Field Strength Measurements Research Articles

A DCNN‐LSTM model for the construction of the road radio map

AbstractIt is crucial for vehicular communications to optimize the field strength coverage on roads, which can be illustrated by the radio map (RM). In this paper, a deep convolutional neural network‐long short‐term memory (DCNN‐LSTM) model for the construction of the road RM is proposed. First, a multi‐modal dataset is built, including the measured field strength, longitude, latitude and elevation data obtained at various measurement points, as well as the outline maps of the buildings that are close to the measurement points. Second, the DCNN‐LSTM model is designed to extract electromagnetic and geographical features separately from the multi‐modal input data and fuse them to predict the field strength at unmeasured points. Finally, the road RM is constructed using the measured and predicted field strength data. The simulation results demonstrate that the field strength prediction accuracy of the proposed model is better than that of the ordinary kriging and the traditional deep learning models. Moreover, it exhibits robust performance even in noise interference environments. The constructed RM also provides an intuitive visualization of field strength coverage along the target road.

Unveiling complex magnetic field configurations in red giant stars

The recent measurement of magnetic field strength inside the radiative interior of red giant stars has opened the way toward full 3D characterization of the geometry of stable large-scale magnetic fields. However, current measurements, which are limited to dipolar (ℓ = 1) mixed modes, do not properly constrain the topology of magnetic fields due to degeneracies on the observed magnetic field signature on such ℓ = 1 mode frequencies. Efforts focused toward unambiguous detections of magnetic field configurations are now key to better understand angular momentum transport in stars. We investigated the detectability of complex magnetic field topologies (such as the ones observed at the surface of stars with a radiative envelope with spectropolarimetry) inside the radiative interior of red giants. We focused on a field composed of a combination of a dipole and a quadrupole (quadrudipole) and on an offset field. We explored the potential of probing such magnetic field topologies from a combined measurement of magnetic signatures on ℓ = 1 and quadrupolar (ℓ = 2) mixed mode oscillation frequencies. We first derived the asymptotic theoretical formalism for computing the asymmetric signature in the frequency pattern for ℓ = 2 modes due to a quadrudipole magnetic field. To access asymmetry parameters for more complex magnetic field topologies, we numerically performed a grid search over the parameter space to map the degeneracy of the signatures of given topologies. We demonstrate the crucial role played by ℓ = 2 mixed modes in accessing internal magnetic fields with a quadrupolar component. The degeneracy of the quadrudipole compared to pure dipolar fields is lifted when considering magnetic asymmetries in both ℓ = 1 and ℓ = 2 mode frequencies. In addition to the analytical derivation for the quadrudipole, we present the prospect for complex magnetic field inversions using magnetic sensitivity kernels from standard perturbation analysis for forward modeling. Using this method, we explored the detectability of offset magnetic fields from ℓ = 1 and ℓ = 2 frequencies and demonstrate that offset fields may be mistaken for weak and centered magnetic fields, resulting in underestimating the magnetic field strength in stellar cores. We emphasize the need to characterize ℓ = 2 mixed-mode frequencies, (along with the currently characterized ℓ = 1 mixed modes), to unveil the higher-order components of the geometry of buried magnetic fields and to better constrain angular momentum transport inside stars.

The Spatial Correlation between CN-line- and Dust-continuum-emitting Regions in High-mass Star-forming Clouds

Measuring the strength of a three-dimensional (3D) magnetic field vector is challenging as it is not easy to recognize whether its line-of-sight (LOS) and plane-of-sky (POS) components are obtained from the same region. CN (N = 1–0) emission has been used to get the LOS component of a magnetic field (B LOS) from its Zeeman splitting lines, while dust continuum emission has been used to get the POS component of a magnetic field (B POS). We use the CN (N = 1–0) data observed with the Taeduk Radio Astronomy Observatory 14 m telescope and the dust continuum data from the Herschel archive toward six high-mass star-forming regions in order to test whether CN line and dust continuum emission can trace a similar region and thus can be used for inferring 3D magnetic field strength. Our comparison between CN and H2 column densities for all targets indicates that CN line emission tends to be strong toward bright continuum regions. The positions of peak CN column densities are particularly well correlated with those of peak H2 column densities, at least over the H2 column density of 8.0 × 1022 cm−2 within one or two telescope beam sizes in all targets, implying that CN-line- and dust-continuum-emitting regions are likely spatially coincident. This enabled us to make the reliable measurement of the 3D magnetic field strengths of five targets by taking a vector sum of their B LOS and B POS, helping to decide the magnetical criticality of the targets as supercritical or transcritical.

