Electromagnetic Emission Signals Research Articles

Investigating electromagnetic acoustic emission signals denoising for alloy materials non-destructive detecting: a CRQA method

Aiming at the problem that signals collected from local electromagnetic loading operations are usually mixed with background noises (especially white noise), this paper proposed an electromagnetic acoustic emission signal denoising technology based on cross recurrence quantification analysis (CRQA). Firstly, the decomposition layer and penalty factor of variational mode decomposition (VMD) are set by experience or optimization algorithm, and then the original signal is decomposed. Secondly, the main components are selected by the CRQA algorithm, and the electromagnetic acoustic emission signal after denoising is obtained by superposition reconstruction. The simulation and experimental results show that when 5dB noise is added, CRQA can effectively remove the background noises in electromagnetic acoustic emission signals compared to the correlation coefficient algorithm, and it can assist in realizing the high-precision non-destructive testing of alloy materials.

White dwarf–white dwarf collisions in AGN discs via close encounters

ABSTRACT White dwarfs (WDs) in active galactic nucleus (AGN) discs might migrate to the inner radii of the discs and form restricted three-body systems with two WDs moving around the central supermassive black hole (SMBH) in close orbits. These systems could be dynamically unstable, which can lead to very close encounters or direct collisions. In this work, we use N-body simulations to study the evolution of such systems with different initial orbital separation p, relative orbital inclination Δi, and SMBH mass M. It is found that close encounters of WDs occur mainly at $1.1R_{\rm H} \lesssim p \lesssim 2\sqrt{3}R_{\rm H}$, where RH is the mutual Hill radius. For p < 1.1RH, the majority of WDs move in horseshoe or tadpole orbits, and only few of them with small initial orbital phase difference undergo close encounters. For p = 3.0RH, WD–WD collisions occur in most of the samples within a time 105P1, and considerable collisions occur within a time t < 62P1 for small orbital radii, where P1 is the orbital period. The peak of the closest separation distribution increases and the WD–WD collision fraction decreases with an increase in relative inclination. The closest separation distribution is similar in cases with different SMBH mass, but the WD–WD collision fraction decreases as the mass of SMBHs increases. According to our estimation, the event rate of cosmic WD–WD collisions in AGN discs is about 300 Gpc−3 yr−1, roughly 1 per cent of that of observed Type Ia supernovae. The corresponding electromagnetic emission signals can be observed through large surveys of AGNs.

Research on Electromagnetic Acoustic Emission Signal Recognition Based on Local Mean Decomposition and Least Squares Support Vector Machine

Research on Electromagnetic Acoustic Emission Signal Recognition Based on Local Mean Decomposition and Least Squares Support Vector Machine

Analyzing the Synchronous Acoustic and Electric Response of Coal Burst Failure: Validation through the On-Site Application

The accurate monitoring and early warning of coal and rock dynamic disasters become challenging in complex geological environments. Mostly, the signal information contains interferences, which misguides the technician, and thus leads to inaccurate monitoring results. To reduce the influence of interference signals, the synchronous response of the acoustic emission (AE) and electromagnetic emission (EME) signals before the failure of coal specimens during uniaxial loading was investigated in this study. Additionally, the coupling relationship between M value, AE energy/AE ringing count per unit time, and the damage of coal is established, and the early warning index of AE and EME (R value) was computed and verified through the field investigations. The results show that a strong synchronization of the acoustoelectric signals occurs only after the specimen enters the strain strengthening area. The analysis of the obtained results showed that the M value of the AE-EME synchronous response signal represents a strong degree of damage occurring in the coal body, however, this is still subject to false alarms. In contrast, the analysis of the R value accurately helped in determining the damage evaluation, thus, it can be regarded as one of the precursors of the imminent failure of coal. With R > 1, the specimen is closed to the failure state, thereby dangerous regions are identified with a dense concentration of R > 1 events. The obtained R value index through on-site AE and EME monitoring corresponds closely with the stress distribution cloud map of the roadway. It is inferred that the anti-interference ability and the reliability of the R value index are stronger than the routine early warning indicators of the single-AE or EME energy.

