Christopher Smartt

A Phase-Space Approach for Propagating Field-Field Correlation Functions

Radiation from complex and inherently random but correlated wave sources can be modelled by exploiting the connection between correlation functions and the Wigner function. Wave propagation can then be directly linked to the evolution of ray densities in phase space. We discuss here in particular the role of evanescent waves in the near-field of non-paraxial sources. We give explicit expressions for the growth rate of the correlation length as function of the distance from the source.

Evolution of transverse correlation in stochastic electromagnetic fields

In this work the evolution of the transverse correlation with increasing distance is investigated analytically and numerically. To characterize a stochastic EM field by measurements we have to sense the electromagnetic field in pairs of sampling points and to compute the correlations of all pairs. In the far-field, the field cross correlation functions depend only on the coordinate differences. This yields a considerable reduction of the measurement effort.

Challenges of time domain measurement of field-field correlation for complex PCBs

Measurements of field-field correlation in the time domain can be used to characterize stochastic broadband emissions from complex sources. A two-probe scanning measurement system is developed and used to sample the stochastic emissions in the near-field of two such sources: a reverberation chamber with a rectangular aperture and a generic printed circuit board (PCB). We show that measured field data can be utilized in numerical wave propagation schemes to predict the stochastic fields in and radiated from a packaged device.

Visualization of Field Distributions of Waveform-Selective Metasurface

We demonstrate numerical simulations of recently reported waveform-selective metasurfaces by developing a new electromagnetic (EM) simulation method based on the Transmission Line Modeling (TLM) method. As opposed to a conventional method integrating an EM simulator with a circuit simulator, this simulation method allows us to fully visualize electromagnetic fields around the metasurfaces. Therefore, this demonstrates how the waveform selectivity varies the surrounding fields in response to the pulse width of the incoming wave even at the same frequency. This simulation method is expected to be useful for testing other kinds of circuit-based metasurfaces and metamaterials as well.

Sensing-Throughput Tradeoff for Cognitive Radio in TV White Spaces

Cognitive Radio (CR) dynamically finds the spectrum opportunity i.e. spectrum hole in space-time-frequency and code to do its adaptive transmission without harming the incumbent or the Primary User (PU). TV white spaces (TVWS) are the unused or underutiliised bands in the UHF and VHF part of the band which according to Federal Communication Commission (FCC) can be exploited if the secondary user (SU) with CR capabilities can adequately accommodate the transmission without introducing the harmful interference to incumbent or Primary Users (PU). TV band offers excellent building penetration and less propagation losses when compared to ISM bands of 2.4GHz and 5GHz. The focus of this article is to study cooperative sensing-throughout trade-off for SU with CR capabilities in TVWS. It is shown that with M cognitive users in cooperation we can get increased throughput with increase in sensing time for a fixed probability of false alarm and target probability of detection.

Characterisation of radiated fields from PCBs in the time domain

In this paper, a method for representing electromagnetic emissions from a printed circuit board (PCB) using an equivalent dipole model deduced from time domain near-field scanning magnetic field measurements is proposed. The basic idea is to replace the PCB with a set of infinitesimal dipoles that generate the same radiated fields. Parameters of the time dependent equivalent dipoles are determined by directly fitting to the measured magnetic near fields. A simulation of a basic test structure is used to demonstrate the principle and accuracy of the approach. The scanning process is then demonstrated through simulation although it is readily applicable experimentally.

Wigner-Function-Based Propagation of Stochastic Field Emissions From Planar Electromagnetic Sources

Modeling the electromagnetic radiation from modern digital systems—acting effectively as extended stochastic sources as part of a complex architecture—is a challenging task. We follow an approach here based on measuring and propagating field-field autocorrelation functions (ACFs) after suitable averaging. From the modeling side, we use the Wigner transform of the ACFs to describe random wave fields in terms of position and direction of propagation variables. An approximate propagator for the components of the radiated magnetic field is constructed for these ACFs based on a linear flow map. Field-field ACFs at the aperture level are obtained from scanning measurements of complex sources. Distance and spatial resolution of the scanning plane is less than a wavelength from the source plane to capture the imprint of evanescent waves in the near-field ACFs. Near-field scanning and efficient near-to-far-field propagation is carried out and compared with measurements. Results of this study will be useful to assist far-field predictions, source reconstruction, and emission source microscopy.

Microwave fields have little effect on α-synuclein aggregation in a Caenorhabditis elegans model of Parkinson's disease.

Potential health effects of radiofrequency (RF) radiation from mobile phones arouse widespread public concern. RF fields from handheld devices near the brain might trigger or aggravate brain tumors or neurodegenerative diseases such as Parkinsons disease (PD). Aggregation of neural α-synuclein (S) is central to PD pathophysiology, and invertebrate models expressing human S have helped elucidate factors affecting the aggregation process. We have recently developed a transgenic strain of Caenorhabditis elegans carrying two S constructs: SC tagged with cyan (C) blue fluorescent protein (CFP), and SV with the Venus (V) variant of yellow fluorescent protein (YFP). During S aggregation in these SC+SV worms, CFP, and YFP tags are brought close enough to allow Foerster Resonance Energy Transfer (FRET). As a positive control, S aggregation was promoted at low Hg(2+) concentrations, whereas higher concentrations activated stress-response genes. Using two different exposure systems described previously, we tested whether RF fields (1.0 GHz CW, 0.002-0.02 W kg(-1); 1.8 GHz CW or GSM, 1.8 W kg(-1)) could influence S aggregation in SC+SV worms. YFP fluorescence in similar SV-only worms provided internal controls, which should show opposite changes due to FRET quenching during S aggregation. No statistically significant changes were observed over several independent runs at 2.5, 24, or 96 h. Although our worm model is sensitive to chemical promoters of aggregation, no similar effects were attributable to RF exposures.

Near-Field Scanning and Propagation of Correlated Low-Frequency Radiated Emissions

Electromagnetic radiation from complex printed circuit boards can occur over a broad frequency bandwidth, ranging from hundreds of megahertz to tens of gigahertz. This is becoming a critical issue for assessment of EMC and interoperability as electronic components become more and more integrated. We use emissions from an enclosure with a single-slot aperture and equipped with operating electronics to exemplify and model such sources. Spatial correlation functions obtained from two-probe measurements are used both to characterize the source and to propagate the emissions. We examine emissions in the submicrowave frequency range, where evanescent decay dominates the measured correlation function at the distances measured. We find that an approximate, diffusion-like propagator describes the measured emissions well. A phase-space approach based on Wigner functions is exploited to develop this approximation and to provide enhanced understanding of the emissions.

EMC-oriented multi-conductor equivalent circuit cable models for spice, including transfer impedance coupling and incident field excitation

This paper describes the development and application of sophisticated multi-conductor cable bundle models for Spice simulation. The cable models developed include frequency dependent parameters, transfer impedance coupling and incident plane wave excitation. The models may be used in frequency domain or transient simulations and are intended for EMC/ EMI studies. Simulations of realistic scenarios are presented to demonstrate typical applications.