76 research outputs found

    An Online Calibration System for Digital Input Electricity Meters Based on Improved Nuttall Window

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    OAPA This paper proposes an improved online calibration technique for digital input electricity meters. The technique employs a double spectral line interpolation fast Fourier transform algorithm with four-item, three-order Nuttall window to reduce the measurement error caused by spectrum leakage, frequency fluctuation, noise pollution and harmonic interference. A calibration system of friendly human-computer interaction is designed using LabVIEW. Simulation and practical results show that the proposed calibration system with improved Nuttall window algorithm is of high accuracy and reliability when compared with the traditional calibration algorithm currently used by industry practice

    Broadband Bioimpedance Spectroscopy Based on a Multifrequency Mixed Excitation and Nuttall Windowed FFT Algorithm

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    Bioimpedance spectroscopy (BIS) has become an important clinical indicator for monitoring the pathological status of biological tissues, and multifrequency simultaneous measurement of BIS may provide more accurate diagnostic information compared with the traditional frequency-sweep measurement technology. This paper proposes a BIS multifrequency simultaneous measurement method based on multifrequency mixed (MFM) signal excitation and a Nuttall windowed interpolation FFT algorithm. Firstly, the excitation source adopts the nine-frequency MFM signal f(9,t), which has excellent spectral characteristic and is very suitable for BIS measurement. On this basis, a Nuttall window is adopted to truncate sample data, and an interpolation FFT algorithm based on Nuttall window is built to perform spectral analysis, in which the parameter correction formula is provided based on polynomial approximation. A BIS measurement simulation experiment is performed on an RC three-element equivalent circuit, and results on the 9 primary harmonic frequencies ranging from 3.9 kHz to 1 MHz show a high accuracy with the impedance amplitude relative error |Ez|<0.3%, and the phase absolute error |Ep|<0.1°. This paper validates the feasibility of BIS multifrequency simultaneous measurement method and establishes an algorithm foundation for the development of practical broadband BIS measurement system

    Design and Optimization of Physical Waveform-Diverse and Spatially-Diverse Radar Emissions

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    With the advancement of arbitrary waveform generation techniques, new radar transmission modes can be designed via precise control of the waveform's time-domain signal structure. The finer degree of emission control for a waveform (or multiple waveforms via a digital array) presents an opportunity to reduce ambiguities in the estimation of parameters within the radar backscatter. While this freedom opens the door to new emission capabilities, one must still consider the practical attributes for radar waveform design. Constraints such as constant amplitude (to maintain sufficient power efficiency) and continuous phase (for spectral containment) are still considered prerequisites for high-powered radar waveforms. These criteria are also applicable to the design of multiple waveforms emitted from an antenna array in a multiple-input multiple-output (MIMO) mode. In this work, three spatially-diverse radar emission design methods are introduced that provide constant amplitude, spectrally-contained waveforms implemented via a digital array radar (DAR). The first design method, denoted as spatial modulation, designs the radar waveforms via a polyphase-coded frequency-modulated (PCFM) framework to steer the coherent mainbeam of the emission within a pulse. The second design method is an iterative scheme to generate waveforms that achieve a desired wideband and/or widebeam radar emission. However, a wideband and widebeam emission can place a portion of the emitted energy into what is known as the `invisible' space of the array, which is related to the storage of reactive power that can damage a radar transmitter. The proposed design method purposefully avoids this space and a quantity denoted as the Fractional Reactive Power (FRP) is defined to assess the quality of the result. The third design method produces simultaneous radar and communications beams in separate spatial directions while maintaining constant modulus by leveraging the orthogonal complement of the emitted directions. This orthogonal energy defines a trade-space between power efficiency gained from constraining waveforms to be constant amplitude and power efficiency lost by emitting energy in undesired directions. The design of FM waveforms via traditional gradient-based optimization methods is also considered. A waveform model is proposed that is a generalization of the PCFM implementation, denoted as coded-FM (CFM), which defines the phase of the waveform via a summation of weighted, predefined basis functions. Therefore, gradient-based methods can be used to minimize a given cost function with respect to a finite set of optimizable parameters. A generalized integrated sidelobe level (GISL) metric is used as the optimization cost function to minimize the correlation range sidelobes of the radar waveform. System specific waveform optimization is explored by incorporating the linear models of three different loopback configurations into the GISL metric to match the optimized waveforms to the particular systems

