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We have theoretically analyzed the effect of acoustic parameters on the electromagnetic density of modes (DOM) in a one-dimensional photonic crystal featuring a defect mode. The whole structure is modulated by a longitudinal acoustic wave. The transfer matrix method and Wigner time approach are used to calculate the transmittance and electromagnetic DOM, respectively. The results show that the electromagnetic DOM is dynamically controlled by the acoustic amplitude. A sharp peak in DOM is found at the defect site whose magnitude decreases with the increase in acoustic amplitude and shows periodic swing with fractional change in time period of acoustic wave. Furthermore, the result of polarization of electromagnetic wave is also discussed and it is found that the location of the defect mode can be modulated in a large frequency rage without changing the structure of the photonic crystal.Key words: acoustic wave, electromagnetic density of modes, photonic crystal, incident angle, fractional time period.Nous faisons une analyse theorique de l'effet des parametres acoustiques sur la densite de modes (DDM) electromagnetiques dans un cristal photonique 1D possedant un mode de defaut. Toute la structure est modulee par une onde acoustique longitudinale. Nous utilisons la methode de la matrice de transfert et l'approche du temps de Wigner pour calculer la transmittance et la DDM respectivement. Les resultats montrent que la DDM electromagnetique est controlee dynamiquement par l'amplitude acoustique. Nous trouvons un pic etroit de la DDM au site du defaut, dont la hauteur diminue lorsque l'amplitude acoustique augmente, et qui oscille avec un changement fractionnaire de la periode de l'onde acoustique. Nous discutons aussi la polarisation de l'onde electromagnetique et nous trouvons que la localisation du mode du defaut peut etre modulee sur une grande bande de frequence, sans changer la structure du cristal photonique. [Traduit par la Redaction]Mots-cles : onde acoustique, densite de modes electromagnetiques, cristal photonique, angle d'incidence, periode de temps fractionnaire., 1. IntroductionThe photonic crystal (PC) has become a new field of research in many areas of science and engineering. This field owes its birth to the pioneer work made by [...]

Measuring the I-V characteristics of a transistor constitutes an important step in an introductory electronics course. We demonstrate the use of a digital oscilloscope with a USB connection to perform a measurement of the characteristic curves with no additional custom circuitry. The setup is presented alongside the open-source software that allows the signal acquisition and analysis of the results. [c] 2010 American Association of Physics Teachers. [DOI: 10.1119/1.3493628]

It takes a lot of trouble to measure and calibrate the sensitivity of ultra-high-frequency couplers which are set in various gas-insulated switchgears (GIS). This paper is related to the approach of calculating the attenuation of the electromagnetic (EM) wave due to the partial discharge propagating through insulators constituting a GIS. The use of a simulator based on the finite-difference time-domain method for analyzing the three-dimensional transient EM fields shows the degree of precision of the modeling descriptions employed and their ability to confirm experimental results. Index Terms--Finite-difference time-domain (FDTD) method, gas-insulated switchgear (GIS), partial discharge (PD), ultra-high frequency (UHF) method.

The cosine error of in situ seven-channel radiometers designed to measure the in-air downward irradiance for ocean color applications was investigated in the 412-683 nm spectral range with a sample of three instruments. The interchannel variability of cosine errors showed values generally lower than [+ or -] 3% below 50 degrees incidence angle with extreme values of approximately 4-20% (absolute) at 50-80 degrees for the channels at 412 and 443 nm. The intrachannel variability, estimated from the standard deviation of the cosine errors of different sensors for each center wavelength, displayed values generally lower than 2% for incidence angles up to 50 degrees and occasionally increasing up to 6% at 80 degrees. Simulations of total downward irradiance measurements, accounting for average angular responses of the investigated radiometers, were made with an accurate radiative transfer code. The estimated errors showed a significant dependence on wavelength, sun zenith, and aerosol optical thickness. For a clear sky maritime atmosphere, these errors displayed values spectrally varying and generally within [+ or -] 3%, with extreme values of approximately 4-10% (absolute) at 40-80 degrees sun zenith for the channels at 412 and 443 nm. Schemes for minimizing the cosine errors have also been proposed and discussed. OCIS codes: 010.4450, 120.5630.

A simultaneous measurement method using a parallel modulated probe array is proposed to measure the electromagnetic field radiated by antennas at different locations simultaneously. Each modulated probe is excited by a local signal with different frequency, so that the received intermediate frequency (IF) signal contains different frequency components which indicate the relative magnitude of the radio-frequency signal at positions of the probes, and all the IF components are measured simultaneously by a broadband microwave receiver. The effect of the local signal on the received IF signal and interaction effect between the probe array and the measured antenna are investigated. The accuracy of the method is shown by measuring the antenna radiation pattern. A 3-D antenna radiation measurement system based on the present method is also developed. The performance of the system is demonstrated by measuring the radiation efficiency of antennas. Index Terms--Electromagnetic (EM) field, measurement, modulation, probe, probe array.

