Showing papers on "Radio wave published in 2007"

New electromagnetic mode in graphene.

Abstract: A new, weakly damped, transverse electromagnetic mode is predicted in graphene. The mode frequency omega lies in the window 1.667<[see text]omega/micro < 2, where micro is the chemical potential, and can be tuned from radio waves to the infrared by changing the density of charge carriers through a gate voltage.

Passive RF Energy Harvesting Scheme For Wireless Sensor

Abstract: A radio frequency energy harvester harvests RF energy from the environment. The energy harvester may include a local power source. The energy harvester may have an associated crystal radio antenna that harvests AM radio waves ubiquitously. The radio frequency energy harvested may be stored via a super capacitor. The stored energy may power a self-contained processing unit directly when the level of the energy harvested remains above a threshold level. However, if the energy harvested drops below the threshold level, the processing unit, which may include a radio, may switch to the local power source and/or a low power mode of operation. The low power mode of operation may reduce the amount of processing and/or transmitting by the radio. The processing unit may be part of a network of radios. The energy harvester may supply energy for a variety of applications, including building automation, industrial automation, power generation, and healthcare.

1E 1547.0–5408: A Radio-emitting Magnetar with a Rotation Period of 2 Seconds

Abstract: The variable X-ray source 1E 1547.0-5408 was identified by Gelfand & Gaensler as a likely magnetar in G327.24-0.13, an apparent supernova remnant. No X-ray pulsations have been detected from it. Using the Parkes radio telescope, we discovered pulsations with period P = 2.069 s. Using the Australia Telescope Compact Array, we localized these to 1E 1547.0-5408. We measure = (2.318 ? 0.005) ? 10-11, which for a magnetic dipole rotating in vacuo gives a surface field strength of 2.2 ? 1014 G, a characteristic age of 1.4 kyr, and a spin-down luminosity of 1.0 ? 1035 ergs s-1. Together with its X-ray characteristics, these rotational parameters of 1E 1547.0-5408 prove that it is a magnetar, only the second known to emit radio waves. The distance is ?9 kpc, derived from the dispersion measure of 830 cm-3 pc. The pulse profile at a frequency of 1.4 GHz is extremely broad and asymmetric due to multipath propagation in the ISM, as a result of which only ?75% of the total flux at 1.4 GHz is pulsed. At higher frequencies the profile is more symmetric and has FWHM = 0.12P. Unlike in normal radio pulsars, but in common with the other known radio-emitting magnetar, XTE J1810-197, the spectrum over 1.4-6.6 GHz is flat or rising, and we observe large, sudden changes in the pulse shape. In a contemporaneous Swift X-ray observation, 1E 1547.0-5408 was detected with record high flux, fX(1-8 keV) ? 5 ? 10-12 ergs cm-2 s-1, 16 times the historic minimum. The pulsar was undetected in archival radio observations from 1998, implying a flux <0.2 times the present level. Together with the transient behavior of XTE J1810-197, these results suggest that radio emission is triggered by X-ray outbursts of usually quiescent magnetars.

Nonlinear effects in the ionosphere

Abstract: The review is based in a report presented by the author at the RAS Physical Sciences Division's session in honor of Vitaly L Ginzburg's 90th birthday. It examines the current status of theoretical and experimental research on nonlinear phenomena arising when a powerful radio wave propagates in the ionosphere. The focus is on the modification of the ionosphere under the resonance excitation of natural plasma oscillations by radio waves. The upper-hybrid resonance gives rise to strong upper- and lower-hybrid plasma waves; excites strongly elongated ionospheric irregularities, and induces artificial ionospheric radio emission. Nonlinear processes are found to undergo complete transformation near double resonances, when the upper-hybrid frequency is close to a multiple of the electron gyromagnetic frequency. In the neighborhood of the Langmuir resonance, intense plasma waves and ion-sound waves are excited, electrons are effectively accelerated, and an artificial glow of the ionosphere appears.