Sensitivity Matrix Update Method for Electrical Resistance Tomography Based on Error-Constrained Cross Fusion Residual Attention Network

Abstract Electrical resistance tomography (ERT) is an imaging technique of conductivity distribution. The image reconstruction algorithm based on the empty field sensitivity matrix is widely used because it provides an approximate solution to the complex ERT inverse problems. However, due to the soft field effect, the sensitivity matrix changes with the media distribution, leading to significant errors in image reconstruction. To address this issue, an error-constrained deep learning scheme for bubble flow, namely cross fusion residual attention network (CFRA-Net) is designed to update the sensitivity matrix during gas-liquid-solid fluidized bed operation. CFRA-Net employs a multi-head self-attention mechanism to enhance bubble features in boundary measurements, a multilevel cross fusion module to fuse empty field strength and boundary measurement information, and a novel serial-channel residual spatial attention block to boost the feature extraction capability of the model. A weighted loss function is designed to give more weight to the gas phase distribution region. Additionally, this paper establishes a dataset for gas-liquid-solid three-phase flow, considering background field conductivity variations. Validation and reliability of the proposed method are assessed through ablation, comparison, and noise experiments. The experimental results demonstrate that CFRA-Net achieves rapid updates of the sensitivity matrix, high imaging accuracy, and robust noise immunity.

Perpendicular Electrical Conductivity in the Topside Ionosphere Derived from Swarm Measurements

The study of the physical properties of the topside ionosphere is fundamental to investigating the energy balance of the ionosphere and developing accurate models to predict relevant phenomena, which are often at the root of Space Weather effects in the near-Earth environment. One of the most important physical parameters characterising the ionospheric medium is electrical conductivity, which is crucial for the onset and amplification of ionospheric currents and for calculating the power density dissipated by such currents. We characterise, for the first time, electrical conductivity in the direction perpendicular to the geomagnetic field, namely Pedersen and Hall conductivities, in the topside ionosphere at an altitude of about 450 km. For this purpose, we use eight years of in situ simultaneous measurements of electron density, electron temperature and geomagnetic field strength acquired by the Swarm A satellite. We present global statistical maps of perpendicular electrical conductivity and study their variations depending on magnetic latitude and local time, seasons, and solar activity. Our findings indicate that the most prominent features of perpendicular electrical conductivity are located at low latitudes and are probably driven by the complex dynamics of the Equatorial Ionisation Anomaly. At higher latitudes, perpendicular conductivity is a few orders of magnitude lower than that at low latitudes. Nevertheless, conductivity features are modulated by solar activity and seasonal variations at all latitudes.

Accuracy of the scalar magnetometer aboard ESA's JUICE mission

Abstract. This paper discusses the accuracy of the scalar Coupled Dark State Magnetometer on board the Jupiter Icy Moons Explorer (JUICE) mission of the European Space Agency (ESA). The scalar magnetometer, referred to as MAGSCA, is part of the J-MAG instrument. MAGSCA is an optical omnidirectional scalar magnetometer based on coherent population trapping, a quantum interference effect, within the hyperfine manifold of the 87Rb D1 line. The measurement principle is only based on natural constants; therefore, it is in principle drift-free, and no calibration is required. However, the technical realisation can influence the measurement accuracy. The most dominating effects are heading characteristics, which are deviations of the magnetic field strength measurements from the ambient magnetic field strength. These deviations are a function of the angle between the sensor axis and the magnetic field vector and are an intrinsic physical property of the measurement principle of the magnetometer. The verification of the accuracy of the instrument is required to ensure its compliance with the performance requirement of 0.2 nT (1σ) with a data rate of 1 Hz. The verification is carried out with four dedicated sensor orientations in a Merritt coil system, which is located in the geomagnetic Conrad Observatory (COBS). The coil system is used to compensate the Earth's magnetic field and to apply appropriate test fields to the sensor. This paper presents a novel method to separate the heading characteristics of the instrument from residual (offset) fields within the coil system by fitting a mathematical model to the measured data and by the successful verification of the MAGSCA performance requirement.

