Showing papers on "Radio wave published in 2006"

Radio communication system

Abstract: It is to provide a radio communication system capable of performing highly reliable reading/writing communication even though the RFID tags face in the random directions. The radio communication system comprises an RFID tag used for identification, a reader/writer for performing transmission and reception of information between the RFID tag by radio waves, and a plurality of reflecting plates in a space where a plurality of RFID tags are accumulated. The reflecting plates direct traveling direction of the radio wave irradiated from the reader/writer towards the RFID tags. A part of the radio waves irradiated from an antenna of the reader/writer is directed to travel three-dimensionally towards the space by the effect of the reflecting plates. Moreover, the radio waves traveling in the same direction among the reflected radio waves by the plurality of reflecting plates together allow attenuation caused due to distance to be reduced extremely.

Design of frequency selective windows for improved indoor outdoor communication

Abstract: The use of low emissivity windows degrades radio communication. This Communication presents design, manufacturing, and test measurements for an energy saving window that is transparent to GSM, GPS, and 3G radio wave frequencies. A frequency selective structure (FSS) is used in the metallic coating of the window to provide the desirable transparency in the frequency range from 900 MHz to 2 GHz. The periodic pattern used for the FSS is of the aperture type and the elements are hexagon loops. The FSS simulations are performed using the mode matching technique as well as the finite-difference time domain method. A frequency selective window was manufactured from a commercially available low emissivity glass. Measurements indicate that the frequency selective window has approximately 10 dB better transmission in the 900 MHz-2 GHz band than the original window.

Frequency, Temperature and Salinity Variation of the Permittivity of Seawater

Abstract: With the emergence of unmanned marine robots, underwater communication systems have received much attention in recent years. To successfully develop radio wave based communication solutions, it is essential to understand properties of electromagnetic wave transmission in seawater. These properties are determined by the frequency variation of the permittivity of seawater. Existing models for the permittivity of saline water are empirical ones that best fit experimental data. We propose a physically realistic model, similar to the one used in plasma physics, for the variation of the dielectric constant of water with varying frequencies and salinities. Our model is in excellent agreement with existing empirical fits for frequencies between 1 and 256 GHz. We use this model to study the propagation of electromagnetic waves in seawater. We explain that large propagation distances would be possible at MHz frequencies if the conductivity of seawater decreases at small field strengths due to the hydrogen bonding of water molecules. However, we were unable to experimentally verify any reduction in the conductivity of seawater

Radio wavelength molecular observations of comets C/1999 T1 (McNaught-Hartley), C/2001 A2 (LINEAR), C/2000 WM1 (LINEAR) and 153P/Ikeya-Zhang

Abstract: We present a comparative study of the relative abundances of CO, CH 3 OH, H 2 CO, HCN, HNC, CS, H 2 S, CH 3 CN, SO and HNCO in comets C/1999 Tl (McNaught-Hartley), C/2001 A2 (LINEAR), C/2000 WM] (LINEAR) and 153P/Ikeya-Zhang, four of the brightest comets seen in 2001-2002. This investigation is based on millimetre/submillimetre observations made with the IRAM 30-m, SEST, CSO and Kitt Peak 12-m telescopes. Although these four comets are expected to originate from the Oort cloud, they present significant differences in molecular abundances, especially as regards to the most volatile species: CO and H 2 S. In particular comet C/2000 WM 1 looks quite depleted in these volatiles, suggesting it may have a different origin than the others. Heliocentric variations of molecular relative abundance in the coma are also investigated. Significant increases in the CS/HCN and HNC/HCN production rate ratios with decreasing heliocentric distances are observed.

