Magnetic Field Probe Research Articles

Neutrino Emissivities as a Probe of the Internal Magnetic Fields of White Dwarfs

The evolution of white dwarfs (WDs) depends crucially on thermal processes. The plasma in their core can produce neutrinos that escape from the star, thus contributing to the energy loss. While in the absence of a magnetic field the main cooling mechanism is plasmon decay at high temperature and photon surface emission at low temperature, a large magnetic field in the core hiding beneath the surface even of ordinary WDs, and undetectable to spectropolarimetric measurements, could potentially leave an imprint in the cooling. In this paper, we revisit the contribution to WD cooling stemming from neutrino pair synchrotron radiation and the effects of the magnetic field on plasmon decay. Our key finding is that even if observations limit the magnetic field strength at the stellar surface, magnetic fields in the interior of WDs—with or without a surface magnetic field—can be strong enough to modify the cooling rate, with neutrino pair synchrotron emission being the most important contribution. This effect may not only be relevant for the quantification and interpretation of cooling anomalies, but suggests that the internal magnetic fields of WDs should be smaller than ∼ 6 × 1011 G, slightly improving bounds coming from a stability requirement. While our simplified treatment of the WD structure implies that further studies are needed to reduce the systematic uncertainties, the estimates based on comparing the emissivities illustrate the potential of neutrino emission as a diagnostic tool to study the interior of WDs.

Tackling the Unique Challenges of Low-frequency Solar Polarimetry with the Square Kilometre Array Low Precursor: The Algorithm

Coronal magnetic fields are well known to be one of the crucial parameters defining coronal physics and space weather. However, measuring the global coronal magnetic fields remains challenging. The polarization properties of coronal radio emissions are sensitive to coronal magnetic fields. While they can prove to be useful probes of coronal and heliospheric magnetic fields, their usage has been limited by technical and algorithmic challenges. We present a robust algorithm for precise polarization calibration and imaging of low-radio frequency solar observations and demonstrate it on data from the Murchison Widefield Array, a Square Kilometre Array (SKA) precursor. This algorithm is based on the Measurement Equation framework, which forms the basis of all modern radio interferometric calibration and imaging. It delivers high-dynamic-range and high-fidelity full-Stokes solar radio images with instrumental polarization leakages <1%, on par with general astronomical radio imaging, and represents the state of the art. Opening up this rewarding, yet unexplored, phase space will enable multiple novel science investigations and offer considerable discovery potential. Examples include detection of low-level circular polarization from thermal coronal emission to estimate large-scale quiescent coronal fields; polarization of faint gyrosynchrotron emissions from coronal mass ejections for robust estimation of plasma parameters; and detection of the first-ever linear polarization at these frequencies. This method has been developed with the SKA in mind and will enable a new era of high-fidelity spectropolarimetric snapshot solar imaging at low radio frequencies.

High Common-Mode-Rejection Magnetic-Field Probe Based on Differential Dual Loop and Integrated Balun

In this article, a magnetic-field probe with improved common-mode rejection ratio (CMRR) is proposed, fabricated, and calibrated. The magnetic-field probe consists of a differential dual loop (DDL) and an integrated balun. The advantage of this integrated design is to sense more magnetic flux and convert the differential signal into a single port signal, which makes the test easier. The CMRR of the proposed probe is more than 35 dB from 0.8 to 2.5 GHz under the condition that the loop size is 4.7 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times4.6$ </tex-math></inline-formula> mm. The probe is verified through the simulation, the comparisons with reference probes and the near-field measurement of a U-shaped microstrip line.

Optical and Spin Properties of NV Center Ensembles in Diamond Nano-Pillars.

Nitrogen-vacancy (NV) color centers in diamond are excellent quantum sensors possessing high sensitivity and nano-scale spatial resolution. Their integration in photonic structures is often desired, since it leads to an increased photon emission and also allows the realization of solid-state quantum technology architectures. Here, we report the fabrication of diamond nano-pillars with diameters up to 1000 nm by electron beam lithography and inductively coupled plasma reactive ion etching in nitrogen-rich diamonds (type Ib) with [100] and [111] crystal orientations. The NV centers were created by keV-He ion bombardment and subsequent annealing, and we estimate an average number of NVs per pillar to be 4300 ± 300 and 520 ± 120 for the [100] and [111] samples, respectively. Lifetime measurements of the NVs’ excited state showed two time constants with average values of τ1 ≈ 2 ns and τ2 ≈ 8 ns, which are shorter as compared to a single color center in a bulk crystal (τ ≈ 10 ns). This is probably due to a coupling between the NVs as well as due to interaction with bombardment-induced defects and substitutional nitrogen (P1 centers). Optically detected magnetic resonance measurements revealed a contrast of about 5% and average coherence and relaxation times of T2 [100] = 420 ± 40 ns, T2 [111] = 560 ± 50 ns, and T1 [100] = 162 ± 11 μs, T1 [111] = 174 ± 24 μs. These pillars could find an application for scanning probe magnetic field imaging.

