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  • Articles  (939)
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  • 1
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    Unknown
    Wiley-Blackwell
    Publication Date: 2018-03-16
    Description: No abstract is available for this article.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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  • 2
    Publication Date: 2018-03-13
    Description: Monitoring of PD activity within high-voltage electrical environments is increasingly used for the assessment of insulation condition. Traditional measurement techniques employ technologies that require either off-line installation or have high power consumption and are hence costly. A wireless sensor network is proposed that utilizes only received signal strength to locate areas of PD activity within a high voltage electricity substation. The network comprises low-power and low-cost radiometric sensor nodes which receive the radiation propagated from a source of PD. Results are reported from several empirical tests performed within a large indoor environment and a substation environment using a network of nine sensor nodes. A portable PD source emulator was placed at multiple locations within the network. Signal strength measured by the nodes is reported via WirelessHART to a data collection hub where it is processed using a location algorithm. The results obtained place the measured location within 2 m of the actual source location.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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  • 3
    Publication Date: 2018-03-13
    Description: In this study, the experimental demonstration of in-place calibration was conducted using the developed time-domain measurement system. Experiments were conducted three calibration methods—in-place calibration and two existing calibrations, i.e., array rotation and differential calibration. The in-place calibration uses dual receivers located at an equal distance from the transmitter. The received signals at the dual receivers contain similar unwanted signals i.e., the directly received signal and antenna coupling. In contrast to the simulations, the antennas are not perfectly matched and there might be unexpected environmental errors. Thus, we experimented with the developed experimental system to demonstrate the proposed method. The possible problems with low signal-to-noise ratio and clock jitter, which may exist in time-domain systems, were rectified by averaging repeatedly measured signals. The tumor was successfully detected by the three calibration methods according to the experimental results. The cross-correlation was calculated using the reconstructed image of the ideal differential calibration for a quantitative comparison between the existing rotation calibration and the proposed in-place calibration. The mean value of cross-correlation between the in-place calibration and ideal differential calibration was 0.80, and the mean value of cross-correlation of the rotation calibration was 0.55. Furthermore, the results of simulation were compared with the experimental results to verify the in-place calibration method. A quantitative analysis was also performed and the experimental results show a tendency similar to the simulation.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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  • 4
    Publication Date: 2018-03-09
    Description: In this paper, we focus on the characteristics of electromagnetic power of characteristic modes (CMs) for magneto-dielectric materials (MDM). A generalized integral form of Poynting's theorem is proposed. Based on the generalized integral form of Poynting's theorem, an explicit formulation for electromagnetic power of traditional VIE (volume integral equation)-based CM and PMCHWT (Poggio, Miller, Chang, Harrington, Wu, and Tsai)-based CM of homogeneous MDM is presented for the first time. Furthermore, from the concept of electromagnetic power, a novel electromagnetic power-based CM for MDM is proposed. Numerical results are given to show that the proposed CM are effective in solving scattering problem.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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  • 5
    Publication Date: 2018-03-09
    Description: The present work is the second of a two-part paper on the Embrace Magnetometer Network. In this part, we provide some of the first scientific findings that we have already achieved with this network. We identified the diurnal and the seasonal natural variations of the H component. We provided the precise determination of SSC and SI. We showed that the ∆ H amplitudes derived from the Embrace MagNet during intense magnetic storm are in very good agreement with the Dst index. We showed that it is possible to investigate of the effects of the Sq systems response to the X-class solar flares occurring during daytime under magnetically quiet conditions.
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    Electronic ISSN: 1944-799X
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  • 6
    Publication Date: 2018-03-09
    Description: This paper presents the implementation and examination of moving signal-average methods (MSAMs) to improve the defects of frequency modulated continuous wave (FMCW) radar in detecting short-range vehicles which may cause false target detection. The MSAM may smooth out the short-term signal fluctuations in the system responses of received data in time series . These signal fluctuations may appear when the antenna radiation has a narrow beamwidth to illuminate only a part of sophisticated vehicle structures. In this examination, the defect phenomena were first investigated by employing the electromagnetic (EM) backscattering simulation. Afterward, experimental measurements were performed by implementing MSAM in a radar system for side-looking vehicle detection. The experimental FMCW radar operates at 24.125 GHz with 250 MHz bandwidth, and implements a linear frequency modulation (LFM) for TX/RX with 2mW for TX power. The output responses to determine the detection are based on the peak value distribution of signals after being processed by the Fast Fourier Transform (FFT) and MASM. Both numerical simulations and experiments have demonstrated the validity of MSAM in the signal treatment to detect the vehicles within the coverage range.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
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  • 7
    Publication Date: 2018-03-09
    Description: In order to solve the damage and interference problems to the electronic devices, which are induced by over voltage excited by the coupling process between lightning electromagnetic wave and overhead lines, the lightning tunnel is set to be equivalent to a radiant wire antenna, Based on the integration model to lightning return stroke tunnel, transmission line and ground, we take advantage of the derived formula gotten from the transmission line model, by combing the theoretical and experimental methods, we conduct a comparative analysis on the coupling process between natural /simulated lightning and overhead line. Besides, we also calculate the amplitude and energy of over-voltage which is caused by the coupling process between lightning electromagnetic wave and overhead lines. Upon these experimental results, we can draw several conclusions as follows: when the amplitude of the lightning current in the tunnel is between 5 kA to 41 kA, it takes on an excellent linear relation between the amplitude of over voltage and the magnitude of the lightning current, the relation between coupling energy and magnitude of the lightning current takes on an exponential trend. When lightning wave transmits on the transmission lines, the high order mode will be excited. Through analysis on the high order mode's characteristics, we find the theoretical analysis is consistent with the experimental results, which has a certain reference value to the protection on overhead lines.