Low-Frequency Gravitational Wave Searches Using Spacecraft Doppler Tracking

Abstract: This paper discusses spacecraft Doppler tracking, the current-generation detector technology used in the low-frequency (∼millihertz) gravitational wave band. In the Doppler method the earth and a distant spacecraft act as free test masses with a ground-based precision Doppler tracking system continuously monitoring the earth-spacecraft relative dimensionless velocity 2Δv/c = Δν/ν0, where Δν is the Doppler shift and ν0 is the radio link carrier frequency. A gravitational wave having strain amplitude h incident on the earth-spacecraft system causes perturbations of order h in the time series of Δν/ν0. Unlike other detectors, the ∼ 1–10 AU earth-spacecraft separation makes the detector large compared with millihertz-band gravitational wavelengths, and thus times-of-flight of signals and radio waves through the apparatus are important. A burst signal, for example, is time-resolved into a characteristic signature: three discrete events in the Doppler time series. I discuss here the principles of operation of this detector (emphasizing transfer functions of gravitational wave signals and the principal noises to the Doppler time series), some data analysis techniques, experiments to date, and illustrations of sensitivity and current detector performance. I conclude with a discussion of how gravitational wave sensitivity can be improved in the low-frequency band.

Radio-wave depolarization and scattering within ice sheets: a matrix-based model to link radar and ice-core measurements and its application

Abstract: Crystal-orientation fabric (COF) has a large influence on ice-sheet flow. Earlier radar studies have shown that COF-based birefringence occurs within ice sheets. Radio-wave scattering in polar ice results from changing physical properties of permittivity and conductivity that arise from differing values of density, acidity and COF. We present an improved mathematical model that can handle all these phenomena together. We use this matrix-based model to study the two-way propagation of depolarized radio waves that scatter at both isotropic and anisotropic boundaries. Based on numerical simulations, we demonstrate how COF affects the radar signals in terms of radar polarization and frequency. We then compare the simulated features with VHF radar data obtained at two contrasting inland sites in East Antarctica, where COF is known from ice-core studies. These two sites are Dome Fuji, located near a dome summit, and Mizuho, located in a converging ice-flow region. Data at Dome Fuji are dominated by typical features resulting from birefringence. In contrast, both birefringence and anisotropic scattering affect the radar data at Mizuho. We argue that radar methods can be used to determine principal axes and strength of birefringence in the ice sheets.

Shaping the Power Spectrum of Ultra-Wideband Radio-Frequency Signals

Abstract: We demonstrate the ability to tailor the power spectrum of ultra-wideband (UWB) RF waveforms via a photonics-based electromagnetic pulse shaper. We describe and experimentally demonstrate a waveform design methodology that allows us to achieve desirable power spectrum properties, such as broad bandwidth and minimal spectral ripple. As one example, we generate a 115% fractional-bandwidth impulsive waveform which spans the 3-10-GHz band, with ripple below plusmn1.5 dB over a 5-GHz band. Furthermore, by treating the RF spectral phase as a design parameter, we demonstrate how to achieve increased power spectral density. We illustrate the spectral design capabilities of our technique by presenting a variety of tailored UWB waveforms (including impulses, chirped signals, and arbitrary waveforms) with bandwidths that range from ~4 to 8 GHz

Performance analysis of optimized millimeter-wave fiber radio links

Abstract: We present a comprehensive performance analysis of several optimized fiber radio distribution schemes for millimeter-wave radio services. The analysis includes the noise and nonlinear characteristics of the transmitter (Tx)-receiver (Rx) pair integrated with the analog optical link in the downlink transmission of a given wavelength without optical amplification. Investigations are focused on four configurations of optimized fiber radio links, which were derived by considering the best performing possible Tx-Rx configuration and specifications of commercially available devices to support multichannel subcarrier multiplexed transmission. It was found that the nonlinear characteristics of the Mach-Zehnder modulator are the major source of performance degradation of the fiber radio links. A comparison of RF-over-fiber and IF-over-fiber transport schemes also shows that RF-over-fiber can yield 3-dB improvement in performance compared to IF-over-fiber techniques.

Object detection method and apparatus

Abstract: Method and apparatus for detecting objects. In one embodiment, a person entering a secured zone is illuminated with low-power polarized radio waves. Differently polarized waves which are reflected back from the person are collected. Concealed weapons are detected by measuring various parameters of the reflected signals and then calculating various selected differences between them. These differences create patterns when plotted as a function of time. Preferably a trained neural network pattern recognition program is then used to evaluate these patterns and autonomously render a decision on the presence of a weapon. An interrupted continuous wave system may be employed. Multiple units may be used to detect various azimuthal angles and to improve accuracy.

