Direct Current Magnetic Field Research Articles

Strain analysis and preliminary test of an all-superconducting high-field magnet generating 32.4 T direct-current magnetic field

Abstract A higher available magnetic field can give more flexibility for significant research and constructions. Inserting feasible high-temperature-superconducting (HTS) magnet inside low-temperature-superconducting (LTS) external is becoming an efficient method to build ultra-high-field (UHF) magnets. However, HTS insert magnets exhibited concentration of magnetic strain during the energization, significantly owing to the screening-current effect. This phenomenon affect the structural integrity of HTS magnets, posing a difficulty for UHF magnets to reach a center field larger than 30 T. In this paper, we report the recent progress of the 35 T all-superconducting UHF magnet project. The full-cycle development of this homemade UHF magnet was a strong collaboration with multiple domestic institutions in China. We used commercial REBa2Cu3O7-x (RE = rare earth element, REBCO) conductors to wind the 20 T HTS insert. Specifically, we optimized the electromagnetic design of this HTS insert with consideration of screening-current induced strain. We applied the no-insulation and metal-as-insulation winding techniques simultaneously to balance the time constant of the two nested REBCO coils. During the excitation test, the HTS insert maintained a 256 A operation current as designed for nearly 18 hours. With the energization of LTS external magnet, the entire facility reached a center field larger than 20 T for 16 hours, 30 T for 6.35 hours and 32 T for 2 hours. It finally reached a 32.4 T center field, at which point the LTS external quenched, inducing the HTS insert to quench as well. After quench, the HTS magnet can maintained 229 A operation current during the postmortem standalone test. This 32.4 T result exhibits effectiveness of considering the screening-current induced strain to enhance the structural integrity of REBCO magnets, and verifies the high reliability of REBCO magnets by generating a long-duration high field environment without any quench accident originating from the REBCO magnet.

Controlling action potentials with magnetoelectric nanoparticles

Non-invasive or minutely invasive and wireless brain stimulation that can target any region of the brain is an open problem in engineering and neuroscience with serious implications for the treatment of numerous neurological diseases. Despite significant recent progress in advancing new methods of neuromodulation, none has successfully replicated the efficacy of traditional wired stimulation and improved on its downsides without introducing new complications. Due to the capability to convert magnetic fields into local electric fields, MagnetoElectric NanoParticle (MENP) neuromodulation is a recently proposed framework based on new materials that can locally sensitize neurons to specific, low-strength alternating current (AC) magnetic fields (50Hz 1.7 kOe field). However, the current research into this neuromodulation concept is at a very early stage, and the theoretically feasible game-changing advantages remain to be proven experimentally. To break this stalemate phase, this study leveraged understanding of the non-linear properties of MENPs and the nanoparticles' field interaction with the cellular microenvironment. Particularly, the applied magnetic field's strength and frequency were tailored to the M − H hysteresis loop of the nanoparticles. Furthermore, rectangular prisms instead of the more traditional “spherical” nanoparticle shapes were used to: (i) maximize the magnetoelectric effect and (ii) improve the nanoparticle-cell-membrane surface interface. Neuromodulation performance was evaluated in a series of exploratory in vitro experiments on 2446 rat hippocampus neurons. Linear mixed effect models were used to ensure the independence of samples by accounting for fixed adjacency effects in synchronized firing. Neural activity was measured over repeated 4-min segments, containing 90 s of baseline measurements, 90 s of stimulation measurements, and 60 s of post stimulation measurements. 87.5 % of stimulation attempts produced statistically significant (P < 0.05) changes in neural activity, with 58.3 % producing large changes (P < 0.01). In negative controls using either zero or 1.7 kOe-strength field without nanoparticles, no experiments produced significant changes in neural activity (P > 0.05 and P > 0.15 respectively). Furthermore, an exploratory analysis of a direct current (DC) magnetic field indicated that the DC field could be used with MENPs to inhibit neuron activity (P < 0.01). These experiments demonstrated the potential for magnetoelectric neuromodulation to offer a near one-to-one functionality match with conventional electrode stimulation without requiring surgical intervention or genetic modification to achieve success, instead relying on physical properties of these nanoparticles as “On/Off” control mechanisms. One-sentence summaryThis in vitro neural cell culture study explores how to exploit the non-linear and anisotropic properties of magnetoelectric nanoparticles for wireless neuromodulation, the importance of magnetic field strength and frequency matching for optimization, and demonstrates, for the first time, that magnetoelectric neuromodulation can inhibit neural responses.