FORMOSAT-3/COSMIC GPS Radio Occultation Mission: Preliminary Results

Abstract: The Formosa Satellite-3 and Constellation Observing System for the Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) radio occultation (RO) mission has been successfully launched on April 14, 2006. The FORMOSAT-3/COSMIC mission uses global positioning system (GPS) signals to study the atmosphere and the ionosphere with global coverage. Receivers that are installed onboard of the six small FORMOSAT-3/COSMIC satellites register the phase and the amplitude of radio waves at two GPS frequencies. We give a preliminary analysis of the first RO measurements that are provided by the FORMOSAT-3/COSMIC mission. The geographical distribution of the first FORMOSAT-3/COSMIC RO experiments is shown. We demonstrate that the performance of the first measurements allows obtaining the vertical profiles of the refractivity, temperature, and pressure for the considered FORMOSAT-3/COSMIC RO events with expected accuracy, which is quite similar to the accuracy of the previous Challenging Mini-Satellite Payload and Gravity Recovery and Climate Experiment RO missions. New elements in the RO technology are suggested for further improving the accuracy and broadening the application range of the RO method. We emphasize new directions in applying the RO method to measure the vertical gradients of the refractivity in the atmosphere, to determine the temperature regime in the upper stratosphere, and to investigate the internal wave activity in the atmosphere. We find a significant correlation between the phase acceleration and the intensity variations in the RO signals that are emitted by GPS satellites and registered by the FORMOSAT-3/COSMIC satellites. This correlation opens a way to locate the layered structures in the propagation medium based on simultaneous observations of the radio wave intensity and the phase variations in trans-ionospheric satellite-to-satellite links.

UWB short-range radar sensing - The architecture of a baseband, pseudo-noise UWB radar sensor

Abstract: The pioneers of radio science made their first trials of wireless information transmission and demonstrated localization of a steel vessel by radio waves more than 100 years ago. Back then, the world of radio frequencies was organized in a very simple way. The researchers could use any frequency band. There was no interference by others and no controlling government bodies. Since then, governmental authorities have established tight regulations that have split up the available frequency band into small partitions for exclusive use. This article discusses the architecture of a baseband, pseudo-noise UWB radar and gives some examples of applications

Propagation Mechanisms of Radio Waves Over Intra-Chip Channels With Integrated Antennas: Frequency-Domain Measurements and Time-Domain Analysis

Abstract: The propagation mechanisms of radio waves over intra-chip channels was studied with integrated antennas for wireless chip area networks. Test vehicles were designed and fabricated on silicon wafers of both low and high resistivities, respectively, using complementary metal oxide semiconductor (CMOS) processes. On-wafer measurements for propagation of radio waves over intra-chip channels were conducted in the frequency domain from 10 to 110 GHz with a network analyzer. Time-domain analysis was performed to characterize intra-chip radio channels and more importantly to understand the propagation mechanisms. It was found that path loss factor is constantly less than two and propagation delay of the first-arrival wave is significantly longer than that by free-space transmission. Thus, we concluded that the propagation of radio waves over intra-chip channels is mainly realized with surface wave rather than space wave. Surface wave is guided on air-wafer interface. In addition, effects of metal lines, in both parallel and normal placements with respect to wave propagation direction, on signal propagation were also investigated.

Optical hotspots speed up wireless communication

Abstract: In the future, equipping rooms with 'optical wireless hotspots' that enable fast free-space data transmission to laptops or mobile phones by means of light beams rather than radio waves, could dramatically boost the speed of wireless communication.

Wireless sensor device

Abstract: A wireless sensor device capable of constant operation without replacement of batteries The wireless sensor device is equipped with a rechargeable battery and the battery is recharged wirelessly Radio waves received at an antenna circuit are converted into electrical energy and stored in the battery A sensor circuit operates with the electrical energy stored in the battery, and acquires information Then, a signal containing the information acquired is converted into radio waves at the antenna circuit, whereby the information can be read out wirelessly

CME Propagation Characteristics from Radio Observations

Abstract: We explore the relationship among three coronal mass ejections (CMEs), observed on 28 October 2003, 7 November 2004, and 20 January 2005, the type II burst-associated shock waves in the corona and solar wind, as well as the arrival of their related shock waves and magnetic clouds at 1 AU. Using six different coronal/interplanetary density models, we calculate the speeds of shocks from the frequency drifts observed in metric and decametric radio wave data. We compare these speeds with the velocity of the CMEs as observed in the plane-of-the-sky white-light observations and calculated with a cone model for the 7 November 2004 event. We then follow the propagation of the ejecta using Interplanetary Scintillation measurements, which were available for the 7 November 2004 and 20 January 2005 events. Finally, we calculate the travel time of the interplanetary shocks between the Sun and Earth and discuss the velocities obtained from the different data. This study highlights the difficulties in making velocity estimates that cover the full CME propagation time.

Broadband room service by light.