Storage and retrieval of microwave pulse in a crystal of molecular magnets based on four-wave-mixing

In this paper, we consider a crystal of molecular magnets interacting with four alternating magnetic fields. When a DC magnetic field applies to molecular magnets, the energy levels of molecular magnets can be recognized as a four-level system. We consider four wave mixing process in the crystal of molecular magnets, By solving the Schrödinger equation, the analytic solutions of the probe and mixing magnetic fields are obtained. We have also numerically investigated the dynamical evolution of the probe and mixing magnetic fields. The results show that probe and mixing filed periodically oscillate in the crystal of molecular magnets medium. By adjusting the frequency detuning and the intensity of the coupled magnetic fields, the storage and retrieval of microwave field can be achieved in molecular magnets. In the end, the second-order correlation function is calculated and the anti-bunching effect can be achieved in this magnetic medium.

A Near-Field Motion Detection Technique Based on a Resonant Magnetic Probe

This letter proposes a near-field motion detection technique based on a resonant magnetic-field probe. The resonant magnetic-field probe consists of a parallel metal plate and a quarter-wave impedance transformer to make the input impedance 50 &#x03A9;. The 5.8-GHz radio frequency (RF) front-end is designed, which consists of a hybrid coupler and the proposed resonant magnetic-field probe that can be regarded as a full duplex antenna. Then, a 5.8-GHz continuous-wave Doppler radar transceiver is designed and integrated with the RF front-end to build the near-field radar system. The equivalent circuit of the RF front-end while detecting the targets in near-field is analyzed, in which the probe loop and the matching circuitry are modeled as a parallel <i>RLC</i> circuit and the coupler and transmission lines are equivalent to a lossy transmission line and an attenuator. The experimental results demonstrate that the proposed system can detect submillimeter displacement motions in the near-field.

Design and Characterization of a Multi-Processed Differential Magnetic Field Probe by Using Asymmetric Calibration Method

In order to improve the spatial resolution of a magnetic near field probe, the design method combining multiple ports with multiple production processes has been proven effective. However, the asymmetry of transmission structure introduced by the junction between two different processes is a key problem that limits the performance of these probes. In this paper, a differential magnetic near field probe (diff-H-probe) combining flexible printed circuit (FPC) process with print circuit board (PCB) process has been manufactured to achieve high spatial resolution. The measurement results show that this probe can recognize a serpentine line with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100~\mu \text{m}$ </tex-math></inline-formula> -width of trace and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100~\mu \text{m}$ </tex-math></inline-formula> -space between traces. Meanwhile, an asymmetric calibration method (ACM) has been applied to significantly improve the performance of the diff-H-probe. Some key parameters of the probe with and without using the ACM are compared by using an air-dielectric microstrip line. The compared results show that the detection frequency range of the proposed probe is broaden to 12 GHz. Moreover, the results also demonstrate that the ACM can improve the differential electric field suppression up to 4.1 dB and improve the common mode electric field suppression to 20 dB at the frequency below 12 GHz.

Bdot probe and Rogowski coil cross-calibration and sensor fusion in pulsed direct current capacitor discharges.

Bdot probes and Rogowski coils are used in the measurement of transient magnetic fields and currents, respectively. They both share the mechanism of creating an induced electromotive force response via Faraday's law, which scales linearly with the pulsed magnetic field. High power capacitor direct current (DC) discharge systems release a single pulse of current that is both very high and very fast (≲1 ms). To capture these transient data and characterize these systems, high current tolerant and fast response time sensors are required. While these measuring devices have been well studied and utilized for almost 100 years, a comprehensive and detailed description of the custom design, calibration, and sensor fusion application of these tools for use in various pulsed DC capacitor value discharges is largely missing in the literature. Using robust analytical calculations, finite element analyses, and empirical methods, we have developed a sensor fusion protocol for current and magnetic field probes (with relative errors of ±13% and ±15%, respectively) for use in any geometry of high speed pulsed DC current calibrated capacitor discharge systems. This paper comprehensively outlines the design and sensor fusion methodologies that allow for the deployment of in-house built Bdot probes and Rogowski coils to a wide range of pulsed DC systems and demonstrates their use in a characteristic plasma environment.

