Search Results (20)

Overhauser magnetometer (OVM) is a proton precession magnetometer (PM) enhanced by electron resonance, and it is widely used in earthquake prediction, UXO detection, geological exploration, etc. For fast measurement, high cycling rate is necessary for OVM to enhance spatial resolution. Due to the impossibility to receive Larmor signal during the polarization process, traditional intermittent measurement is limited in fast mobile measurement applications owing to the long polarization time. Since it is difficult for proton magnetization to align rapidly for the long longitudinal relaxation time of liquid proton, we combined RF continuous excitation with a series 90° pulse to achieve fast measurement. To achieve the best alignment, a dynamic equation of Larmor precession is constructed and calculated, and the influences such as pulse waveform, pulse strength, and pulse duration on the proton magnetization alignment were investigated. The influence of different waveform pulses on the Larmor signal was studied experimentally, and the experimental results verified that the polarization time can be significantly shortened and fast measurement can be achieved by optimizing the waveform, strength, and duration of the 90° pulse. By using the optimized 90° pulse, the proton magnetization can be saturated within 3 ms, and 0.02 nT sensitivity was observed at 1 Hz cycling rate. Consistency between theory and the experiment indicates that the dynamic equation of Larmor motion can provide theoretical guidance for the investigation of fast measurement. Full article

Optically pumped magnetometers (OPMs) provide a non-cryogenic alternative to superconducting quantum interference devices (SQUIDs) for detecting weak biomagnetic fields. We report the design, construction, and characterization of a single-cell intrinsic OPM gradiometer. The gradiometer employs a rubidium-87 vapor cell in an orthogonal pump and probe beam configuration. The pump beam was split to illuminate two parallel sensing regions of the cell, separated by a baseline of 3 cm, with opposing circular polarization. A linearly polarized probe beam propagated through both regions and was captured by a balanced polarimeter whose output directly measured the spatial magnetic gradient. This prototype achieved a common-mode rejection ratio exceeding 50 dB and a sensitivity of 267 pT/cm/√Hz without passive magnetic shielding, using active ambient-field coils. As a proof of concept, we recorded preliminary cardiac-synchronous magnetic measurements using an optical pulse sensor for beat segmentation. After bandpass filtering and ensemble averaging, a cardiac-synchronous waveform was observed, consistent with cardiac timing. Unlike many multi-cell gradiometers that require complex calibration, modulation, and passive shielding, this single-cell design reduces cost and complexity. Full article

Wiegand sensors are essential components in self-powered Internet of Things (IoT) nodes, as they can output pulse voltages without an external power supply. Previous research has established that the attachment of ferrite beads to Wiegand wire terminals substantially enhances the sensor’s pulse voltage output. However, the fundamental mechanism responsible for this enhancement remains unclear at the microscopic magnetic level. This investigation systematically examines how ferrite bead attachments alter magnetization reversal processes, Barkhausen jump characteristics, and the energy output in Wiegand wires. Experimental results reveal that ferrite beads enhance irreversible magnetization, modify interaction distributions, and transform the magnetic structure of Wiegand wires. These modifications collectively result in a 1.5–2.0 times higher pulse voltage amplitude and 30–40% greater output energy, establishing a theoretical framework for Wiegand sensor optimization. The research methodology combines vibrating sample magnetometer (VSM) measurements with first-order reversal curve (FORC) analysis to elucidate the underlying micromagnetic mechanisms. Full article