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    Electronic ISSN: 1944-799X
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  • 8
    Publication Date: 2018-03-06
    Description: In this paper, a novel integral equation formulation expressed in the spatial domain is proposed for the analysis of rectangular waveguide step discontinuities. The important novelty of the proposed formulation is that allows to easily take into account the electrical influence of a given number of arbitrarily shaped conducting and dielectric posts placed close to the waveguide discontinuity. For the sake of simplicity, and without loss of generality, the presented integral equation has been particularized and solved for inductive rectangular waveguide geometry. In this case, the integral equation mixed-potentials kernel is written in terms of parallel plate Green's functions with an additional ground plane located on the waveguide step. Therefore, the unknowns of the problem are reduced to an equivalent magnetic surface current on the step aperture and equivalent magnetic and electric surface currents on the dielectric and conducting posts close to the discontinuity. The numerical solution of the final integral equation is efficiently computed after the application of acceleration techniques for the slowly convergent series representing the Green's functions of the problem. The numerical method has been validated through several simulation examples of practical microwave devices, including compact size bandpass cavity filters and coupled dielectric resonators filters. The results have been compared to those provided by commercial full-wave electromagnetic simulation software packages, showing in all cases a very good agreement, and with substantially enhaced numerical efficiencies.
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  • 9
    Publication Date: 2018-03-06
    Description: Artificial E -region field-aligned plasma density irregularities (AFAIs) have been generated using the HAARP ionospheric modification facility in Gakona and observed with a 30-MHz coherent scatter radar imager in Homer, Alaska. The AFAIs were generated using a distinctive, twisted-beam antenna pattern that illuminated a particularly broad volume overhead. The broad beam facilitates studies of natural sporadic E layer patches when they are present. The center of the pattern was pointed at different angles between zenith and magnetic zenith to examine the effects on the AFAI morphology. Radar images of AFAIs generally resemble the radiation pattern of the HF source, but the irregularities are strongest within a narrow range of zenith angles bounded approximately by the Spitze angle. A number of factors which might influence AFAI generation and detection are examined. The most important is most likely the requirement for the pump mode to have a standing-wave component for thermal parametric instability to operate.
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  • 10
    Publication Date: 2018-02-25
    Description: Travelling Ionospheric Disturbances (TIDs) are the ionospheric signatures of atmospheric gravity waves (AGWs). Their identification and tracking is important because the TIDs affect all services that rely on predictable ionospheric radio wave propagation. Although various techniques have been proposed to measure TID characteristics, their real-time implementation still has several difficulties. In this contribution, we present a new technique, based on the analysis of oblique Digisonde-to-Digisonde (D2D) “skymap” observations, to directly identify TIDs and specify the TID wave parameters based on the measurement of angle-of-arrival, Doppler frequency, and time-of-flight of ionospherically reflected high-frequency (HF) radio pulses. The technique has been implemented for the first time for the Net-TIDE project with data streaming from the network of European Digisonde DPS4D observatories. The performance is demonstrated during a period of moderate auroral activity, assessing its consistency with independent measurements such as data from auroral magnetometers and electron density perturbations from Digisondes and GNSS stations. Given that the different types of measurements used for this assessment were not made at exactly the same time and location, and that there was insufficient coverage in the area between the AGW sources and the measurement locations, we can only consider our interpretation as plausible and indicative for the reliability of the extracted TID characteristics. In the framework of the new TechTIDE project (European Commission H2020), a retrospective analysis of the Net-TIDE results in comparison with those extracted from GNSS TEC-based methodologies is currently being attempted, and the results will be the objective of a follow up paper.
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    Topics: Geosciences , Physics
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