Fourier and Chirp-Z Transforms in the Estimation Values Process of Horizontal and Vertical Synchronization Frequencies of Graphic Displays

The electromagnetic protection of IT devices includes a number of organizational and technical measures aimed at ensuring control over radiated and conducted revealing emissions. This is of particular importance for ensuring information security in wireless communication and the processing of data presented in graphic form. In each of these cases, the occurring electromagnetic emissions pose the risk of a lack of electromagnetic immunity to the so-called eavesdropping process based on forming revealing emissions. Included in the elements of the security chain preventing electromagnetic eavesdropping on wireless communication and the devices building such systems are activities related to the determination of the Technical Device Security Level (TDSL) or its class. The above is related to the performance of electromagnetic emissions tests and identifying which of them must be treated as revealing emissions, which are only disturbances and do not threaten the security of the processed information. It is intuitively understandable that it is particularly important to ensure the security of interfaces that process video data. The nature of the electromagnetic emission signals generated by these interfaces means that the related information can be intercepted with the use of relatively simple methods, and under favorable circumstances even with the use of a receiving device not very technologically advanced. In the case of the electromagnetic safety assessment of video devices, common practice is therefore activities aimed at reconstructing information related to the video signal. This requires the parameters of the reconstructed image appropriate for the eavesdropped device operation mode and the conditions of recording the revealing emission signals to be determined. The article presents the results of works related to the analysis of the possibility of using spectral analysis methods (Fast Fourier FFT transform and Chirp-Z transform) to automate the process of determining the above-mentioned parameters in the case of reproducing images from emission signals recorded by using the ADC analog-to-digital converter.

A Coal Bump Risk Assessment and Prediction Model Based on Multiparameter Indices

Coal bump, a common dynamic disaster in mining of deep coal resources, its assessing and predicting is an important component in safety management. This paper presents a model to assess and predict coal bump risk based on multiparameter indices. A new energy accumulation index S was proposed by considering acoustic emission and electromagnetic emission signal characteristics in mine shocks. Combined with indices E (energy of microseisms) and N (frequency of microseisms) of microseismic monitoring, a static and dynamic coal bump risk assessment and prediction model was established. We studied coal bump events that occurred during extraction in 311305 working face of Bayangale coal mine in Inner Mongolia, China. We obtained the acoustic emission and electromagnetic emission signal distribution and change law, using principal component analysis method and density ellipse to establish the index S . A typical precursory of coal bumps is that AE and EME strength has obvious fluctuation period of 3-4 days, index S showing an obvious decreasing trend, while the time-series curve of the microseismic energy is relatively stable, and the vibration frequency curve has a significant upward trend. After predict the potential coal bump risk and its area of occurrence, large diameter drilling (Φ150 mm) on-site was used to relief pressure concertation in coal seam and roof. The results demonstrate that this model based on multiparameter indices is capable of quantitatively prewarning rock burst risk.

Micromechanics of impact damage of ductile (ZnS) and hard (MgAl2O4) ceramics

AbstractThe time‐resolved generation of the electromagnetic emission (EME) and acoustic emission (AE) excited by the point impact loading of ductile ZnS and hard MgAl2O4 ceramics was detected. It has been found that the EME generation precedes the AE activity in loaded ZnS ceramics, while the EME signal lags the AE generation from MgAl2O4. This dissimilarity of temporal patterns was explained by the difference between the mechanisms of the excitation of electrical charges in loaded ductile and hard ceramics. The EME from loaded ZnS is caused by the motion of charged dislocations, while, the EME effect in MgAl2O4 is due to the annihilation of opposite electric charges emerged on microcrack edges. The AE energy yield from growing microcracks in both ceramics as well as the EME activity in MgAl2O4 were found to be random (Poissonian‐like), which is typical of the localized fracture of solids occurring without long‐range interactions between perturbed structural localities. The energy distribution in EME time series generated in ductile ZnS prior to cracking followed a power law, which is characteristic for the correlated motion of charged dislocations at the stage of plastic flow. The temporal patterns of damage accumulation at different structural levels were specified through physical and mechanical properties of tested materials.