    A Comparative Study On Spectrogram And S-Transform For Batteries Parameters Estimation

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    This research presents the analysis of battery charging and discharging signals using spectrogram, and S-transform techniques. The analysed batteries are lead acid (LA), nickel-metal hydride (Ni-MH), and lithium-ion (Li-ion). From the equivalent circuit model (ECM) simulated using MATLAB, the constant charging and discharging signals are presented, jointly, in time-frequency representation (TFR). From the TFR, the battery signal characteristics are determined from the estimated parameters of instantaneous means square voltage (V RMS (t)), instantaneous direct current voltage (V DC (t)), and instantaneous alternating current voltage (V AC (t)). Hence, an equation for battery remaining capacity as a function of estimated parameter of V AC (t) using curve fitting tool is presented. In developing a real-time automated battery parameters estimation system, the best time-frequency distribution (TFD) is chosen in terms of accuracy of the battery parameters, computational complexity in signal processing, and memory size. The advantages in high accuracy for battery parameters estimation, and low in memory size requirement makes the S-transform technique is selected to be the best TFD. Then, field testing is conducted for different cases, and the results show that the average mean absolute percentage error (MAPE) calculated is around 4%

    Theory and Applications of Aperiodic (Random) Phased Arrays

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    A need for network centric topologies using mobile wireless communications makes it important to investigate new distributed beamforming techniques. Platforms such as micro air vehicles (MAVs), unattended ground sensors (UGSs), and unpiloted aerial vehicles (UAVs) can all benefit from advances in this area utilizing advantages in stealth, enhanced survivability and maximum maneuverability. Moreover, in this dissertation, electromagnetic radiation is investigated such that the signal power of each element is coherently added in the far-field region of a specified target direction with net destructive interference occurring in all other regions to suppress sidelobe behavior. This provides superior range and resolution characteristics for a variety of applications including; early warning radar, ballistic missile defense and search and rescue efforts. A wide variety of topologies can be used to confine geometrically these mobile random arrays for analysis. The distribution function for these topologies must be able to generalize the randomness within the geometry. By this means it is feasible to assume the random element distribution of a very large volumetric space will yield either a normal or Gaussian distribution. Therefore the underlying assumption stands that the statistically averaged beam pattern develops from an arrangement of uniformly or Gaussian distrusted elements; both confined to a variety of geometry of radius A and is further generalized using a simple theory based upon the Fourier Transform. Hence, this theory will be derived and serve as the foundation for advanced performance characteristics of these arrays such as its ability for sidelobe tapering, adaptive nulling and multi beam control. In addition it will be shown that for the most ideal of conditions a steerable beam pattern free of sidelobe behavior (better known as a Gaussian distribution) is quite possible. As well these random array structures will be shown to provide superior bandwidth capability over tradiational array structures since they are frequency independent. Last of all a summary of the random array analysis and its results concludes this dissertation

    Middle Atmosphere Program. Handbook for MAP. Volume 30: International School on Atmospheric Radar

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    Broad, tutorial coverage is given to the technical and scientific aspects of mesosphere stratosphere troposphere (MST) meteorological radar systems. Control issues, signal processing, atmospheric waves, the historical aspects of radar atmospheric dynamics, incoherent scatter radars, radar echoes, radar targets, and gravity waves are among the topics covered

    Engineering evaluations and studies. Volume 3: Exhibit C

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    High rate multiplexes asymmetry and jitter, data-dependent amplitude variations, and transition density are discussed

    Searching for the Cosmic Dawn with the Hyperfine Structure Transition of Hydrogen