In the paper we consider the pulsed disturbances caused in the ionosphere by an extreme G5-level geomagnetic superstorm on 10 May 2024, and by the X1.0 and M-class solar flares on 8 May 2024, which preceded the storm. Particular attention is paid to the short-term delays and the sequence of disturbance appearance in the ionosphere and geomagnetic field during these extreme events. The results of a continuous Doppler sounding of the ionosphere on an inclined radio path with a sampling frequency of 25 Hz were used, as well as the data of a ground-based mid-latitude fluxgate magnetometer LEMI-008, and an induction magnetometer IMS-008, which operated with a sampling frequency of 66.6 Hz. Ionization of the ionosphere by the intense X-ray and extreme ultraviolet radiation of solar flares was accompanied by the equally sudden and similarly timed disturbances in the Doppler frequency shift (DFS) of the ionospheric signal, which had an amplitude of 2.0–5.8 Hz. The largest pulsed burst in DFS was registered 68 s after an X1.0 flare on 8 May 2024 at the time when the change of the X-ray flux was at its maximum. Following onto the effect in the ionosphere, a disturbance in the geomagnetic field appeared with a time delay of 35 s. This disturbance is a secondary one that arose as a consequence of the ionosphere response to the solar flare. It was likely driven by the contribution of ionospheric currents and electric fields, which modified the Earth’s magnetic field. On 10 May 2024, a G5-level geomagnetic superstorm with a sudden commencement triggered an impulsive reaction in the ionosphere. A response in DFS at the calculated reflection altitude of the sounding radio wave of 267.5 km was detected 58 s after the commencement of the storm. The sudden impulsive changes in Doppler frequencies showed a bipolar character, reflecting complex dynamic transformations in the ionosphere at the geomagnetic storm. Consequently, the DFS amplitude initially rose to 5.5 Hz over 86 s, and then its sharp drop to $-3.2$ Hz followed. Using the instruments that operated in a mode with a high temporal resolution allowed us to identify for the first time the impulsive nature of the ionospheric reaction, the time delays, and the sequence of disturbance appearances in the ionosphere and geomagnetic field in response to the X1.0 solar flare on 8 May 2024 as well as to the sudden commencement of the extreme G5-level geomagnetic storm on 10 May 2024. Full article

Visible Light Positioning (VLP), leveraging Light-Emitting Diodes (LEDs) and smartphone CMOS cameras, provides a high-precision solution for indoor localization. However, existing systems face challenges in accuracy, latency, and robustness due to line-of-sight (LOS) limitations and inefficient signal encoding. To overcome these constraints, this paper introduces a real-time VLP framework that integrates Multi-Pulse Position Modulation (MPPM) with smartphone multi-sensor fusion. By employing MPPM, a high-efficiency encoding scheme, the proposed system transmits LED identifiers (LED-IDs) with reduced inter-symbol interference, enabling robust signal detection even under dynamic lighting conditions and at extended distances. The smartphone’s camera is a receiver that decodes the MPPM-encoded LED-ID, while accelerometer and magnetometer data compensate for device orientation and motion-induced errors. Experimental results demonstrate that the MPPM-driven approach achieves a decoding success rate of over 97% at distances up to 2.4 m, while maintaining a frame processing rate of 30 FPS and sub-35 ms latency. Furthermore, the method reduces angular errors through sensor fusion, yielding 2D positioning accuracy below 10 cm and vertical errors under 16 cm across diverse smartphone orientations. The synergy of MPPM’s spectral efficiency and multi-sensor correction establishes a new benchmark for VLP systems, enabling scalable deployment in real-world environments without requiring complex infrastructure. Full article

Pulse wave velocity (PWV) has been recognised as the gold standard for assessing arterial stiffness and a relevant indicator in diagnosing cardiovascular disease. Conventional approaches can be affected by factors such as the size of the probe, its positioning on the skin with the appropriate angle and magnitude of the incident force, or influenced by optical properties. Aiming at improving the assessment of PWV parameter, an important cardiovascular risk marker, the present study introduces a new arterial pulse wave measurement technique based on measurements of the impedance phase characteristics of giant magneto-impedance (GMI) sensors submitted to slight magnetic field variations caused by the displacement of a small magnetic marker placed on the patient’s skin, whose movement is coordinated by the local pressure wave. The proposed method eliminates the necessity of using probes with mechanical amplification, enhancing spatial resolution and usability in hard-to-reach anatomical regions through a contactless device unaffected by optical parameters. The obtained experimental results indicate the potential of the developed measurement system in measuring arterial pulse waveform and PWV. Full article

Solar-terrestrial interaction is a dynamic process that manifests itself in the ionosphere. Interplanetary (IP) shocks or solar wind dynamic pressure pulses can generate enhanced brightening in dayside aurora. Foreshock transients are capable of inducing pressure changes, larger in magnitude than solar wind pressure pulses, which also contribute to intensifying dayside aurora. These pressure variations can accelerate particles into the ionosphere, generating field-aligned currents that produce magnetic impulse events and enhanced dayside auroral activity with periods of increased brightening. This study presents several dayside auroral brightening events that are not associated with IP shocks or solar wind dynamic pressure pulses. The dayside auroral brightening events are associated with a green (557.7 nm) to red (630.0 nm) ratio which is greater than 15. These extreme brightening events (EBEs) begin on the eastern or western end of a pre-existing dayside auroral arc. Periodic pulses of enhanced brightening are correlated with large sharp increases in the X-component (points toward the north-geographic pole) from ground magnetometers in the IMAGE network. EBEs occur predominately before magnetic noon and with X-component signatures from high-latitude stations. Ground-based data were obtained from the Kjell Henriksen Observatory in Longyearbyen and the IMAGE magnetometer network. Full article