Experimental and numerical study on the fracture characteristics of concrete under uniaxial compression

Since concrete infrastructure may lose its expected physical and functional properties over time, accurate inspection and assessment of such infrastructure systems is necessary to ensure safety and serviceability and prevent unsafe working conditions and the occurrence of hazards. In this paper, an experimental investigation was conducted on several concrete specimens under uniaxial compression to fully explore the fracture process and mechanical characteristics of concrete materials under compressive loading conditions. More specifically, a high-resolution industrial camera and a real-time geophysical acquisition system were employed to capture the fracture process and the microseismic (MS) and electromagnetic emission (EME) signals simultaneously. Based on digital image processing, a robust crack extraction algorithm was proposed for automatically identifying cracks on a concrete surface at the pixel level, and then two novel crack features were introduced to depict the dynamic crack propagation process quantitatively. Then, the correlation between MS, EME, stress drop and dynamic crack evolution characteristics was analyzed. The results indicate that: (1) the MS and EME signals of the concrete specimens have good consistency in the time domain, especially in the fully fractured stage; (2) the crack area, to a certain extent, can reflect the stress drop of a concrete specimen under the compression fracture process; (3) the crack propagation velocity parallel to the loading axis (along the vertical direction) is faster than that the perpendicular one to the loading axis (along the horizontal direction); and (4) the crack area, stress, MS signal, and EME signal reach their peak values nearly simultaneously. Finally, a novel mesh-free numerical model based on peridynamic (PD) theory was established to simulate the fracture process, and the displacement fields were presented to further reveal the failure mechanism of concrete under compressive loading.

Search for anomalies in pulse flows of acoustic and electromagnetic emissions

Timely warning of disasters caused by earthquakes ensures life safety. Therefore, the search for markers of pre-seismic events preceding earthquakes remains an important research task. The article presents experimental methods for assessing seismic activity in the Kamchatka region based on the results of processing and analysis of geoacoustic and electromagnetic emission signals. The research is aimed at detecting anomalies in quantitative and qualitative indicators that characterize the pulse streams of acoustic emission of near-surface rocks and electromagnetic emission in the surface layer of the atmosphere. Signal processing and analysis are carried out using special algorithms that take into account the structural features of the variety of pulse shapes and their distribution over time.

An efficient multi-parameter approach for FPGA hardware Trojan detection

Hardware Trojan (HT) detection in the wild is a challenging endeavor since the inspector cannot have access to “golden chips” or special and trusted test measurements in order to be assisted in his assessment. Apart from detection, a HT analyzer sometimes needs to be able to understand the behavior of a HT, its activation principles and preconditions. In this paper an FPGA based HT detection and analysis methodology is proposed that uses multiple parameter processing in order to detect a HT and analyze its behavior without the presence of “golden” chip or measurements. The methodology introduces a series of scientifically sound stages to be followed in order to refine the HT detection process and proposes the scientific interconnection between these steps that makes this refinement possible. More specifically, in the paper, we propose the appropriate combination of a logic testing method, a run-time method and a side-channel analysis method to structure the proposed methodology and we apply this methodology on a design implemented in an off-the-shelf FPGA board in order to detect a HT and analyze its behavior. The logic testing and side-channel analysis methods are non-invasive. The run-time method is an invasive one where on-chip digital sensors are used to detect unexpected differentiations in the layout of the Integrated Circuit (IC). The side channel analysis method uses power or Electromagnetic emission signals during the cryptography process in order to perform a proposed statistical analysis approach and correlate logically the outcomes of the analysis collected with the previous methods’ results. The proposed approach does not rely on the presence of a “Golden chip” or any trusted known test values for detecting the HT. On the contrary, it proposes a statistical, heuristic, analysis using specific features, to reduce false positive HT detections, to analyze HT activations, find what triggers them and in what point in time that happens. The overall methodology is implemented, showcased and evaluated on an actual FPGA board using actual experiments and results that validate our assumptions. To the best of our knowledge this is the first attempt at combining three different parameter analysis methods for HT detection without using “trusted” measurements or chips on an off-the-shelf FPGA board.

