Electromagnetic Radiation Signals Research Articles

The effect of high temperature environment on rock properties-an example of electromagnetic radiation characterization.

High temperature causes thermal damage to rock; the macrofracture and microfracture of rock can be produced under the action of temperature treatment. Under the influence of high temperature, the surrounding rock of deep underground engineering will suffer instability damage and cause serious harm to the people. In order to use the electromagnetic radiation (EMR) technology (a non-contact geophysical method) for evaluating the thermal stability of rock in underground thermal engineering applications, we established the EMR testing experimental system of rock under the action of a continuous heat source. The variation of EMR signals of rock under different temperatures was tested, and the EMR signals generates during the process of rock thermal deformation and thermal fracture, which were later analyzed. Under the action of a continuous heat source, the rock materials produced EMR signals with three kinds of frequencies. With the increase of rock temperature, the variation trends of EMR signals varied from the slow growth rate to the rapid growth rate, EMR signals can be divided into five stages. The increase of EMR signals is positively correlated with temperature, the Hurst exponent was higher than 0.7. The thermal stress was responsible for thermal deformation and fracture, thus generating the EMR signals. The research results have important guiding significance for the application of EMR technology to the evaluation of rock thermal stability.

An experimental study for characterization the process of coal oxidation and spontaneous combustion by electromagnetic radiation technique

Abstract Coal spontaneous combustion results from a complex reaction between coal and oxygen. Previous studies on coal oxidation spontaneous combustion process provided guidance for fire prevention and control. In this work, we present a novel electromagnetic radiation (EMR) method to detect spontaneous combustion of coal. We established a multi-index experimental system for estimating various factors during coal oxidation (heating) and combustion and analyzed the characteristic temperature, index gases, and EMR signals. With the increase of temperature, the central temperature of coal varies significantly with the temperature around the coal oxidation heating device. Besides, we simultaneously tested the EMR signals generated during coal oxidation and combustion. EMR signals showed a positive correlation with temperature changes (i.e., EMR signal intensity increases with the increase in temperature and vice versa). The change trend of EMR signals with the CO is notable, and there is a good correspondence between the EMR signals and the change rule of CO gas. With the increase of temperature, the dielectric properties of coal change quickly, resulting in the occurrence of thermal deformation and rupture in the coal body, which produces significant EMR signals. The research results are of great significance for applying the EMR technique to directly detect hidden fire hazards in coal mines.

Effect of Low Temperature on Electromagnetic Radiation from Soft PZT SP-5A Under Impact Loading

We report electromagnetic radiation (EMR) detection from Soft PZT (SP-5A) under impact at low temperature (300–203 K). EMR from our sample was detected by a copper loop antenna placed around the sample. We found that EMR amplitude decreases with lowering the temperature at which the sample was placed. Low temperatures restrict the domain wall motion, due to which dipole movement becomes hindered, which hampers the movement of the charges. Reduced acceleration of charges under impact corresponds to the reduced amplitude of the EMR signals. EMR voltage decreases from 68 V to 21 V as temperature decreases from 300 K to 203 K. The average EMR energy release rate shows a smoothly declining pattern with the decrease in the sample temperature, as well as in hf/kT. EMR detection was made by elastically deforming the samples. Significant EMR voltage even at adverse operating temperatures suggests potential of these materials and this technique for structural health monitoring.

Study on electromagnetic radiation in crack propagation produced by fracture of rocks

The physics of electromagnetic radiation due to rock facture is complex, and understanding of this phenomena and its relationship with the extent of rock damage is imperative and remains challenging. In this paper, the relationship between the electric dipole moment and the stress change rate at the crack tip and the crack propagation characteristics are established. The stress change process is divided into three stages, the characteristics of electric dipole moment of each stage are analyzed. Simulation studies showed that the dipole frequencies, the angles between the electric dipole and detectors have a significant influence on the detection of those radiations. Self-expanding destructive experiments were designed and carried out for different types of rocks to observe more details of this phenomenon. In the rupture process of the sample, a number of electromagnetic radiation signals were detected. The duration of the signal is about 2 to 3 ms, and the interval between signals varies from 23 to 210 ms. The spectrum of the signal is between 4 kHz and 50 kHz. The complex variation of the signal spectrum and amplitude are due to the different electric dipoles produced by the different stages of crack propagation, and the change in the distance and angle of the radiation source from the detector during the crack propagation.