For the insulation diagnosis of gas-insulated switchgears, the UHF method, which detects electromagnetic wave (EM-wave) in the UHF band (300 MHz to several GHz) with little noise influence, has rapidly developed in recent years. The study in this paper has proposed the evaluation of the location of adhering metallic particles based on the theory of EM-wave propagation by only using the time-waveform information of the EM-wave emitted due to partial discharge, and also analyzed and studied the validity using the FD-TD method. As a result, the duration of the time-waveform differed with respect to the location of the adhering metallic particle, and this difference was caused by the difference in the relative electric field intensity at the tip of the metallic particle among EM-wave modes and the difference was more when the tank diameter was larger. Based on this result, the method for evaluating the location of metallic particle according the time-waveform was studied. In addition, the characteristics of the leakage EM-wave at the spacer aperture were analyzed, and based on the result obtained, two types of antennas, patch and waveguide slot antennas, achieving compactness and a high sensitivity were proposed. Index Terms--Gas insulated switchgear (GIS), partial discharge detection, electromagnetic wave propagation, FD-TD calculation, higher order mode, spacer aperture, leakage electromagnetic wave, waveguide slot antenna.

This paper presents a method for partial discharge (PD) source location in power transformers based on detecting electromagnetic (EM) radiation emitted from PD. The key problem of PD location by EM waves is the difficulty in getting the accurate time arrivals of the signals from the source to multiple sensors. Several measures are taken to improve the time arrival resolution. Firstly, a measuring frequency band (1 GHz--5 GHz) within RF band is proposed to accurately pick up the fast rise time of the signals. Secondly, an antenna array with diamond-shaped configuration is designed to improve the correlation coefficient of the waveforms from multiple sensors. Thirdly, two antenna arrays are proposed to eliminate the influences of the EM wave scattering caused by the iron core. Fourthly, an algorithm is proposed to increase the signal to noise radio and to measure the time arrivals automatically through cross-correlation and averaging operation. Lastly, a Hyperboloid-Genetic algorithm is developed to search the PD source. Experiments on a single-phase transformer model were conducted in the laboratory. The tested results proved the validity of the proposed method and showed that the location error in 16 cm, mostly is about several cm. Index Terms--Electromagnetic radiation, partial discharge, power transformer, source location, time delay.

The electromagnetic component waves, comprising together with their generating oscillatory massless charge a material particle, will be Doppler shifted when the charge hence particle is in motion, with a velocity [...]

When radiometers on satellites point toward Earth with the goal of sensing an important variable quantitatively, rather than just creating a pleasing image, the task at hand is often not simple. The electromagnetic energy detected by the radiometers is a puzzle of various signals; it must be solved to quantify the specific physical variable. This task, called the retrieval or remote-sensing process, is important to most satellite-based observation programs. It would be ideal to test the algorithms for retrieval processes in a sealed laboratory, where all the relevant parameters could be easily measured. The size and complexity of the Earth make this impractical. NASA's Clouds and the Earth's Radiant Energy System (CERES) project has done the next-best thing by developing a long-term radiation observation site over the ocean. The relatively low and homogeneous surface albedo of the ocean make this type of site a simpler environment for observing and validating radiation parameters from satellite-based instruments. To characterize components of the planet's energy budget, CERES uses a variety of retrievals associated with several satellite-based instruments onboard NASA's Earth Observing System (EOS). A new surface observation project called the CERES Ocean Validation Experiment (COVE), operating on a rigid ocean platform, is supplying data to validate some of these instruments and retrieval products. This article describes the ocean platform and the types of observations being performed there, and highlights of some scientific problems being addressed.

Electromagnetic wave surface velocimeters (ESVs) measure the Doppler shift in electromagnetic waves reflected from the water surface. They provide nonintrusive water surface velocity measurements from bridges and river banks. Comparisons with laboratory and field tests show very good agreement over a wide range of elevation and planview angles. Laboratory testing shows comparable results between ESV and other measurement techniques when 0.4< V< 1.6 m/s and 15 < [theta] CE Database subject headings: Velocity; Discharge measurement; Channel flow; Flow rates; Overland flow.

