Electromagnetic Radiation Signals Research Articles

Electromagnetic signal characteristics and energy response pattern of briquette hammer fracturing

AbstractBriquette hammer fracturing experiments were conducted with different impact energies and molding pressures to investigate the characteristics of the electromagnetic signals. The response pattern of the electromagnetic radiation energy as a function of the impact energy and the coal firmness during impact fracturing of a coal mass were analyzed. The characteristics of the electromagnetic radiation signals during the uniaxial compression fracture of a coal mass were also used to analyze their source during fracture. The results show that the generation of electromagnetic radiation during coal mass fracturing can be divided into three stages: compaction, crack propagation and sliding friction. Electromagnetic energy is mainly radiated during the sliding friction stage. The electromagnetic radiation during briquette hammer fracturing is characterized by a frequency below 2000 Hz, an amplitude in the range from 0.05 to 0.6 mV, and a total energy on the order of ∼10−14–10−10 J. For coal masses with the same firmness, as the impact energy increases, the total energy of the electromagnetic radiation increases. For the same impact energy, as the firmness of the coal mass increases, the total energy of the electromagnetic radiation first increases and then decreases.

Problems and Remedies in Writing Skill

Communication is a process through which meaning is assigned, ascertained and conveyed. It is an attempt to create shared understanding through the replication of tautologies in the universe. This process requires a vast repertoire of skills in interpersonal processing, listening, observing, speaking, questioning, analyzing, gestures, and evaluating enables collaboration and cooperation. Over time the forms and ideas about communication have evolved through the continuing progression of technology. The progression of written communication can be divided into three informative communication revolutions. First the written communication emerged through the use of pictographs. The second happened when writing began to appear on paper and other media with commonly shared writing systems, leading to the mobility in written communication. The final stage is the transfer of information through controlled waves of electromagnetic radiation and other electronic signals. Though there are several means and modes of communication process to establish meaning, it is only the written communication which has been globally recognized to be a powerful means for communicating ideas. But not everyone could communicate easily through written communication. It is hard to achieve and requires a lot of practice and patience. This paper entitled “Problems and Remedies in Writing Skills” deals with the problems that one come across in writing and also suggests some remedial measures to overcome them.

Analysis of geoacoustic emission and electromagnetic radiation signals accompanying earthquake with magnitude Mw = 7.5

The paper is devoted to the analysis of frequency spectra and pulse waveform variety of the geoacoustic and electromagnetic signals recorded on Kamchatka Peninsula at “Karymshina” site during seismically calm and active periods. Signal pre-processing includes pulse detection and their waveforms reconstruction. A frequency spectrum is analyzed using the Adaptive Matching Pursuit algorithm. To study a variety of waveforms, each pulse is encoded by a special descriptive matrix. Then pulse classification based on similarity of the descriptive matrices is performed. Thus, a signal alphabet is formed. The authors analyzed the geophysical signals recorded before, during and after the earthquake with the magnitude Mw = 7.5 dated March 25, 2020. The obtained estimates of frequency spectra and signal alphabets are compared with the analysis results of signal recoded during the seismically calm period of March 22, 2020.

A Method for Blind Source Separation of Multichannel Electromagnetic Radiation in the Field

Considering the multichannel instability, spectral overlap and strong interference of electromagnetic radiation signals in the integrated electric propulsion systems of ships, a new method is proposed which combines multivariate empirical mode decomposition (MEMD) with independent component analysis (ICA) for synchronous blind source separation of multichannel electromagnetic radiation in the field. In order to construct virtual channels, noise-aided MEMD is first applied to decompose multichannel data in this approach. Then the comprehensive screening algorithm is used to filter the intrinsic mode functions (IMFs) produced by the decomposition procedure. Finally, the new multivariate input signal is analyzed after screening using ICA to obtain the original electromagnetic radiation source signal. This method is able to effectively addresses several limitations of EMD including the mode mixing problem, its inability to handle multichannel data, as well as the indeterminacy problem in ICA. The efficacy of the MEMD-ICA algorithm was evaluated using simulated signals and real world data from a cruise ship, and comparing ensemble empirical mode decomposition-ICA(EEMD-ICA).