Reconfigurable Three-Dimensional Thermal Dome

Thermal metamaterial represents a groundbreaking approach to control heat conduction, and, as a crucial component, thermal invisibility is of utmost importance for heat management. Despite the flourishing development of thermal invisibility schemes, they still face two limitations in practical applications. First, objects are typically completely enclosed in traditional cloaks, making them difficult to use and unsuitable for objects with heat sources. Second, although some theoretical proposals have been put forth to change the thermal conductivity of materials to achieve dynamic invisibility, their designs are complex and rigid, making them unsuitable for large-scale use in real three-dimensional (3D) spaces. Here, we propose a concept of a thermal dome to achieve 3D invisibility. Our scheme includes an open functional area, greatly enhancing its usability and applicability. It features a reconfigurable structure, constructed with simple isotropic natural materials, making it suitable for dynamic requirements. The performance of our reconfigurable thermal dome has been confirmed through simulations and experiments, consistent with the theory. The introduction of this concept can greatly advance the development of thermal invisibility technology from theory to engineering and provide inspiration for other physical domains, such as direct current electric fields and magnetic fields.

Enhancing high cycle fatigue performance of plasma nitrided AISI 4140 steel by post-aging treatment and direct current magnetic field

Machine elements become unable to perform their duties as a result of fatigue damage. In addition, machine elements that are subjected to fatigue under cyclic loads are exposed to electric and magnetic fields when they are close to electrical and magnetic field sources such as electric motors. Moreover, plasma nitriding is often used to increase the fatigue strength of materials. Although the fatigue properties of surface-treated materials are frequently studied, the fatigue behavior of these materials under a magnetic field is not fully known. Therefore, this study focuses on examining the effects of magnetic field on the fatigue properties of surface-treated materials. For this purpose, AISI 4140 steel samples were plasma nitrided and subsequently post-aged, and then they were tested using a rotating bending fatigue testing system by exposing them to a magnetic field for 30 % and 100 % of their fatigue life. ε-Fe2–3N and γ’-Fe4N phases were seen in surface-treated samples, in addition to these phases, peaks belonging to the α”-Fe16N2 phase were observed in post-aged samples. Plasma nitriding raised the hardness of the material because of nitride phases and α”-Fe16N2 caused an extra increase. The highest diffusion depth was seen in the post-aged samples because post-aging facilitated the diffusion of nitrogen. Surface treatments increased the fatigue strength of the material. All samples tested under a magnetic field exhibited higher fatigue strength than samples tested without a magnetic field because fatigue crack initiation was prolonged by the magnetic field. Compared to non-magnetic and 30 % magnetic samples, the fatigue strengths of the samples in a 100 % magnetic field were lower. Furthermore, it was observed that applying a magnetic field had no effect on the samples' fractographic structure.

26.86-tesla direct-current magnetic field generated with an all-REBCO superconducting magnet

This paper reports an all REBCO (REBa2Cu3Ox, where RE = Y, Gd) superconducting magnet that generated a direct-current magnetic field of 26.86 T at 4.2 K in self-field, which is the highest magnetic field achieved by the high temperature superconducting (HTS) magnet. The magnet consists of a stack of 10 double pancake (DP) coils wound with two different width REBCO conductors, and the no-insulation (NI) winding technology was applied to increase its engineering current density. The inner and outer winding diameters and overall height of the magnet are 30 mm, 103.98 mm, and 102.6 mm, respectively. In order to control the stress risk in HTS magnet, the over-banding made of high elastic modulus stainless steel tapes was employed to the magnet. In addition, no obvious degradation was found in the performance of the magnet after quench at 26.86 T of 295.5 A. These test results demonstrate the great potential of REBCO magnets in high field applications.

