Electromagnetic Field Measurements Research Articles

Гибридный метод индукционного зондирования для обнаружения подземных кабельных линий и трубопроводов

The analysis of the principles of searchers construction was carried out. It was found that induction route methods based on measurements of secondary electromagnetic fields, which are created by currents induced in a cable by independent radiating systems using third-party power sources, have received the greatest use. For the implementation of these methods, radiating systems of various types are used, such as frame or vibrator antennas. When building locators, the mutual distribution of the receiving and transmitting coils is of particular importance. The research group considered options for the mutual arrangement of the coils. It was found that when building a track finding equipment, two basic methods of control are widely used: the response method of the electromagnetic field parameters to the internal or surface impedance of the medium when the electromagnetic field propagates in or above the ground, respectively, and the input impedance response method of the receiving frame on the electromagnetic properties of the medium being probed. Based on the features of these two methods, a new hybrid method of induction sounding was proposed, which actually combines these two methods. When implementing this hybrid method, an induction probe (IP), which is an induction transducer of a magnetic field into an electrical signal, contains a receiving ferrite antenna (FA) and a loop antenna (LA), and LA combines the functions of transmitting and receiving antennas. A design variant of an IP with coplanar placement of FA relative to LA, which provides full geometric compensation of the primary field, is proposed. When IP operates, information is recorded on one information channel from LA (the current value of the amplitude of the exciting current) and on two information channels from the FA (current values of the amplitudes of the voltages of the active and reactive components of the output signal of the FA, respectively). The implementation of such information redundancy significantly increases the information content, efficiency and reliability of the proposed hybrid method.

Recent Progress on Electromagnetic Field Measurement Based on Optical Sensors.

Electromagnetic field sensors are widely used in various areas. In recent years, great progress has been made in the optical sensing technique for electromagnetic field measurement, and varieties of corresponding sensors have been proposed. Types of magnetic field optical sensors were presented, including probes-based Faraday effect, magnetostrictive materials, and magnetic fluid. The sensing system-based Faraday effect is complex, and the sensors are mostly used in intensive magnetic field measurement. Magnetic field optical sensors based on magnetic fluid have high sensitivity compared to that based on magnetostrictive materials. Three types of electric field optical sensors are presented, including the sensor probes based on electric-optic crystal, piezoelectric materials, and electrostatic attraction. The majority of sensors are developed using the sensing scheme of combining the LiNbO3 crystal and optical fiber interferometer due to the good electro-optic properties of the crystal. The piezoelectric materials-based electric field sensors have simple structure and easy fabrication, but it is not suitable for weak electric field measurement. The sensing principle based on electrostatic attraction is less commonly-used sensing methods. This review aims at presenting the advances in optical sensing technology for electromagnetic field measurement, analyzing the principles of different types of sensors and discussing each advantage and disadvantage, as well as the future outlook on the performance improvement of sensors.

Wavenumber Analysis of EMIC Waves

AbstractIt has been highly controversial as to whether and how efficient electromagnetic ion cyclotron (EMIC) waves can scatter sub–megaelectronvolt (MeV) to multi–megaelectron volt electrons into the atmospheric loss cone. The capability of EMIC wave scattering essentially depends on the wavenumber spectra, instead of readily available frequency spectra. We present a method to obtain the EMIC wavenumbers directly from the wave electromagnetic field measurements, from which we further evaluate the characteristics of electron minimum resonant energy and electron scattering rate due to EMIC waves. Based on the analysis of EMIC waves identified from 5.5 years of Van Allen Probes field measurement, we find that only a small fraction of H+ band wave events can resonate with electrons down to MeV, while none of He+ band waves at the maximum wave power can. The electron scattering rate increases with increasing levels of geomagnetic activities. The scattering rate for H+ band is sufficient to cause significant precipitation of electrons for a broad energy range (including MeV electrons), especially during times with high geomagnetic activity.