The magnetocaloric effect (MCE) in iron (Fe) nanoparticles incorporated within a titanium nitride (TiN) thin-film matrix grown using pulsed laser deposition (PLD) is investigated in this study. The study demonstrates the ability to control the entropy change across the magnetic phase transition by varying the size of the Fe nanoparticles. The structural characterization carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and scanning transmission electron (TEM) showed that TiN films are (111) textured, while the Fe-particles are mostly spherical in shapes, are single-crystalline, and have a coherent structure with the surrounding TiN thin-film matrix. The TiN thin-film matrix was chosen as a spacer layer since it is nonmagnetic, is highly corrosion-resistive, and can serve as an excellent conduit for extracting heat due to its high thermal conductivity (11 W/m K). The magnetic properties of Fe–TiN systems were investigated using a superconducting quantum interference device (SQUID) magnetometer. In-plane magnetic fields were applied to record magnetization versus field (M–H) and magnetization versus temperature (M–T) curves. The results showed that the Fe–TiN heterostructure system exhibits a substantial isothermal entropy change (ΔS) over a wide temperature range, encompassing room temperature to the blocking temperature of the Fe nanoparticles. Using Maxwell’s relation and analyzing magnetization–temperature data under different magnetic fields, quantitative insights into the isothermal entropy change (ΔS) and magnetocaloric effect (MCE) were obtained for the Fe–TiN heterostructure system. The study points out a considerable negative change in ΔS that reaches up to 0.2 J/kg K at 0.2 T and 300 K for the samples with a nanoparticle size on the order of 7 nm. Comparative analysis revealed that Fe nanoparticle samples demonstrate higher refrigeration capacity (RC) in comparison to Fe thin-film multilayer samples, with the RC increasing as the Fe particle size decreases. These findings provide valuable insights into the potential application of Fe–TiN heterostructures in solid-state cooling technologies, highlighting their enhanced magnetocaloric properties. Full article

Nuclear magnetic resonance (NMR) magnetometers are considered due to their ability to map magnetic fields with high precision and calibrate other magnetic field measurement devices. However, the low signal-to-noise ratio of low-strength magnetic fields limits the precision when measuring magnetic fields below 40 mT. Therefore, we developed a new NMR magnetometer that combines the dynamic nuclear polarization (DNP) technique with pulsed NMR. The dynamic pre-polarization technique enhances the SNR under a low magnetic field. Pulsed NMR was used in conjunction with DNP to improve measurement accuracy and speed. The efficacy of this approach was validated through simulation and analysis of the measurement process. Next, a complete set of equipment was constructed, and we successfully measured magnetic fields of 30 mT and 8 mT with an accuracy of only 0.5 Hz (11 nT) at 30 mT (0.4 ppm) and 1 Hz (22 nT) at 8mT (3 ppm). Full article

In this work, we look to compare three methods of feedback for the ultimate purpose of measuring the transverse vector components of a magnetic field using a synchronous light-pulse atomic scalar magnetometer with a few tens of fT/$\sqrt{\mathrm{Hz}}$ sensitivity in Earth-field-scale magnetic environments. By applying modulation in the magnetic field to orthogonal axes, the respective vector components may, in principle, be separated from the scalar measurement. Success of this technique depends in significant part on the ability to measure and respond to these perturbations with low measurement uncertainty. Using high-speed least-squares fitting, the phase response of the atomic spins relative to the first harmonic of the optical pump pulse repetition rate is monitored and correspondingly adjusted into resonance with the natural Larmor precession frequency. This paper seeks to motivate and compare three distinct methods of feedback for this purpose. As a first step toward the full development of this technique, the present work uses a simplified version with modulation applied only along the bias field. All three methods investigated herein are shown to provide results that match well with the scalar magnetometer measurements and to depend on both the applied modulation amplitude and optimal feedback response to achieve low relative uncertainty. Full article

