Medium Frequency Signals Research Articles

Acoustic emission characteristics of rock salt under multi-stage cyclic loading

Rock salt is a common sedimentary rock found in the crust and is widely used for underground energy storage and waste disposal. This research conducted multi-stage cyclic loading on impure Huai'an rock salt while monitoring acoustic emissions (AE) in real-time. The results show that as the loading stress increases, the cumulative AE energy increases in a stepwise manner. The frequency distribution displays a band pattern of low, medium, and high frequencies. As the loading stress increases, the proportion of high-frequency signals decreases while that of low-frequency signals increases. The proportion of medium-frequency signals remains consistently the highest. The b-value initially decreases and then increases, with a sharp drop near the failure. Compared to the increased lower limit stress (ILLS), the constant lower limit stress (CLLS) causes higher cumulative AE energy and amplitude, and smaller b-values for the salt samples. These results indicate that the CLLS increases the size of cracks and damage in the salt samples. Based on the RA (risetime/ amplitude)-AF (average frequency) distribution, it is found that the primary mode of failure for rock salt under multi-stage cyclic loading is tensile cracking. Compared to the ILLS, the CLLS promotes the development of shear cracks. The AE test results of the rock salt provide an important basis for explaining the in-situ microseismic signals generated during the operation of salt cavern energy storage.

Detecting development scenarios of dynamic events in electric power networks smart-grid Part1 “Method”

A method for constructing a semantic S-detector for the senior hierarchical level of pattern recognition in dynamic objects is proposed. The S-detection method is based on a uniform synthesis of all hierarchically subordinate detectors and information preparation schemes, based on the tasks of the upper hierarchical level of recognition of scenarios for the development of processes in an object. The method can be used to solve problems of relay protection, emergency control automation, to identify rare events in impulse, short-term input signals when implementing the concept of developing of electric power smart-grid. The synthesis of the S-detector of scenarios for the development of transient processes was the result of the development of a structural-information SI-method for processing information components. A mathematical SI-model is presented that allows you to control the mutual correspondence of the structure of the formation tree in the object and the device recognition tree. The task is to improve the stability of the device recognition algorithm. The Part 1 describes the theoretical provisions of the application of the recognition method. It is proposed to unify the trees for generating recognition scenarios in the industry, similar to the IEEE high-voltage network diagrams. The S-detector algorithm based on the formation of a semantic signal and on the selective search for the required amount of information for automatic decision-making is presented. The facts of the appearance of elementary information events in the input signals of the detector are controlled by Ξ,H-selectivity windows, which are sequentially opened depending on the previous development of events. The block diagram of the S-detector of the scenario is presented, which can be synchronous, multichannel, with a high signal processing speed, without losing rapidly changing information when slow and infraslow information is detected. Combines useful properties of instantaneous and inertial detection algorithms. The output of the S-detector is a series of responses with different weights. This allows elementary detectors to be combined into sequential chains at different hierarchical levels of recognition. Part 2 provides an example of the application of the scenario detection method to solve the problem of increasing the stability of the operation of a selective protection relay against single-phase earth faults based on medium-frequency signals in 6-35 kV networks with an arc suppression Petersen’scoil. The results of modellingthe operation of the S-detector algorithm on the signals of real emergency files recorded by high-frequency recorders of transient processes in the network are presented.

A Comprehensive Study on the Improved Radio-Frequency Magnetic Field Measurement for the Initial Upward Leader of a Negative Rocket-Triggered Lightning Flash

The spectrum analysis of the lightning current in the experiment campaign of 2019 reveals that the lightning current waveform contains rich medium-frequency (MF) radiation signals in the initial stage. However, there is a lack of resolution for MF signals by using conventional magnetic sensors. The bandwidth of radio-frequency magnetic field measurement is improved by extending to 20 kHz–1.2 MHz in the Guangdong Comprehensive Observation Experiment on Lightning Discharge (GCOELD). During the previously noticed “quiet period” that can only maintain the upward propagation with relatively small-scale breakdown, magnetic pulses of quiet period (MPQPs) are discerned more clearly than the previous experiment in GCOELD. Aided by the improvement of a magnetic sensor, this paper captures richer magnetic field signals radiated from the weak discharge of the precursory phage than previous experiments in GCOELD. The analysis shows that both aborted UPLs and UPLs are caused by weak discharge pulses called initial precursor pulses (IPPs), which are very similar to the amplitude of the streamer discharge obtained in the laboratory. In summary, the signals detected by an improved magnetic sensor will provide an important reference for exploring the pulse characteristics of the whole discharge process and formation mechanism of the UPL in the initial stage of triggered lightning.

