Triaxial Magnetic Field Research Articles

Characterization of AI-enhanced magnetophoretic transistors operating in a tri-axial magnetic field for on-chip bioparticle sorting.

We demonstrate two general classes of magnetophoretic transistors, called the "trap" and the "repel-and-collect" transistors, capable of switching single magnetically labeled cells and magnetic particles between different paths in a microfluidic chamber. Compared with prior work on magnetophoretic transistors operating in a two-dimensional in-plane rotating field, the use of a tri-axial magnetic field has the fundamental advantages of preventing particle cluster formation and better syncing of single particles with the general operating clock. We use finite element methods to investigate the energy distribution on the chip surface and to predict the particle behavior at various device geometries. We then fabricate the proposed transistors and compare the experimental results with the simulation predictions. We found that with gate electrical currents of ~ 40mA for a transistor with proper geometry, complete switching of magnetic particles with diameters in the range of 8-15μm is achieved. We show that the device is reliable and works well at different magnetic field strengths (50-100 Oe) and frequencies (0.05-0.5Hz). We also employed an image processing code with a trained convolutional neural network to automate the proposed transistors for identifying and sorting particles with various sizes and magnetic susceptibilities with accuracies higher than 98%. The proposed transistors can be used in designing novel magnetophoretic circuits for important applications in biomedical microdevices and single-cell biology.

In situ measurement of triaxial coil constants for optically pumped magnetometer based on higher-order parametric resonance

We demonstrated a method for in-situ measurement of triaxial magnetic field coil constants of optically pumped magnetometer (OPM) operating in the spin-exchanged relaxation-free (SERF) regime based on higher-order parametric resonances. The triaxial coil constants play a vital role in achieving optimal operation of the OPM and amplitude calibration of weak signals such as magnetoencephalography (MEG). The measurement of the triaxial magnetic field coil constants is therefore particularly critical. Compared to the previous methods, our method is convenient and universal for practical application and commercialization. It does not require a complicated fitting process for measurements, and is applicable to both single- and dual-beam configurations of OPMs which are prevalent in current applications. The feasibility of the method is verified by simulation and experiment, and the average measurement errors of the triaxial coil constants of the OPM in single- and dual-beam configurations are 0.75 % and 1.74 %, respectively. This method holds substantial implications for calibrating and optimizing arrayed OPM systems, with the potential to enhance the measurement sensitivity and the accuracy of magnetic source localization in triaxial OPM-MEG systems.

Unidirectional particle transport in microfluidic chips operating in a tri-axial magnetic field for particle concentration and bio-analyte detection

Unidirectional particle transport in microfluidic chips operating in a tri-axial magnetic field for particle concentration and bio-analyte detection

In Situ Triaxial Magnetic Field Compensation for the Spin-Exchange-Relaxation-Free Optically Pumped Magnetometer

In Situ Triaxial Magnetic Field Compensation for the Spin-Exchange-Relaxation-Free Optically Pumped Magnetometer

Magnetorheology in unsteady fields: From uniaxial DC to rotating AC fields

Magnetorheological fluids structured under precession fields are thoroughly investigated. Having complete dynamic triaxial magnetic field control, we are able to study both the structural and magnetorheological response via videomicroscopy and rheometry integration for a wide range of magnetic field configurations, once previously limited to traditional uniaxial fields. Optimal precession fields for driving the formation of more robust particle structures enhancing yield stress response are identified. It is believed that structural reinforcement comes from chain coarsening through lateral chain coalescence and particle compactness within the structures such that a lower energy configuration is found for certain field configurations. Particle level simulations supplement our understanding of lateral chain coalescence and structure strengthening.

Tuned drop-shape magnetophoretic conductors for controlled single-particle transport in microfluidic chips