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    The 21 cm hyperfine structure transition of neutral hydrogen promises to open a window into the first billion years of the Universe (z &#62; 6). With the exception of rare lines of sight towards exceptionally distant and luminous galaxies, this period of the universe's history remains largely unexplored. During this time the 21 cm transition is expected to be detectable as a 10--100 mK perturbation in the thermal Cosmic Microwave Background (CMB) spectrum. Due to the large field of view of low frequency radio telescopes (typically composed of dipole antennas) and the fact that the line of sight distance can be inferred from the measured frequency of the transition, the ultimate goal of 21 cm cosmology is to produce three dimensional tomographic maps of the 21 cm brightness temperature. In this way, the formation of the first stars and galaxies will be revealed through their influence on the neutral gas around them. This thesis saw the construction of the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA), a new low frequency (27--85 MHz) radio telescope located near Bishop, California. Composed of 288 crossed-dipole antennas, the OVRO-LWA is capable of imaging the entire visible hemisphere in a single 13 s snapshot image with 8 arcmin angular resolution. The primary challenges faced by efforts to detect the highly redshifted 21 cm transition are seeing past the blinding glow of foreground radio emission that is five orders of magnitude brighter than the cosmological emission, and calibrating the instrument to a level where it's possible to make the separation between foreground emission and the 21 cm signal. In this thesis I will present foundational work using the OVRO-LWA to place upper limits on spatial fluctuations of the 21 cm transition during the Cosmic Dawn---the period of first star formation. In this thesis I present the highest angular resolution maps of the full sky below 100 MHz, and generated with a new widefield imaging technique that is specialized for drift scanning interferometers. These sky maps are a 10-fold improvement in angular resolution over existing maps at comparable frequencies, and are publicly available now for use in modeling and subtracting the contamination of foreground emission in 21 cm experiments. Using a 28 hr integration with the OVRO-LWA, I place to-date the most constraining upper limits on the amplitude of the 21 cm spatial power spectrum at the Cosmic Dawn, and the first limits at z &#62; 18. Although the current constraints Δ212 ≲ (104mK)2 do not meaningfully restrict the parameter space of models of early star formation, they do inform the design and calibrations necessary for future measurements to push towards a detection of the high-redshift 21 cm transition. In making this measurement I demonstrate the application of a new foreground filter that accounts for the full covariance of the foreground emission, and provide an updated measurement of the foreground angular covariance. Finally, I interpret the limiting factors in this measurement and determine the instrumental calibration and characterization requirements the OVRO-LWA will need to achieve in order to make a detection of the 21 cm power spectrum of the Cosmic Dawn.</p

    Effects of errorless learning on the acquisition of velopharyngeal movement control

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    Session 1pSC - Speech Communication: Cross-Linguistic Studies of Speech Sound Learning of the Languages of Hong Kong (Poster Session)The implicit motor learning literature suggests a benefit for learning if errors are minimized during practice. This study investigated whether the same principle holds for learning velopharyngeal movement control. Normal speaking participants learned to produce hypernasal speech in either an errorless learning condition (in which the possibility for errors was limited) or an errorful learning condition (in which the possibility for errors was not limited). Nasality level of the participants’ speech was measured by nasometer and reflected by nasalance scores (in %). Errorless learners practiced producing hypernasal speech with a threshold nasalance score of 10% at the beginning, which gradually increased to a threshold of 50% at the end. The same set of threshold targets were presented to errorful learners but in a reversed order. Errors were defined by the proportion of speech with a nasalance score below the threshold. The results showed that, relative to errorful learners, errorless learners displayed fewer errors (50.7% vs. 17.7%) and a higher mean nasalance score (31.3% vs. 46.7%) during the acquisition phase. Furthermore, errorless learners outperformed errorful learners in both retention and novel transfer tests. Acknowledgment: Supported by The University of Hong Kong Strategic Research Theme for Sciences of Learning © 2012 Acoustical Society of Americapublished_or_final_versio
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