Export Transformer Switching Transient Mitigation in HVDC Connected Offshore Wind Farms

An increasing number of offshore wind farms are connected to the public grid with large-scale HVDC links. The electrical transients caused by the energization of the export transformers appear more significant in the converter-driven offshore AC grid with low short-circuit power, than in direct AC grid connections. This may lead to a violation of the 2% voltage dip criterion, thus seriously affecting the production of neighboring wind farms. Additionally, the transformer and the entire insulation system are exposed to mechanical and dielectric stress. This paper investigates the influence of three factors, namely excitation, switching angle, and remnant core magnetization, onto the inrush current. Electromagnetic transient simulations and field measurements show that with a smart use of the on load tap changer, point on wave switching, and a demagnetization of the core by a cable-shunt swing circuit, the three factors above can be used as degrees-of-freedom to effectively mitigate the inrush current phenomenon.

Multiple-Station Measurements of a Return-Stroke Electric Field From Rocket-Triggered Lightning at Distances of 68–126 km

Far-field measurements of lightning-produced electromagnetic fields are of high importance for lightning location systems. Data from recorded lightning strokes can be, for example, used to assess the risk of lightning-induced damage in some geographical areas. Artificially triggered lightning, usually generated using rocket-wire technology, plays an important role in the study of lightning physics. Multiple-station observations of far (typically larger than 20 km) electric field waveforms produced by rocket-triggered lightning are quite rare. In 2014, electric field waveforms were measured for return strokes through the rocket-and-wire technique at Conghua. They were measured by electric field sensors at nine sites belonging to the lightning locating system in Foshan, Guangzhou, China. A total of 38 events were recorded and overall statistics of those waveforms are presented. The results were compared to previous experimental data related to natural and artificially triggered lightning to validate their similarity.

Antenna Investigation by a Thermoelastic Optical Indicator Microscope: Defects Measurement and 3D Visualization of Electromagnetic Fields

Using the thermoelastic optical indicator microscopy (TEOIM) technique, we perform the visualization of the near-field distribution of a patterned frequencymodulation (FM) antenna. For the defect characterization, subtraction of images is done, whereas a background image is used for the defect-free antenna image. The electromagnetic fields distribution in the overall antenna structure is changed due to the defects, and this indicates the local impedance changes of the antenna pattern. The sensitivity of the proposed inspection technique is estimated to be in orders of a few milliwatts. In addition, a 3D visualization of the antenna transmission is realized to describe the field intensity and distribution dependences on the distance from the antenna surface. This type of investigation with a visualization opportunity may become an important tool for engineers and researchers, and it can successfully be a supplement for existing measurement techniques.

On the Relative Strength of Electric and Magnetic ULF Wave Radial Diffusion During the March 2015 Geomagnetic Storm

AbstractIn this paper, we study electron radial diffusion coefficients derived from Pc4‐Pc5 ultralow frequency (ULF) wave power during the intense geomagnetic storm on 17–18 March 2015. During this storm the population of highly relativistic electrons was depleted within 2 hr of the storm commencement. This radial diffusion, depending upon the availability of source populations, can cause outward radial diffusion of particles and their loss to the magnetosheath, or inward transport and acceleration. Analysis of electromagnetic field measurements from Geostationary Operational Environment Satellite (GOES), Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite, and ground‐based magnetometers shows that the main phase storm‐specific radial diffusion coefficients do not correspond to statistical estimates. Specifically, during the main phase, the electric diffusion ( ) is reduced, and the magnetic diffusion ( ) is increased, compared to empirical models based on Kp. Contrary to prior results, the main phase magnetic radial diffusion cannot be neglected. The largest discrepancies, and periods of dominance of over , occur during intervals of strongly southward IMF. However, during storm recovery, both magnetic and electric diffusion rates are consistent with empirical estimates. We further verify observationally, for the first time, an energy coherence for both and where diffusion coefficients do not depend on energy. We show that, at least for this storm, properly characterizing main phase radial diffusion, potentially associated with enhanced ULF wave magnetopause shadowing losses, cannot be done with standard empirical models. Modifications, associated especially with southward IMF, which enhance the effects of and introduce larger main phase outward transport losses, are needed.