In recent years, lab-on-a-chip devices have attracted many researchers due to their numerous advantages, making them suitable for important bioapplications. One of the key challenges in this field is manipulating a group of particles and cells at single-particle resolution. Different techniques have been proposed to tackle this challenge; however, none of them offer the controllability and scalability required in most bioapplications. Recently, drop-shape magnetophoretic circuits have been introduced as an advanced technique for the precise transport of a great number of particles simultaneously. However, in moving along the magnetic track, the particles experience a sudden jump from one magnet to the next one, which may not be in a highly controlled fashion and can be problematic. To overcome this issue, in the current work, we introduce a new design equipped with a tuning gate electrode added to the blind spots of the magnetophoretic conductor. This design transports the particles in a tri-axial magnetic field, with a vertical bias field that reduces the attraction force between particles and inhibits the particle cluster formation. We study the effect of straight and curved current-carrying gates and show that they positively affect the resulting magnetic energy. Based on our finite element method, we found the curved gate offers controlled smooth particle transport at lower electrical currents. We fabricate the proposed chip based on this design and show that the experimental results agree well with the simulation predictions. The introduced design enhances the reliability of the magnetophoretic circuits operating in a tri-axial magnetic field and makes them good candidates for fundamental applications in single-cell biology and medicine.

Triaxial closed-loop measurement based on a single-beam zero-field optically pumped magnetometer

In this study, we propose an approach for the simultaneous measurement of triaxial magnetic fields using a single-beam zero-field optically pumped atomic magnetometer, in which a rotational high-frequency (ω1) and another high-frequency (ω2) modulated magnetic field magnetic fields are applied along the transverse directions and the longitudinal direction, respectively. Theoretical analysis, numerical simulation, and experiments are conducted to demonstrate this method. Experimental sensitivities of 18 fT/Hz1/2 along the two transverse directions and 140 fT/Hz1/2 along the longitudinal direction are simultaneously achieved. On this basis, we operate the magnetometer in closed-loop mode to expand the bandwidth and dynamic range, and to keep the triaxial magnetic field sensed by the magnetometer at zero. The triaxial bandwidths are increased from below 100 Hz to over 1.6 kHz. The triaxial dynamic ranges are all extended to ±150 nT. Plus, we verify the ±1,000 nT dynamic range of the triaxial magnetometer through increasing the triaxial coil constants. The synchronization of triaxial closed-loop measurement, simplicity of magnetometer structure, and closed-loop detection with high sensitivities make it applicable and attractive for biomagnetism imaging in challenging environments.

Analysis of the Feasibility of UAS-Based EMI Sensing for Underground Utilities Detection and Mapping

This paper investigates the feasibility of using a linear current sensing (LCS) technique integrated on an unmanned aerial system (UAS) for detecting and mapping underground infrastructure rapidly and cost-effectively. The LCS technique is based on data from a wide band of electromagnetic induction frequencies (50 kHz to 2 MHz) using a vector magnetic field gradiometer. This technique takes advantage of a slowly decaying secondary magnetic field in order to achieve greater standoff detection distance (1R2 vs. 1R6 for compact metallic targets during EMI sensing, where R is the distance from a target to the sensor). These secondary magnetic fields are produced by the excite current on long conductors, allowing detection at a distance of 10 meters or more. The system operates between tens of kHz to a few MHz and uses either an active EMI source or existing EM fields to excite this linear current on a long metallic subsurface target. Once excited, these linear currents produce a secondary magnetic field that is detected with an above ground triaxial magnetic field gradiometer. By moving and tracking its geolocation, the system outputs rich datasets sufficient to support high-fidelity forward and inverse EMI models for estimating the depth and orientation of deep underground long linear metallic infrastructure. The system’s hardware and its integration to a UAS system are outlined, along with the formulation of LCS theory, and numerical and experimental data are presented. The results illustrate that the LCS technique offers large standoff detection, is adaptable to UAS, and could be used effectively for detecting deep underground infrastructure such as wires and pipes.

Triaxial precise magnetic field compensation of a zero-field optically pumped magnetometer based on a single-beam configuration.

Triaxial magnetic field compensation is crucial for a zero-field optically pumped magnetometer (OPM) in pursuit of a zero-field environment. In this work, we demonstrate a triaxial magnetic field compensation method for zero-field OPM based on single-beam configuration. It consists of two procedures: (1) pre-compensation to preliminarily cancel out ambient residual magnetic field by low-frequency magnetic field modulation; and (2) precise compensation to further compensate the residual magnetic field by high-frequency magnetic field modulation. This scheme enables rapid and precise compensation of a large-scale magnetic field and supports real null-point acquisition of the triaxial residual magnetic fields with simple processes. The experimental results show that the compensation resolution on the sensitive axis is better than 1 pT and significantly less than the fluctuation of experimental environments. Our work targets on the quick generation of a zero-field environment for high precision OPM, which is especially advantageous for emerging applications including magnetocardiography (MCG) and magnetoencephalography (MEG).