Comparisons of Rice Seed Growths Due to Alternating and Direct Current Electric and Magnetic Field Influences

It is commonly known that electric and magnetic fields of power transmission negatively and positively influence plants. Unfortunately, studies on these influences are minimal, particularly considering the comparison between magnetic field and electric field, on both DC (direct current) and AC (alternating current). This research aims to compare the influences of magnetic field and electric field, both on AC and DC, on rice plant growth. Firstly, prototypes, including the equipment, were constructed to generate AC and DC electric fields using parallel plates of a medium voltage transformer and Cockroft-Walton circuits. Meanwhile, the AC and DC magnetic fields were prepared using three different diameter current-injected coils. The rice seeds were exposed to electric and magnetic fields for one month, with plate distance and coil diameter variations. The results showed that the rice seeds grew differently according to the respective types and magnitudes of the fields. In the first two days, the rice seed growths exposed to electric and magnetic fields were higher than those without field exposures. However, since the thirteenth day, the rice growth rate with field exposure was lower than without. This study also shows that the influences of the DC electric and magnetic fields were more potent than the AC fields. The averages of rice seed growth decreasing rate for the AC and DC electric fields and AC and DC magnetic fields were 0.00827 cm/(kV/m), 0.01167 cm/(kV/m), -0.13267 cm/mT and 1.99005 cm/mT, respectively. As a general suggestion in sites, rice plants should be avoided from a transmission line due to high voltage direct current (DC) rather than that alternating current (AC).

Magnetically-induced enhancement of photocatalytic dye decomposition in ferroelectric Hf0.5Zr0.5O2 films

The film photocatalyst is easily recycled and has attracted the widely research interesting. Here the ferroelectric Hf0.5Zr0·5O2(HZO) thin film synthesized through the atomic layer deposition (ALD) method is used as a photocatalyst for the rhodamine B (RhB) dye decomposition under visible light irradiation. The photocatalytic RhB dye decomposition performances with or without an external magnetic field excitation provided by a commercial NdFeB magnet are experimentally characterized. With the increasing of the external direct-current (DC) magnetic field from 0 to 3000 Gs, the photocatalytic RhB dye decomposition ratio by HZO film obviously increases from 87.20 % to 98.17 %, which is attributed to the enhanced separation of the photo-induced positive and negative carrier due to the magnetic Lorentz effect. The magnetically-induced enhancement of photocatalysis in the ferroelectric HZO film, provides a method with these advantages of simple external excitation method, remarkable promotion effect and friendly-environment to enhance the dye decomposition ratio, and is potential in the practical application of photocatalytic dye wastewater treatment through harvesting the clean solar energy in future.

Field-Induced Slow Magnetization Relaxation of a Tetrahedral S=2 FeIIS4-Containing Complex.

In the work described herein, the spin relaxation properties of the mononuclear tetrahedral S=2 [Fe{(SPiPr2)2N}2] complex (1) were studied by employing static and dynamic magnetic measurements at liquid helium temperatures. In the absence of an external direct current (DC) magnetic field, 1 exhibits fast magnetization relaxation. However, in the presence of external magnetic fields of a few kOe, slow relaxation is induced as monitored by alternating current (AC) magnetic susceptibility measurements up to 10 kHz, in the temperature range 2-5 K. Analysis of the temperature dependence of the corresponding relaxation time reveals contributions by Quantum Tunnelling of Magnetization, and the Direct and Orbach processes in the magnetization relaxation mechanism of 1. The energy barrier, Ueff, of the Orbach process, as determined by this analysis, is compared with that related to the zero-field splitting parameters of 1 which were previously determined by high- frequency and -field electron paramagnetic resonance and Mössbauer spectroscopies.

Insight into the mechanisms of combining direct current magnetic field with phosphate in promoting emulsifying properties of myofibrillar protein

This study investigated the combined effects of direct-current magnetic field (DC-MF, 9.5 mT) and tetrasodium-pyrophosphate (TSPP, 1-5 g/L) on emulsified gel properties of porcine myofibrillar protein (MP). Results showed that MP at DC-MF and 3 g/L TSPP had decreased spectrum intensity of UV and fluorescence compared to that without DC-MF, owing to the changes of MP tertiary structure caused by DC-MF, especially tryptophan and tyrosine. The emulsion treated with DC-MF behaved better emulsifying activity and stability than that without DC-MF under such condition. And emulsion had lower creaming index and better storage stability. Gels prepared by this MP emulsion had low porosity and stable structure, accompanying with smaller size and more uniform distribution of oil droplets. Microstructure images showed that gels were covered with microporous structure, which was conducive to the good WHC of the emulsified gels (97.12%). These results showed the feasibility of DC-MF and TSPP in improving MP emulsion/emulsified gel.

