32,710 research outputs found
Comparing D-Bar and Common Regularization-Based Methods for Electrical Impedance Tomography
Objective: To compare D-bar difference reconstruction with regularized linear reconstruction in electrical impedance tomography. Approach: A standard regularized linear approach using a Laplacian penalty and the GREIT method for comparison to the D-bar difference images. Simulated data was generated using a circular phantom with small objects, as well as a \u27Pac-Man\u27 shaped conductivity target. An L-curve method was used for parameter selection in both D-bar and the regularized methods. Main results: We found that the D-bar method had a more position independent point spread function, was less sensitive to errors in electrode position and behaved differently with respect to additive noise than the regularized methods. Significance: The results allow a novel pathway between traditional and D-bar algorithm comparison
An overview of microflown technologies
The Microflown is an acoustic sensor measuring particle velocity instead of sound pressure, which is usually measured by conventional microphones. Since its recent invention it is mostly used for measurement purposes (1D and 3D-sound intensity measurement and acoustic impedance). The Microflown is also used for measuring DC-flows, that can be considered as particle velocity with a frequency of 0Hz. Furthermore the Microflown is used in the professional audio as a low frequency add on microphone for pressure gradient microphones (figure of eight; directional microphones). Due to its small dimensions and silicon based production method the Microflown is very suitable for mobile applications like mobile telephones or smartcards. Nowadays sound-energy determination, array applications and three-dimensional impulse response are under investigation. Although the Microflown was invented only some years ago, the device is already commercially available
A 16 x 16 CMOS amperometric microelectrode array for simultaneous electrochemical measurements
There is a requirement for an electrochemical sensor technology capable of making multivariate measurements in environmental, healthcare, and manufacturing applications. Here, we present a new device that is highly parallelized with an excellent bandwidth. For the first time, electrochemical cross-talk for a chip-based sensor is defined and characterized. The new CMOS electrochemical sensor chip is capable of simultaneously taking multiple, independent electroanalytical measurements. The chip is structured as an electrochemical cell microarray, comprised of a microelectrode array connected to embedded self-contained potentiostats. Speed and sensitivity are essential in dynamic variable electrochemical systems. Owing to the parallel function of the system, rapid data collection is possible while maintaining an appropriately low-scan rate. By performing multiple, simultaneous cyclic voltammetry scans in each of the electrochemical cells on the chip surface, we are able to show (with a cell-to-cell pitch of 456 μm) that the signal cross-talk is only 12% between nearest neighbors in a ferrocene rich solution. The system opens up the possibility to use multiple independently controlled electrochemical sensors on a single chip for applications in DNA sensing, medical diagnostics, environmental sensing, the food industry, neuronal sensing, and drug discovery
A Review of Fault Diagnosing Methods in Power Transmission Systems
Transient stability is important in power systems. Disturbances like faults need to be segregated to restore transient stability. A comprehensive review of fault diagnosing methods in the power transmission system is presented in this paper. Typically, voltage and current samples are deployed for analysis. Three tasks/topics; fault detection, classification, and location are presented separately to convey a more logical and comprehensive understanding of the concepts. Feature extractions, transformations with dimensionality reduction methods are discussed. Fault classification and location techniques largely use artificial intelligence (AI) and signal processing methods. After the discussion of overall methods and concepts, advancements and future aspects are discussed. Generalized strengths and weaknesses of different AI and machine learning-based algorithms are assessed. A comparison of different fault detection, classification, and location methods is also presented considering features, inputs, complexity, system used and results. This paper may serve as a guideline for the researchers to understand different methods and techniques in this field
The MIDAS telescope for microwave detection of ultra-high energy cosmic rays
We present the design, implementation and data taking performance of the
MIcrowave Detection of Air Showers (MIDAS) experiment, a large field of view
imaging telescope designed to detect microwave radiation from extensive air
showers induced by ultra-high energy cosmic rays. This novel technique may
bring a tenfold increase in detector duty cycle when compared to the standard
fluorescence technique based on detection of ultraviolet photons. The MIDAS
telescope consists of a 4.5 m diameter dish with a 53-pixel receiver camera,
instrumented with feed horns operating in the commercial extended C-Band (3.4
-- 4.2 GHz). A self-trigger capability is implemented in the digital
electronics. The main objectives of this first prototype of the MIDAS telescope
- to validate the telescope design, and to demonstrate a large detector duty
cycle - were successfully accomplished in a dedicated data taking run at the
University of Chicago campus prior to installation at the Pierre Auger
Observatory.Comment: 13 pages, 18 figure
System configuration, fault detection, location, isolation and restoration: a review on LVDC Microgrid protections
Low voltage direct current (LVDC) distribution has gained the significant interest of research due to the advancements in power conversion technologies. However, the use of converters has given rise to several technical issues regarding their protections and controls of such devices under faulty conditions. Post-fault behaviour of converter-fed LVDC system involves both active converter control and passive circuit transient of similar time scale, which makes the protection for LVDC distribution significantly different and more challenging than low voltage AC. These protection and operational issues have handicapped the practical applications of DC distribution. This paper presents state-of-the-art protection schemes developed for DC Microgrids. With a close look at practical limitations such as the dependency on modelling accuracy, requirement on communications and so forth, a comprehensive evaluation is carried out on those system approaches in terms of system configurations, fault detection, location, isolation and restoration
Fast and Accurate Simulation Technique for Large Irregular Arrays
A fast full-wave simulation technique is presented for the analysis of large
irregular planar arrays of identical 3-D metallic antennas. The solution method
relies on the Macro Basis Functions (MBF) approach and an interpolatory
technique to compute the interactions between MBFs. The Harmonic-polynomial
(HARP) model is established for the near-field interactions in a modified
system of coordinates. For extremely large arrays made of complex antennas, two
approaches assuming a limited radius of influence for mutual coupling are
considered: one is based on a sparse-matrix LU decomposition and the other one
on a tessellation of the array in the form of overlapping sub-arrays. The
computation of all embedded element patterns is sped up with the help of the
non-uniform FFT algorithm. Extensive validations are shown for arrays of
log-periodic antennas envisaged for the low-frequency SKA (Square Kilometer
Array) radio-telescope. The analysis of SKA stations with such a large number
of elements has not been treated yet in the literature. Validations include
comparison with results obtained with commercial software and with experiments.
The proposed method is particularly well suited to array synthesis, in which
several orders of magnitude can be saved in terms of computation time.Comment: The paper was submitted to IEEE Transaction on Antennas and
Propagation on 01 - Feb.- 2017. The paper is 12 pages with 18 figure
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