Optimal Design of Planar Coils With Reverse Current Distribution for Atomic Devices

The uniform magnetic field coil is an essential component for providing a controllable and uniform magnetic field in applications such as scientific instruments, industrial equipment, and sensors. In recent years, the rapidly developing atomic devices are being miniaturized and have high requirements on the uniformity of the magnetic field. This study proposes an optimal design method for planar uniform magnetic field coils suitable for atomic devices, which can achieve high uniformity in a simple configuration and small volume. The proposed method combines the magnetic field relative errors of the target field points, and innovatively introduces the reverse current distribution to compensate for the non-uniform magnetic field. Additionally, the genetic algorithm (GA) was used to calculate the structural parameters and the current direction under optimal uniformity. The simulation and experimental results demonstrated that the maximum magnetic field relative error of the designed planar coils on the two central axes improved by 89.7% and 31.9%, respectively, in contrast to the commonly used Helmholtz coils. Furthermore, the integration of the triaxial magnetic field was realized without increasing the overall volume of the coil. For the triaxial magnetic field coil, the proportion of the uniform magnetic field area of the designed coil can be increased by over three times compared to the Helmholtz coil, which is conducive to the improvement of the performance of atomic devices.

In SituCompensation of Triaxial Magnetic Field Gradient for Atomic Magnetometers

Magnetic field gradients affect numerous modern sensitive measurements and physics studies using atomic ensemble, resulting in the loss of coherence. In some cases, the presence of small gradients can reduce the performance significantly. In this study, we propose an effective <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> method to compensate the triaxial magnetic field gradient for atomic magnetometers, based on multichannel atomic signals in one vapor cell. We design two novel gradient coils by solving closed-form equations to improve the accuracy and efficiency of compensation. We demonstrate the performance of the compensation method in a spin-exchange relaxation-free atomic magnetometer, which reduces the magnetic linewidth by 4.2%–7.6% under the same conditions at a compensation resolution of 50 pT/cm. The proposed coils generate gradients only along two axes and achieve triaxial decoupling, which compensates for the gradient completely without iteration. Our results may aid in suppressing atomic spin relaxations due to magnetic field gradients in several modern measurements and improve their performance, such as the detection of electric dipole moments, ultralow-field nuclear magnetic resonance, and biomagnetism.

In-situ triaxial residual magnetic field measurement based on optically-detected electron paramagnetic resonance of spin-polarized potassium

We present an approach that allows detecting all three components of the residual magnetic field inside shielding, based on the electron paramagnetic resonance (EPR) of spin-polarized K atoms. The residual field experienced by spin-polarized K atoms dominates Larmor precession frequency, the smaller the frequency is, the more benefits it has to realize spin-exchange relaxation-free (SERF) regime under a definite spin-exchange rate. The measurements are accomplished based on depopulation optical pumping and optically-detected peak of the K EPR spectrum. The EPR-based cross modulation method is employed to determine all three components of the residual field independently by modulating the frequency of transverse field and the strength of longitudinal field. The weighted averages of all measurements with the corresponding uncertainties are (9.60 ± 0.06) nT, (2.25 ± 0.03) nT, and (2.83 ± 0.17) nT along with the negative directions of their related axes, respectively.

Single-channel vector magnetic information detection method based on diamond NV color center* *Project supported by the National Natural Science Foundation of China (Grant Nos. 51635011, 51805493, 51775522, 51727808, and 51922009), the Applied Basic Research Program in Shanxi Province, China (Grant No. 201901D111011(ZD)), the Key Research and Development Program in Shanxi Province, China (Grant No. 201803D121067), the Fund from the Key

A method of detecting the single channel triaxial magnetic field information based on diamond nitrogen-vacancy (NV) color center is introduced. Firstly, the incident angle of the bias magnetic field which can achieve the equal frequency difference optically-detected magnetic resonance (ODMR) spectrum of diamond NV color center is calculated theoretically, and the triaxial magnetic information solution model is also constructed. Secondly, the microwave time-controlled circuit module is designed to generate equal timing and equal frequency difference microwave pulse signals in one channel. Combining with the optical detection magnetic resonance technology, the purpose of sequentially locking and detecting the four formant signals on one side of the diamond NV color center (m s = –1 state signal) is achieved, and the vector magnetic field information detection is accomplished by combining the triaxial magnetic information solution model. The system can obtain magnetic field detection in a range of 0 mT–0.82 mT. The system’s magnetic noise sensitivity is 14.2 nT/Hz1/2, and the deviation angle errors of magnetic field detection θx and θy are 1.3° and 8.2° respectively.