Natural Timestamps in Powerline Electromagnetic Radiation

The continuous fluctuation of electric network frequency (ENF) presents a fingerprint indicative of time, which we call natural timestamp . This article studies the time accuracy of these natural timestamps obtained from powerline electromagnetic radiation (EMR), which is mainly excited by powerline voltage oscillations at the rate of the ENF. However, since the EMR signal is often weak and noisy, extracting the ENF is challenging, especially on resource-limited sensor platforms. We design an efficient EMR conditioning algorithm and evaluate the time accuracy of EMR natural timestamps on two representative classes of IoT platforms—a high-end single-board computer with a customized EMR antenna and a low-end mote with a normal conductor wire acting as EMR antenna. Extensive measurements at six sites in a city, which are away from each other for up to 24km, show that the high-end and low-end nodes achieve median time errors of about 50ms and 150ms, respectively. To demonstrate the use of the EMR natural timestamps, we discuss three applications: time recovery, runtime clock verification, and secure clock synchronization.

A comparative evaluation of arid inflow-dependent vegetation maps derived from LANDSAT top-of-atmosphere and surface reflectances

ABSTRACTIn remote sensing, it is commonly accepted that land remote-sensing satellite (LANDSAT) top-of-atmosphere (TOA) reflectance is less accurate than atmospheric correction (AC) reflectance, as the former is not calibrated for possible modifications in the electromagnetic radiation signals due to atmospheric scattering and absorption. This article investigates whether LANDSAT data calibrated for TOA reflectance are an appropriate information source for delineating inflow-dependent vegetation (IDV) in regions with an arid and desert climate, such as the Pilbara region in Western Australia. Knowledge of where IDVs are in the landscape underpins planning their protection and define the baseline for their monitoring when water resource management options are considered. The appropriateness of TOA calibration for the delineation of IDV in the Pilbara was assessed through its comparison with IDV maps derived from AC reflectance. Both radiometric calibration methods (TOA and AC) were applied to a multi-date LANDSAT 5 TM (Thematic Mapper) dataset of 10 images acquired in 2009 and 2010. Two methods based on the application of remote-sensing techniques to identify the extent of temporally invariant vegetation were applied for IDV delineation in the study area. The first method, groundwater-dependent ecosystems mapping (GEM), employs a two-date normalized difference vegetation index (NDVI) dataset for identifying ‘no-change’ clusters of land cover and detecting those related to IDV. The second method applies principal component analysis (PCA) to a multi-date NDVI dataset. The first principal component (PC1) typically contains features that remain unchanged over time. This includes vegetation with continuous or frequent access to surface and/or groundwater, such as IDV. To delineate the extent of IDV, a thresholding technique was further employed. Spatial similarity between IDV maps produced from TOA and AC reflectance was quantitatively evaluated by the Kappa coefficient. The results showed that TOA and AC IDV maps are in ‘almost perfect’ agreement with the Kappa values above 0.83. This suggests that TOA reflectance is equally appropriate to AC reflectance for mapping in arid and desert climate such as in Pilbara. When the GEM- and PCA-based methods are applied in other study areas with arid or desert climate, the accuracy of the delineated IDV extent may vary. Therefore, the results need to be validated using ground-truth information about known IDV occurrences in the area of interest.

Medium-Term Strength and Electromagnetic Radiation Characteristics of Cemented Tailings Backfill Under Uniaxial Compression

It is important to grasp the medium-term mechanical properties of cemented tailings backfilling (CTB) for the structural parameter design. The CTB samples with the cement to tailings (c/t) ratio of 1:4, the slurry mass of 70 and 75%, respectively. The uniaxial compressive tests were carried out on the CTB samples of curing time of 56 and 90 days respectively by SANS servo and CTA-1 acoustic–electric dynamic data acquisition system. The experimental results show that: (1) the CTB samples are accompanied with the electromagnetic radiation signal release during the loading process. The stress of the CTB samples are almost linearly distributed before the peak compressive strength. After the peak strength, the uniaxial stress decreases rapidly with the increase of the loading time, and the specimens of CTB rapidly damage; (2) during the loading process, the pulse count and energy of the electromagnetic pulse show the initial calming stage, the first active stage, the second calm stage before the peak strength, second active and the calming stage with the increase of the loading time, showing “calm-active-calm-active-calm”. The accumulated pulse count and cumulative energy increase with the loading time, and gradually stabilize after the second active stage. And the results may provide a beneficial inference for researches on production mechanism and forecast of the fugitive disaster of CTB.

