz and 3MHz and achieves about -11dBfT/vHz sensitivity at 1.5MHz.

Battery cells with metal casings are commonly considered incompatible with nuclear magnetic resonance (NMR) spectroscopy because the oscillating radio-frequency magnetic fields ("rf fields") responsible for excitation and detection of NMR active nuclei do not penetrate metals. Here, we show that rf fields can still efficiently penetrate nonmetallic layers of coin cells with metal casings provided "B1 damming"configurations are avoided. With this understanding, we demonstrate noninvasive high-field in situ 7Li and 19F NMR of coin cells with metal casings using a traditional external NMR coil. This includes the first NMR measurements of an unmodified commercial off-the-shelf rechargeable battery in operando, from which we detect, resolve, and separate 7Li NMR signals from elemental Li, anodic β-LiAl, and cathodic LixMnO2 compounds. Real-time changes of β-LiAl lithium diffusion rates and variable β-LiAl 7Li NMR Knight shifts are observed and tied to electrochemically driven changes of the β-LiAl defect structure.

Coupled Mode Theory (CMT) is a classic model that addresses many diverse problems in physics and electrical engineering. Although CMT is well-established in areas such as directional coupler design, its significance in antenna engineering is less well-recognized. Recently, Characteristic Mode Analysis (CMA) has shown how CMT quantitatively models a wide variety of multi-mode patch structures. In this paper, we extend these ideas to a double-tuned slot antenna utilizing some unique features of the method of moments code FEKO. The modeled slot antenna has a stable radiation pattern throughout its 50% impedance bandwidth. CMA decomposition indicates the antenna consists of two resonators: the slot and a lumped LC resonator that represents the feed probe. The two are electromagnetically coupled to produce broad impedance bandwidth. An equivalent circuit whose values are derived directly from the CMA results is given.

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Narrowband and broadband low frequency magnetic field sensors have applications in EMI/EMC measurements and atmospheric and space research. This report gives analytical development of such sensors.

The impedance bandwidth of a microstrip patch antenna may be increased by additional resonances in the antenna structure. This work uses Characteristic Mode Analysis to show that a text-book coplanar parasitically coupled patch design is well described by Coupled Mode Theory. Comparisons to other multimode patch antennas also described by Coupled Mode Theory are made, and some intrinsic properties of the coplanar parasitically coupled patch geometry are noted.

Since its introduction 25 years ago, the probe-fed U-slot patch antenna has remained popular. Recently, Characteristic Mode Analysis (CMA) revealed these devices are governed by Coupled Mode Theory (CMT). Although this principle is conceptually simple, achieving this understanding is only possible through a systematic analysis using CMA. This paper uses the U-slot patch to illustrate a general process for analyzing electrically small antennas using CMA with the software package FEKO.

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The impedance bandwidth of a microstrip patch antenna may be increased by additional resonances in the antenna structure. This work uses Characteristic Mode Analysis to show that a classic stacked patch design from the literature operates in this manner and that Coupled Mode Theory governs its operation.

The impedance bandwidth of a microstrip patch antenna may be increased by additional resonances in the antenna structure. This work uses Characteristic Mode Analysis to show that the E-shaped patch operates in this manner and that its operation is well-modeled by Coupled Mode Theory.

The impedance bandwidth of a microstrip patch antenna may be increased by additional resonances in the antenna structure. This work uses Characteristic Mode Analysis to show that the E-shaped patch operates in this manner and that its operation is well-modeled by Coupled Mode Theory.

The European Association on Antennas and Propagation Software Working Group has found significant discrepancy between computer model and measurement of the RangeStar Ultima™ 'World GSM' antenna. This work shows good agreement between our model and the Working Group model as well as with our measurement. It briefly explores several possible sources of error in the Working Group measurements.

Many applications benefit from the ability of an RFID tag to operate both on and off a conducting ground plane. This paper presents an electrically small loop antenna at 433 MHz that passively maintains its free-space tune and match when located a certain distance away from a large conducting ground plane. The design achieves this using a single radiation mechanism (that of a loop) in both environments without the use of a ground plane or EBG/AMC structure. An equivalent circuit model is developed that explains the dual-environment behavior and shows that the geometry balances inductive and capacitive parasitics introduced by the ground plane such that the free-space loop reactance, and thus resonant frequency, does not change. A design equation for balancing the inductive and capacitive parasitic effects is derived. Finally, experimental data showing the design eliminates ground plane detuning in practice is presented. The design is suitable for active, 'hard' RFID tag applications.

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Patch antennas incorporating a U-shaped slot are well-known to have relatively large (about 30%) impedance bandwidths. This paper uses Characteristic Mode Analysis to show a classic U-slot patch geometry supports in-phase and anti-phase coupled modes that occur within Coupled Mode Theory.

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Abstract not provided.

Patch antennas incorporating a U-shaped slot are well-known to have relatively large (about 30%) impedance bandwidths. This work uses characteristic mode analysis (CMA) to explain the impedance behavior of a classic U-slot patch geometry in terms of coupled mode theory and shows the relevant modes are in-phase and anti-phase coupled modes whose resonant frequencies are governed by coupled mode theory. Additional analysis shows that one uncoupled resonator is the conventional TM01 patch mode and the other is a lumped LC resonator involving the slot and the probe. An equivalent circuit model for the antenna is given wherein element values are extracted from CMA data and which explicitly demonstrates coupling between these two resonators. The circuit model approximately reproduces the impedance locus of the driven simulation. A design methodology based on coupled mode theory and guided by CMA is presented that allows wideband U-slot patch geometries to be designed quickly and efficiently. The methodology is illustrated through example.