Method for improving accurate measurement of the magnetic field of wireless passive micro-magnetic stimulator micro-coil

In recent years, the wireless passive micro-magnetic stimulator (WP-μMS) has emerged as a focal for implantable neuromagnetism modulation research. However, accurately measuring the magnetic field strength of the micro-coil presents a significant challenge due to its small size and low mutual inductance (M). Firstly, this paper establishes a theoretical model of magnetic coupling with a three-stage structure of transmitting coil-micro-coil-detecting coil. The calculation method of detecting the coil to measure the magnetic field is determined by calculating the M between each pair of coils. Secondly, the magnetic coupling resonance method enhances the measured value M to the nH-scale. This approach also eliminates the influence of the M between the transmitting coil-detecting coil on the measurement of the transmitting coil-micro-coil M, thereby achieving accurate measurement of the mT-scale magnetic field strength of the WP-μMS micro-coil. Finally, the effectiveness of the measured mT-scale magnitude magnetic stimulation is validated biologically.

Design and application of a power frequency electric field measuring device for a high‐humidity environment

AbstractThe power frequency electric field is the most important electromagnetic environmental factor in alternating current power transmission projects. The humidity has a negative influence on available electric field measuring devices, which may lead to discrepancies of up to seven times the actual value at a relative humidity exceeding 80%. The changes in the support and probe shell impedance may be the reason for the error. The optimization measures include modifying the communication mode, designing a suitable structure and circuit for the probe, and using composite insulating material with strong hydrophobicity for the support. A three‐axis omnidirectional electric field measuring device was developed based on wireless communication and composite support. The variation of the measured electric field strength value is less than 1% at relative humidities ranging from 45% to 90% in the laboratory, and the measured results obtained in high humidity at the high‐voltage test site and under the transmission line demonstrated high accuracy. The research demonstrates that the composite support can be used to improve the performance of conventional devices. The proposed device can better meet the needs for accurate measurement of electric field strength in a high‐humidity environment and overcome the technical problems raised by the IEC standard.

Time-resolved investigations of a glow mode impulse dielectric barrier discharge in pure ammonia gas by means of E-FISH diagnostic

Time-resolved electric field strength measurements have been performed, using an electric-field induced second harmonic (E-FISH) diagnostic, in a nanosecond glow discharge of an impulse dielectric barrier discharge, in an ammonia gas environment. A temporal resolution of 2 ns and a spatial resolution estimated at 70 µm (given by laser waist) have been achieved. The comparative study of E-FISH measurements with and without a plasma discharge, operated at 4 kHz, reveal the presence of a persistent counter electric field, which is assumed to be caused by charge accumulation in between the AlN dielectrics used. Furthermore, by studying the influence of the applied voltage, the pressure, and the inter-dielectric distance, measurements seem to indicate the presence of charges remaining also in the post-discharge volume from the previous discharge to the next one.

MODELING OF THE EXTERNAL MAGNETIC FIELD OF ELECTRIC MACHINES

Powerful electric machines – such as electric generators, electric motors generate a magnetic field of great tension. These fields negatively effect on personnel and can to violate the stability of electronic equipment. To determine safe areas for workers, laying communication cables and placing sensitive electronic equipment, it is advisable to model the propagation of magnetic fields of electrical machines. This will make it possible to rationalize the placing of electrical equipment at design stages. The most common high-power electrical machines are four-pole electrical machines with a dipole-quadrupole structure of the external magnetic field. The purpose of the research is a development of models of the propagation of the external magnetic field generated by alternating current electric machines. Results of the research: it is substantiated that to simulate the propagation of the magnetic field of electric machines, it is advisable to use the Gauss equation for the magnetic scalar potential. This will make it possible to take into account the required number of spatial harmonics of the magnetic field to ensure an acceptable calculation error. An electric machine is considered in a spherical approximation. Calculations were carried out in spherical coordinates. The distances were determined in relative radii of the electric machine - the ratio of the radius of the machine to the definition of field strength. The calculations were made for two planes of spherical coordinates and a three-dimensional image was obtained. As a result of the simulation, it is possible to determine the magnetic field strength of a four-pole electric machine at selected distances and directions around the electric machine with the required accuracy. It has been established that there are points of zero external magnetic field strength around electrical machines. Verification of the simulation results was carried out using the method of full-scale measurements of the magnetic field strength around a real four-pole machine. The measurement results showed acceptable agreement with the calculated data. Conclusions: the chosen approach and the results of modeling the propagation of the external magnetic field of electrical machines can be used to design the placement of electrical equipment, taking into account the requirements for electromagnetic safety and electromagnetic compatibility of technical equipment.