Characteristics and precursor information of electromagnetic signals of mining-induced coal and gas outburst

Coal and gas outburst disasters can cause serious casualties and property losses, which can be effectively avoided by means of early warning. In this paper, based on the theoretical analysis of the electromagnetic radiation (EMR) response law of mining-induced coal and gas outburst, this paper studied the variation law and precursory characteristics of EMR signals before and after the outburst. The results show that: (1) Coal and gas outburst is induced under the disturbance of mining and promoted by gas pressure and highly concentrated mining stress. (2) The EMR signal is related to changes in stress state, fracturing activity and gas flow state in the process of mining, and the increase of the outburst danger will change characteristics of EMR signal in time and frequency domains. (3) In the time domain, the EMR intensity is positively correlated with the outburst danger of coal seam. The variable coefficient of EMR intensity is greater than 0.15 during the dynamic appearance. The peak value of variable coefficient of EMR intensity is positively correlated to the local instability of coal. (4) In the frequency domain, the amplitude of EMR grows, and the signal frequency moves toward a high level. The dominant frequency rises from 6.6 kHz to 17.4 kHz, and the EMR signal components become more complicated. In practical application, the evolution process of coal and gas outburst danger can be monitored in real time through a comprehensive use of EMR intensity value and its variable coefficient, waveform and frequency distribution characteristics, so that the occurrence of coal and gas outburst disasters can be eliminated.

An effect evaluation method of coal seam hydraulic flushing by EMR

Present coal seams in China are characterized by great gas pressure and content, low permeability features, and thus, the extraction of gas is difficult and gas disaster remains serious. To improve the permeability of coal seam, the hydraulic flushing is adopted, so the effect evaluation of stree relief and permeability enhancement will be necessary before gas extraction. In this paper, an electromagnetic radiation (EMR) experiment system of coal seam hydraulic flushing was established, and the EMR characteristics of coal during hydraulic flushing were studied. The EMR test of hydraulic flushing was carried out in the Liangbei coal mine, China, and the gas extraction flow and coal stress were measured simultaneously. And then, the variation laws of EMR and the effect evaluation of hydraulic flushing were analyzed. The results showed that coal deformation and fracture produced abundant EMR signals during hydraulic flushing. The variation of the EMR signals was synchronous with the variation of load, and the large the load variation was, the greater the EMR intensity and count were. Compared with before hydraulic flushing, the EMR signals changed significantly after hydraulic flushing, and the variation amplitude of the EMR intensity was consistent with the variation amplitude of the coal stress and gas extraction flow. So the EMR method achieved the objective of effect evaluation. It's feasible and dependable to evaluate the effect of coal seam hydraulic flushing by EMR.

Lightweight Display-to-device Communication Using Electromagnetic Radiation and FM Radio

This paper presents Shadow, a novel display-to-device communication system working in radio frequency. It leverages Electromagnetic Radiation (EMR) signals emanating from displays to transmit information. Specifically, Shadow modulates the high-frequency electric signals flowing in the display interface and makes the leaked EMR signals fall into the FM band. In this way, nearby mobile devices can receive information from the display through FM receivers. Compared with other display-to-device communication approaches, Shadow does not rely on cameras, and is thus more lightweight and requires fewer user actions. Furthermore, Shadow's transmissions do not incur any degradation in the display quality, as they only take place in the Blanking Interval, which will not be shown on the display panel. Shadow requires no modification to existing hardware. The prototype is implemented with commodity display systems and mobile devices. Results show that it can achieve 1.5 kbps at distances of up to 20 cm from the display panel.

Study on characteristics of EMR signals induced from fracture of rock samples and their application in rockburst prediction in copper mine

A rockburst is a dynamic disaster that occurs during underground excavation or mining which has been a serious threat to safety. Rockburst prediction and control are as important as any other underground engineering in deep mines. For this paper, we tested electromagnetic radiation (EMR) signals generated during the deformation and fracture of rock samples from a copper mine under uniaxial compression, tension, and cycle-loading experiments, analyzed the changes in the EMR intensity, pulse number, and frequency corresponding to the loading, and a high correlation between these EMR parameters and the applied loading was observed. EMR apparently reflects the deformation and fracture status to the loaded rock. Based on this experimental work, we invented the KBD5-type EMR monitor and used it to test EMR signals generated in the rock surrounding the Hongtoushan copper mine. From the test results, it is determined the responding characteristics of EMR signals generated by changes in mine-generated stresses and stress concentrations and it is proposed that this EMR monitoring method can be used to provide early warning for rockbursts.