Detection and Imaging of Magnetic Field in the Microwave Regime With a Combination of Magnetic Losses Material and Thermofluorescent Molecules

Characterization of the electromagnetic field emitted by various sources (antenna, radar, etc.) is an important issue, either for civil or defense applications. The measurement of electromagnetic field may be performed either by local probes or by thermography imaging, in particular with an infrared camera. The latter method, called electromagnetic infrared (EMIR) has been developed several years ago. We have recently successfully implemented this technique in the domain of visible light thanks to the combination of a film sensitive to either electric field (slightly conductive film) or magnetic field (insulating film with ferromagnetic particles) and a polymer coating doped with fluorescent molecules with an emission depending on temperature, indeed a thermofluorescent sensor. We present our recent results obtained imaging the microwave magnetic field emitted in the near field of a zeroth-order resonator (ZOR) antenna. The sensing film is a stack of FLEX-TOKIN magnetic absorber, already tested by EMIR infrared thermography in our group. A 20 µm film composed of a mixture of rhodamine B (RhB) in an epoxy matrix is screen printed on the FLEX surface. RhB, in ethanol solution, has a thermofluorescence coefficient of ∼2%/K at room temperature at its maximum of fluorescence of 595 nm. Excitation light is delivered by an array of blue 470 nm LEDs. The 4.29 GHz microwave excitation of the ZOR device is amplitude modulated at 0.1-0.5 Hz in order to cancel any thermal drift and convection of the thermofluorescence image. Low-frequency excitation modulation also allows noise cancellation via image pixel demodulation postprocessing. We present the deduced temperature mapping of the sensing film placed 2 mm above the ZOR patch antenna.

Development of Side Bidirectional Leader and Its Effect on Channel Branching of the Progressing Positive Leader of Lightning

AbstractFine time‐resolved images of the development of lightning bidirectional leaders below the cloud base were captured by a high‐speed camera in association with multiband electromagnetic field measurements. The bileaders tended to originate at a radial distance of about 200 m from a progressing positive leader channel, propagating more or less radially toward and away from the main channel. Significant asymmetrical channel extensions at opposite ends were clearly recognized. The positive ends of the bileaders propagated in single paths with average speed of 6.1 × 104 m/s, while the opposite negative end involved obvious branching and stepping propagation with average speed of 1.6 × 105 m/s. The bidirectional leaders eventually connected to the existing main positive leader, producing new branches of the flash. Another cause of positive leader branching was that the positive leader split at its head and developed into different branches synchronously, which were sometimes invisible but were revealed by recoil leaders.

Rapid measurement of electromagnetic fields induced from transcranial electric stimulation using magnetic resonance imaging

Rapid measurement of electromagnetic fields induced from transcranial electric stimulation using magnetic resonance imaging

1961 symposium digest — Third part of the digest

When considering interference to electromagnetic systems, there are no limited areas of measurement peculiar to the subject. These areas are almost as inclusive as life itself. The measurement of electromagnetic fields has been singled out for purposes of illustration. These measurements are admittedly difficult, complex, usually involve a substitution procedure, and encompass many facets of the subject — from the radiation of the generator to the immersion of the receiver.

Research on measurement of electromagnetic fields generated by electric and combustion powered rolling stock.

Axle counters are more and more often applied in train detection systems. The wheel sensor is a main part of each axle counter system. In parallel, more and more complex railway vehicles, especially traction ones, are a potential source of interferences influencing the operation of these train detection systems. It is the reason to verify the electromagnetic compatibility (EMC) between the signalling equipment, particularly train detection systems and new vehicles in the process of obtaining the permission for their exploitation. The measurement of interfering magnetic fields generated by vehicles is one of tests to be carried out. For the simplification and unification purpose of the applied interference test methods the EN 50238 standard and TS 50238-3 technical specification were developed. The specification defines unified testing procedures. However, it is necessary to verify if it may replace different testing methods used in particular European states. It is the goal of the European research project financed from the TEN-T network resources.

On Measuring Electromagnetic Fields in 5G Technology

At the awakening of the new 5G network as the network of services, issues related to electromagnetic fields (EMFs) will become one of the key aspects for the cost-effective establishment of the 5G infrastructure. The new 5G services will meet the rigorous demand for bandwidth through the implementation of a large number of densely located base stations operating in the millimeter-wave range. Introduction of new emission sources, working in parallel with already existing 2G/3G/4G mobile technologies, raises concerns about exceeding the admissible EMF exposure limits. This paper analyzes issues and challenges related to EMF measurements in 5G technology, which are crucial for the assessment of EMF compliance with regulatory limits. We point out that the existing methodologies, dedicated to EMF measurements in 2G, 3G, and 4G networks, are not suitable for 5G. The reason is the use of new techniques, such as massive MIMO and precise beamforming together with higher frequency bands so that the existing measurement methods can lead to significantly overestimated results when they will be applied to 5G networks. Such results, in conjunction with the restrictive legislation on the EMF limits that apply in some countries, may have the negative impact on 5G network deployment, making it difficult to achieve the intended 5G network capabilities. We also propose an alternative method of EMF exposure assessment that is based on calculations and simulations and allows obtaining an accurate estimation of the EMF distribution in the 5G environment.

