Direct Current Magnetic Field Research Articles

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 al 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.

Luminescence, CPL and magnetic properties of 1D enantiopure Ln3+ complexes with (S-) and (R-) α-methoxyphenylacetate ligand.

The reaction of Ln(NO3)2·6H2O (Ln = Eu, Tb, Dy and Sm) with (R)-(-)-α-methoxyphenylacetic acid (R-HMPA) and 1,10-phenanthroline (phen) in EtOH/H2O allows the isolation of 1D chiral compounds of formula [Ln(μ-R-MPA)(R-MPA)2(phen)]n in which Ln = Eu (R-Eu), Tb (R-Tb), Dy (R-Dy) and Sm (R-Sm). The same synthesis by using (S)-(+)-α-methoxyphenylacetic acid (S-HMPA) instead of (R)-(-)-α-methoxyphenylacetic acid allows the isolation of the enantiomeric compounds with formula [Ln(μ-S-MPA)(S-MPA)2(phen)]n where Ln = Eu (S-Eu), Tb (S-Tb), Dy (S-Dy) and Sm (S-Sm). Single crystal X-Ray diffraction measurements were performed for compounds R/S-Eu, R/S-Tb, S-Dy and S-Sm. The luminescence and the circular dichroism measured in the solid state are reported. All compounds show sensitized luminescence, notably the Eu3+ and Tb3+ ones, whose emission color can be perceived by the naked eye. For the Eu3+ and Tb3+ derivatives the quantum yield and the circular polarized luminescence have been measured. For the magnetic allowed transition 5D0 → 7F1 of the Eu3+ compound, the anisotropy factor glum is ±0.013 (+for S-Eu). Also, magnetic properties of all compounds were studied with the Dy3+ analogue showing slow relaxation of the magnetization under a direct current magnetic field of 1000 Oe.

Magnetic anisotropy and structural flexibility in the field-induced single ion magnets [Co{(OPPh2)(EPPh2)N}2], E = S, Se, explored by experimental and computational methods.

During the last few years, a large number of mononuclear Co(II) complexes of various coordination geometries have been explored as potential single ion magnets (SIMs). In the work presented herein, the Co(II) S = 3/2 tetrahedral [Co{(OPPh2)(EPPh2)N}2], E = S, Se, complexes (abbreviated as CoO2E2), bearing chalcogenated mixed donor-atom imidodiphosphinato ligands, were studied by both experimental and computational techniques. Specifically, direct current (DC) magnetometry provided estimations of their zero-field splitting (zfs) axial (D) and rhombic (E) parameter values, which were more accurately determined by a combination of far-infrared magnetic spectroscopy and high-frequency and -field EPR spectroscopy studies. The latter combination of techniques was also implemented for the S = 3/2 tetrahedral [Co{(EPiPr2)2N}2], E = S, Se, complexes, confirming the previously determined magnitude of their zfs parameters. For both pairs of complexes (E = S, Se), it is concluded that the identity of the E donor atom does not significantly affect their zfs parameters. High-resolution multifrequency EPR studies of CoO2E2 provided evidence of multiple conformations, which are more clearly observed for CoO2Se2, in agreement with the structural disorder previously established for this complex by X-ray crystallography. The CoO2E2 complexes were shown to be field-induced SIMs, i.e., they exhibit slow relaxation of magnetization in the presence of an external DC magnetic field. Advanced quantum-chemical calculations on CoO2E2 provided additional insight into their electronic and structural properties.

Enhanced Magnetic Hyperthermia Performance of Zinc Ferrite Nanoparticles under a Parallel and a Transverse Bias DC Magnetic Field.

The collective organization of magnetic nanoparticles (MNPs) influences significantly their hyperthermic properties, relevant for their in vitro and in vivo applications. We report a systematic investigation of the effects of the concentration and the static bias direct current (DC) magnetic field superposed over the alternating magnetic field (AMF), both in a parallel and perpendicular configuration, on the specific absorption rate (SAR) by using zinc ferrite MNPs. The nonmonotonic dependence of the SAR on the concentration, with a maximum at very small concentrations (c ≤ 0.1 mgFe/mL), followed by a minimum at 0.25 mgFe/mL, and the second maximum of 3.3 kW/gFe at around 1 mgFe/mL, was explained by the passage of the MNPs from a single particle behavior to a collective one and the role of the dipolar interactions. By superposing a static 10 kA/m bias DC field on the AMF we obtained an increase in the SAR for both parallel and perpendicular orientations, up to 4285 W/gFe and 4070 W/gFe, respectively. To the best of our knowledge, this is the first experimental proof of a significant enhancement of the SAR produced by a perpendicular DC field. The effect of the DC field to increase the SAR is accompanied by an increase in the hyperthermia coercive field (HcHyp) for both configurations. No enhancement of the DC fields was noticed for the MNPs immobilized in a solid matrix but the DC field increases the HcHyp only in the parallel configuration. This translates into a higher SAR value for the perpendicular configuration as compared to the parallel configuration. These results have practical applications for magnetic hyperthermia.