Investigation on Acoustic Emission Kaiser Effect and Frequency Spectrum Characteristics of Rock Joints Subjected to Multilevel Cyclic Shear Loads

Rock joints have obvious acoustic emission (AE) Kaiser effect and Felicity effect under multilevel cyclic shear conditions. The TFD-20H/50J rock shear apparatus was used to carry out cyclic loading and unloading joint shear tests, and the acoustic emission parameters and frequency spectrum characteristics of the whole shearing process were analyzed. The results show that, under the cyclic loading, the shear stress-displacement curve forms several cyclic hysteresis loops, and the number of loops increases with the increase of normal stress. With the cycles increase, the shear damage gradually increases, and the Felicity ratio gradually decreases. The Felicity ratio at the final shear failure moment is about 0.94~0.99. The ratio of the RA value (rise time/amplitude) and the average frequency value (RA-AF) is used to classify the cracking mode of the joint sample. There are two AE crack signal types (tensile type and shear type) during shear damage. The peak frequency is displayed as high, medium, and low three frequency bands, which are distributed in the range of 0~35 kHz, 35~122 kHz, and 122~300 kHz, respectively. Both low-frequency and high-frequency signals account for less than 10%, and medium-frequency signals account for more than 90%. The research of the AE monitoring signals of multilevel shear behaviors can help understand the shear-friction mechanisms of rock joints.

Analyzing high-frequency seismic signals generated during a landslide using source discrepancies between two landslides

High-frequency seismic signals are generated during landslides and can be analyzed to obtain detailed information regarding landslide dynamics. However, a better understanding of the physical process that produces such high-frequency signals is required. The two massive landslides that occurred on April 11, 2013 in the Bingham Canyon Mine pit (Utah, USA) generated low- and high-frequency seismic signals. Using the low-frequency signals, we inverted the force-time functions of the two events and estimated their dynamics. We used the signals generated by the two events and filtered in three frequency bands to obtain the source discrepancies between the two events. By analyzing these source discrepancies, we found that the low- and medium-frequency signals were generated due to the bulk movement of sliding material. Furthermore, the medium-frequency signals contained information regarding small-particle impacts along the sliding path. The high-frequency (1–3 Hz) signals are controlled by small-scale process of sliding materials, and are sum of stochastic phenomena. This clarification of the source of the high-frequency signals is expected to improve the analyses of seismic signals generated during landslides.

An Enhanced Scheme of Multi-Stage Amplifier With High-Speed High-Gain Blocks and Recycling Frequency Cascode Circuitry to Improve Gain-Bandwidth and Slew Rate

With the existing circuit topologies, the conventional multi-stage amplifiers (MSA) can only achieve low gain-bandwidths (<;5 MHz) and low slew rates (<;10 V/μs). These specifications are not satisfied by most operational amplifier (OPA) related circuit designers. To solve this issue, a novel enhanced scheme of multi-stage (ESMS) amplifier is proposed by this study. The scheme of the proposed ESMS includes a recycling frequency cascade (RFC) amplifier with a shunt current source and high-speed current mirrors, a high-speed block (HSB), and a high-gain block (HGB). Briefly, the circuitry mechanism of the ESMS amplifier demonstrates two key functions. Firstly, when an input signal is feeding into the first stage, the RFC amplifier along with the shunt current source and the current mirrors, play an important role to enhance the slew rate. Secondly, as the signal goes to the consecutive stage, low and medium frequency signals go through to the direct-coupled high-gain block (HGB), and the high-frequency signal goes to the high-speed block (HSB). Thus, the total DC gain and gain-bandwidth are improved. To test the gain-bandwidth and slew rate characteristics, the proposed ESMS amplifier was simulated by using a TSMC 0.18-μm CMOS process standard technology with a 1.8 V power supply. The results of the experiment showed that when driving a 5-pF/1-kΩ load, the proposed ESMS amplifier achieved 105.5 dB DC gain, 231.77 MHz gain-bandwidth, and 13.25 V/μs average slew rate. Compared to the NMC amplifier, one of the most well-known conventional MSAs, the proposed ESMS amplifier boosted the gain-bandwidth by 55.32 times and improved the average slew rate by 1.55 times.