Resonant reflection of plane microwave electromagnetic waves by the linear dielectric-ring structures

Artificial materials with negative magnetic and dielectric permittivity have unique electrodynamic properties that are not present in natural materials. We present the results of studying of the main magnetic LC resonance induced by a plane electromagnetic wave of GHz range in the linear structures of subwavelength dielectric ring elements with a high relative permittivity. The dielectric constant of the ring material (capacitor ceramics) is 160. Resonant scattering on the main magnetic mode and wave properties of linear structures consisting of subwavelength dielectric elements in the form of flat thin rings were studied. A single ring or ring structures were arranged in such a way that the vectors of the electric and magnetic fields of a plane incident electromagnetic wave were parallel to the plane of the ring, whereas the wave vector was perpendicular to the plane of the ring. Linear structures consisting of two or three rings were oriented along the magnetic vector of the incident wave. The magnetic field probe was placed on the line of the axis of symmetry of the ring and structures relative to the wave vector at the side of the structures most distant from the antenna. The spectra of transmitted radiation were measured during resonant excitation of magnetic fields in a system of dielectric rings in the near (distance — 2 mm) and remote (distance — 30 mm) zones from the ring. It is shown that in the near wave zone, splitting of the resonant frequency occurs due to mutual inductance and interaction of the rings. As the number of rings increases, the number of additional peaks also increases. A bandwidth of ~200 MHz with an amplitude 25 dB greater than the amplitude of the incident electromagnetic wave in the specified spectrum appears between the split levels. In the far zone, the transmitted radiation at the resonance frequency for a single ring practically does not change due to the splitting of this resonance frequency due to the interaction of the rings in the structure. The results obtained can be used in the development of new materials.

Feasibility analysis of machine learning applied to magnetized plasma diagnosis

AbstractIn the paper, machine learning is demonstrated for the diagnostic enhancement of magnetized plasma probes. In the plasma experiment, the magnetic field greatly affects the properties of plasma and the performance of the probe, which limits the range of measurement parameters and reduces the accuracy of probe diagnostic results. Existing probe correction methods based on improved theory and mechanics cannot completely eliminate the influence of magnetic field and often introduce additional errors. In this paper, a novel machine learning method is proposed to improve magnetized plasma probe diagnostic based on existing methods and traditional probe correction theory. The pressure of the plasma, the total voltage of the circuit, and the magnetic induction intensity are used as input parameters, and the electron density obtained from the probe diagnostics are used as output parameters. The paper presents experiments to analyse the original probe results and the probe results revised by magnetic field probe theory through the machine learning algorithm and compare them with the results of theoretical simulations. The experimental results prove that the machine learning model based on revised data has better learning efficiency and prediction results, which can expand the application scope of traditional probe correction theory and predict results closer to the theoretical value.

Miniature Active Differential Magnetic Field Probe With High Sensitivity for Near-Field Measurements

In this communication, a magnetic field probe with high common-mode rejection ratio (CMRR) and high sensitivity for the near-field measurement is proposed, fabricated, and calibrated. The proposed magnetic field probe consists of a differential dual loop (DDL) to improve the CMRR to the electric field, a balun to convert the differential end to the single end, and a two-stage amplifier achieving proper gain to further enhance the sensitivity. The sensitivity of the probe is raised by more than 50 dB at 30 MHz compared with the reference probes. The measured CMRR is more than 40 dB from 200 kHz to 1 GHz. The measurements of the passive circuits are conducted, and validating that the sensitivity of the proposed probe is significantly improved.

Development of a Magnetic Field Probe for Near-Field Measurement

Current electronic circuits are characterised by their compact design of miniaturisation; however, such a feature has also contributed to the rise of electromagnetic compatibility issues. This study introduces a technique to develop a magnetic field probe for near-field measurement. The probe aims at performing the debugging of electromagnetic interference on an integrated circuit. Certain processes, such as designing a microstrip line in simulation and a prototype for the validation as well as developing a functional magnetic field probe for near-field scanning and calibration measurement to determine the probe factor, have been performed under a frequency domain. The microstrip line model is built both as a simulation and a real prototype, and the handcrafted loop probe is developed with the same diameter as a commercial probe. Calibration measurement is set-up with a vector network analyser (VNA) to capture the magnetic field on radiated plane. The performance of the handcrafted probe in terms of measuring the configuration of the H-field source on the scattering region is conducted. Two types of measurements which are S11 and S21 will be conducted using a VNA. The comparison of the S11 and S21 results against simulation results are plotted using MATLAB. S11 represents the return loss of the microstrip line while S21 represents the power received by the magnetic field probe relative to power input to the microstrip line. The results of the S11 parameter indicate that the customised microstrip line board has a similar waveform pattern that matches the one on the simulation model. The S21 results for the handcrafted probe revealed that it can only function well up to the frequency of 2.644 GHz, the abnormal result obtained after the frequency mentioned. Some factors may have affected the results, such as material loss, fabrication tolerance and interferences from other devices. Therefore, calibration measurement is conducted under a less reflected radiation environment, and the designated substrate should be a perfect material correlated with the measurement.