Abstract: This article explores the wireless delivery of multimedia Internet services to multiple users. The author suggests that light beams may be a better transmission medium than radio waves. Light photons offer a broader bandwidth that allows many users to operate simultaneously. Photons do not interfere with each other as radio waves can and they do not pass through walls which would provide for better privacy. INSETS: KEY CONCEPTS;RADIO VS. INFRARED;Optical Wireless Network;HOLOGRAPHIC FILTERS DEFEAT ECHOES

Propagation Characteristics of Polarized Radio Waves in Cellular Communications

Abstract: Narrowband and wideband measurements of the radio channel using different combinations of transmit and receive polarization have been performed. The measurements cover a range of scenarios including urban, suburban and open terrain, as well as both outdoor and indoor terminals. The vertical-to-vertical (V-V) and horizontal-to-horizontal (H-H) polarization combinations are found to provide equal received power on average, while the cross-polarized combinations (V-H) and (H-V) typically provide 5-15 dB weaker received power due to the limited amount of cross-polarization scattering in the radio channel. Fast fading variations are further found to be uncorrelated between different combinations of transmit and receive polarization.

Radio propagation and adaptive antennas for wireless communication links : terrestrial, atmospheric and lonospheric [i.e. ionospheric]

Abstract: Preface. Chapter One: Fundamentals of Radio Communications. 1.1. Radio Communication Link. 1.2. Frequency Band for Radio Communications. 1.3. Noise in Radio Communication Links. 1.4. Main Propagation Characteristics. 1.5. Problems in Adaptive Antennas Application. Bibliography. Chapter Two: Antenna Fundamentals. 2.1. Radiation Pattern. 2.2. Field Regions of an Antenna. 2.3. Radiation Intensity. 2.4. Directivity and Gain. 2.5. Polarization. 2.6. Terminal Antennas in Free Space. 2.7. Antenna Types. Bibliography. Chapter Three: Fundamentals of Wave Propagation in Random Media. 3.1. Main Wave Equations and Random Functions. 3.2. The Perturbation Method for Multiple Scattering. The Mean Perturbed Propagator. The Mean Double Propagator. Mass Operator and Dyson Equation. 3.3. An Exact Solution of 1D-Equation. 3.4. Approximations of the Perturbation Method. 3.5. Random Taylor Expansion at Short Wavelengths. 3.6. An Exact Solution of the Scalar Wave Equation. Approximate Evaluations of the Functional Integral (3.137). 3.7. The Electromagnetic Wave Equation. 3.8. Propagation in Statistically Inhomogeneous Media. 3.9. Propagation in Homogeneous Anisotropic Media. Bibliography. Chapter Four: Electromagnetic Aspects of Wave Propagation over Terrain. 4.1. Waves Propagation in Free Space. 4.2. Path Loss in Free Space. 4.3. Radio Propagation Above Flat Terrain. 4.4. Propagation Above Rough Terrain Under LOS Conditions. 4.5. Propagation Above a Smooth Curved Terrain. 4.6. Effect of a Single Obstacle Placed on a Flat Terrain. Bibliography. Chapter Five: Terrestrial Radio Communications. 5.1. Characterization of the Terrain. 5.2. Propagation Scenarios in Terrestrial Communication Links. 5.3. Propagation over a Flat Terrain in LOS Conditions. 5.4. Propagation over a Hilly Terrain in NLOS Conditions. 5.5. Effect of a Building on the Radio Propagation Channel. 5.6. Propagation in Rural Forest Environments. 5.6.1. A Model of Multiple Scattering in a Forested Area. 5.6.2. Comparison with Other Models. 5.7. Propagation in Mixed Residential Areas. 5.8. Propagation in Urban Environments. Bibliography. Chapter Six: Effects of the Troposphere on Radio Propagation. 6.1. Main Propagation Effects of the Troposphere as a Spherical Layered Gaseous Continuum. 6.2. Effects of the Hydrometeors on Radio Propagation in the Troposphere. 6.3. Effects of Tropospheric Turbulences on Radio Propagation. 6.4. Link Budget Design for Tropospheric Communication Links. Bibliography. Chapter Seven: Ionospheric Radio Propagation. 7.1. Main Ionospheric Effects on Radio Propagation. 7.2. Effects of the Inhomogeneous Ionosphere on Radio Propagation. 7.3. Back and Forward Scattering of Radio Waves by Small-Scale Ionospheric Inhomogeneities. Bibliography. Chapter Eight: Indoor Radio Propagation. 8.1. Main Propagation Processes and Characteristics. 8.2. Modeling of Loss Characteristics in Various Indoor Environments. 8.3. Link Budget Design Verification by Experimental Data. Bibliography. Chapter Nine: Adaptive Antennas for Wireless Networks. 9.1. Antenna Arrays. 9.2. Beamforming Techniques. 9.3. Adaptive Antenna for Wireless Communication Applications. 9.4. Network Performance Improvement Using an Antenna Array. Summary. Bibliography. Chapter Ten: Prediction of Signal Distribution in Space, Time and Frequency Domains in Radio Channels for Adaptive Antenna Applications. 10.1. Predicting Models for Indoor Communication Channels. 10.2. Predicting Models for Outdoor Communication Channels. 10.3. Experimental Verification of Signal Power Distribution in Azimuth, Elevation, and Time Delay Domains. 10.4. Signal Power Spectra Distribution in Frequency Shift Domain. Bibliography. Chapter Eleven: Multipath Fading Phenomena in Land Wireless Links. 11.1. Prediction of Loss Characteristics for Land Radio Links. 11.2. Link Budget Design for Various Land Environments. 11.3. Characterization of Multipath Radio Channel by Rician Factor. 11.4. Main Algorithm of Radio Coverage (Radio Map) Design. Bibliography. Chapter Twelve: Cellular Communication Networks Design Based on Radio Propagation Phenomena. 12.1. Grade of Service (GOS) Design Operating in Multipath Fading Environment. 12.2. Propagation Aspects of Cell Planning. 12.3. Prediction of Parameters of Information Data Stream. Channel Capacity and Spectral Efficiency. Relations Between Main Parameters. Bibliography. Chapter Thirteen: Prediction of Operational Characteristics of Adaptive Antennas. 13.1. Experimental Verification of Signal Distribution in Azimuth, Time Delay, and Doppler Shift Domains. 13.2. Prediction of Adaptive Antenna Characteristics Based on Unified Stochastic Approach. Bibliography. Chapter Fourteen: Land-Satellite Communication Links. 14.1. Objective. 14.2. Type of Signals in Land-Satellite Communication Links. 14.3. Statistical Models. 14.4. Physical-Statistical Models. 14.5. The Unified Algorithm for Fading Phenomena Prediction. 14.6. Mega-Cell Concept for Land Satellite Communication Links. 14.7. "Mega-Cell" Global Networks Design. Summary. Bibliography. Index.

