Kurt Schab

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

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.

Eigenvalue Crossing Avoidance in Characteristic Modes

The theory of characteristic modes (TCM) provides a set of eigenvalues and eigenvectors that are determined entirely by a structures 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.

Radiation and Energy Storage Current Modes on Conducting Structures

The method of moments (MoM) impedance matrix is decomposed into three matrix operators related to stored energies and radiated power. The eigenvalue problems associated with each of these operators are solved in order to obtain three unique sets of modal currents and their corresponding eigenvalues. Projecting a general current into one of the three basis sets provides a convenient means of identifying currents which contribute to stored energies and radiated power. An electrically small antenna mounted to a larger ground plane is analyzed using these new methods.

Energy Stored by Radiating Systems

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.

A Group Theory Rule for Predicting Eigenvalue Crossings in Characteristic Mode Analyses

The von Neumann–Wigner theorem is used to demonstrate the general result that objects without inherent geometric symmetry will have entirely noncrossing characteristic mode eigenvalues. This suggests that objects of this kind can be analyzed without the need of advanced eigenvalue tracking routines, save for special treatment of modes that numerically appear and disappear from the spectrum. Asymmetry introduced by meshing is examined, along with the convergence and lack of convergence of certain parameters related to symmetry with mesh refinement.

Classifying characteristic mode crossing avoidances with symmetry and energy coupling

Crossing avoidances in characteristic mode eigenvalues are discussed in the context of modal symmetry and inter-modal energies. Imperfect symmetry enforcement by coarse meshing is identified as a potential cause of spurious crossing avoidances. Inter-modal energy is discussed as a possible a priori analysis to guide fast, wideband modal tracking algorithms.

Calculation of radiation transients in direct antenna modulation systems

Transient features of on-off-keyed signals generated by a direct antenna modulation system are examined. Equivalent frequency-domain impressed current sources are used to reveal the interaction between an antennas broadband input resistance profile and the high bandwidth input current. Two dipole-type antennas are compared using this method.

Minimum energy storage in dissipative electromagnetic systems

This contribution discusses the concept of recoverable energy of a general electromagnetic system and practical way of its evaluation. The paper also shows how the concept is linked to fractional bandwidth, and, more significantly, how it is related to minimum energy storage and a minimum-phase-shift of Darlingtons synthesis.

Antenna bounds for reduced basis problems

Bounds on antenna performance parameters are examined for arbitrary geometries and their substructures. The relation between a geometry and its substructures is cast in terms of basis reduction. Antenna parameters expressible as Rayleigh quotients are shown to be bounded for all substructures by the corresponding bound on the full structure. Certain parameters have secondary bounds arising from the Poincaré Separation Theorem.

Identifying radiation mechanisms on small conducting objects using radiation modes

A modal decomposition based on the real part of the method of moments impedance matrix is used to analyze the radiation mechanisms of small planar conducting objects. Here we show analytically that spatially-uniform current components are solutions to the corresponding continuous eigenvalue operator equation for the real component of the scattered electric field on the surface of the radiating object. Power is predominately radiated through these uniform modes. We present an example demonstrating the relatively small variance of low-order spatially-varying modes on a planar object with various geometry modifications.