Research on denoising processing of computer video electromagnetic leakage reduction image based on fuzzy degree

On the basis of analyzing, receiving, and parsing the computer video electromagnetic leakage emission signal, an image of the screen display content can be obtained. Due to the interference noise existing in the receiving process, the received image information may be drifted, the recognition may be poor, and the definition might be low. In order to improve the recognizability of the restored image, firstly, based on image noise analysis, cumulative averaging and noise smoothing, this paper proposes an image processing method based on ambiguity for electromagnetic leakage emission reduction image. Secondly, according to image denoising implementation steps, combined with computer video reproduction example, the image processing method was verified by comprehensive experiments. Lastly, the image evaluation and signal-to-noise ratio analysis of the experimental results were carried out. The results show that the image processing method based on the ambiguity of electromagnetic leakage emission reduction image has some improvement in subjective and objective evaluation with obvious promotion.

Complex analysis of pre-seismic geoacoustic and electromagnetic emission signals

The article describes the results of complex analysis of pre-seismic signals of electromagnetic and geoacoustic radiation. We analyzed the frequency content of single sferics and geoacoustic impulses recorded before the Zhupanov earthquake that occurred on January 30, 2016. The signals were analyzed using sparse approximation method, in particular Adaptive Matched Pursuit. Background signals were studied together with pre-seismic ones. Distributions of frequencies, that are part of background and pre-seismic signals, were compared. Differences in the frequency content of pre-seismic sferics and geoacoustic impulses were found. The revealed features of pre-seismic signals in the future can be used in the design of systems for monitoring, forecasting and prevention of natural disasters. The research was supported by Russian Science Foundation (project No. 18-11-00087).

Research on Acoustic Emission and Electromagnetic Emission Characteristics of Rock Fragmentation at Different Loading Rates

The relationships among the generation of acoustic emission, electromagnetic emission, and the fracture stress of rock grain are investigated, which are based on the mechanism of acoustic emission and electromagnetic emission produced in the process of indenting rock. Based on the relationships, the influence of loading rate on the characteristics of acoustic emission and electromagnetic emission of rock fragmentation is further discussed. Experiment on rock braking was carried out with three loading rates of 0.001 mm/s, 0.01 mm/s, and 0.1 mm/s. The results show that the phenomenon of acoustic emission and electromagnetic emission is produced during the process of loading and breaking rock. The wave forms of the two signals and the curve of the cutter indenting load show jumping characteristics. Both curves have good agreement with each other. With the increase of loading rate, the acoustic emission and electromagnetic emission signals are enhanced. Through analysis, it is found that the peak count rate, the energy rate of acoustic emission, the peak intensity, the number of pulses of the electromagnetic emission, and the loading rate have a positive correlation with each other. The experimental results agree with the theoretical analysis. The proposed studies can lead to an in-depth understanding of the rock fragmentation mechanism and help to prevent rock dynamic disasters.

On the interference characteristics of fully steerable radio telescope

Fully steerable radio telescope is a complex system including actuators, antenna high power driving subsystem, high sensitive receiving terminal, data transmission and control subsystem. Because of the great difference in electrical level between strong electricity subsystem and weak electricity subsystem, the very weak celestial RF signals which need to be received will be interfered by the interactive electromagnetic interferences which exist in the system, the electromagnetic emission signals generated by devices in operation and the different electromagnetic signals of environment. The electromagnetic compatibility (EMC) of radio telescopes has become the key technology of the development of and the usage of systems. In this paper, the research progresses of EMC technology of the radio telescope are summarized. From the view of system engineering, the electromagnetic interference characteristics of radio telescope system are studied, the critical control factors are determined, and an interference coupling matrix is established. Based on the electromagnetic topology theory, the EMC modeling approach to radio telescope system is presented, which provides the theoretical bases for the EMC technology researches in radio telescopes.

Measurement and Study of Electromagnetic Emission Generated by Tensile Fracture of Polymers and Carbon Fibres

Electromagnetic emission (EME) signals generated by tensile fracture of four different types of polymers and three different carbon fibre types are presented and discussed. A suitable set-up for the detection of the electric field component of EME generated by fracture of solids is proposed. Basic theoretical considerations are made about the coupling between these field components and the capacitive sensors used to directly measure the short ranged and low frequency (kHz–MHz) electric fields emitted by the generation of free surface charges and their spatial movement as dictated by the vibrational motion of the crack walls. Special focus is put on solids with low conductivity, where the influences of the material on the emitted fields is small and the detected electric signals almost solely depend on the source dynamics and the sensor characteristics. Analysis of the influence of the acquisition circuit is presented. The discussion of the electric signals emitted by tensile fracture of carbon fibres and polymer specimens comprises the influences of the material properties on the signals as well as correlations between the signals and the crack dynamics, including the crack propagation velocities.