Compensation of acoustic attenuation for high-resolution photoacoustic imaging with line detectors

Abstract: Photoacoustic imaging is based on the generation of acoustic waves in a semitransparent sample after illumination with short pulses of light or radio waves. The goal is to recover the spatial distribution of absorbed energy density inside the sample from acoustic pressure signals measured outside the sample (photoacoustic inverse problem). We have proposed a numerical method to calculate directly the time reversed field by retransmitting the measured pressure on the detection surface in reversed temporal order. This model-based time reversal method can solve the photoacoustic inverse problem exactly for an arbitrary closed detection surface. Recently we presented a set up which requires a single rotation axis and line detectors perpendicular to the rotation axis. Using a two-dimensional reconstruction method, such as time reversal in two dimensions, and applying the inverse two-dimensional radon transform afterwards gives an exact reconstruction of a three-dimensional sample with this set up. The resolution in photoacoustic imaging is limited by the acoustic bandwidth and therefore by acoustic attenuation, which can be substantial for high frequencies. This effect is usually ignored in reconstruction algorithms but has a strong impact on the resolution of small structures. It is demonstrated that the model based time reversal method allows to partly compensate this effect.

Radio Frequency Interference Suppression Techniques in FMCW Modulated HF Radars

Abstract: High-frequency (HF) radars are operated in the 3-30 MHz frequency range and need to share the frequency bands with other radio services. Due to their over-the-horizon (OTH) capabilities, HF radars play an important role in remote sensing and surveillance. The propagation conditions of the electromagnetic wave depend on the earth's ionosphere and mailnly follow a daily cycle. Communication paths between the HF radar and other radio services, some thousands of kilometres off, open and close with a high variability. Special care must be taken to dynamically adapt the HF radar's characteristics to the varying electromagnetic environment. The impact of a frequency modulated continuous wave (FMCW) HF radar on other radio services is not very strong, because of its low transmit power and utilisation of the radio spectrum. However, strong signals from other radio services can significantly reduce the performance of the oceanographic measurements. Several radar control and signal processing steps are discussed in this paper. All together form an effective procedure to reduce the impact of Radio Frequency Interference (RFI) on the oceanographic measurements.