Investigation of Brillouin scattering in optical fibers for the generation of Millimeter waves

Abstract: Stimulated Brillouin scattering (BS) in optical fibers is investigated for the generation of millimeter waves (mm-waves) for radio over fiber systems. Predictions of a numerical simulation are compared to experimental results, and both are in good agreement with each other. With the numerical simulation, the optimum parameter for the technique is calculated. It will be shown that the optimum length of the fiber for BS depends on the signal rather than on the pump power. This gives us the opportunity to adjust the parameters for any given fiber length. The advantages and limits of the proposed method for mm-wave generation are discussed.

Interference patterns in solar radio spectra: high-resolution structural analysis of the corona

Abstract: Aims. We present a new method for high-resolution structural analysis of the solar corona. Methods. The relationship between the spectral features of various types of solar radio bursts and the physical properties of their sources have been extensively studied by many authors. On the other hand, it is plausible to accept that the spectral properties of the solar radio radiation received on the Earth are – besides the physics of the radio source – influenced by an inter-laying medium that radio waves propagate through. In particular, the regular structures in the solar corona – such as coronal waves, oscillations in shock fronts, the fine structures of coronal loops, streamer current sheets, etc. – might efficiently filter transferred radio radiation just as (broad-band) X-rays are filtered by a periodic atomic structure of crystals; the difference is only in the spatial scale. Using the wave optics methods, we investigate the prospective influence of considered coronal structures on the propagating radio waves originating in an external remote source. Results. Preliminary results have shown that the resulting modelled radio emission may recall the spectra of observed zebra patterns for the simple 1D density structure considered here and for a reasonable set of parameters. Conversely, it is suggested that the spectra of the zebra patterns might be used for an analysis of those coronal structures that made these traces on the radiation by methods similar to those used in crystallography. The possibility of the presence of such regular small scale structures in the solar corona is demonstrated. For completeness, a brief review of contemporary models of the zebra patterns is provided.

Folded Fields as the Source of Extreme Radio-Wave Scattering in the Galactic Center

Abstract: A strong case has been made that radio waves from sources within about half a degree of the Galactic center undergo extreme diffractive scattering. However, problems arise when standard ("Kolmogorov") models of electron density fluctuations are employed to interpret the observations of scattering in conjunction with those of free-free radio emission. Specifically, the outer scale of a Kolmogorov spectrum of electron density fluctuations is constrained to be so small that it is difficult to identify an appropriate astronomical setting. Moreover, an unacceptably high turbulent heating rate results if the outer scale of the velocity field coincides with that of the density fluctuations. We propose an alternative model based on folded magnetic field structures that have been reported in numerical simulations of small-scale dynamos. Nearly isothermal density variations across thin current sheets suffice to account for the scattering. There is no problem of excess turbulent heating, because the outer scale for the velocity fluctuations is much larger than the widths of the current sheets. We speculate that interstellar magnetic fields could possess geometries that reflect their origins: fields maintained by the Galactic dynamo could have large correlation lengths, whereas those stirred by local energetic events might exhibit folded structures.

ISACCO: an Italian project to monitor the high latitudes ionosphere by means of GPS receivers

Abstract: As the high latitude ionosphere is directly connected with outer space by means of the field line reconnection of the geomagnetic field through the magnetopause, it is highly sensitive to the enhancement of the electromagnetic radiation and energetic particles coming from the Sun. Under such conditions the ionosphere may become highly turbulent showing the presence of small-scale (from centimetres to meters) structures or irregularities imbedded in the large-scale (tens of kilometres) ambient ionosphere. These irregularities can produce short-term phase and amplitude fluctuations in the carrier frequency of the radio waves which pass through them, commonly called ionospheric amplitude and phase scintillations (see, e.g., Morrissey et al. 2004, and references therein). The high latitude ionosphere encounters significant fading, with the most intense fading depths in the polar cap regions and less intense fading in the auroral regions. Severe amplitude fading and strong phase scintillation affect the reliability of GPS navigational systems and satellite communications. As the scarceness of a continuous and systematic monitoring of ionospheric scintillations over polar and auroral regions, the deployment of network(s) of GPS receivers, opportunely configured to observe the ionosphere under quiet and stormy conditions, could represent an important achievement for both space weather purposes and scientific aims. In this paper, a general overview on ISACCO (Ionospheric Scintillations Arctic Campaign Coordinated Observation) is given. ISACCO is an Italian project to monitor ionospheric scintillations at polar regions by means of modified GPS receivers. After some historical and technical notes on the project, the paper presents examples of some of our current investigations based on the data acquired during the almost 3 years of the ISACCO project.