Measurement and Calibration of EMF: A Study Using Phone and GBDT for Mobile Communication Signals

AbstractElectromagnetic exposure caused by mobile communication signals has always been a cause of concern. Due to the cost and inconvenience of professional measurement equipment, researchers have turned to smartphone APPs to study and assess the electric field strength caused by mobile communication signals. However, existing cell phone‐based measurements have two weaknesses. First, no system architecture suitable for large‐scale crowdsourced testing has been proposed. Second, since smartphone sensors cannot measure electric field strength directly, existing methods for converting the received signal power of the phone and electric field strength have errors of more than 5 dB. This paper proposes a measurement and calibration method for electric field strength of mobile communication signals based on a smartphone app and gradient boosting decision tree (GBDT). This method consists of a downlink signal acquisition system based on an APP and a calibration model based on GBDT to convert received signal power into electric field strength. The experimental results show that the proposed model achieves a R2 score of 0.93 and a MAE of 0.97 dB. Compared with the existing methods, our method improves the calibration accuracy by 4 dB, enabling large‐scale, low‐cost, and high‐precision direct measurement of the electric field strength of mobile communication signals.

Разработка нового метода измерения напряженности электрического поля на основе сдвоенного электроиндукционного датчика

A new method for measuring electric field strength is proposed. The method is based on the mean value measurement method, which uses a dual electroinduction spherical sensor. The use of the dual sensor for the method implementation allows to extend the functionality of the method by mean value. The method of measurement by the mean value assumes simultaneous measurement of two values of intensity E1 and E2 in one point of electric field with opposite sign errors. As the theory of construction of the new method has shown, it is possible to determine not only the measurement result as an average of two values of the strengths, but also to estimate the error of the measurement result and tentatively determine the distance to the field source. In order to determine the distance to the field source, a coefficient of the ratio of the two found strengths at each point of the field is introduced, by which the empirical dependence of the relative distance to the field source is found. The relative distance is the ratio between the radius of the spherical sensor and the distance to the field source. By determining the relative distance at each measuring point according to this relationship and substituting it into the known expression for the error, the error of the result at the measuring point is determined. The relative distance is also used to determine the distance to the field source. Thus, the new method of measurement allows to increase the accuracy of measurement of electric field strength, determined by the relative distance to the source of the field.

Prerequisites for Construction of a Device for Measurements of Electric Field Strength with Determination of the Measurement Error

Prerequisites for Construction of a Device for Measurements of Electric Field Strength with Determination of the Measurement Error

EURAMET.EM.RF-S46 (EURAMET Project No 1538) EURAMET supplementary comparison on magnetic field strength measurements for frequencies up to 30 MHz

Main textThe results of the supplementary comparison in the area of magnetic field probe calibration of the field strength are presented. This supplementary comparison has been discussed to organize a comparison on magnetic field strength measurements during the EURAMET TC-EM Subcommittee Radiofrequency and Microwave (SC-MW) meeting, including an EMC meeting, organized as a virtual (online) meeting on 20-21 April 2021. The comparison was conducted in accordance with the Technical Protocol of "Comparison of Magnetic Field Strength Measurements for Frequencies up to 30 MHz, EURAMET Project No 1538, EURAMET.EM.RF-S46", which was prepared by the TÜBİTAK UME and approved by the participants. The measurements started in January 2022 and were completed in May 2023. Measurement results reported by nine participants for magnetic field strength values were compared and degrees of equivalence are reported.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Increasing the accuracy of electrostatic fields strength measurement by using an improved differential transimpedance amplifier circuit