Field Measurement of Natural Electromagnetic Emissions near the Active Tectonic and Mass-Movement Fractures in Caves

Laboratory tests on a wide range of solid materials shoved that the electromagnetic emission (EME) signals are generated during the samples mechanical stress. EME anomalies have been observed also under natural conditions in association to fracture processes, tectonic loading, stress redistribution and crack propagation prior to earthquake or in relation to deep-seated gravitational mass movements. This paper describes a first prototype of the Emission data logger, which was specially developed for the continual EME monitoring in field conditions. Our equipment has been installed and tested in Obir Caves (Austria) at an active tectonic fault. The pilot long-term EME measurement results from this location are also presented in this paper.

Akustična in elektromagnetna emisija lahkega betona s polipropilenskimi vlakni

This paper is focused on failure monitoring in lightweight concrete (special high-performance concrete that contains porous aggregate with a low bulk density) with high-strength polypropylene fibers under mechanical loading. The aim was to determine how the cracks’ generation intensity in the tested concrete samples depends on the fibers’ length and quantity. Our diagnostic method is based on a measurement of the acoustic and electromagnetic emission signals, which occur when solid dielectric materials are mechanically stressed. Several groups of lightweight concrete samples with various types and concentrations of high-strength polypropylene fibers were prepared for our experiment. We made two-channel measurements of the concrete samples from each group for defined loading conditions. The first channel was electromagnetic emission (EME) and the second was acoustic emission (AE). The electromagnetic emission and acoustic emission methods are promising methods to study the generation and behavior of cracks. The main advantage of EME and AE is their ability to be detected already in the stressed stage, which prevents macroscopic deterioration in solids. From the obtained results it can be concluded that the generated cracks’ intensity is significantly affected by the presence of polypropylene fibers and by their length and dosage.

Electromagnetic emission in the development of macroscopically unstable plastic deformation of a metal

Electromagnetic emission accompanying the serrated deformation of the aluminum‒magnesium alloy Al-6Mg has been revealed and studied experimentally. By means of high-speed video recording and a complex of methods for measuring the strain, load, and electric potential, it has been found that there is a relation between the electromagnetic emission signals and the dynamics of deformation bands. Possible mechanisms of the generation of electromagnetic signals have been discussed.

Monitoring dynamic rock pressure events using improved EME recording instrumentation

The article reports electromagnetic emission (EME) measurements in rocks using REMI-2 equipment and recording–diagnosing system RDS REMI-3 developed jointly at the Institute of Mining and Novosibirsk State Technical University. REMI-2 measures EME signal strength and displays the results digitally. RDS REMI-3 is advantageous over earlier designed equipment as it downloads measurement data in the embedded memory. The EME records are displayed as oscillograms to enable detecting initial stage of rock failure based on analysis of change in structure, parameters and spectrum-and-time behavior of EME signals.

Pattern Recognition of Signals for the Fault-Slip Type of Rock Burst in Coal Mines

The fault-slip type of rock burst is a major threat to the safety of coal mining, and effectively recognizing its signals patterns is the foundation for the early warning and prevention. At first, a mechanical model of the fault-slip was established and the mechanism of the rock burst induced by the fault-slip was revealed. Then, the patterns of the electromagnetic radiation, acoustic emission (AE), and microseismic signals in the fault-slip type of rock burst were proposed, in that before the rock burst occurs, the electromagnetic radiation intensity near the sliding surface increases rapidly, the AE energy rises exponentially, and the energy released by microseismic events experiences at least one peak and is close to the next peak. At last, in situ investigations were performed at number 1412 coal face in the Huafeng Mine, China. Results showed that the signals patterns proposed are in good agreement with the process of the fault-slip type of rock burst. The pattern recognition can provide a basis for the early warning and the implementation of relief measures of the fault-slip type of rock burst.