Reverse shock emission as a probe of gamma-ray burst ejecta

Abstract: We calculate the reverse shock (RS) synchrotron emission in the optical and the radio wavelength bands from electron-positron pair-enriched gamma-ray burst ejecta with the goal of determining the pair content of gamma-ray bursts (GRBs) using early-time observations. We take into account an extensive number of physical effects that influence radiation from the RS-heated GRB ejecta. We find that optical/infrared flux depends very weakly on the number of pairs in the ejecta, and there is no unique signature of ejecta pair enrichment if observations are confined to a single wavelength band. It may be possible to determine if the number of pairs per proton in the ejecta is ≥100 by using observations in optical and radio bands; the ratio of flux in the optical and radio at the peak of each respective RS light curve is dependent on the number of pairs per proton. We also find that over a large parameter space, RS emission is expected to be very weak: GRB 990123 seems to have been an exceptional burst in that only a very small fraction of the parameter space produces optical flashes this bright. Also. it is often the case that the optical flux from the forward shock is brighter than the RS flux at deceleration. This could be another possible reason for the paucity of prompt optical flashes with a rapidly declining light curve at early times as was seen in GRBs 990123 and 021211. Some of these results are a generalization of similar results reported in Nakar & Piran.

Cognitive communication system, database device used in the system, and wireless communication apparatus

Abstract: PROBLEM TO BE SOLVED: To determine a frequency when a radio apparatus of a cognitive radio starts communication by correctly grasping not only the use situation of a radio wave that can be detected by the radio apparatus but also the use situation of a frequency of the reaching range of the radio wave. SOLUTION: In the cognitive communication system, the database device for frequency use situation management for a wireless communication system for performing cognitive radio is made into a network and hierarchized. A first database device 2-4 included in a wireless communication system 3 is located at a lower rank of the hierarchy. As a result, the wireless communication system 3 can obtain information that can not be independently known and information collected by other database devices from second database devices 2-3a, 2-2a and 2-1 being a database device of a higher rank. COPYRIGHT: (C)2007,JPO&INPIT

Portable communication terminal

Abstract: PROBLEM TO BE SOLVED: To provide a portable communication terminal that can have a function for broadcast reception while reducing power consumption SOLUTION: A CPU 28 sets a reception time for broadcasting radio waves through an antenna 11 for broadcast reception, turns off the power fed to a receiving circuit 12 from a power supply circuit 34 until the reception time of the broadcasting radio waves, synchronizes with the reception time of the broadcasting radio waves and turns on the power fed to the receiving circuit 12 from the power supply circuit 34 to thereby make the receiving circuit 12 operating only when particular broadcasting is performed, and stops the operation of the receiving circuit 12 when the particular broadcasting is not on COPYRIGHT: (C)2006,JPO&NCIPI

Dispersion tolerant radio-over-fibre transmission of 16 and 64 QAM radio signals at 40 GHz

Abstract: Generation of a 399 GHz microwave carrying 16 and 64 QAM radio signals up to 20 MS/s, exploiting FM-IM conversion through a periodic bandpass filter, is demonstrated The dispersion tolerance of the approach is also investigated

Portable information recording medium and reader

Abstract: PROBLEM TO BE SOLVED: To provide a portable information recording medium continuously operating as it is even when power feeding becomes unstable because of a contact failure or the like, and to provide a reader. SOLUTION: An IC card 10 is provided with a contact terminal 16 and an antenna. When the IC card 10 is inserted into the reader 20, a contact communication part 21a of the reader 20 supplies power in a contact manner, and the contact terminal 16 of the IC card 10 receives the power in a contact manner. Even when the contact terminal 16 of the IC card 10 receives the power, a radio wave output device 27 of the reader 20 emits radio waves, the IC card 10 receives the radio waves to generate power. COPYRIGHT: (C)2008,JPO&INPIT