Localization Performance Under Middle and Low Frequency Sound Source Based on Time Reversal Method in Enclosed Space

Multipath interference, reflection, sound absorption, and obstacles are important factors affect the sound source localization performance in enclosed space. Time reversal has the advantages of adaptive focusing, strong anti-reverberation capability, and the ability to overcome multipath effects, which are quite suitable for sound source localization in enclosed space due to its complex environment that many methods (e.g., beamforming, high-resolution spectral estimation, and the time delay of arrival) are not applicable. Therefore, this paper studies the localization performance under middle and low frequency sound sources cover single-frequency sinusoidal signal, bandwidth signal, and impulse signal through dual-channel matching based on time reversal method. When the frequency is below 1 kHz, the media’s absorption is generally negligible. Therefore, this paper only studies frequencies within 1 kHz. In this paper, numerical simulations are used to verify the feasibility of dual-channel matching under middle and low frequency sound sources in ordinary enclosed space. Then, actual experiments are conducted in an ordinary office on the case of different sound sources. The numerical simulation and experiment results show that dual-channel matching method has satisfying localization effect. The localization effect of medium frequency signal is superior to low frequency signal. Bandwidth signals have better localization effect than single-frequency sinusoidal signals, and steady state sound source has better localization effect than impulse sound source. In general, dual-channel matching method has strong robustness and applicability for sound source localization in enclosed space.

The effects of ice cover and oceanography on medium-frequency acoustic propagation on the Chukchi Shelf

The Canada Basin Acoustic Propagation Experiment (CANAPE) was a year-long experiment exploring the changing nature of sound propagation and ambient noise in the Arctic ocean. As part of this experiment, medium-frequency signals at 0.7–1 kHz and 1–4 kHz were transmitted by two sources on the Chukchi Shelf. One of these sources was located in an area of 150 m of water depth, approximately 350 m from a directional receiver array and 50 km from an 8-element vertical line array in a water depth of about 125 m. Oceanographic sensors were located both on the arrays and on a set of moorings on the shelf, and an ice-profiling sonar was located between the arrays about 15 km from the source. In this talk, we will focus on using the measured environmental data and propagation modeling to characterize the variability observed in the short-range and long-range received acoustic signals over the course of CANAPE.The Canada Basin Acoustic Propagation Experiment (CANAPE) was a year-long experiment exploring the changing nature of sound propagation and ambient noise in the Arctic ocean. As part of this experiment, medium-frequency signals at 0.7–1 kHz and 1–4 kHz were transmitted by two sources on the Chukchi Shelf. One of these sources was located in an area of 150 m of water depth, approximately 350 m from a directional receiver array and 50 km from an 8-element vertical line array in a water depth of about 125 m. Oceanographic sensors were located both on the arrays and on a set of moorings on the shelf, and an ice-profiling sonar was located between the arrays about 15 km from the source. In this talk, we will focus on using the measured environmental data and propagation modeling to characterize the variability observed in the short-range and long-range received acoustic signals over the course of CANAPE.

Study on an effective algorithm of acquiring and tracking BD2 medium-frequency signals

According to the modulation characteristics of NH code in MEO/IGSO satellites, a simple and effective serial-parallel combined method of capturing the BD2 satellite signals was presented and a complete software receiver of the B1 frequency point was realized. Based on Kalman filter, a new kind of vector tracking loop structure of pseudo code and carrier wave to adapt to the high dynamic situation was put forward, and the half-vector deeply-coupled structure based on CKF pre-filter was further studied. Simulation and practical test results showed that the new acquisition algorithm had high sensitivity, stronger adaptability for weak signal, and less computation, and that nonlinear filtering methods could not only be applied to KFPLL, but also track high dynamic signal of 100g.

Simulation and Measurement of Medium-Frequency Signals Coupling From a Line to a Loop Antenna.

The underground-mining environment can affect radio-signal propagation in various ways. Understanding these effects is especially critical in evaluating communications systems used during normal mining operations and during mine emergencies. One of these types of communications systems relies on medium-frequency (MF) radio frequencies. This paper presents the simulation and measurement results of recent National Institute for Occupational Safety and Health (NIOSH) research aimed at investigating MF coupling between a transmission line (TL) and a loop antenna in an underground coal mine. Two different types of measurements were completed: 1) line-current distribution and 2) line-to-antenna coupling. Measurements were taken underground in an experimental coal mine and on a specially designed surface test area. The results of these tests are characterized by current along a TL and voltage induced in the loop from a line. This paper concludes with a discussion of issues for MF TLs. These include electromagnetic fields at the ends of the TL, connection of the ends of the TL, the effect of other conductors underground, and the proximity of coal or earth. These results could help operators by providing examples of these challenges that may be experienced underground and a method by which to measure voltage induced by a line.