Magneto-plasmonic Ag/Ni and Ag/Fe nanoparticles (NPs) were synthesized in this work using the environmentally safe and contaminant-free dual-pulsed Q-switched Nd:YAG 1064 nm laser ablation method. The optical and magnetic characteristics of synthesized nanomaterials were investigated using a vibrating sample magnetometer and an ultraviolet-visible absorption spectrometer. According to transmission electron microscopy (TEM), the shape of Ag/Ni and Ag/Fe NPs seems to be spherical, with mean diameters of 7.3 nm and 11.5 nm, respectively. X-ray diffraction (XRD) was used in order to investigate and describe the phase structures of the synthesized nanomaterials. The synthesized NPs reached maximum temperatures such as 48.9, 60, 63.4, 70, 75, and 79 °C for Ag/Ni nanofluid and 52, 56, 60, 68, 71, and 72 °C for Ag/Fe nanofluid when these nanofluids were subjected to an NIR 808 nm laser with operating powers of 1.24, 1.76, 2.36, 2.91, 3.5, and 4 W, respectively. Because of the plasmonic hyperthermia properties of nanoparticles, nanofluids display higher temperature profiles than pure water. According to these findings, plasmonic nanoparticles based on silver might be used to treat hyperthermia. Full article

The manufacture and study of the properties of magnetic materials requires the development of new automated devices for measuring their magnetic properties. To obtain nanosized materials with a pure phase, it is necessary to modernize former methods and develop new methods for synthesizing materials. As part of this study, a pulse magnetometer was made to study magnetic hysteresis loops. An exceptional feature of this device is the ability to conduct studies of the full cycle of the hysteresis loop using pulsed magnetic fields. M-type BaFe₁₂O₁₉ hexagonal ferrites were synthesized by standard ceramic, mechanochemical, and sol–gel methods. The structural, phase, and magnetic characteristics of the barium hexaferrites were studied. Methods for the synthesis of BaFe₁₂O₁₉ hexagonal ferrites were estimated and compared. Their structural and magnetic properties essentially depend on the method of synthesis. The mechanochemical technology makes it possible to obtain materials without impurity phases through the use of hydrated reagents in the synthesis. The use of sol–gel technology allows the synthesis to be carried out at much lower temperatures. Full article

In recent decades, one of the scientists’ main concerns has been to improve the accuracy of satellite attitude, regardless of the expense. The obvious result is that a large number of control strategies have been used to address this problem. In this study, an adaptive neuro-fuzzy integrated system (ANFIS) for satellite attitude estimation and control was developed. The controller was trained with the data provided by an optimal controller. Furthermore, a pulse modulator was used to generate the right ON/OFF commands of the thruster actuator. To evaluate the performance of the proposed controller in closed-loop simulation, an ANFIS observer was also used to estimate the attitude and angular velocities of the satellite using magnetometer, sun sensor, and data gyro data. However, a new ANFIS system was proposed that can jointly control and estimate the system attitude. The performance of the proposed controller was compared to the optimal PID controller in a Monte Carlo simulation with different initial conditions, disturbance, and noise. The results show that the proposed controller can surpass the optimal PID controller in several aspects including time and smoothness. In addition, the ANFIS estimator was examined and the results demonstrate the high ability of this designated observer. Consequently, evaluating the performance of PID and the proposed controller revealed that the proposed controller consumed less control effort for satellite attitude estimation under noise and uncertainty. Full article

In this work, we demonstrate that cutting diamond crystals with a laser (532 nm wavelength, 0.5 mJ energy, 200 ns pulse duration at 15 kHz) produced a ≲20 nm thick surface layer with magnetic order at room temperature. We measured the magnetic moment of five natural and six CVD diamond crystals of different sizes, nitrogen contents and surface orientations with a SQUID magnetometer. A robust ferromagnetic response at 300 K was observed only for crystals that were cut with the laser along the (100) surface orientation. The magnetic signals were much weaker for the (110) and negligible for the (111) orientations. We attribute the magnetic order to the disordered graphite layer produced by the laser at the diamond surface. The ferromagnetic signal vanished after chemical etching or after moderate temperature annealing. The obtained results indicate that laser treatment of diamond may pave the way to create ferromagnetic spots at its surface. Full article

We present a noninvasive procedure that measures the flow velocity of a fluid by using polarized hydrogen nuclei in the fluid. The measurement procedure is based on a time-of-flight method where magnetic information is applied on the fluid with a permanent magnet and an RF-pulse. In contrast to other methods, this magnetic-marking method works without tracers. The read-out of the magnetic information is performed by optically pumped magnetometers downstream. In order to function, the magnetometers have to be operated in a magnetic shield with magnetic field strengths lower than 100 nT, i.e., in the zero-to-ultra-low-field regime. In this regime, the magnetometers are capable of detecting induced magnetic signals of 10 pT or less with an inline-flow setup. The results presented in this paper demonstrate the viability of optically pumped magnetometers for flow metering. The first metering results yielded an average accuracy of 3% at flow velocities between 13 cm/s and 22.4 cm/s. Full article