The “Sura” facility: Study of the atmosphere and space (a review)

Abstract: We present a short review of research using “Sura,” a multipurpose radio facility of the Radiophysical Research Institute of Nizhny Novgorod, which is aimed at studying space, the atmosphere, the Earth’s crust, and radio wave propagation and at developing new methods for diagnostics and monitoring of the environment.

The IDV source J 1128+5925, a new candidate for annual modulation?

Abstract: Context. Short time-scale radio variations of compact extragalactic radio sources, known as IntraDay Variability (IDV), can be explained in at least some sources by a source-extrinsic effect, in which the variations are interpreted as scintillation of radio waves caused by the turbulent interstellar medium of the Milky Way. One of the most convincing observational arguments in favour of propagation-induced variability is the so-called “annual modulation” of the characteristic variability time-scale, which is due to the orbital motion of the Earth. So far there are only two sources known which show such a well-defined seasonal cycle, a few more sources with fewer data can be regarded as possible candidates for this effect. However, source-intrinsic effects, such as structural variations, can also cause the observed changes of the variability time-scale. Data for the new, recently discovered, and highly variable IDV source J 1128+5925 are presented. Aims. We study the frequency and time dependence of the IDV in this compact quasar. We measure the characteristic variability time-scale of the IDV throughout the year, and analyze whether the observed changes in the variability time-scale are consistent with annual modulation. Assuming a radio wave propagation effect as origin, we are able to constrain some physical properties (such as distance, scattering-strength, and possible anisotropy) of the “plasma” screen, which may cause the scintillation. Methods. We monitored the flux density variability of J 1128+5925 with dense time sampling between 2.7 and 10.45 GHz. We observed with the 100 m Effelsberg radio telescope of the Max-Planck-Institut fur Radioastronomie (MPIfR) at 2.70 GHz, 4.85 GHz, and 10.45 GHz, as well as with the 25 m Urumqi radio telescope (China) at 4.85 GHz. From ten observing sessions, each of which lasted several days during the period between 2004–2006, we determine the variability characteristics and time-scales which we investigate in view of possible scintillation and annual modulation. Results. The observed pronounced changes of the variability time-scale of J 1128+5925 are modelled with an anisotropic annual modulation model. The observed frequency dependence of the variation is in good agreement with the prediction from interstellar scintillation. Adopting a simple model for the annual modulation model and also using the frequency dependence of the IDV, we derive a lower limit to the distance the scattering screen and an upper limit for the scintillating source size. The latter is found to be consistent with the measured core size from Very Long Baseline Interferometry (VLBI).

Determining Weather Radar Antenna Pointing Using Signals Detected from the Sun at Low Antenna Elevations

Abstract: A method to determine the elevation and azimuth biases of the radar antenna using solar signals observed by a scanning radar is presented. Data recorded at low elevation angles where the atmospheric refraction has a significant effect on the propagation of the radio wave are used, and a method to take the effect of the refraction into account in the analysis is presented. A set of equations is given by which the refraction of the radio waves as a function of the relative humidity can easily be calculated. Also, a simplified model for the calculation of the atmospheric attenuation is presented. The consistency of the adopted models for the atmospheric refraction and atmospheric attenuation is confirmed by data collected at a single elevation pointing, but over a long observing time. Finally, the method is applied to datasets based on operational measurements at the Finnish Meteorological Institute (FMI) and Royal Netherlands Meteorological Institute (KNMI), and elevation and azimuth biases of the ...

Jovian S burst generation by Alfvén waves

Abstract: [1] Jupiter's radio emissions are dominated in intensity by decametric radio emissions due to the Io-Jupiter interaction. Previous analyses suggest that these emissions are cyclotron-maser emissions in the flux tubes connecting Io or Io's wake to Jupiter. Electrons responsible for the emission are thought to be accelerated from Io to Jupiter. We present simulations of this hot electron population under the assumption of acceleration by Alfven waves in the Io flux tube. Outside of limited acceleration regions where a parallel electric field associated with Alfven waves exists, the electrons are supposed to have an adiabatic motion along the magnetic field lines. Near Jupiter a loss cone appears in the magnetically mirrored electron population, which is able to amplify extraordinary (X) mode radio waves. The X-mode growth rate is computed, which allows us to build theoretical dynamic spectra of the resulting Jovian radio emissions, whose characteristics match those observed for Jovian S bursts.