Two gesture-computing approaches by using electromagnetic waves

We are concerned with a novel sensor-based gesture input/ instruction technology which enables human beings to interact with computers conveniently. The human being wears an emitter on the finger or holds a digital pen that generates a time harmonic point charge. The inputs/instructions are performed through moving the finger or the digital pen. The computer recognizes the instruction by determining the motion trajectory of the dynamic point charge from the collected electromagnetic field measurement data. The identification process is mathematically modelled as a dynamic inverse source problem for time-dependent Maxwell's equations. From a practical point of view, the point source should be assumed to move in an unknown inhomogeneous background medium, which models the human body and the surroundings. Moreover, a salient feature is that the electromagnetic radiated data are only collected in a limited aperture. For the inverse problem, we develop, from the respectively deterministic and stochastic viewpoints, a dynamic direct sampling method and a modified particle filter method. Both approaches can effectively recover the motion trajectory. Rigorous theoretical justifications are presented for the mathematical modelling and the proposed recovery methods. Extensive numerical experiments are conducted to illustrate the promising features of the two proposed recognition approaches.

257. Workplace Safety: Risks assessment of electromagnetic fields exposure

Purpose The European Directive 2013/35/UE, implemented in Italy by Legislative decree 159 dated 1 August 2016, introduces new exposure limits and it modifies the procedures for evaluating the exposure of workers to electromagnetic fields. Since June 2016, UBT srl, in collaboration with ARPA Umbria, has analyzed the issues recalled by the new Directive. In particular, this study focuses on investigating the instrumentation for performing electromagnetic fields measurements and on drafting of guidelines for standard assessment of electromagnetic fields exposure. Methods The devices here analyzed are magnetotherapies, electrosurgical units, welders, magnetizers, radio frequency dryers and test banks, both in healthcare and in general work environments. The instruments, used for measurements, are broadband probes from different manufacturers and with different characteristics. The data analysis method was chosen based on frequencies and waveform of electromagnetic radiations generated by different kinds of devices; specifically, the weighted peak method has been used. Results The measurements highlight different and complex exposure conditions based on the type of source (i.e. device) and workplace. In the case of magnetotherapy rooms, the worker’s weighted peak index was lower than unit; whereas, in the same rooms, general public limits can be exceeded 4 times also. Regarding welders and electrosurgical units, the exposure conditions were more complex and, before evaluation, a detailed analysis of radiation source was required. Conclusions The exposure assessment showed the necessity to delimit the area and/or to use dedicated warning signs so that non-exposed workers or the general public (for example, people accompanying patients) don’t have access to areas in which exposure limits are higher than the action levels. Finally, professional training is fundamental in preventing risks [1] .

The Electromagnetic Field in the Vicinity of Radio-Navigation Systems

AbstractToday, electromagnetic waves are the basic medium for all communication tasks. This applies also to navigation, where the most commonly waves have lengths measured in centimetres (radar, GPS) and longer, such as the waves used in the AIS or DGPS technologies. Navigators are mostly interested in the communication functionality of the used systems, i.e. such factors as range of the system and signal-to-noise ratio. This leads directly to increasing the transmitters’ power. However, it is important to bear in mind that the electromagnetic field can endanger human health, therefore, establishing the level of radiation both on vessels and near the shore transmitters is crucial in this context. The experience of authors shows that the knowledge of the most of navigators hereupon is not large. From this result extremely irresponsible behaviors of one persons, as well as inexplicable phobias others.This article presents the subject using the example of the electromagnetic field present near a lighthouse emitting AIS and DGPS signals. Relevant measurements were made at the Rozewie lighthouse by certified laboratory of Maritime Institute in Gdansk according the polish standards and internal, certified procedures. Results of the measurements were related to the national and European standards for electromagnetic field measurements in the context of occupational health and safety.