Effects of anthropogenic magnetic fields on the behavior of a major predator of the intertidal and subtidal zones, the velvet crab Necora puber

With the progress of the offshore renewable energy sector and electrical interconnection projects, a substantial rise in the number of submarine power cables is expected soon. Such cables emit either alternating or direct current magnetic fields whose impact on marine invertebrates is currently unknown and hardly studied. In this context, this study aimed to assess potential short-term exposure (30 min) effects of both alternating and direct magnetic fields of increasing intensity (72–304 μT) on the behavior of the high-ecological value velvet crab (Necora puber). Three experiments were designed to evaluate whether the strongest magnetic field intensities induce crabs’ attraction or repulsion responses, and whether foraging and sheltering behaviors may be modified. We extracted from video analyses several variables as the time budgets crabs spent immobile, moving, feeding, or sheltering as well as total and maximal distance reached in the magnetic field (MF) gradient. The crabs exposed to artificial MF did not exhibit significant behavioral changes compared with those exposed to the “natural” MF. Overall, our results suggest that, at such intensities, artificial magnetic fields do not significantly alter behaviors of N. puber. Nevertheless, future studies should be conducted to examine the effects of longer exposure periods and to detect potential habituation or resilience processes.

Sagnac Magnetic Field Sensor Based on Sinusoidal Modulation and Empirical Mode Decomposition

A direct current (DC) Sagnac magnetic field sensor is a kind of fiber sensor based on alternate current magnetic field (ACMF) demodulation and empirical mode decomposition (EMD) to detect the magnetic field by measuring the phase variety caused by direct current magnetic field (DCMF). Commonly, Sagnac DCMF sensors can improve the magnetic detection sensitivity by using high Verdet constant (HVC) medium, which is expensive to prepare, or optical resonant cavity. However, the polarization diffraction in cavity restricts the performance of these devices. Meanwhile, none of them can suppress the electrical noise of the system such as 1/f noise. In this paper, we use ACMF modulation to couple the phase containing the DCMF information into the amplitude of the fundamental frequency component of the interference signal. Then we demodulate the signal by EMD to extract the fundamental frequency component. The designed sensor demonstrates a sensitivity of 4.651 mV/μT with an accuracy of 1.649 nT in the magnetic field range of 0-40 mT. It has the advantages of high stability, anti-electromagnetic interference and miniaturization.

Temperature-compensated DC magnetic field sensor based upon a microcapillary resonator

A temperature-compensated direct current (DC) magnetic field sensor based on a whispering gallery mode (WGM) microcapillary resonator is described in which both temperature-compensation and magnetic field sensing is realized by resonant wavelength difference in two high-order modes. A simulation and experimental results verified that the temperature response of the sensor is significantly reduced using the resonant wavelength difference between two high-order optical modes. In addition, the magnetic field response of resonant wavelength difference between two high-order optical modes was characterized. The results show that the resonant wavelength difference first blue-shifted and subsequently red-shifted as the magnetic field strength increased to provide DC magnetic field sensitivities of −0.03 and 0.01 pm/Oe from 34.79 to 62.56 Oe and 62.56 to 181.012 Oe, respectively. This temperature-compensated DC magnetic field sensor is anticipated to applications for current and rotation angle detection.

