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Electrodynamics Of Continuous Media

Efficacy of virtual reality in pedestrian safety research.

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Computational Methods For Electromagnetics

Wiley Series in Microwave and Optical Engineering

The tradeoff between radiation efficiency and antenna bandwidth, expressed in terms of Q-factor for small antennas, is formulated as a multiobjective optimization problem in current distributions of predefined support. Variants on the problem are constructed to demonstrate the consequences of requiring a self-resonant current as opposed to the one tuned by an external reactance. The tradeoffs are evaluated for sample problems and the resulting Pareto-optimal sets reveal the relative cost of valuing low radiation Q-factor over high efficiency, the cost in efficiency to require a self-resonant current, the effects of lossy parasitic loading, and other insights. Observations are drawn from the sample problems selected, though the tradeoff evaluation method is valid for studying arbitrary antenna geometries. In the examples considered here, we observe that small increases in Q-factor away from its lower bound allow for dramatic increases in efficiency toward its upper bound.

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Tradeoff Between Antenna Efficiency and Q-Factor

The theory of characteristic modes (TCM) provides a set of eigenvalues and eigenvectors that are determined entirely by a structure’s geometry at a particular frequency. When examining a design over a range of frequencies, consistent interpretation of the modal data is crucial. Here, we present a way of interpreting crossing avoidances observed when tracking characteristic-mode eigenvalue traces over frequency. Using the framework of coupled-mode theory, a method for decomposing a pair of characteristic modes into auxiliary modes is developed. The auxiliary modes have a degeneracy (eigenvalue crossing) and maintain continuity of modal current distributions through the coupling region of the original characteristic modes. We demonstrate several examples using our method on simple objects. Furthermore, we explore the effect of multiplicative noise and lumped reactive loading on induced crossing avoidance.

Eigenvalue Crossing Avoidance in Characteristic Modes

Optimal currents on arbitrarily shaped radiators with respect to the minimum quality factor are found using a simple and efficient procedure. The solution starts with a reformulation of the problem of minimizing quality factor $Q$ as an alternative, so-called dual, problem. Taking advantage of modal decomposition and group theory, it is shown that the dual problem can easily be solved and always results in minimal quality factor $Q$ . Moreover, the optimization procedure is generalized to minimize quality factor $Q$ for embedded antennas, with respect to the arbitrarily weighted radiation patterns, or with prescribed magnitude of the electric and magnetic near fields. The obtained numerical results are compatible with previous results based on the composition of modal currents, convex optimization, and quasi-static approximations; however, using the methodology in this paper, the class of solvable problems is significantly extended.

Minimization of Antenna Quality Factor

Though commonly used to calculate Q-factor and fractional bandwidth, the energy stored by radiating systems (antennas) is a subtle and challenging concept that has perplexed researchers for over half a century Here, the obstacles in defining and calculating stored energy in general electromagnetic systems are presented from first principles as well as using demonstrative examples from electrostatics, circuits, and radiating systems Along the way, the concept of unobservable energy is introduced to formalize such challenges Existing methods of defining stored energy in radiating systems are then reviewed in a framework based on technical commonalities rather than chronological order Equivalences between some methods under common assumptions are highlighted, along with the strengths, weaknesses, and unique applications of certain techniques Numerical examples are provided to compare the relative margin between methods on several radiating structures

Energy Stored by Radiating Systems

OBJECTIVE: A fully immersive, high-fidelity street-crossing simulator was used to examine the effects of texting on pedestrian street-crossing performance. BACKGROUND: Research suggests that street-crossing performance is impaired when pedestrians engage in cell phone conversations. Less is known about the impact of texting on street-crossing performance. METHOD: Thirty-two young adults completed three distraction conditions in a simulated street-crossing task: no distraction, phone conversation, and texting. A hands-free headset and a mounted tablet were used to conduct the phone and texting conversations, respectively. Participants moved through the virtual environment via a manual treadmill, allowing them to select crossing gaps and change their gait. RESULTS: During the phone conversation and texting conditions, participants had fewer successful crossings and took longer to initiate crossing. Furthermore, in the texting condition, smaller percentage of time with head orientation toward the tablet, fewer number of head orientations toward the tablet, and greater percentage of total characters typed before initiating crossing predicted greater crossing success. CONCLUSION: Our results suggest that (a) texting is as unsafe as phone conversations for street-crossing performance and (b) when subjects completed most of the texting task before initiating crossing, they were more likely to make it safely across the street. APPLICATION: Sending and receiving text messages negatively impact a range of real-world behaviors. These results may inform personal and policy decisions. Keywords: Driver distraction; Language: en

Kurt Schab

Papers

Tradeoff Between Antenna Efficiency and Q-Factor

Eigenvalue Crossing Avoidance in Characteristic Modes

Minimization of Antenna Quality Factor

Energy Stored by Radiating Systems

The effects of cell phone and text message conversations on simulated street crossing