A theoretical model for the electromagnetic radiation emission from ferroelectric ceramics

This paper presents a mathematical model for electromagnetic radiation (EMR) from a ferroelectric material under applied alternating electric field. Well known ferroelectric material BaTiO3 has been chosen for the investigation. For calculations a cylindrical sample of the material was chosen and uniform oscillations of the electric dipoles on the application of electrical field have been considered. For substantiating the theoretical results, fresh experimental results on EMR signals have been obtained. Continuous EMR signal is obtained both theoretically and experimentally under the influence of alternating electric field. As expected the strength of EMR signal changes upon variation in the alternating electric field strength. The obtained theoretical and experimental values of signal were found to be close to each other. The EMR signal from the material is found to have strong dependence on the number of electric dipoles within the skin depth of the material.

Determining the Parameters of Microcracks from Their Electromagnetic Radiation Signals

This paper proposes a model for determining the characteristics of the evolution of the microcrack field in a loaded rock sample from electromagnetic radiation signals. Calculations were made, whose results were summarized in the form of spatial-temporal tables. Factors determining changes in the hierarchy of microcracks were established. The adequacy of the model was verified using the Zhurkov concentration criterion. Regions of scale invariance were revealed in graphs of the concentration of microcracks versus their size in logarithmic coordinates.

The Analysis of Electromagnetic Radiation at Destruction of Structural Materials

The processes occurring in the structural material under load, leading to the formation of electromagnetic radiation, are briefly considered. It is shown that there is a relationship between the duration of the anterior front of the electromagnetic radiation pulse and the length of the crack responsible for the formation of this pulse. The task of the analysis of electromagnetic radiation signals is to establish quantitative relations between the parameters of the signal and the parameters of the crack responsible for the formation of this signal. The development of the method of spectral–temporal analysis in this application is briefly described. The application of the fractal analysis method for qualitative estimation of the fracture surface size is considered, as well as the relations are introduced: frequency of the spectral component–characteristic size of the crack (length), amplitude of the spectral component – the number of cracks. On the basis of the model, which combines the principles of both linear and nonlinear mathematical physics, the transition to the quantitative evaluation of crack parameters by electromagnetic radiation signals is performed. The phenomenon called High-Frequency Trace, the main property of which is inversely proportional, almost linear dependence of the number of cracks on their size, was found. Some parts of these dependencies have logarithmic scale invariance.

Investigation of Electromagnetic Radiation Emission during Sheet Metal Incremental Micro Forming

Edge dislocations within the plastic zone ahead of a crack tip form accelerated electric line dipoles which give rise to the electromagnetic radiation (EMR) emissions in metal and alloys. This paper reports an experimental investigation to determine EMR radiation during incremental microforming of a thin aluminum sheet. The EMR signals emit from aluminum grade Al3003 during deformation under unrestricted quasi-static micro-deformation is reported. The EMR emission characteristics are influenced by the microstructural changes rather than forming parametric conditions. The EMR emissions are followed by micro-deformation locally in predetermined loci in continuous deformation pattern through a rotating tool with two different depths. The nature, amplitude and frequency of the observed EMR emissions are in conformity with the predictions of the theoretical model developed by the Misra and co-authors.24-29

Study of EMR and AE during Coal Fracture under Quasi-static Uniaxial Compression Load

A quasi-static uniaxial compression experiment was designed to simulate creep damage in coal. During the experiment, electromagnetic radiation (EMR) and acoustic emission (AE) signals were synchronously acquired. The energy of EMR and AE signals were subsequently calculated after the background noise from the equipment and the environment were filtered out. We then analyzed the change in signal energy associated with the sample strength, loading time and other factors. The results showed that as the loading time increases, the frequency of the periodic signal in the EMR energy also increases. In addition, the dominant AE signal energy release occurs only in the final stage of sample failure. However, intermittent AE pulse clusters were recorded during the entire loading cycle. The analysis of data provided a strong correlation between the change in the AE signal energy and the expansion of micro-cracks in the materials, which is manifested as an irreversible deformation of the material at the macroscopic scale.