Direct current magnetic field: An optional strategy for reducing pyrophosphate in gelatinous meat products

This study was to investigate effects of direct-current magnetic field (DC-MF) and tetrasodium-pyrophosphate (TSPP) on properties of myofibrillar protein (MP) gels, to understand potential mechanisms of action, and to clarify feasibility of TSPP reduction by applying DC-MF. MP was either untreated or treated with DC-MF (9.5 mT) and TSPP (0–5 g/L) for 3 h, and then heat-induced gel was prepared for further analysis. Secondary structure, microstructure and water distribution of MP gels were measured respectively by Raman spectroscopy, scanning-electron-microscopy and low field NMR. The relationship between gel properties and protein structure was visualized by PCA. WHC obviously increased, while hardness, fracture and apparent viscosity became lower under DC-MF and high-level TSPP, with more significant effect on WHC, hardness and fracture as TSPP level changed than DC-MF. The texture of gels treated by DC-MF and 3 g/L TSPP was indistinguishable from that of 5 g/L control, delightfully, with TSPP usage decreasing from 5 to 3 g/L. DC-MF and TSPP could affect MP gel hydration ability by influencing microstructure, the content of α-helix and β-sheet, and exposing side-chain-residues. Gel texture was strongly correlated with random coil and β-turn. Overall, DC-MF and TSPP affected gel properties by altering protein and gel structure, DC-MF might be considered an optional strategy for reducing pyrophosphate in gelatinous meat products.

Effects of direct current magnetic field co-treated with stirring on gel properties of chicken batter: Hydration and textural properties

This study constructed an in-house assembled device that allowed the stirring and direct current magnetic field (DC-MF) to be simultaneously applied to pretreat meat batters. The effects of stirring and DC-MF on the hydration and textural properties of chicken batter gels were investigated, and potential mechanisms were explored. The results demonstrated that the combined treatment (3 mT, 15 min, and 250 rpm) improved the texture and gel properties of meat batter gels, as well as the rheological behavior. It also increased the proportion of immobilized water (PT22) to 97.95% and enhanced protein hydration, decreasing cooking losses by 4.66% (P < 0.05). Microstructural images revealed that the DC-MF was conducive to forming a denser and more homogeneous gel structure with pores ranging from 10 to 100 μm. Specifically, the combined treatment exerted preferable properties in water retention and texture and could be used as a physical modification in emulsified meat products.

Enhancement of potato (Solanum tuberosum L) postharvest quality by use of magnetic fields – A case of shangi potato variety

Production of potatoes in the developing countries has been on the rise. This reinforces the growing importance of potatoes throughout Africa, Asia, and Latin America as a source of food and livelihood. However, this crop continues to experience major postharvest losses that are associated with a lack of effective storage facilities in these regions. This study used magnetic fields (MF) as an innovative technology to reduce potato losses while under storage. The effects of test variables; sources of magnetic fields intensity and exposure time on physicochemical properties of stored shangi potatoes were investigated. Double Helmholtz coils were used to generate MF. The coils were supplied with either direct current (DC) or alternating current (AC). Potatoes were then exposed to MF and stored in either the control or the commercial store. At the end of storage, physicochemical analyses were done following standard methods. AC MF resulted in significant (ρ < 0.05) higher specific gravity, dry matter, starch, and the number of sprouts per tuber but lower weight reduction, total sugars, reducing sugars, and non-reducing sugars than DC MF. Exposing potatoes to 3.00 mT of both DC and AC MF resulted in significant (ρ < 0.05) lower weight reduction, internal and external greening, sprouting, and the number of sprouts per tuber than in potatoes that were not exposed to MF. The current work has shown that it is possible to extend the shelf-life of the shangi potato variety by about 1 month, by use of MF, without compromising on quality parameters.

Evaluation of Harmonic Signals Derived From Multiple Spatially Separated Samples for Magnetic Particle Imaging

We studied the harmonic components of signals derived from magnetization of magnetic nanoparticles depending on the direct current magnetic field at magnetic particle imaging (MPI). When single sample was located, the field free point confirmed that the third harmonic has the maximum value and the second harmonic has the minimum value. We proposed a new analytical method that takes the ratio of the third harmonic to the second harmonic to improve the resolution. Moreover, the complex signal obtained from separately located two samples was measured under a gradient magnetic field. We discussed the important issues with respect to the even harmonics in application of MPI for diagnostics in human body.