Analysis of Electromagnetic Information Leakage Based on Cryptographic Integrated Circuits.

Cryptographic algorithm is the most commonly used method of information security protection for many devices. The secret key of cryptographic algorithm is usually stored in these devices’ registers. In this paper, we propose an electromagnetic information leakage model to investigate the relationship between the electromagnetic leakage signal and the secret key. The registers are considered as electric dipole models to illustrate the source of the electromagnetic leakage. The equivalent circuit of the magnetic field probe is developed to bridge the output voltage and the electromagnetic leakage signal. Combining them, the electromagnetic information leakage model’s function relationship can be established. Besides, an electromagnetic leakage model based on multiple linear regression is proposed to recover the secret key and the model’s effectiveness is evaluated by guess entropy. Near field tests are conducted in an unshielded ordinary indoor environment to investigate the electromagnetic side-channel information leakage. The experiment result shows the correctness of the proposed electromagnetic leakage model and it can be used to recover the secret key of the cryptographic algorithm.

An improved measurement scheme of the large-caliber steady-state magnetic-field testing system for ITER

The large-caliber steady-state magnetic-field testing system is an important device for the International Thermonuclear Experimental Reactor, which is mainly used for electromagnetic compatibility tests in a strong magnetic field environment. The uniform magnetic field area needs to be measured to ensure the correctness of the design after the completion of the platform. This paper mainly analyzes the relationship between the magnetic field probe and error, studies the detection effect of different arrangement methods of magnetic field probe points, and obtains a more accurate probe arrangement method through comparative analysis. Then, the principle and structure of the acquisition and detection system are studied, and the multipoint synchronous Hall array magnetic field detection system of the magnetic field is built by using the Hall probe to realize the omnidirectional measurement of the magnetic field. Finally, the Hall probe is calibrated and tested by experiments, and a test platform is built to test the magnetic field. The results verify the correctness of the analysis.

Li-Ion Battery Aging Parameter: Porosity Behavior Analysis Using Magnetic Field Probing

Ageing in Li-ion batteries is a prime concern, due to the rapid increase of their use as a power source for numerous applications from stationary applications to automotive industries. During a battery lifetime, state of health is deteriorating due to irreversible physical and chemical changes like loss of active Li+ ions, internal resistance rise, solid electrolyte interphase (SEI) growth, electrolyte oxidation and loss of active electrode material. This paper aims to demonstrate the potential of a non-invasive method: Magnetic Field Probing (MFP) for monitoring loss of porosity due to ageing in the battery. A multi-physics model using COMSOL Multiphysics simulation tool evaluates the magnetic field response, battery polarization (ohmic potential drop) and internal resistance (IR) of the Li-ion battery. The electrode porosity variation has a significant influence on the magnetic field response (MFR). The analysis shows that the porosity loss at graphite electrode has a major impact on the battery ageing factors (polarization and internal resistance). Moreover, research work infers that the MFR and IR have higher sensitivity at the anode. Approach: The Li-ion battery works on rock n chair concept. Li-ions travels back and forth between electrodes. The concentration of Li-ion shows the amount of energy the battery contains. During simulation the external magnetic field is applied with Li-ion battery module.Li-ion is a paramagnetic ion that alters the magnetic field. At anode, the change in Li-ions concentration during cycling will certainly change the applied magnetic field.Lithium metal oxide is used as cathode material. During charge-discharge cycle, lithium metal oxide converts to metal oxide. The process changes the phase and valency of metal ions. The phase and valency change of ions affect its magnetic properties and alters the value of applied magnetic field.The model uses LiMn2O4 as the cathode, LiC6 as the anode, and the electrolyte consists of LiPF6 salt in 1:2 EC:DMC solvent. A bidirectional coupling is used between the Li-ion battery an external applied magnetic field. Physics based Li-ion battery model equations and standard Maxwell's and Lorentz force equations are coupled Figure 1