Study on the characteristics of coal rock electromagnetic radiation (EMR) and the main influencing factors

Coal rock would produce electromagnetic radiation (EMR) in the loading process, but study on the influence factors influence on the coal rock EMR characteristics in the mesoscopic level is not insufficient. In the paper, the EMR characteristics of coal and rock samples under uniaxial loading are studied. Several typical microcosmic mechanisms affecting the characteristics of EMR are discussed, such as strength, composition and microstructure of the samples. Results show that the macroscopic structure of the outburst coal is soft, the corresponding EMR signal increases slowly with the loading increase and the EMR peak is smaller. The rockburst coal has a strong brittleness, the EMR signal increases quickly and EMR peak appears while the coal breaks is larger than the outburst coal. The EMR characteristics of rock samples are similar to the rockburst coal, but the EMR peak is the largest. When the coal rock microstructure is complete, the coal rock block is larger and the brittleness is stronger, then the corresponding strength would be larger. And the free charge generated by thermal excitation, field emission and intergranular chemical bond breakage would also be more. In the meantime, the crack propagation rate becomes greater, therefore the EMR is more stronger. The piezoelectric effect is mainly caused by the linear elastic stage of the specimen deformation and rupture, which contributes less to the EMR signals. This study is of great theoretical and practical value for assessing the mechanical state of coal rock through EMR technology, and accurately monitoring and predicting the coal rock dynamic disasters.

A Novel DC Arc Fault Detection Method Based on Electromagnetic Radiation Signal

Because of lack of current zero, dc arc is hard to be extinguished, which has become the main reason causing faults in dc system. To find an effective method to detect dc arc faults is of great significance. In this paper, a method for detecting dc arc fault based on electromagnetic radiation signal is presented. A dc arc generating device is designed to simulate dc arc faults caused by loose connection in dc systems. A fourth-order Hilbert curve fractal antenna is adopted to detect the electromagnetic radiation signals of dc arc. The amplitude and spectrums of electromagnetic radiation signals measured under different circuit currents are analyzed. A photovoltaic (PV) system is constructed and the dc arc generated in that system is measured. The test results show that, under the present experimental condition, the electromagnetic radiation pulses have an obvious characteristic frequency, which are in a range of 39–41 MHz. The characteristic frequency of electromagnetic radiation of dc arc generated in PV system is around 39 MHz. Moreover, the characteristic frequency of dc arc is compared with that of switch operation. The dc arc has higher characteristic frequency and longer interval of each electromagnetic radiation pulse than those of the switch operation. The results indicate that the characteristic frequency of electromagnetic radiation signals can be used as the detection parameter of dc arc.

EMR: An effective method for monitoring and warning of rock burst hazard

Rock burst may cause serious casualties and property losses, and how to conduct effective monitoring and warning is the key to avoid this disaster. In this paper, we reviewed both the rock burst mechanism and the principle of using electromagnetic radiation (EMR) from coal rock to monitor and forewarn rock burst, and systematically studied EMR monitored data of 4 rock bursts of Qianqiu Coal Mine, Yima Coal Group, Co. Ltd. Results show that (1) Before rock burst occurrence, there is a breeding process for stress accumulation and energy concentration inside the coal rock mass subject to external stresses, which causes it to crack, emitting a large amount of EMR; when the EMR level reaches a certain intensity, which reveals that deformation and fracture inside the coal rock mass have become serious, rock burst may occur anytime and it's necessary to implement an early warning. (2) Monitored EMR indicators such as its intensity and pulses amount are well and positively correlated before rock bursts occurs, generally showing a rising trend for more than 5 continuous days either slowly or dramatically, and the disaster bursts generally occurs at the lower level within 48 h after reaching its peak intensity. (3) The rank of EMR signals sensitive to rock burst in a descending order is maximum EMR intensity > rate of change in EMR intensity > maximum amount of EMR pulses > rate of change in the amount of EMR pulses.

Time-varying characteristics of electromagnetic radiation during the coal-heating process

Forecasting and predicting coalfield fire and coal concealed fire are difficult components of coal fire control, and there is currently a lack of widely applicable effective methods for these processes. Electromagnetic radiation (EMR) has the advantage of multi-direction cross-locating and has been widely used to monitor and provide early warnings for coal and rock dynamic disasters. In this paper, the time-varying characteristics of EMR during 3 metamorphic grades of the coal-heating process were studied. EMR signals were clearly generated in different metamorphic grades of the coal-heating process. The variation trend of the EMR signals was different for 3 metamorphic grades of coal. According to R/S statistical analysis of the EMR signal time series, all Hurst values were greater than 0.5 and the correlation coefficient was above 0.9. There is a positive correlation between the EMR signals and coal temperature. In the coal-heating process, the EMR signal intensity varied if the EMR test frequency was 1kHz, 15kHz and 50kHz. Thermal deformation and thermal cracking of the coal body occurred in the coal-heating process. The free electrons and electric dipole in coal migrate and generate EMR. Based on the changing characteristics of the EMR in the coal-heating process, we present the conceptual design of a method to detect concealed fire in underground mines.