One must employ many frequency points to synthesize a wide-band time-domain signal scattered or radiated from a given linear device. If the structure is large relative to wavelengths of interest, the large number of required frequency-domain computations may require significant computational resources. An active learning framework is introduced to reduce the number of frequencies needed for frequency-domain numerical computations or measurements. This method is used to optimally select frequency points at which a computation of measurement should be performed, resulting in nonuniform frequency sampling and often a reduced number of total frequency points (vis-a-vis uniform sampling). In this paper we focus on wide-band frequency-domain numerical modeling, demonstrating a reduction in the required number of computations. The method consists of two basic steps, tied to fitting the frequency-domain data to a simple parametric model. One step involves estimation of model parameters using a least-square (LS) algorithm. This process is based on data from frequency points computed thus far by the rigorous numerical model. The next step is to optimally choose the next frequency point for analysis by the numerical model. This new frequency point is selected with the goal of reducing uncertainty in the simplified parametric model (quantified via the Fisher information matrix). Iterating these two steps, a sequence of numerical computations are performed, each at the most informative frequency for learning the parameters of the associated simpler parametric model. After demonstrating this technique with scattering problems, the idea is employed for design of an ultrawide-band antenna. In this design, a genetic algorithm (GA) is employed to optimize the geometry and the resistive loading of an antenna, with the number of required frequency-domain numerical computations reduced by the parametric model and active learning. Index Terms--Active learning, Fisher information, genetic algorithm (GA), method of moments (MoM).

The Ewald method is applied to accelerate the evaluation of the Green's function of an infinite periodic phased array of line sources. The Ewald representation for a cylindrical wave is obtained from the known representation for the spherical wave, and a systematic general procedure is applied to extend previous results. Only a few terms are needed to evaluate Ewald sums, which are cast in terms of error functions and exponential integrals, to high accuracy. Singularities and convergence rates are analyzed, and a recipe for selecting the Ewald splitting parameter E is given to handle both low and high frequency ranges. Indeed, it is shown analytically that the choice of the standard optimal splitting parameter Co will cause overflow errors at high frequencies. Numerical examples illustrate the results and the sensitivity of the Ewald representation to the splitting parameter [epsilon]. Index Terms--Arrays, series acceleration, fast methods, green function, gratings, numerical methods, periodic structures.

Byline: Tayeb A. Denidni (1), Qinjiang Rao (1) Keywords: Microstrip slot antennas; patch antenna; front--back radiation ratio Abstract: This paper proposes a new and simple design for a broadband planar antenna with bi- and uni-directional radiation for WLAN applications. The broadband operation is realized by loading a patch into a circular aperture slot, which is fed by a microstrip line on the other side of the slot. The frequency characteristics and the radiation performance of the antenna were studied theoretically and experimentally. The obtained results show that the proposed antenna can offer effective bandwidth for the two cases in bi- and uni-directional radiation. For the former, more than 75% impedance bandwidth can be obtained whereas for the latter, better than 20 dB front--back radiation ratio can be achieved. Author Affiliation: (1) Institut National de la recherche Scientifique (INRS), University of Quebec, Canada Article History: Registration Date: 01/01/2005 Article note: Tayeb A. Denidni (M'98-SM04) received the B.Sc. degree in electronic engineering from the University of Setif, Setif, Algeria, in 1986, and the M.Sc. and Ph.D. degrees in electrical engineering from Laval University, Qubec City, QC, Canada, in 1990 and 1994, respectively. From 1994 to 1996, he was an Assistant Professor with the engineering department, Universit du Qubec in Rimouski (UQAR), Rimouski, QC, Canada. From 1996 to 2000, he was also an Associate Professor at UQAR, where he founded the Telecommunications laboratory. Since August 2000, he has been with the Personal Communications Staff, Institut National de la Recherche Scientifique (INRS-EMT), Universit du Qubec, Montreal, QC, Canada. His current research interests include planar microstrip antennas, dielectric resonator antennas, adaptive antenna arrays, microwave and RF design for wireless applications, phased arrays, microwave filters, RF instrumentation and measurements, microwave and development for wireless communications systems. Dr. Denidni is a Member for the Order of Engineers of the Province of Qubec, Canada. He is also a Member of URSI (Commission C). He has authored more than 60 papers in refereed journals and conferences. Qinjiang Rao received the Ph.D. degree from Peking University, Beijing, China, in July 1999. Now he is a postdoctoral fellow at INRS-EMT, University of Quebec, Montreal, Canada. Before this term, he even worked as a postdoctoral fellow at Kyoto University, Kyoto, Japan, and University of Calgary, Calgary, Canada, respectively. His research fields focus on antennas, high-frequency electromagnetic simulators, radio wave propagation and scattering. In 1999, he was the recipient of a Post-doctoral Fellowship awarded by the JSPS (Japan Society for the Promotion of Science.)