Simultaneous observations of radio wave phase and intensity variations for locating the plasma layers in the ionosphere

Abstract: 7 [1] A new method is introduced to locate the layered 8 structures in the ionosphere based on simultaneous 9 observations of radio wave temporal intensity and phase 10 variations in trans-ionospheric satellite-to-satellite links. 11 The method determines location of the tangent point on the 12 trans-ionospheric ray trajectory where gradient of 13 refractivity is perpendicular to the ray trajectory and the 14 influence of a layered structure on radio wave parameters is 15 maximal. This new technique was applied to the 16 measurements provided during CHAMP radio occultation 17 (RO) mission. For the considered RO events, the locations 18 of the inclined plasma layers in the lower ionosphere are 19 found and the electron density distributions are retrieved. 20 The method is checked by measuring the location of the 21 tangent point on the ray trajectory in the neutral gas in the 22 atmosphere. The results showed a fairly good agreement. 23 Citation: Liou, Y. A., and A. G. Pavelyev (2006), Simultaneous 24 observations of radio wave phase and intensity variations for 25 locating the plasma layers in the ionosphere, Geophys. Res. Lett., 26 33, LXXXXX, doi:10.1029/2006GL027112.

Radio-frequency pacemaker with receiver coil implanted on the heart.

Abstract: Our first clinical experiments with artificial heart stimulation by means of a pacemaker with myocardiac electrodes did not achieve the results we expected. Therefore in 1959, we devoted our efforts to the study of remote heart stimulation by means of a new method1j2 with the following conditions: (1) complete abolition of any direct connection between pacemaker and the heart; and (2) an external pacemaker. With regard to the first condition, it seemed necessary to dispense with the wire electrodes due to the extreme brittleness of the filiform electrode, which may very easily break or get detached. As to the second condition, we thought it necessary to place the pacemaker externally because we were convinced that a device on which the life of a human being is dependent should be easily inspected, perfected, controlled and regulated. With the aim of achieving these conditions, we began to use Radio-Frequency impulses for the transmission of the stimulation from pacemaker to heart. Thanks to the progressive improvement of our devices and to animal experimentation performed for a long time on numerous dogs we were finally able to achieve a stimulating system that gave very satisfactory experimental results. In 1961 we considered that this new method could be safely applied to human patients afflicted with atrioventricular b l o ~ k s . ~ , ~

Recent advances and difficulties of infrasonic wave investigation in the ionosphere

Abstract: Acoustic waves have a remarkable ability to transfer energy from the ground up to the uppermost layers of the atmosphere. On the ground, there are many permanent sources of infrasound, and also pulsed and/or sporadic sources (e.g., sea waves, infrasonic and sonic noise of cities, lightning, earthquakes, explosions, etc.). The infrasonic waves carry away the major part of their energy upwards through the atmosphere. What are the consequences of the upward energy transfer? What heights of the atmosphere are supplied by energy from various sources of an infrasonic wave? In most cases, the answers to these questions are not well known at present. The only opportunity to monitor the propagation of an infrasonic wave to high altitudes is to watch for its influence on the ionospheric plasma. Unfortunately, most of standard equipment for ionospheric sounding, as a rule, cannot detect plasma fluctuations in the infrasonic range. Besides, the form of an infrasonic wave strongly varies during propagation due to nonlinear effects. However, the development of the Doppler method of radiosounding of the ionosphere has enabled progress to be made. Simultaneously, the ionospheric method for sensing aboveground and underground explosions has been developed. Its main advantage is the remote observation of an explosion in the near field zone by means of short radio waves, i.e., the radio sounding of the ionosphere directly above the explosion. The theory of propagation of an acoustic pulse produced by an explosion on the ground up to ionospheric heights has been developed better than the theory for other sources, and has been quantitatively confirmed by experiments. A review of some advances in the area of infrasound investigations at ionospheric heights is given and some current problems are presented.

