Kent Chamberlin

Finite difference time-domain calculation of transients in antennas with nonlinear loads

Transient currents for an antenna with a nonlinear load are calculated using finite-difference-time-domain (FDTD) methods. The FDTD electric field across the nonlinear load (which determines the voltage across the load) is calculated by solving a nonlinear equation at each time step. This allows the time step to be at the Courant limit, and is more efficient than reducing the time step size in all the FDTD cells to maintain stability in just the cell containing the nonlinear load. The stability of this approach relative to a simpler approach of approximating the diode as a variable resistor is demonstrated. As a validation of the method the transient current in a long dipole antenna with a nonlinear load excited by a pulsed plane wave is computed and compared with calculated results obtained by another method. The approach given here extends the applicability of the FDTD method to problems involving radiation and scattering from antennas including nonlinear loads. >

Two-dimensional, electrostatic finite element study of tip–substrate interactions in electric force microscopy of high density interconnect structures

Two-dimensional electrostatic finite element modeling is used to estimate the variation of tip force as a function of potential, dielectric film thickness, and tip-substrate spacing when imaging using electric force microscopy. Blanket dielectric films and approximately 1000 nm thick interconnect structures were studied. We conclude that sidewall damage regions can be detected but will require special processing to make an unambiguous measurement.

Wavelet analysis of quadriceps power spectra and amplitude under varying levels of contraction intensity and velocity

Introduction: We investigated the effect of contraction intensity [100%, 75%, 50%, and 25% maximum voluntary contraction (MVC)] and movement velocity (50°, 100°, 200°, and 400°/s) on surface electromyography root mean square amplitude (SEMGRMS) and median frequency (SEMGMDF) of rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM). Methods: SEMGs during knee extension were resolved into their respective frequencies using wavelet transformations. Results: RF, VL, and VM muscles displayed increased SEMGMDF as contraction intensity increased from 25% to 50% MVC and from 75% to 100% MVC, and each muscle displayed its own unique frequency shifting patterns. The SEMGMDF was not influenced by movement velocity. SEMGRMS increased in all 3 muscles as contraction intensity increased and was influenced by movement velocity, with the highest values observed at 400° and 200°/s. Conclusions: We infer that increasing contraction intensity facilitates greater recruitment of fast‐twitch muscle fibers, but there are differing responses in RF, VL, and VM muscles. Muscle Nerve 50: 844–853, 2014

Analysis of finite-differencing errors to determine cell size when modeling ferrites and other lossy electric and magnetic materials using FDTD

The focus of this paper is the modeling of materials that have both significant electric and magnetic losses, such as ferrites, using finite-difference time domain (FDTD). The primary contribution is identifying appropriate cell sizes when modeling these types of materials. It is shown that finite-differencing errors increase in lossy media compared to lossless media when sampling at the same number of cells per wavelength. Losses in a medium are defined by the ratio of the attenuation constant, /spl alpha/, to the phase constant, /spl beta/, since that ratio accounts for all losses, whether they be electric or magnetic. In addition to a detailed finite-differencing error analysis, a simple approximation is given for selecting a cell size in a lossy material that will give the same finite-differencing error as ten cells per wavelength in a lossless material. This paper also presents a means for deriving pure real constitutive parameters from complex constitutive parameters. Being able to make such calculations is useful in cases where complex constitutive parameters are given for a material, and the FDTD model being used only accepts pure real constitutive parameters, as is the case for several contemporary models. Comparisons of theoretical and FDTD-modeled reflection and transmission show that the derived, real constitutive parameters are valid.

A robust solution for preprocessing terrain profiles for use with ray-tracing propagation models

In order for ray-tracing propagation models to analyze scattering from irregular terrain, some form of preprocessing must be performed to create a linearized terrain profile to approximate the actual profile. This paper describes a preprocessing algorithm that has proven effective in working with large terrain-data files (over 2,000 points) and a 16-ray, geometric theory of diffraction propagation model. The algorithm is based upon Fermats principle, and it enables a quantitative evaluation of how well the linearized profile created approximates the actual terrain profile in terms of its effect on propagation. The accuracy of the fit can be adjusted to achieve a balance between overall model accuracy and propagation model execution time.