Synchronous control of magnetic particles and magnetized cells in a tri-axial magnetic field.

Precise manipulation of single particles is one of the main goals in the lab-on-a-chip field. Here, we present a microfluidic platform with "T" and "I" shaped magnetic tracks on the substrate to transport magnetic particles and magnetized cells in a tri-axial time-varying magnetic field. The driving magnetic field is composed of a vertical field bias and an in-plane rotating field component, with the advantage of lowering the attraction tendency and cluster formation between the particles compared to the traditional magnetophoretic circuits. We demonstrate three fundamental achievements. First, all the particle movements are synced with the external rotating field to achieve precise control over individual particles. Second, single-particle and single living cell transport in a controlled fashion is achieved for a large number of them in parallel, without the need for a complicated control system to send signals to individual particles. We carefully study the proposed design and introduce proper operating parameters. Finally, in addition to moving the particles along straight tracks, transporting them using a ∼60° bend is demonstrated. The proposed chip has direct applications in the fields of lab-on-a-chip, single-cell biology, and drug screening, where precise control over single particles is needed.

Design and assembly of an apparatus system based on the Villari effect for detecting stress concentration zone on ferromagnetic materials

This paper presents the study results on the fabrication of a structural integrity assessment apparatus by determining stress concentration zones in pressure pipeline and equipment. The apparatus uses a triaxial magnetic field sensor to measure magnetic field components in three axes Ox, Oy, and Oz, in the working range of the magnetic field from -300 µT to 300 µT. The investigation of the selfmagnetic leakage field by this apparatus in the API 5L steel specimens under tensile stress shows a high variation of the magnetic field at a steel elongation lower than 1 mm (corresponding to the elastic deformation state of the material). In the case of an artificial defect, the apparatus can detect a change in the magnetic field caused by stress concentration.

Design of Highly Uniform Three Dimensional Spherical Magnetic Field Coils for Atomic Sensors

In this paper, three dimensional spherical magnetic field coils are proposed and optimized for atomic sensors that require highly uniform magnetic field coils within a limited volume. The design objective of the uniform coil is transformed into a nonlinear optimization model with constraints, which is solved by combining with the particle swarm optimization algorithm. Compared with the traditional cylindrical tri-axial magnetic field coil system whose volume is limited by the aspect ratio of the coil structure, the three dimensional spherical coils not only effectively reduce the volume but also provide consistent magnetic field performance in the three coordinate axis directions. It is of great significance to the miniaturization of atomic sensors. The theoretical calculation shows that the uniformity of spherical coil is improved by about 2 to 3 orders of magnitude compared with the Lee-Whiting coil and the saddle coil. The measurements show that the magnetic field uniformity of our design reached $1.5\times 10^{-4}$ along the ${z}$ -axis within a range of $\pm 0.25{R}$ . The actual magnetic field distribution is basically consistent with the theory. However, due to the limited processing and experimental conditions, the actual magnetic field uniformity is 1 to 2 orders of magnitude lower than the theory.

A New Calibration Method for Triaxial Fluxgate Magnetometer Based on Magnetic Shielding Room