An interhemispheric model of artificial ionospheric ducts

Abstract: [1] A duct in Earth's ionosphere is characterized by density gradients perpendicular to the magnetic field, which enhance refractive indices and act as waveguides to whistler-range waves Interhemispheric ducts along magnetic field lines have implications for the transmission of ELF radio waves across the globe Strong HF ionospheric heating has been shown to create a depletion of electrons at the heated region and could lead to a pressure perturbation that propagates along the entire magnetic field line, potentially forming an artificial duct Here we present results from an ionospheric numerical model used to study the effects of localized HF heating on an interhemispheric magnetic flux tube The existing Sami2 is Another Model of the Ionosphere (SAMI2) ionospheric model has been modified to include a flexible source of strong HF heating that can be varied to mimic the fluctuations in HF heating efficiencies and ionospheric conditions Our parametric study includes varying the heating source intensity and location along the magnetic field line, revealing both linear and nonlinear relationships connecting these source parameters to maximum pressure, temperature, and density perturbations; propagation velocity of density perturbations; and characteristic heating and cooling times of the irradiated region After a transient state, the duct structure achieves a quasi-steady state, showing electron depletion at the heated region and density enhancements in the regions just below and above the heated region The density perturbations propagate deep inside the plasmasphere to the conjugate F2 peak, with density enhancements along the traveling pulse boundary The possibility of generating interhemispheric ducts is discussed

Location estimation method and location estimation system

Abstract: PROBLEM TO BE SOLVED: To simplify the initial setting for starting the location estimation of radio terminal. SOLUTION: The location estimation system is provided with a radio node 1 for receiving radio wave from a radio terminal 10, and a location estimation device 2. The location estimation device 2 comprises: a parameter calculation means for calculating the parameter by making the evaluation function minimum while calculating the evaluation function based on the differential value between the actually measured value and the theoretical value of the receiving radio wave intensity by using the parameter depending on the environment and the temporally position of the radio terminal 10 for every radio node, the value based on the difference between the actually measured value and the theoretical value is made an evaluation function; a temporally position calculation means for obtaining the temporally position where the evaluation function becomes minimum; a repeating means for making alternatively perform processing the parameter calculation means and the temporally position calculating means; and a position determining means for making the temporally position at the time of the termination condition is satisfied the estimated position of the radio terminal 10 is made the estimated position. COPYRIGHT: (C)2008,JPO&INPIT

Radio propagation in frequency selective buildings

Abstract: Predicting and improving Radio propagation conditions has been a major topic of research since wireless communications started to emerge. The aim is to increase signal coverage and reliability, meet the increased traffic demands and provide high quality signal to the higher levels of the OSI model. Moreover, the coexistence of various wireless networks in a wireless communication environment, operating on various frequency bands increases the need for a frequency selective solution for improving radio propagation conditions of the various networks. For this reason, this work proposes a novel way to improve and controllably manipulate radio propagation by transforming the building interfaces into frequency selective. Naturally, buildings can present some natural frequency selectivity. The web and void design of the individual blocks and their arrangement within a building wall/interface, creates a periodic structure, which exhibits frequency dependent transmission and reflection characteristics. This behaviour as well as the scattering behaviour of conventional periodic building structures have been studied through the RCWA method. However, since the internal structure and the parameters of the building interfaces are usually unknown, it is not currently very practical to utilise this natural frequency selectivity. This may change if an easy way is found to "x-ray" the wall. Therefore, the novel way proposed, is to artificially transform the building interfaces into frequency selective ones, tuneable at a desired frequency through the deployment of Frequency Selective Surfaces (FSS). FSS are planar periodic structures consisting of identical thin conducting elements, usually printed on dielectric substrates. They behave as spatial electromagnetic filters selectively reflecting or attenuating a desired frequency band. Investigation was focused on studying through CFDTD simulations and anechoic chamber measurements the behaviour of FSS when these are attached on conventional building materials. It was found that beyond a certain distance (one tenth of the wavelength) away from the wall, the frequency response of the FSS remains unchanged. The potential benefits in signal coverage, interference reduction and capacity increase through a MIMO system have been studied through a custom written Hybrid Ray Tracing model, which incorporates the behaviour of frequency selective surfaces. It is to the author best knowledge that such a hybrid Ray Tracing model has never been proposed in open literature.