Effect and mechanism of DC magnetic field combined with calcium chloride on saltiness and flavor enhancement of low salt pork gel

This study intended to investigate the synergistic effect of direct current magnetic field (DC-MF) and calcium chloride (CaCl2) on improving the saltiness and quality of pork gel and to explore the potential adjustment mechanisms involved. Pork mince was subjected to low-salt treatment of DC-MF for 3 h (T1), CaCl2 substitution (T2) or DC-MF combined with CaCl2 (T3) respectively under high and low salt controls (HC and LC). Heat-induced gels of pork mince were prepared and analyzed in terms of gel texture, saltiness perception, moisture status, salt release and protein structure. Results indicated that DC-MF combined with CaCl2 treatment could reduce the addition of sodium chloride by 5% while maintaining the saltiness and overall acceptability of mince as well as improving its texture and yield. Further studies revealed that DC-MF in concert with CaCl2 treatment could not only increase the moisture content of mince gel, but also enhance saltiness perception by causing gel matrix to release salt-bearing juices under external forces. The energy spectrum analysis also illustrated that co-treatment technique could avoid the salt loss of minced meat during cooking process. Finally, a possible potential regulatory mechanism was speculated that the synergistic action of DC-MF and CaCl2 could alter the gel texture and sodium salt availability by modifying protein conformation and inducing a competitive binding reaction site for calcium and sodium ions. In conclusion, synergistic treatment by DC-MF and CaCl2 was a potential strategy in meat salt reduction.

Preparation and characterization of CMT wire arc additive manufacturing Al-5%Mg alloy depositions through assisted longitudinal magnetic field

The presence of hydrogen pores and cracks has been identified as the leading cause of the poor mechanical properties of the cold metal transfer (CMT) wire arc additive manufacturing aluminum alloy depositions. A comparison of additive specimens with porosity defects, microstructure and mechanical properties was conducted through the application of magnetic field-assisted CMT wire arc additive manufacturing Al-5%Mg alloy depositions. The results showed that the longitudinal direct-current (DC) magnetic field affected the flow of liquid metal by changing the arc morphology, which improved the forming quality, microstructure and mechanical properties of the arc additive manufacturing Al-5%Mg alloys. It can be concluded that the longitudinal DC magnetic field plays a significant optimized role in the generation of porosity defects and forming morphology in the additive specimens. At an excitation current of 2A, the average microhardness is 81.42 HV, which is 11.28 % higher than that of the additive specimen without an applied magnetic field. The application of a longitudinal DC magnetic field effectively reduced the grain size, increased the number of large-angle grain boundaries, reduced the grain orientation difference, and made the grain boundaries less prone to cracking, thereby enhancing the microhardness and tensile properties of the additive specimens.

Analysis and suppression of the three-axis crosstalk effect in the modulated SERF atomic magnetometer

In this paper, the effects of modulation fields frequency configuration, modulation fields phase configuration and three-axis direct-current (DC) magnetic fields on the three-axis crosstalk are analyzed in the modulated spin-exchange relaxation-free (SERF) atomic magnetometer. Based on three-axis modulation fields configuration, a method is proposed to suppress the three-axis crosstalk, and the results show that the three-axis crosstalk is lower than 2%. This paper also demonstrates an in-situ magnetic compensation method, and the magnetic compensation accuracy of this method is on the order of pT. Additionally, the three-axis magnetic field closed-loop mode is showed to suppress the effect of the DC magnetic field on the three-axis crosstalk. The three-axis crosstalk is finally reduced by nearly two times compared with that of before crosstalk suppression, and the three-axis sensitivities are better than 30 fT/Hz1/2. The reduction of crosstalk is beneficial to realize the high-precision measurement of the three-axis SERF magnetometer.

A 20 A bipolar current source with 140 μA noise over 100 kHz bandwidth

The precise control of direct current (dc) magnetic fields is crucial in a wide range of experimental platforms, from ultracold quantum gases and nuclear magnetic resonance to precision measurements. In each of these cases, the Zeeman effect causes quantum states to shift in energy as a function of the magnetic field. The development of low-noise current sources is essential because electromagnets are the preferred tool to dynamically control the magnetic field. Here, we describe an ultra-low noise bipolar current source using pairs of complementary n- and p-channel metal–oxide–semiconductor field-effect transistors controlled by zero-drift operational amplifiers. Our source has a 90 kHz inherent bandwidth and provides current from −20 to 20 A with noise (0.1 Hz to 100 kHz) of 140 µA at ±20 A.

