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In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission used in digital modulation for encoding digital (binary) data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication, used in applications such as digital television and audio broadcasting, DSL internet access, wireless networks, power line networks, and 4G/5G mobile communications.
In signal processing, phase noise is the frequency-domain representation of random fluctuations in the phase of a waveform, corresponding to time-domain deviations from perfect periodicity (jitter). Generally speaking, radio-frequency engineers speak of the phase noise of an oscillator, whereas digital-system engineers work with the jitter of a clock.
A time-domain reflectometer (TDR) is an electronic instrument used to determine the characteristics of electrical lines by observing reflected pulses.
Power-line communication (PLC) is the carrying of data on a conductor that is also used simultaneously for AC electric power transmission or electric power distribution to consumers. The line that does so is known as a power-line carrier.
Broadband over power lines (BPL) is a method of power-line communication (PLC) that allows relatively high-speed digital data transmission over public electric power distribution wiring. BPL uses higher frequencies, a wider frequency range, and different technologies compared to other forms of power-line communications to provide high-rate communication over longer distances. BPL uses frequencies that are part of the radio spectrum allocated to over-the-air communication services; therefore, the prevention of interference to, and from, these services is a very important factor in designing BPL systems.
A digital watermark is a kind of marker covertly embedded in a noise-tolerant signal such as audio, video or image data. It is typically used to identify ownership of the copyright of such a signal. "Watermarking" is the process of hiding digital information in a carrier signal; the hidden information should, but does not need to, contain a relation to the carrier signal. Digital watermarks may be used to verify the authenticity or integrity of the carrier signal or to show the identity of its owners. It is prominently used for tracing copyright infringements and for banknote authentication.
In an electric power system, a fault or fault current is any abnormal electric current. For example, a short circuit is a fault in which a live wire touches a neutral or ground wire. An open-circuit fault occurs if a circuit is interrupted by a failure of a current-carrying wire or a blown fuse or circuit breaker. In three-phase systems, a fault may involve one or more phases and ground, or may occur only between phases. In a "ground fault" or "earth fault", current flows into the earth. The prospective short-circuit current of a predictable fault can be calculated for most situations. In power systems, protective devices can detect fault conditions and operate circuit breakers and other devices to limit the loss of service due to a failure.
Distributed temperature sensing systems (DTS) are optoelectronic devices which measure temperatures by means of optical fibres functioning as linear sensors. Temperatures are recorded along the optical sensor cable, thus not at points, but as a continuous profile. A high accuracy of temperature determination is achieved over great distances. Typically the DTS systems can locate the temperature to a spatial resolution of 1 m with accuracy to within ±1 °C at a resolution of 0.01 °C. Measurement distances of greater than 30 km can be monitored and some specialised systems can provide even tighter spatial resolutions. Thermal changes along the optical fibre cause a local variation in the refractive index, which in turn leads to the inelastic scattering of the light propagating through it. Heat is held in the form of molecular or lattice vibrations in the material. Molecular vibrations at high frequencies (10 THz) are responsible for Raman scattering. Low frequency vibrations (10–30 GHz) cause Brillouin scattering. Energy is exchanged between the light travelling through the fibre and the material itself and cause a frequency shift in the incident light. This frequency shift can then be used to measure temperature changes along the fibre.
GNSS reflectometry involves making measurements from the reflections from the Earth of navigation signals from Global Navigation Satellite Systems such as GPS. The idea of using reflected GNSS signals for earth observation was first proposed in 1993 by Martin-Neira. It was also investigated by researchers at NASA Langley Research Center and is also known as GPS reflectometry.
An intermittent fault, often called simply an "intermittent", is a malfunction of a device or system that occurs at intervals, usually irregular, in a device or system that functions normally at other times. Intermittent faults are common to all branches of technology, including computer software. An intermittent fault is caused by several contributing factors, some of which may be effectively random, which occur simultaneously. The more complex the system or mechanism involved, the greater the likelihood of an intermittent fault.