A two‐turn loop active magnetic field probe design for high sensitivity near‐field measurement

This paper develops an active magnetic near field probe (H-field probe) by using a four-layer printed circuit board (PCB) technique. Two-turn detection structure and a low noise amplifier are used to improve probe's frequency response. The two-turn detection structure can maximize the use of PCB stack resources, and a 14.5 dB gain amplifier can increase signal output capability. The probe can then be used for electromagnetic compatibility (EMC) test from 150 kHz to 3 GHz. Compared with traditional active shielded-loop H-field probe (TAHP) with loop area of 500 μm 2 , the frequency response of the proposed probe can improve 20 dB at 0.5 GHz. Different from the method of comparing the sensitivity of the probe only through the frequency response, this paper measures and analyzes the real sensitivity of the probing device composed of the proposed probe. Under the condition of the same receiver parameter setting, the sensitivity at 0.5 GHz is increased by 11.7 dB compared with commercial passive probing device and 20.2 dB at 0.5 GHz compared with the probing device with TAHP device. It reaches −32.4 dB μA. In addition, the proposed probe has acceptable spatial resolution of 1.28 mm at 1 GHz, which is more suitable for printed circuit board level EMI analysis.

Phase-Modulated Cavity Magnon Polaritons as a Precise Magnetic Field Probe

We describe and operate a spin-magnetometer based on the phase modulation of cavity magnon polaritons. In this scheme a rf magnetic field is detected through the sidebands it induces on a pump, and the experimental configuration allows for a negligible pump noise and a high-frequency readout. The demonstrator setup, based on a copper cavity coupled to an yttrium iron garnet sphere hybrid system, reached a sensitivity of $2.0\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}$ at 220 MHz, evading the pump noise and matching the theoretical predictions. An optimized setup can attain a rf magnetic field sensitivity of about $8\phantom{\rule{0.2em}{0ex}}\mathrm{fT}/\sqrt{\mathrm{Hz}}$ at room temperature. An orders of magnitude improvement is expected at lower temperatures, making this instrument one of the few magnetometers accessing the subfemtotesla limit.

Design and Study of a Wide-Band Printed Circuit Board Near-Field Probe

Magnetic near-field probes (NFP) represent a suitable tool to measure the magnetic field level from a small electromagnetic interference (EMI) source. This kind of antenna is useful as a magnetic field probe for pre-compliance EMC measurements or debugging tasks since the user can scan a printed circuit board (PCB) looking for locations with strong magnetic fields. When a strong H-field point is found, the designer should check the PCB layout and components placement in that area to detect if this could result in an EMI source. This contribution focuses on analyzing the performance of an easy to build and low-cost H-field NFP designed and manufactured using a standard PCB stack-up. Thereby, the frequency range and sensitivity of the NFP-PCB are analyzed through a Finite Element Method (FEM) simulation model that makes it possible to evaluate its sensibility and effective frequency range. The numerical results obtained with the FEM models are validated against measurements to verify the design and performance of our NFP. The FEM model reproduces the experimental procedure, which is used to evaluate the performance of the NFP in terms of sensitivity by means of the simulated near-field distribution. The NFP-PCB has almost a flat response from 180 MHz to 6 GHz, with an almost perfect concordance between numerical and experimental S21 results. The numerical results show an average transmission loss of −27.9 dB by considering the flat response bandwidth, whereas the experimental one is −29.7 dB. Finally, the designed NFP is compared to two high-quality commercial probes in order to analyze its performance.

Competition between off-resonant and on-resonant processes in electromagnetically induced transparency in presence of magnetic field

We have analyzed and discussed the multiple Zeeman electromagnetically induced transparency (EIT) observed in R87b atomic vapor in presence of the magnetic field. We found that by tuning the power of the probe beam and magnetic field all the transmission peaks can be converted to absorption dips and vice-versa. Our theoretical analysis is based on double Λ systems formed in the presence of the magnetic field. We have argued that by limiting the interaction of various velocity classes of atoms with the probe beam, the off-resonant process can be resolved which dominates the spectra at low probe power. An alternative explanation is also provided in terms of dark and bright states which explains the quantum interference effects present in the system. Finally, our findings are also demonstrated experimentally.

Magnetic Field Probes the Impact of the Ionic Micellar Interface on Photoinduced Charge-Transfer Kinetics of Carbon Dots

Magnetic Field Probes the Impact of the Ionic Micellar Interface on Photoinduced Charge-Transfer Kinetics of Carbon Dots