An electrostatic field mill (EFM) is widely used to measure the strength of electrostatic fields, the main drawback of which is the occurrence of large measurement errors (up to 15 % in the range from 0 to 1 kV/m). This paper examines the aspects of using transimpedance amplifiers (TIAs) for the tasks of converting the current received from the EFM sensor into voltage, which will make it possible to reduce the instrumental error and ensure the linearity of the atmospheric electrostatic field strength measurement. In the general case, for the functional circuits of the electrostatic field mill, which include a differential transimpedance amplifier, there is the use of two TIA circuits, which are connected in parallel. Despite the simplicity of implementation, such a configuration contains a number of disadvantages and is not optimal. In the paper, a comparative analysis of a typical circuit of a differential TIA and a circuit of an ungrounded differential transimpedance amplifier with zero voltage drop proposed by the authors is carried out. As a result of the analysis, it was established that the designed authentic circuit of the ungrounded differential transimpedance amplifier with zero voltage drop has better parameters of linearity and interference resistance, in contrast to the generally accepted one. The value of the signal-to-noise ratio for the proposed scheme improved by 42 % on average compared to the typical one. The main difference of the proposed scheme is that the stability of the amplification factor is ensured, the influence of the bias parameters of the operational amplifier is leveled, and the overall noise level is reduced. The use of the designed scheme of an ungrounded differential transimpedance amplifier with zero voltage drop could make it possible to increase the accuracy of the measurement of the electrostatic field strength

A facile approach for estimating radio-frequency field strength of low-receptivity nuclei

Radio-frequency (RF) field calibration is essential in NMR spectroscopy. A common practice is to collect a nutation curve by varying the pulse length in a direct single-pulse excitation experiment or in a cross-polarization magic-angle spinning with a flip-back pulse experiment. From the null points on this curve, one can calculate the RF field strength. Nevertheless, the practical implementation is not always straightforward or can even be unrealizable, especially for low-receptivity nuclei owing to their associated low sensitivity. Several researchers used an approach that involves utilizing other nuclei with more sensitivity but nearly identical Larmor frequencies to that of the nucleus of interest. However, such an approach has not been a common practice so far. In this work, we have systematically revisited this approach using 3.2 mm rotors on different sets of nuclei covering a Larmor frequency range up to 80 MHz. The effect of solid- and solution-states on RF field strength measurements has been investigated. The detection of each set of nuclei is then carried out with a resonant circuit in the NMR probe consisting of identical coils and capacitors. Our methodology is illustrated by recording 135/137Ba NMR spectra of BaTiO3 without prior 135/137Ba RF field calibration.

Dark halos around solar active regions

Context. Dark areas around active regions (ARs) were first observed in chromospheric lines more than a century ago and are now associated with the Hα fibril vortex around ARs. Nowadays, large areas surrounding ARs with reduced emission relative to the quiet Sun (QS) are also observed in spectral lines emitted in the transition region (TR) and the low corona. For example, they are clearly seen in the SDO/AIA 171 Å images. We name these chromospheric and TR-coronal dark regions “dark halos” (DHs). Coronal DHs are poorly studied and, because their origin is still unknown, to date it is not clear if they are related to the chromospheric fibrillar ones. Furthermore, they are often mistaken for coronal holes (CHs). Aims. Our goal is to characterize the emission properties of a DH by combining, for the first time, chromospheric, TR, and coronal observations in order to provide observational constraints for future studies on the origin of DHs. This study also aims to investigate the different properties of DHs and CHs and provide a quick-look recipe to distinguish between them. Methods. We studied the DH around AR NOAA 12706 and the southern CH that were on the disk on April 22, 2018 by analyzing IRIS full-disk mosaics and SDO/AIA filtergrams to evaluate their average intensities, normalized to the QS. In addition, we used the AIA images to derive the DH and CH emission measure (EM) and the IRIS Si IV 1393.7 Å line to estimate the nonthermal velocities of plasma in the TR. We also employed SDO/HMI magnetograms to study the average magnetic field strength inside the DH and the CH. Results. Fibrils are observed all around the AR core in the chromospheric Mg II h&k IRIS mosaics, most clearly in the h3 and k3 features. The TR emission in the DH is much lower than in the QS area, unlike in the CH. Moreover, the DH is much more extended in the low corona than in the chromospheric Mg II h3 and k3 images. Finally, the intensities, EM, spectral profile, nonthermal velocity, and average magnetic field strength measurements clearly show that DHs and CHs exhibit different characteristics, and therefore should be considered as distinct types of structures on the Sun.