Test results of resonant single wire system transmitting power to the infrastructure objects of the JSC “RZD”

The paper provides test results of pilot sample of resonant single wire transmission system to a distance of 2000 m at a higher frequency. Cable power lines used as the power line based on coaxial cable. Operating principle of resonant single-wire transmission system is based on the use of two resonance transformers with frequency of 5–15 kHz, wire line voltage between the line is 1–10 kV when operating in a resonant mode. Resonant power transformers consist of a resonant circuit and step-up/step-down winding. Resonance system for high efficiency energy transfer system when adjusting all parameters at certain voltage, frequency and load. With the set of equipment, which operates at a frequency of 7–9 kHz and at a voltage of 980 V, power line can transmit electricity on a single transmission line up to 3000 watts. The article describes the possibility of applying a resonant sin-gle-wire power transmission system at a frequency of about 7 kHz for the transmission of electric power up to 3 kW from a stationary power supply system (three-phase voltage is 380 V AC, 50 Hz) for single-phase load, and earthed on the individual earthing inverter. Efficiency of resonant single-wire electric power transmission system increases with increasing load capacity. It can reach 88–91 % directly at the maximum load with efficient conversion equipment. Measurements of electromagnetic fields from unscreened power lines were carried out. The results of the measurements show that the maximum value of the alternating electric field in the frequency range of 2–400 kHz is 100–150 V/m, well below the maximum permissible level. The advantage of the resonance system compared to a single-phase system is in operating at the frequency of 7 kHz.

Stochastic electromagnetic field propagation- measurement and modelling.

This paper reviews recent progress in the measurement and modelling of stochastic electromagnetic fields, focusing on propagation approaches based on Wigner functions and the method of moments technique. The respective propagation methods are exemplified by application to measurements of electromagnetic emissions from a stirred, cavity-backed aperture. We discuss early elements of statistical electromagnetics in Heaviside's papers, driven mainly by an analogy of electromagnetic wave propagation with heat transfer. These ideas include concepts of momentum and directionality in the realm of propagation through confined media with irregular boundaries. We then review and extend concepts using Wigner functions to propagate the statistical properties of electromagnetic fields. We discuss in particular how to include polarization in this formalism leading to a Wigner tensor formulation and a relation to an averaged Poynting vector.This article is part of the theme issue ‘Celebrating 125 years of Oliver Heaviside's ‘Electromagnetic Theory’’.

Dealing with crosstalk in electromagnetic field measurements of portable devices.

Portable devices measuring radiofrequency electromagnetic fields (RF-EMF) are affected by crosstalk: signals originating in one frequency band that are unintentionally registered in another. If this is not corrected, total exposure to RF-EMF is biased, particularly affecting closely spaced frequency bands such as GSM 1800 downlink (1,805-1,880 MHz), DECT (1,880-1,900 MHz), and UMTS uplink (1,920-1,980 MHz). This study presents an approach to detect and correct crosstalk in RF-EMF measurements, taking into account the real-life setting in which crosstalk is intermittently present, depending on the exact frequency of the signal. Personal measurements from 115 volunteers from Zurich canton, Switzerland were analyzed. Crosstalk-affected observations were identified by correlation analysis, and replaced by the median value of the unaffected observations, measured during the same activity. DECT is frequently a victim of crosstalk, and an average of 43% of observations was corrected, resulting in an average exposure reduction of 38%. GSM 1800 downlink and UMTS uplink were less often corrected (6.9% and 8.9%), resulting in minor reductions in exposure (7.1% and 0.92%). The contribution of DECT to total RF-EMF exposure is typically already low (3.2%), but is further reduced after correction (3.0%). Crosstalk corrections reduced the total exposure by 1.0% on average. Some individuals had a larger reduction of up to 16%. The code developed to make the corrections is provided for free as an R function which is easily applied to any time series of EMF measurements. Bioelectromagnetics. 39:529-538, 2018. © 2018 Wiley Periodicals, Inc.

Microwave Photonic Detector for Measuring Pulsed Electric Field Strengths in the Sub-Nanosecond Region

We provide a validated approach for microwave photonics as a means of developing high-speed noise-immune devices for measurement of strong pulsed electromagnetic fields. We develop a microwave photonic detector for measuring pulsed electric field strengths with a maximum transient-response rise time of 100 psec.