Systems Engineering of Datacasting for Public Safety Vehicles

Public safety officers need current, accurate and complete information to maintain the security of their communities. Existing communications systems for public safety officers consist of analog and digital radios, supplemented with cell phone communications. Dispatchers with a need to broadcast information can only do so via voice. Small data packets can be exchanged via point-to-point methods with modern digital radios, but no data broadcast exists for public safety communications. Broadcasting images, audio and text to officers in the field will offer a better collection of information necessary to make critical, time-sensitive public safety decisions. Live updates to in-vehicle databases and computer systems will provide officers with critical, up-to-the-minute information. Working with New Hampshire Public Television and the National Institute of Justice, we are researching a system to utilize excess bandwidth available in the public television broadcast spectrum. The system is to be implemented using the onboard data and car management system known as Project54TM. The use of this excess bandwidth for the delivery of digital data in a one-way, high-speed, broadcast stream is called datacasting. While datacasting has existed since the initial draft ATSC standards defining digital television, few locations have installed full datacasting capabilities, and no other datacasting effort has implemented a mobile, two-way datacasting system. This paper will outline the design of the datacasting environment for the New Hampshire Department of Safety, the results of field tests performed by 10 State Police vehicles collecting data during routine public safety patrols, and the status of the two-way datacasting implementation.

Detection of plasma-induced, nanoscale dielectric constant variations in carbon-doped CVD oxides by electrostatic force microscopy

Electrostatic force microscopy was used to detect nanoscale dielectric constant variations in two different, carbon-doped oxide low-k dielectrics deposited by plasma-enhanced chemical vapour deposition and subjected to oxidizing isotropic plasmas and inert gas isotropic plasmas. Samples were polished at 10\r{} to the sample normal to enhance the through-the-thickness spatial resolution. We observed that the technique was able to detect k{}~{}0.1 variations of dielectric constant with ~10 nm spatial resolution. We also observed that the oxidizing isotropic plasma caused damage to a depth of approximately 10-50 nm and that one of the carbon-doped oxides was more susceptible to plasma-induced damage. The estimated increase of dielectric constant from the oxidizing plasma was from k~2.5-3 to k>4-5. The damage from the inert gas plasma was observed to be deeper but less severe.

The Effect of Tree Cover on Air-Ground, VHF Propagation Path Loss

A theory accounting for attenuation caused by tree cover for line-of-sight propagation paths at VHF using vertical polarization is presented. An approach to implementing this theory using a terrainsensitive GTD propagation model is also given. Comparisons of model predictions and airborne measurements show that the approach is valid.

Using Two-Way Datacasting to Deliver Real-Time Public Safety Information

Datacasting involves the use of the excess bandwidth in a digital terrestrial television stations stream to deliver broadcasted data to a variety of receivers. Initially developed as a stationary fixed technology, this project involves receiving this broadcast in a mobile environment. This one-way transmission allows the datacast receiver to decouple data packets at a rate of up to 2.5 Mbps. Utilizing these data rates, various real-time applications can play a major role in placing information in the field where the existing low-speed data transmission methods in use today cannot. Researchers at the University of New Hampshire have already reported in various papers the successes achieved in datacasting in the mobile environment, an implementation that the original developers of datacasting had not intended. The introduction of two-way communication using multiple channels coordinated with datacasting has allowed the datacasting system to achieve real-time, asymmetric broadband communication in the mobile environment that is both cost-effective and viable for delivering critical data to the field in a timely and reliable fashion. This paper explains the technical concepts jointly engineered to deliver the two-way datacasting model, as well as highlights the results of prototype applications and devices installed in a mobile environment. Further, future challenges and enhancements of the technology are highlighted.

Evaluation of Datacasting in the Mobile Environment

Datacasting employs the excess bandwidth from digital television signals for use in one-way data transmission, and it is being used successfully for high-speed downloads at fixed locations. There is considerable interest in extending datacast usage to mobile users, although there are reception challenges in the mobile environment that can significantly impact system performance. To explore the feasibility of using datacasting in this environment, datacasting receivers and data logging equipment have been installed in 10 emergency vehicles to record performance characteristics over a wide range of operational conditions. Summary conclusions from that study are described in this paper along with details about the equipment used to make the test and the environmental factors that were found to have the greatest impact on system performance. The use of the low-speed (9600 baud) VHF, emergency-band data channel in conjunction with the datacast channel to provide two- way data transmission is also evaluated and discussed for the mobile environment.