In statistical signal processing, the goal of spectral density estimation (SDE) or simply spectral estimation is to estimate the spectral density of a signal from a sequence of time samples of the signal. Intuitively speaking, the spectral density characterizes the frequency content of the signal. One purpose of estimating the spectral density is to detect any periodicities in the data, by observing peaks at the frequencies corresponding to these periodicities.
Fault detection, isolation, and recovery (FDIR) is a subfield of control engineering which concerns itself with monitoring a system, identifying when a fault has occurred, and pinpointing the type of fault and its location. Two approaches can be distinguished: A direct pattern recognition of sensor readings that indicate a fault and an analysis of the discrepancy between the sensor readings and expected values, derived from some model. In the latter case, it is typical that a fault is said to be detected if the discrepancy or residual goes above a certain threshold. It is then the task of fault isolation to categorize the type of fault and its location in the machinery. Fault detection and isolation (FDI) techniques can be broadly classified into two categories. These include model-based FDI and signal processing based FDI.
Spread-spectrum time-domain reflectometry (SSTDR) is a measurement technique to identify faults, usually in electrical wires, by observing reflected spread spectrum signals. This type of time-domain reflectometry can be used in various high-noise and live environments. Additionally, SSTDR systems have the additional benefit of being able to precisely locate the position of the fault. Specifically, SSTDR is accurate to within a few centimeters for wires carrying 400 Hz aircraft signals as well as MIL-STD-1553 data bus signals. AN SSTDR system can be run on a live wire because the spread spectrum signals can be isolated from the system noise and activity.
An arc fault is a high power discharge of electricity between two or more conductors. This discharge generates heat, which can break down the wire's insulation and trigger an electrical fire. Arc faults can range in current from a few amps up to thousands of amps, and are highly variable in strength and duration.
Rayleigh scattering based distributed acoustic sensing (DAS) systems use fiber optic cables to provide distributed strain sensing. In DAS, the optical fiber cable becomes the sensing element and measurements are made, and in part processed, using an attached optoelectronic device. Such a system allows acoustic frequency strain signals to be detected over large distances and in harsh environments.
Audio forensics is the field of forensic science relating to the acquisition, analysis, and evaluation of sound recordings that may ultimately be presented as admissible evidence in a court of law or some other official venue.
Reflectometry is a general term for the use of the reflection of waves or pulses at surfaces and interfaces to detect or characterize objects, sometimes to detect anomalies as in fault detection and medical diagnosis.
A TDR moisture sensor employs time-domain reflectometry (TDR) to measure moisture content indirectly based on the correlation to electric and dielectric properties of materials, such as soil, agrarian products, snow, wood or concrete.
Switching Control Techniques address electromagnetic interference (EMI) mitigation on power electronics (PE). The design of power electronics involves overcoming three key challenges:
- power losses
- EMI
- harmonics
Cynthia M. Furse is an American electrical engineer, the director of graduate studies and a distinguished professor in the University of Utah Department of Electrical & Computer Engineering. Her research involves the use of finite-difference time-domain methods in computational simulations of the absorption and reflection of radio waves by other materials, with applications including the use of spread-spectrum time-domain reflectometry to diagnose aircraft wiring systems, the design of antennae in medical implants, and the effects of cell phone emissions on the human body. Her publications also include works on engineering education.
References
- ↑ Lo, Chet & Furse, Cynthia (February 2005). "Noise-Domain Reflectometry for Locating Wire Faults" (PDF). IEEE Transactions on Electromagnetic Compatibility. 47 (1). via livewiretest.com: 97–104. doi:10.1109/TEMC.2004.842109. S2CID 10421959. Archived from the original (PDF) on 2010-07-03. Retrieved April 4, 2013.
- ↑ Smith, Paul; Furse, Cynthia; Gunther, Jacob (December 2005). "Analysis of Spread Spectrum Time Domain Reflectometry for Wire Fault Location" (PDF). IEEE Sensors Journal. 5 (6). via livewiretest.com: 1469. Bibcode:2005ISenJ...5.1469S. doi:10.1109/JSEN.2005.858964. S2CID 12576432. Archived (PDF) from the original on April 4, 2013. Retrieved April 4, 2013.