Characteristics of electromagnetic radiation signal of coal and rock under uniaxial compression and its field application

Rockburst is a serious threat to the safety and efficiency of coal-mine production in China. Accurate monitoring and prediction of rockburst is an ongoing challenge in coal mining. Electromagnetic radiation (EMR) technology is a real-time and non-contact prediction method for changes in the mechanical parameters of coal or rock. In this paper, uniaxial compression testing of coal and rock samples was carried out, EMR data were collected and analysed from deformation to failure. The rescaled range (R/S) analysis method was applied to study the Hurst index of the EMR signals during the uniaxial compression test. The results showed that the higher the degree of deformation and failure, the larger the Hurst index. On the basis of the experimental and theoretical results, the Hurst index of the EMR signal during the ‘8.11’ rockburst in the Yuejin coal mine was analysed. The results showed that the Hurst index was low before the rockburst, and increased to 0.9 in the pre-rupture stage, then decreased 1–2 days before the rockburst. This suggests a correlation between EMR and the conditions leading to a rockburst event. Therefore, further study on the characteristics of EMR can contribute to development of early-warning technology for rockburst.

Effect of water on the time-frequency characteristics of electromagnetic radiation during sandstone deformation and fracturing

In order to study the effect of water on the electromagnetic radiation (EMR) signals released during rock deformation and fracturing, uniaxial compression experiments were performed on sandstone samples with different water contents. During the experiments, the EMR signals were acquired. Furthermore, the time-frequency characteristics of the signals were analyzed, and their generation mechanism and the effect of water were discussed in depth. The results show that the EMR energy released decreases gradually with the increase of water content, and the EMR energy and water content can be linked by a binomial equation. For sandstone with higher water content, the precursor characteristics of EMR released in the fracturing process are more obvious. With the increase of water content, the proportion of signals in the low frequency band grows gradually, while that of signals in high frequency band falls gradually. Water reduces the macroscopic mechanical strength and fracture mechanical characteristics of sandstone, which weakens the EMR signals produced by piezoelectric effect and charge separation. Besides, with respect to the microscopic fracturing mode, the sandstone with higher water content is more likely to undergo inter-granular fracturing, which may be an important microscopic reason for the weakening of EMR of water-bearing sandstone. An EMR-based damage evolution model of water-bearing sandstone was preliminarily established, and the model helps to calculate the stress state of water-bearing rock.

Application of electromagnetic radiation detection in high-temperature anomalous areas experiencing coalfield fires

Accurate and efficient detection of coal spontaneous combustion at high temperature remains a global problem. As such, there is a great demand for noncontact detection and location of hidden fire sources of coal spontaneous combustion. Electromagnetic radiation (EMR) has the advantages of orientation and cross-location, but the mechanisms underlying EMR signals generated during coal spontaneous combustion and the field application of EMR detection have not yet been investigated. In this paper, using an EMR testing system, the EMR change laws of coal with different metamorphic degree are obtained during the coal oxidation heating process. The thermal deformation and rupture of coal cause accumulation of free charge, and the change of velocity of free electrons caused by thermal electron transition produces EMR signals. Furthermore, an innovative method is presented to apply electromagnetic radiation technology to detect high-temperature anomalous areas in a coalfield (Daquan Lake fire area). The EMR signals in the high-temperature area have a good correspondence with the temperature. The abnormal area of high temperature in the coalfield fire area is delineated successfully by the change characteristics of EMR signals.

Effect of notch-depth ratio on intermittent electromagnetic radiation from Cu-Ni alloy under tension

Abstract This paper presents some experimental results on the effect of the notch–depth ratio on intermittent electromagnetic radiation during the progressive plastic deformation of a Cu-Ni alloy sheet specimen under tension. An electromagnetic antenna was used for receiving the electromagnetic waves emitted by the deforming specimen. The specimens (with varied notch-depth ratios) first emit electromagnetic radiation near yield which is always oscillatory in nature. However, the axial strain at the initial emission of the electromagnetic radiation increases with an increase in the notch-depth ratio. The nature of electromagnetic radiation signals changes from oscillatory to exponential until instability is reached. This shows that the viscous coefficient of the material of the specimens increases during strain-hardening. The paper also presents a correlation between electromagnetic radiation emission parameters and the radius of the plastic zone created ahead of the advancing crack tip, an important parameter in fracture mechanics. With an increase in the plastic zone size, the amount of intermittent electromagnetic radiation decreases asymptotically: the first electromagnetic radiation amplitude increases linearly and a maximum energy burst first decreases the electromagnetic radiation frequency parabolically. Initial electromagnetic radiation characteristics differ considerably from optimum electromagnetic radiation emissions within the strain-hardening region. These experimental results show a novel technique for studying various fracture mechanics parameters and also for developing a non-contact crack growth monitor.