Simultaneous determination of AC and DC magnetic field by a whispering gallery mode optical resonator

Alternating current (AC) and direct current (DC) magnetic fields are monitored by an optical whispering gallery mode (WGM) microcapillary resonator filled with magnetostrictive material. The DC magnetic field is demodulated with the signal-to-noise ratio of an AC-modulated magnetic field at a particular frequency and a sensitivity of 2.1 dB/mT is obtained across a detection range of 0.9 mT. An AC field sensitivity of 2.08 μT/ H z at 346 kHz is obtained with the same resonator. Introducing a biased DC field of 90Gs provides a four-fold improvement in AC field sensitivity. The AC and DC fields may be used to improve the corresponding DC and AC sensing. Therefore, this scheme may play a role monitoring magnetic fields in defence, biomedical analysis, and consumer electronics.

Intracellular Magnetic Control over the Reversible Assembly of Silica-Based Magnetic Composite Particles for Photothermal Therapy

Many photothermal materials have been developed in recent years to achieve efficient photothermal therapy. Although larger-sized materials are preferred to ensure a better photothermal performance, upsizing hampers the cellular uptake of these materials. To overcome this dilemma, we proposed an active control system to manipulate the assembly of magnetic composite particles (MCPs) at the cellular level. Herein, MCPs of different sizes (small, medium, and large) were synthesized, and their surfaces were modified with a polymer. These MCPs were then cultured with HeLa cells, and their uptake and mobility were investigated. Small-sized MCPs (dv = 206 nm) and medium-sized MCPs (dv = 312 nm) could be introduced into HeLa cells. However, a smaller amount of the large-sized MCPs was introduced as compared to the other MCPs. Using a direct current magnetic field [DCMF (B = 150 mT)], medium-sized MCPs were observed to quickly assemble in cells; however, redispersal did not occur after the DCMF was turned off. To improve the particle dispersibility, polyethylene glycol and polyethyleneimine (PEI) were used to modify the medium-sized MCPs. Coating the MCPs with PEI (a polymer molecular weight of 25,000 or 270,000) improved their dispersibility in phosphate-buffered saline and cellular uptake. In addition, the redispersal of assembled PEI-coated MCPs was observed after the DCMF was turned off. The photothermal conversion efficiency of the MCPs was also improved using the DCMF. Consequently, the PEI-coated MCPs were first introduced into cells in a dispersed state, and their assembly was induced at the subcellular scale by applying a DCMF, and the assembly was spontaneously redispersed by switching off the DCMF. Such a remote control could improve the cytotoxicity of MCPs under near-infrared laser irradiation.

Slow Magnetic Relaxation and Modulated Photoluminescent Emission of Coordination Polymer Based on 3-Amino-4-hydroxybenzoate Zn and Co Metal Ions

As a starting point, a new 3D porous framework with the {[CoL]·0.5DMF·H2O}n chemical formula (where L = 3-amino-4-hydroxybenzoate) is described. Its performance as a single molecule magnet was explored. The study of magnetic properties reveals that Co-MOF shows no frequency-fdependant alternating current (ac) signals under zero direct current (dc) magnetic field, whereas single-molecule magnet behaviour is achieved when CoII ions are diluted in a ZnII based matrix. Interestingly, this strategy renders a bifunctional [CoxZn1-xL]n material that is also characterized by a strong photoluminescent emitting capacity.

Modal engineering of electromagnetic circuits to achieve rapid settling times.

Inductive circuits and devices are ubiquitous and important design elements in many applications, such as magnetic drives, galvanometers, magnetic scanners, applying direct current (DC) magnetic fields to systems, radio frequency coils in nuclear magnetic resonance (NMR) systems, and a vast array of other applications. They are widely used to generate both DC and alternating current (AC) magnetic fields. Many of these applications require a rapid step and settling time, turning the DC or AC magnetic field on and off quickly. The inductive response normally makes this a challenging thing to do. In this article, we discuss open loop control algorithms for achieving rapid step and settling times in four general categories of applications: DC and AC systems where the system is either under- or over-damped. Each of these four categories requires a different algorithm, which we describe here. We show the operation of these drive methods using Simulink and Simscape modeling tools, analytical solutions to the underlying differential equations, and experimental results using an inductive magnetic coil and a Hall sensor. Finally, we demonstrate the application of these techniques to significantly reduce ringing in a standard NMR circuit. We intend this article to be practical, with useful, easy-to-apply algorithms and helpful tuning tricks.