The triaxial fluxgate magnetometers (TFMs) are widely used in space exploration, positioning and navigation, geological exploration, etc. As a high-precision vector magnetometer, the measurement accuracy will directly determine the accuracy of the obtained magnetic field data. The TFM has three kinds of own errors in measurement: zero offset error, proportional coefficient error, and nonorthogonal error. These three kinds of errors will cause the TFM to deviate from the actual magnetic field value, and the fluxgate magnetometer needs to be calibrated. At present, the accuracy of the calibration method adopted by the fluxgate magnetometer depends on the stability of the natural environment magnetic field and the triaxial turntable (there is an uncontrollable residual magnetic interference), which limits the further improvement of the calibration accuracy. And due to the wide application of electromagnetic equipment, the natural electromagnetic environment is further damaged, and the calibration accuracy is subject to deterioration. In this paper, a magnetic shielding room (MSR) is used to provide a near-zero magnetic environment, and a triaxial uniform magnetic field coil (TUMC) is installed inside the MSR to construct a controllable arbitrary vector direction magnetic field, which solves the magnetic field disturbance problem of the original method. The TUMC and TFM error models were built and the MSR magnetic ambient noise model was added. The emphasis is on the degree of distortion of the magnetic field generated by the MSR as a ferromagnetic boundary condition and the influence of the deviation of the center point of TUMC on the calibration accuracy. Then, based on the above error model and magnetic environmental conditions, the calibration accuracy of the calibration magnetic field distribution is analyzed. Finally, the calibration experiment of the TFM is carried out by using the existing MSR, which proves the feasibility and effectiveness of the calibration method, and the method can greatly improve the calibration efficiency.

A Non-Modulated Triaxial Magnetic Field Compensation Method for Spin-Exchange Relaxation-Free Magnetometer Based on Zero-Field Resonance

In this study, we demonstrate a non-modulated triaxial magnetic field compensation method for spin-exchange relaxation-free (SERF) atomic magnetometers. We realize simultaneous compensation of the magnetic field along the pump and probe directions by maximizing the first order differential value of the zero-field resonance signal. The magnetic field perpendicular to the pump-probe plane is compensated by zeroing the DC response of the magnetometer. The zero-field resonance is obtained by applying a linearly changed magnetic field along the direction perpendicular to that of the pump-probe plane. The first order differential of the zero-field resonance is acquired using the second order central difference method in real time. Compared with the conventional compensation methods, this method does not involve modulation and demodulation. Therefore, it requires no lock-in amplifier, thus making it more applicable in miniature atomic devices. Moreover, this method compensates the magnetic field along the pump and probe directions using only one criterion. It avoids the cross-talk effect between the pump and probe directions in the presence of non-orthogonal coils. The experiment results show that the compensation resolution is 9 pT, 7 pT and 0.05 pT for the probe, pump, and direction perpendicular to the pump-probe plane, respectively.

Energy expenditure associated with walking speed and angle of turn in children

PurposeRecent studies have suggested that turning is power intensive. Given the sporadic and irregular movement patterns of children, such findings have important implications for the assessment of true energy expenditure associated with habitual physical activity. The purpose of this study was to investigate the influence of walking speed and angle, and their interaction, on the energy expenditure of healthy children.Methods20 children (10.1 ± 0.5 years; 10 boys) participated in the study. On two separate days, participants completed a turning protocol involving 3-min bouts of walking at one of the 16 speed (2.5, 3.5, 4.5, and 5.5 km h− 1) and angle (0°, 45°, 90°, and 180°) combinations, interspersed by 3 min seated rest. The movement involved 5 m straight walking interspaced with prescribed turns with speed dictated by a digital, auditory metronome. Breath-by-breath gas exchange was measured, in addition to tri-axial acceleration and magnetic field intensity recorded at 100 Hz.ResultsMixed models revealed a significant main effect for speed (p < 0.006) and angle (p < 0.006), with no significant interaction between speed and angle (p > 0.006). Significant differences to straight-line walking energy expenditure within speed were established for 3.5 and 5.5 km h− 1 for 180° turns (~ 13% and ~ 30% increase, respectively).ConclusionThese findings highlight the importance of accounting for the magnitude and frequency of turns completed when estimating children’s habitual physical activity and have significant implications for the assessment of daily energy expenditure.

Influence of the Microstructure on Magnetic Stray Fields of Low-Carbon Steel Welds

This study examines the relationship between the magnetic mesostructure with the microstructure of low carbon steel tungsten inert gas welds. Optical microscopy revealed variation in the microstructure of the parent material, in the heat affected and fusion zones, correlating with distinctive changes in the local magnetic stray fields measured with high spatial resolution giant magneto resistance sensors. In the vicinity of the heat affected zone high residual stresses were found using neutron diffraction. Notably, the gradients of von Mises stress and triaxial magnetic stray field modulus follow the same tendency transverse to the weld. In contrast, micro-X-ray fluorescence characterization indicated that local changes in element composition had no independent effect on magnetic stray fields.