Experimental and Theoretical Investigations of Electromagnetic Radiation Emission from Soft and Hard PZT Ceramics

Electromagnetic radiation (EMR) signals from soft (SP 5A) and hard (SP 4) PZT ceramics under the influence of alternating electric fields have been investigated. The 180° oscillations of dipoles present in the piezoelectric ceramics give rise to EMR voltage signals. The soft PZT shows higher EMR signals as compared to the hard PZT which is due to the ease in the movement of dipoles in the soft PZT because of the existing vacancies which is its characteristic feature. On the other hand, the hard PZT having no vacancies does not allow that much free movement of dipoles under the effect of the external stimulus. The EMR signals have been measured using the non-contact detection technique in which an annular antenna made up of copper was placed around the samples to obtain the EMR signals which were measured during the application of an alternating electric field on the samples. The effect of frequency has been experimentally explored and it has been observed that the EMR signal increases with the increase in the frequency of the applied alternating electric field due to the increase in the frequency of oscillations of the dipoles. When the EMR voltage is measured with increasing distance from the sample, it shows the decaying pattern which matches the pattern with which electromagnetic radiations fall off with distance. The results from the analytical model are in agreement with the experimental results. These materials and measurement technique show their potential for wireless sensing applications using piezoelectric materials which have the potential to replace the currently used wired sensors.

Pantograph–Catenary Arcing Detection Based on Electromagnetic Radiation

Currently, the detection equipment for offline arcing on high-speed trains is of great interest because it can evacuate the contact state between the contact wire and the strip. In order to ensure the safety of the train under the effect of the arcing, the self-designed fourth-order Hilbert curve fractal antenna is chosen to detect the arcing, in this paper, based on its electromagnetic radiation signal. Aspects of time-, frequency-, and joint time–frequency-domain analyses of the signals were considered. Meanwhile, the experiments were conducted several times with different circuit currents and different electrode gaps, and the electromagnetic pulses under different moments were studied. Results indicated that the electromagnetic radiation pulses were corresponding to the abrupt variations of voltage during arcing, and all the characteristic frequencies were located at similar values (18 MHz). Mechanisms of using the short-time Fourier transform method to obtain an accurate arcing moment, extinguished time, and arcing duration have been explained in detail. Thus, the characteristics of arcing electromagnetic radiation could become the significant and efficient parameters to detect the pantograph–catenary operation state of high-speed trains.

Weak Transient Electromagnetic Radiation Signal Detection Method Considering the New Watershed Image Segmentation Algorithm

In order to study the detection methods of weak transient electromagnetic radiation signals, a detection algorithm integrating generalized cross-correlation and chaotic sequence prediction is proposed in this paper. Based on the dual-antenna test and cross-correlation information estimation method, the detection of aperiodic weak discharge signals under low signal-to-noise ratio is transformed into the estimation of periodic delay parameters, and the noise is reduced at the same time. The feasibility of this method is verified by simulation and experimental analysis. The results show that under the condition of low signal-to-noise ratio, the integrated method can effectively suppress the influence of 10 noise disturbances. It has a high detection probability for weak transient electromagnetic radiation signals, and needs fewer pulse accumulation times, which improves the detection efficiency and is more suitable for long-distance detection of weak electromagnetic radiation sources.

Mechanical behavior and AE and EMR characteristics of natural and saturated coal samples in the indirect tensile process

Abstract The differences between mechanical properties and acoustic emission (AE) and electromagnetic radiation (EMR) characteristics of natural coal samples and saturated coal samples were analyzed by performing indirect tensile experiments. The experimental results show that coal samples go through four stages: compaction, elastic deformation, plastic deformation and failure. There is good correspondence between AE and EMR signals and the damage to coal samples. Under the action of water, tension strength of samples is reduced, while the plasticity is enhanced; also, the softening coefficient of tensile strength becomes 0.65. The saturated coal samples have a longer plastic stage and a more obvious AE quiet period. The damage to natural coal samples is tension damage, while that of saturated coal samples is due to tension and shear damage, which is more sufficient and irregular. EMR is still remarkable when AE is in a quiet period, and EMR is better for the precursor of rupture. Water weakens the generation and propagation of AE and EMR signals, especially in the earlier stage. AE and EMR damage factor D, defined by AE and EMR counts, has a better description of the damage degree in the indirect tensile process. This study is of great significance for research on the damage mechanism of water-bearing coal, the stability monitoring of water-bearing coals in the actual engineering process and the effect evaluation of hydraulic flushing.