Radio communication method and radio base transmission station

Abstract: An antenna pattern assigning method capable of avoiding interference between a plurality of base transmission stations constituting a radio system in a cellular type broad band communication. In the radio system, when assigning a fixed beam pattern different for each frequency, each of the radio base transmission station devices transmits a radio wave having a directivity pattern having a peak in the same direction in two or more different frequencies, and between adjacent radio base transmission station devices, radio transmission is performed by using different directivity patterns in the two or more frequencies.

Vertical sheets of dense plasma in the topside Martian ionosphere

Abstract: [1] The low-frequency radar, Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), on board the Mars Express spacecraft is used to sound electron densities in the topside Martian ionosphere. The radar records the delay times to echoes of reflected radio waves as a function of frequency, yielding spectrograms with traces of radar echoes. At times, two traces are present in spectrograms of the Martian ionosphere. One of these traces corresponds to reflections from the direction to nadir. The other trace originates in a localized reflector in the ionosphere. The local reflectors can be associated with the cusplike regions of near-vertical crustal magnetic fields. The apparent nadir angle of reflection can occasionally increase to 90°. This suggests that steep gradients of the altitude of the electron isodensity exist in the Martian ionosphere and indicates rapid horizontal spatial variations of vertical diffusion of Martian plasma. Such gradients may arise owing to preferential access of solar wind to the cusplike regions or to precipitation of energetic electrons from acceleration regions located on cusp magnetic field lines high above the ionosphere.

The IDV source J1128+5925, a new candidate for annual modulation?

Abstract: Short time-scale radio variations of compact extragalactic radio sources, known as IntraDay Variability, can be explained in at least some sources by a source-extrinsic effect, in which the variations are interpreted as scintillation of radio waves caused by the turbulent ISM of the Milky Way. One of the most convincing observational arguments in favour of propagation-induced variability is the so called annual modulation of the characteristic variability time-scale, which is due to the orbital motion of the Earth. Data for the recently discovered and highly variable IDV source J1128+5925 are presented. We study the frequency and time dependence of the IDV in this compact quasar. We measure the characteristic variability time-scale of the IDV throughout the year, and analyze whether the observed changes in the variability time-scale are consistent with annual modulation. We monitored the flux density variability of J1128+5925 with dense time sampling between 2.7 and 10.45GHz with the 100m Effelsberg radio telescope of the MPIfR and with the 25m Urumqi radio telescope. From ten observing sessions, we determine the variability characteristics and time-scales. The observed pronounced changes of the variability time-scale of J1128+5925 are modelled with an anisotropic annual modulation model. The observed frequency dependence of the variation is in good agreement with the prediction from interstellar scintillation. Adopting a simple model for the annual modulation model and using also the frequency dependence of the IDV, we derive a lower limit to the distance of the scattering screen and an upper limit to the scintillating source size. The latter is found to be consistent with the measured core size from VLBI.

Temporal evolution of pump beam self-focusing at the High-Frequency Active Auroral Research Program

Abstract: [1] On 4 February 2005 the High-Frequency Active Auroral Research Program (HAARP) facility was operated at 2.85 MHz to produce artificial optical emissions in the ionosphere while passing through the second electron gyroharmonic. All-sky optical recordings were performed with 15 s integration, alternating between 557.7 and 630 nm. We report the first optical observations showing the temporal evolution of large-scale pump wave self-focusing in the magnetic zenith, observed in the 557.7 nm images. These clearly show that the maximum intensity was not reached after 15 s of pumping, which is unexpected since the emission delay time is <1 s, and that the optical signature had intensified in a much smaller region within the beam after 45 s of pumping. In addition, adjacent regions within the beam lost intensity. Radar measurements indicate a plasma depletion of ∼1% near the HF reflection altitude. Ray tracing of the pump wave through the plasma depletion region, which forms a concave reflecting radio wave mirror, reproduces the optical spatial morphology. A radio wave flux density gain of up to ∼30 dB may occur. In addition, the ray trace is consistent with the observed artificial optical emissions for critical plasma frequencies down to ∼0.5 MHz below the pump frequency.