Causality puts certain constraints on the change of the electromagnetic field due to the change in motion of charged particles. Naive calculations of the electromagnetic energy and the work performed by the electromagnetic fields which take these constraints into account might lead to paradoxes involving the apparent nonconservation of energy. A few paradoxes of this type for the simple motion of two charges are presented and resolved in a quantitative way providing deeper insight into various relativistic effects in classical electromagnetic theory. 2002 American Association of Physics Teachers.

Knowledge of the differences in radiated susceptibility (RS) testing in anechoic (AC) and reverberation chambers (RC) is essential for analysis of the susceptibility of electronic systems to microwave radiation. We have studied microwave field-to-wire coupling for some basic wire geometries above a ground plane in ACs and RC. Results for receiving parameters such as the antenna receiving cross section [[sigma].sub.w] and the effective antenna length of the wire, [h.sub.e], are presented. The ratio between the maximum and average values of [[sigma].sub.w] may exceed 15 dB in the AC, the average being equal to [[sigma].sub.w] measured in the RC. Large variations in [[sigma].sub.w] show that the outcome of an RS test in an AC may depend strongly on the direction and polarization of the incident field. For a realistic RS test in ACs only a few angles of incidence can typically be afforded, implying a substantial risk for undertesting. Furthermore, [[sigma].sub.w] measured in the RC follows a [chi square]-distribution with two degrees of freedom. The measurements in the AC do not follow the same distribution. Index Terms--Anechoic chamber, EMC, field-to-wire coupling, HPM, microwaves, reverberation chamber.

No other component of a broadcast system offers as many options in terms of performance and efficiency as the antenna system. The radiation pattern of a MF (medium frequency) antenna is one of the major characteristics to describe the performance of the system. To optimize the reach and effectiveness of broadcast antennas and to prove regulatory compliance it is essential to know their radiation pattern for a given operating environment. Consequently it is of great interest for the broadcaster to verify the specified patterns on the installed antenna system. A tried and trusted method is to fly a helicopter or a plane carrying special recording equipment to perform far field measurements over the site. Besides being costly, this is not always possible. In this article, ground based methods where the calculated radiation patterns are verified by near field measurements are presented. This method provides good results with less expenditure compared to the above mentioned airborne far field measurements. Index Terms--MF AM antennas, near field measurements, radiation pattern verification.

A simple, rigorous electromagnetic formula is derived for predicting the electromagnetic power provided by sources located in transparent or dissipative planar microcavities. With this simple approach, we compare numerically and experimentally the electromagnetic power that escapes the microcavity when the source is located in a metallodielectric or in an all-dielectric resonant planar structure. Although a strong light-extraction coefficient might be expected for metallodielectric microcavities, we show that these attractive structures suffer from metal absorption even when thin metallic layers are used. Experiments implemented with europium chelates located in metallodielectric or in all-dielectric microcavities confirm this result.

High-power broad-band millimeter-wave radiation is emitted from a plasma in a strong Langmuir turbulence state driven by an intense relativistic electron beam. We measured directivity and spectrum of this radiation with a filter-bank spectrometer, a heterodyne spectrometer, and a filter-waveguide-combination spectrometer covering 18-140 GHz. The directivity measurement indicated that the radiation was relativistically beamed. The observed spectra were nearly flat up to about 40 GHz and declined steeply above 40 GHz. Discussion is given on the experimental results in connection with the collective Compton boosting model proposed by Benford and Weatherall. Index Terms - Beam bunching, broad-band millimeter-wave radiation, heterodyne spectrometer, IREB, strong Langmuir turbulence.

Research was conducted to examine a novel type of self-synchronizing two-dimensional Josephson junction arrays based on special symmetry breaking network architectures. The calculations prove that the Josephson oscillators mutually synchronize into a coherent in-phase state and that such arrays can emit maximum coherent microwave power in the entire theoretically expected frequency range. Experimental results indicate that the symmetry breaking array architecture will be applicable for an implementation with Josephson junctions made from high critical temperature superconductors.

Numerical modeling provides one means for realistic assessment of the electric field and current density levels induced in the bodies of live-line utility workers during occupational exposure to 60-Hz nonuniform magnetic fields. An efficient scalar potential finite difference method is applied to anatomically-derived high-resolution heterogeneous human body conductivity models, to provide such estimates for four representative posture and exposure scenarios. Dosimetric data are presented in terms of volumetric maximum and root mean square fields induced in various tissue groups by unit current. The results scale linearly with total source current, which allows the data to be applied to arbitrary current levels. Index Terms: Power transmission biological effects, Conductivity, Magnetic field effects, Electromagnetic analysis, Frequency domain analysis, Finite difference methods