Medium-Frequency Signal Propagation Characteristics of a Lifeline as a Transmission Line in Underground Coal Mines

Underground coal mines in the United States of America are required to install lifeline (LL) cable inside escapeways to guide miners out of a mine when visibility becomes poor due to heavy smoke. Some LLs consist of single or multiple steel conductors covered with a protective plastic outer layer. Research has shown that this type of LL can be a good conductor to guide a medium-frequency (MF) communication system signal to travel over large distances. To understand the MF propagation characteristics of an LL, National Institute for Occupational Safety and Health researchers took measurements on a section of LL in a coal mine, and obtained propagation parameters for analysis. The measurement data show that MF signals have a low attenuation which can enable the use of an LL for communication throughout a mine. The propagation parameters measured are presented in this paper.

Medium frequency propagation characteristics of different transmission lines in an underground coal mine.

A medium frequency (MF) communication system operating in an underground coal mine couples its signals to a long conductor, which acts as an MF transmission line (TL) in a tunnel to permit communications among transceivers along the line. The TL is generally the longest signal path for the system, and its propagation characteristics will have a major impact on the performance of the MF communication system. In this study, the propagation characteristics of three types of MF TLs in two layouts-on the roof and on the floor of a coal mine tunnel-were obtained in an effort to understand the propagation characteristics of different TLs in different locations. The study confirmed a low MF signal loss on all of these TLs. The study also found that the TLs in different layouts had substantially different propagation characteristics. The propagation characteristics of these different TLs in different layouts are presented in the paper.

Measurements of Medium-Frequency Propagation Characteristics of a Transmission Line in an Underground Coal Mine

In underground coal mines, medium frequency (MF) communication systems couple their signals to metal infrastructures such as ac power cables and wire-based telephone lines, which guide the signals to propagate for a long distance. To better understand the propagation characteristics of MF signals, an easy-to-use measurement method was recently developed at the National Institute for Occupational Safety and Health. The method will be introduced along with an equivalent transmission line model for a long metallic infrastructure in underground coal mines. The model serves as the fundamental driver for the method development. Propagation measurements on a twisted pair of telephone lines in an underground mine were made using this method. The measurements confirmed the low MF signal attenuation rate and the dependence of the propagation characteristics of the line on the electrical properties of surrounding coal and rock as theoretical studies predicted.

Displacement and proximity sensors using Fe 77.5Si 7.5B 15, Fe 73.5Cu 1Nb 3Si 13.5B 9, and Co 68.25Fe 4.5Si 12.25B 15 amorphous micro-ribbon cores

Displacement sensors of the toroidal transformer type with cores of amorphous ribbons from different alloys, namely Fe 77.5Si 7.5B 15, Fe 73.5Cu 1Nb 3Si 13.5B 9, and Co 68.25Fe 4.5Si 12.25B 15, have been manufactured and tested. The distance between the sensor and the proximity target is established by measuring the level of a medium-frequency signal transmitted by the transformer according to the distance between the transformer and a permanent micro-magnet target. We suggest some applications for distance measurement and also for the precise position identification. The outlined method ensures high levels of noise immunity.

MEM Analysis of Geomagnetic Field Variations Over Narssarssuaq

—Maximum entropy spectral analysis (MESA) has been applied to 24 series of hourly daily data and only one daily mean series for the horizontal (H) and vertical (Z) components of the geomagnetic field for the year 1983 as observed at Narssarssuaq, Greenland (71.2°N, 36.7°E) (gm coordinate). The method has isolated some prominent medium frequency signal components. The maximum peaks for H are at 06 hr (0.174 cycles per day (cpd), 3.2 × 104 db) and 08 hr (0.09 cpd, 3.5 × 104 db). Similarly, the maximum peak in Z is observed at 04 hr (0.114 cpd, 5.7 × 104 db). The spectral results for the daily-mean data indicate periods are greater than two days, with 178.5 days (nearly semiannual) being common to both H and Z. Other harmonics have been found for all the series of H and Z components which are mainly caused by the "Effective Period", i.e., the period produced by the combined effect of the sunspot numbers and the sun’s rotation period. Such frequencies correspond very well with those found in the geomagnetic indices Ap , Cp and AE. This suggests that the disturbance transient variations are caused by viscous interaction of the solar energies emanating from sunspot regions with the outermost magnetospheric boundary which, in turn, influences the magnetosphere-iono sphere coupling and produces the medium intensity long-duration continuous auroral activities (MILD CAAs) over high latitude regions. Thus, the higher latitude geomagnetic activities are nothing but the "effective period driven MILDCAAs" having a recurrence tendency of 27/n, where n is an integer.

Comparison of Measured and Predicted Signal Strengths of Nighttime Medium Frequency Signals in the U S A

Comparison of Measured and Predicted Signal Strengths of Nighttime Medium Frequency Signals in the U S A