A Novel Cooperative Sensing Technique for Cognitive Radio

Abstract: Cognitive radio, which utilizes frequency effectively, needs a highly reliable sensing technique. Cooperative sensing techniques have been studied to meet this need. However, conventional techniques have a high false alarm rates. To solve this problem, we propose an innovative cooperative sensing technique in which the power levels at several radio stations are multiplied by different weights and added. Whether or not radio waves are present is determined based on this added power level. We used computer simulations to evaluate the proposed technique and demonstrated that it can perform at the required misdetection rate but has a lower false alarm rate than conventional techniques. We also propose an improved technique that takes account of correlated shadowing and is more effective in correlated shadowing environments.

Spatiotemporal evolution of radio wave pump-induced ionospheric phenomena near the fourth electron gyroharmonic

Abstract: On 12 November 2001, the European Incoherent Scatter (EISCAT) high-frequency (HF) radio wave transmitter facility, operating in O-mode at 5.423 MHz with 550 MW effective radiated power, produced artificial optical rings which appeared immediately at transmitter turn-on and collapsed into blobs after ∼60 s while descending in altitude. A similar descent in altitude was observed in the EISCAT ultra high frequency (UHF) ion line enhancements. Likewise, the stimulated electromagnetic emission (SEE) spectra changed as the pump frequency approached the fourth electron gyroharmonic due to pump-induced variations in electron concentration. Optical recordings were made from Skibotn at 630.0 and 557.7 nm and from Ramfjord in white light. The altitude of the initial optical ring and steady state blob has been estimated by triangulation. The evolution in altitude of the optical emissions, ion line enhancements, and SEE spectra all show a similar morphology but are generally not at exactly the same height. Typically, the optical height is close to and a few kilometers below that of the radar backscatter but sometimes above it, both of which are above the SEE generation altitude. There is evidence that upper hybrid (UH) waves, which propagate perpendicular to the magnetic field line, and Langmuir (L) waves, which propagate parallel to the magnetic field line, act simultaneously to accelerate electrons even in the steady state.

Communication system and communication device

Abstract: PROBLEM TO BE SOLVED: To transmit a high-frequency signal by utilizing electric field coupling by preventing generation of an electrostatic field and an induction field for transmitting a communication signal from being disturbed and suppressing generation of a radiation electric field as a disturbance wave to the outside. SOLUTION: A high-frequency coupler is composed of an electrode for coupling, and a distributed constant circuit for impedance matching and resonance between respective electrodes for coupling, thus widening a band. A magnetic loss material is arranged near the electrode for coupling. Radio waves including both electric field waves and magnetic field waves, mainly absorb a magnetic field and suppress spurious noise and the influence of external interference radio waves. In the meantime, the electrostatic field and induction field are not easily affected by the magnetic field loss, thus establishing stable data communication by electric field coupling in a short distance. COPYRIGHT: (C)2009,JPO&INPIT

The electromagnetic environment of hospitals: how it is affected by the strength of electromagnetic fields generated both inside and outside the hospital.

Abstract: Most problems with the electromagnetic environment of medical institutions have been related to radiated electromagnetic fields and have been constructed from reports about electromagnetic interference (EMI) with electronic medical equipment by the radio waves emitted from mobile telephone handsets. However, radiated electromagnetic fields are just one of the elements. For example, little attention has been placed on problems with the electric power source. Apparatus for clinical treatment and diagnosis that use electric power sources have come into wide use in hospitals. Hospitals must pay careful attention to all elements of the electromagnetic environment. Herein, I will show examples of measurements and measuring methods for radiated electromagnetic fields, static magnetic fields, and power-source noise, common components of the medical electromagnetic environment.

Are There Radio-quiet Solar Flares?

Abstract: Some 15% of solar flares having a soft X-ray flux above GOES class C5 are reported to lack coherent radio emission in the 100 – 4000 MHz range (type I – V and decimetric emissions). A detailed study of 29 such events reveals that 22 (76%) of them occurred at a radial distance of more than 800″ from the disk center, indicating that radio waves from the limb may be completely absorbed in some flares. The remaining seven events have statistically significant trends to be weak in GOES class and to have a softer non-thermal X-ray spectrum. All of the non-limb flares that were radio-quiet above 100 MHz were accompanied by metric type III emission below 100 MHz. Out of 201 hard X-ray flares, there was no flare except near the limb (R>800″) without coherent radio emission in the entire meter and decimeter range. We suggest that flares above GOES class C5 generally emit coherent radio waves when observed radially above the source.