Experimental Validation of Enhanced GPR Signals by A Broadband Metasurface

In this paper, the potential of a broadband metasurface for ground penetrating radar (GPR) signal enhancement is investigated by simulation and experiments. Simulation results show that the reflection at the air-MUT interface can be reduced from 35% to 5% over a broad frequency range (relative bandwidth up to 44%) when the broadband metasurface is in place. Measured reflectance is consistent with the simulation results. Meanwhile, the electric field strength measurement results demonstrate that the transmitted electromagnetic signals can be amplified when the reflection is reduced over the same frequency range. GPR experiments verified that clear hyperbolic signals emerged for commonly undetectable pipes when the high-frequency signals are enhanced. The proposed broadband metasurface can be an effective solution for the detection of nonmetallic inclusions in high-lossy media.

Analysis of modern atmospheric electrostatic field measuring instruments and methods

The object of research is the process of measuring the strength of the atmospheric electrostatic field. This paper is devoted to an analytical review and comparative analysis of modern methods and instruments for measuring atmospheric electrostatic field strength. The results of scientific research and modern practical technologies, which are used to develop technical means and increase the accuracy of measuring the strength of electrostatic fields, are considered. In the work, the general functional requirements for the hardware of systems for measuring the atmospheric electrostatic field strength are formed and the main directions of research and practical tasks for its creation are defined. The design features and characteristics of existing measuring instruments are considered in detail. The advantages and disadvantages of electrometers, electrostatic field mills, microelectromechanical electrostatic field mills, and electric field imaging systems are determined given their portability, sensitivity, measuring frequency, accuracy, measurement range, linearity, and cost. The analysis of the state of modern methods and measuring instruments for the strength of the electrostatic field showed that one of the best solutions for measuring the electrostatic field strength of the atmosphere today is the use of an improved electrostatic field mill. It was determined that one of the important problems for ensuring the development of methods and means of atmospheric electrostatic field strength measuring is the need to generalize the structure of the measuring instruments and calculate its metrological characteristics. It has been established that solving the problem of increasing the accuracy of atmospheric electrostatic field strength measurement requires a comprehensive approach based on improving the design of the sensor structure of the meter, increasing the accuracy of navigation and positioning, increasing the autonomy of work, improving communication and data transmission systems, as well as ensuring high stability and reliability of work under the influence of external factors. Improving the structure and improving the characteristics of electrostatic field mills in the future will ensure the necessary accuracy, compactness, and availability for measurement and its inclusion in the automated system of atmospheric electrostatic field monitoring and forecasting.

Metrological traceability of the results of testing for electromagnetic compatibility in accordance with the NATO standards

Ensuring the electromagnetic compatibility of special-purpose equipment used in a complex saturated radio frequency environment requires testing in accordance with procedures that guarantee a valid verification of its immunity to external electromagnetic fields. The paper presents the national measurement standards and equipment used at the National Scientific Centre “Institute of Metrology” for the NRE02, NRE03 and NRS02 testing in accordance with the AESTR-500 standard. It is shown how metrological traceability to the SI units of the measurement results is ensured during tests. The paper presents the results of evaluating the uncertainty of the results of measurements of the electromagnetic field strength using the NARDA-550 meter for the frequency ranges of 10 kHz – 1 GHz when using the GTEM chamber, and for the frequency ranges of 1-43 GHz when using the anechoic chamber. The studies have proven that the measurement uncertainties, when calibrating the antenna in the anechoic chamber, and the uneven distribution of the electromagnetic field in the GTEM chamber are the most critical. The obtained results of the uncertainty evaluation of the NARDA-550 calibration coefficient are used for high-precision measurements of radio frequency signals both at emission and being exposed to electromagnetic fields when the disturbances have limit values as regards the provisions of these standards. These results with a discrepancy of no more than 0.05 dB confirm the characteristics of the device provided by the manufacturer. It is shown that the set of national measurement standards and test equipment of the NSC “Institute of Metrology” allows testing special equipment for electromagnetic compatibility according to the NATO standards with the required accuracy.