Recent advances in remote sensing technologies for hydrocarbon exploration and environmental evaluation

Remote sensing detects and monitors the physical and spatial characteristics of the earth's oceans, surface, and atmosphere by measuring the reflected or scattered downwelling or emitted upwelling electromagnetic radiation or acoustic signal using passive or active sensors at a distance. It plays an important role in today's energy and environmental sustainability efforts. Remote sensing from spaceborne, airborne, terrestrial, and marine platforms has long been used in hydrocarbon exploration to map surface geology, topography, and hydrocarbon seepages, as well as to evaluate environments that relate to petroleum industry activities. Since the mid-2000s, remote sensing technologies have undergone substantial advances in data acquisition, processing, and interpretation. In the last decade, rapid advances in satellite systems, unmanned autonomous vehicles (UAVs), sensors, and scale of surveys have further expanded applications.

Application of EMR Signature in Health Assessment and Monitoring of IGBT-Based Converters

In this paper, a non-invasive method based on electromagnetic radiation (EMR) signature is proposed for the health assessment of the converters. Converters use insulated gate bipolar transistor (IGBT) because of its robustness. However, it suffers from internal degradation due to the rapid power cycle and thermal stress. Degradation of IGBT primarily increases the turn- off time as a consequence of elevated junction temperature. The coupling of IGBT with the parasitics of the circuit results in EMR and depends on the turn- off time of IGBT. It has been found that the EMR signature reduces with the increase in turn- off time. This concept is taken forward for the health assessment of the converters. However, in a practical scenario, the EMR generated from multiple converters get mixed up. This is commonly known as a problem of near-field source localization. We use a uniform linear array to capture the EMR signals near the converters. Subsequently, ESPRIT and MUSIC algorithms are used to localize all the converters. An inverse transformation of the localization algorithm separates the EMR signature of all the individual converters. The proposed health assessment algorithm computes the degradation level of converters, and the experimental results validate the proposed approach.

STUDY ON THE FEATURE OF ELECTROMAGNETIC RADIATION UNDER COAL OXIDATION AND TEMPERATURE RISE BASED ON MULTIFRACTAL THEORY

During coal oxidation and temperature rise, a significantly large amount of electromagnetic radiation (EMR) signals are generated as a result of thermal deformation and thermal cracking. The generation of EMR signal is the comprehensive embodiment of the physical and chemical changes in coal during its oxidation and subsequent heating. Therefore, the generated signals contain complex and rich messages that can reflect the changes in the internal structure of coal. In this work, the characteristics of EMR signal were analyzed by multifractal theory. Multifractal analysis was used to deconstruct EMR signals. Our preliminary study indicated that the multifractal spectrum of the EMR signal had a feature of small probability event. Further analysis demonstrated that the characteristic parameters of EMR signal are quite different at the later heating stage from those at the early heating stage. At the initial stage of coal spontaneous combustion, the multifractal spectrum of the signal is wider, but when coal combustion is reached, the scale range of EMR signal increases significantly, and its structure changes at different temperature ranges. The research results presented provide a basis for monitoring and presenting an early warning of coal spontaneous combustion risk.

Research on AE and EMR response law of the driving face passing through the fault

In this paper, the response characteristics of acoustic emission (AE) and electromagnetic radiation (EMR) to the driving face crossing a fault are analysed and tested. The method of real-time monitoring of the fault in front of the driving face by AE and EMR form coal is put forward. The results are as follows: (1) When passing through the fault, the large increase of stress in mining and fault superimposed stress, which makes it more likely to accumulate and release energy in the coal seam, is the main reason for the high risk of coal and gas outburst. (2) During crossing the fault, AE and EMR signals vary in stages, both the intensity and amplitude of the main frequency points of AE and EMR increase first and then decrease. (3) When the driving face is close to the fault, the main frequency of AE and EMR signals decreases and the frequency band concentrates. The main frequency ranges of AE and EMR signals are 3.66–22.5 kHz and 0.3–17.3 kHz, respectively. (4) The amplitudes of the main frequency points of the AE and EMR signals to the fault response. The change of the main frequency amplitude of AE and EMR signals can be used as the response index of the fault, and the response range is about 10 m. The research provides an effective monitoring method for structures in coal seam, which is of great significance to the safety production and rapid excavation of coal mines.

Dark quark nuggets

"Dark quark nuggets", a lump of dark quark matter, can be produced in the early universe for a wide range of confining gauge theories and serve as a macroscopic dark matter candidate. The two necessary conditions, a nonzero dark baryon number asymmetry and a first-order phase transition, can be easily satisfied for many asymmetric dark matter models and QCD-like gauge theories with a few massless flavors. For confinement scales from 10 keV to 100 TeV, these dark quark nuggets with a huge dark baryon number have their masses vary from $10^{23}~\mathrm{g}$ to $10^{-7}~\mathrm{g}$ and their radii from $10^{8}~\mathrm{cm}$ to $10^{-15}~\mathrm{cm}$. Such macroscopic dark matter candidates can be searched for by a broad scope of experiments and even new detection strategies. Specifically, we have found that the gravitational microlensing experiments can probe heavier dark quark nuggets or smaller confinement scales around 10 keV; collision of dark quark nuggets can generate detectable and transient electromagnetic radiation signals; the stochastic gravitational wave signals from the first order phase transition can be probed by the pulsar timing array observations and other space-based interferometry experiments; the approximately massless dark mesons can behave as dark radiation to be tested by the next-generation CMB experiments; the free dark baryons, as a subcomponent of dark matter, can have direct detection signals for a sufficiently strong interaction strength with the visible sector.

Study on the discharge mechanism and EM radiation characteristics of Trichel pulse discharge in air

The Trichel pulse stage is an unstable stage of negative corona discharge that can also involve electromagnetic (EM) radiation signals. In this paper, the discharge mechanism and radiation characteristics of the Trichel pulse are studied in the needle-plate electrode configuration. The Trichel pulse current and its EM radiation signals are measured at different applied voltages. The results show that Trichel pulse discharge changes from the random pulse stage to the continuous pulse stage as the applied voltage increases. During these different stages, the normalized shape of the Trichel pulses remains unchanged, while the frequency of the EM radiation generated by the discharge remains unchanged. The discharge mechanism and EM radiation characteristics of the Trichel pulse are theoretically analyzed in the different stages. Both the positive ion sheath and the negative ion cloud play key roles in the formation of the Trichel pulse. The EM radiation signal is generated by the rapidly changing Trichel pulse current, and the Trichel pulse current waveform determines the characteristics of the EM radiation signal.

The noncontact determination technique research of dangerously loaded zones in the underground mining

The electromagnetic radiation signals associated with the destruction of rock samples were studied under field and laboratory conditions. The parameters of the signal were found that preceded the violation of the integrity of the rock in laboratory studies. It is shown that the highest efficiency of the method of electromagnetic radiation is achieved when predicting the dynamic manifestations of rock pressure in the form of rock shock.

Electromagnetic Radiation Characteristics of Series DC Arc Fault and Its Determining Factors

A dc arc fault can be a serious threat to the safe operation of a low-voltage dc system. Typically, a fair amount of electromagnetic radiation (EMR) accompanies the arcing process. To investigate the characteristics of EMR of the series dc arc fault, a fourth-order Hilbert fractal antenna is used to detect the EMR signals generated by the dc arc. The factors influencing the characteristics of EMR including electrode material, diameter, current, and pressure are considered. The amplitudes of the EMR pulses at the arc initiation moment are measured, and fast Fourier transform is used to analyze the characteristics of the frequency spectrums. The test results indicate that the amplitudes of the EMR pulses generated by stainless steel electrodes are higher than those generated by brass, copper, and aluminum electrodes. Furthermore, the trends of the amplitudes of the EMR pulses with increasing current are different for electrodes with different diameters. Finally, it is observed that the influence of the pressure is different for different electrode materials. The characteristic frequency band of the EMR pulses of the dc arcs generated under various test conditions is in a certain range (36–41 MHz), which can be used as a detecting characteristic parameter for the series dc arc.