Novel Deperming Protocols to Reduce Demagnetizing Time and Improve the Performance for the Magnetic Silence of Warships

Magnetic silence of warships is necessary to prevent damage caused by the magnetic mines detecting the magnetic field of the warship. Anhysteretic and Deperm-ME protocols are used to reduce permanent magnetization among magnetic signals. However, they have some disadvantages. Therefore, this paper proposes an effective deperming protocol that is easily controlled and reduces the demagnetization time. A protocol composed of two Anhysteretic protocols is presented using the Preisach model to easily manage and ensure excellent performance. Each stage has its own advantages by considering the Preisach density distribution. In Stage 1, the existing magnetic history is erased, and the demagnetization time is reduced. In Stage 2, the demagnetization performance is improved. The effectiveness of the protocol was verified via simulations using the Preisach model and experiments using a specimen. When the proposed protocol was applied, the results were excellent when applying Anhysteretic and Deperm-ME. In addition, even if the number of magnetic fields was reduced by 4 and 8 in the proposed protocol, the demagnetization result was maintained. Therefore, if the proposed protocol is applied, excellent demagnetization results can be obtained and the time required to perform demagnetization can be reduced, thereby improving the operational capability of the warship.

Shape programming of a magnetic elastica

We consider a cantilever beam which possesses a possibly non-uniform permanent magnetization, and whose shape is controlled by an applied magnetic field. We model the beam as a plane elastic curve and we suppose that the magnetic field acts upon the beam by means of a distributed couple that pulls the magnetization towards its direction. Given a list of target shapes, we look for a design of the magnetization profile and for a list of controls such that the shapes assumed by the beam when acted upon by the controls are as close as possible to the targets, in an averaged sense. To this effect, we formulate and solve an optimal design and control problem leading to the minimization of a functional which we study by both direct and indirect methods. In particular, we prove that minimizers exist, solve the associated Lagrange-multiplier formulation (besides non-generic cases), and are unique at least for sufficiently low intensities of the controlling magnetic fields. To achieve the latter result, we use two nested fixed-point arguments relying on the Lagrange-multiplier formulation of the problem, a method which also suggests a numerical scheme. Various relevant open question are also discussed.

Anisotropy of out-of-phase magnetic susceptibility: an approach for magnetic subfabrics determination

<p>The Anisotropy of Magnetic Susceptibility (AMS) represents the contribution of all minerals in rock samples (paramagnetic, diamagnetic, and/or ferromagnetic minerals). An intermediate AMS tensor may be recorded in rocks where a composite fabric is present, due to the presence of both paramagnetic and ferromagnetic minerals, being possible to be resolved into two distinct subfabrics using techniques as out-of-phase AMS (opAMS). The magnetic susceptibility measured in alternating field can be resolved into in-phase and out-of-phase components. In-phase AMS (ipAMS) measures the bulk response of all minerals in a sample however, opAMS is only sensitive to selected ferromagnetic minerals such as hematite, titanomagnetite, and ultrafine magnetite. The opAMS can be harnessed as a tool for direct determination of magnetic subfabrics defined by ferromagnetic minerals. This work focuses on three Portuguese plutons: Lamas de Olo, Lavadores-Madalena, and Santa Eulália. The preliminary results show that magnetic susceptibility is lower in opAMS, the degree of magnetic anisotropy is much higher in opAMS and the ellipsoid shape parameter has no significant differences in opAMS or ipAMS. The ipAMS and opAMS tensors are in general coaxial, pointing out that standard AMS fabric is parallel to the subfabric of minerals like hematite, titanomagnetite, and ultrafine magnetite. Two sites from Lamas de Olo Pluton with low in-phase magnetic susceptibility (ipK<sub>m</sub>) values were also measured, showing two different scenarios: (i) the coaxially is present in one site, pointing out the presence of minerals like hematite (after magnetite) but with the same orientation as the matrix; (ii) different orientation of K<sub>1</sub> and K<sub>3</sub> in ipAMS and opAMS suggesting the presence of a ferromagnetic oxide like hematite (after magnetite) but with a different orientation from the paramagnetic minerals. Nevertheless, it should be noted that in samples with low K<sub>m</sub> values, the presence of ferromagnetic minerals is scarce (or absent) and the opAMS has minor accuracy (the associated error is greater). The opAMS findings attain similar results to the anisotropy of anhysteretic remanent magnetization (AARM) studies, once both are related to the presence of ferromagnetic minerals, and their magnetic properties. However, the opAMS does not require the permanent magnetization of samples and is measured simultaneously with the ipAMS. With further works, a larger number of samples will be measured to accomplish more information, and AARM measurements will be performed on the same samples to compare the ipAMS, opAMS, and AARM tensors.</p><p>Acknowledgements: This work was funded by the Fundação para a Ciência e a Tecnologia (FCT) under UIDB/04683/2020 project.</p>

Stability of Soft Magnetic Helical Microrobots

Nano/microrobotic swimmers have many possible biomedical applications such as drug delivery and micro-manipulation. This paper examines one of the most promising classes of these: rigid magnetic microrobots that are propelled through bulk fluid by rotation induced by a rotating magnetic field. Propulsion corresponds to steadily rotating and translating solutions of the dynamics of such microrobots that co-rotate with the magnetic field. To be observed in experiments and be amenable to steering control, such solutions must also be stable to perturbations. In this paper, we analytically derive a criterion for the stability of such steadily rotating solutions for a microrobot made of soft magnetic materials, which have a magnetization that depends on the applied field. This result generalizes previous stability criteria we obtained for microrobots with a permanent magnetization.

Modeling and comparison of superconducting linear actuators for highly dynamic motion

This paper presents a numerical modeling method for AC losses in highly dynamic linear actuators with high temperature superconducting (HTS) tapes. The AC losses and generated force of two actuators, with different placement of the cryostats, are compared. In these actuators, the main loss component in the superconducting tapes are hysteresis losses, which result from both the non-sinusoidal phase currents and movement of the permanent magnets. The modeling method, based on the H-formulation of the magnetic fields, takes into account permanent magnetization and movement of permanent magnets. Calculated losses as function of the peak phase current of both superconducting actuators are compared to those of an equivalent non-cryogenic actuator.

Iron oxide catalysts: Fenton and Fentonlike reactions – a review

Iron is the fourth most common element by mass in the Earth's crust and forms compounds in several oxidation states. Iron (hydr)oxides, some of which form inherently and exclusively in the nanometre-size range, are ubiquitous in nature and readily synthesized. These facts add up to render many Fe (hydr)oxides suitable as catalysts, and it is hardly surprising that numerous studies on the applications of Fe (hydr)oxides in catalysis have been published. Moreover, the abundant availability of a natural Fe source from rocks and soils at minimal cost makes the potential use of these as heterogeneous catalyst attractive.Besides those Fe (hydr)oxides that are inherently nanocrystalline (ferrihydrite, Fe5HO8.4H2O, and feroxyhyte, δ’-FeOOH), magnetite (Fe3O4) is often used as a catalyst because it has a permanent magnetization and contains Fe in both the divalent and trivalent states. Hematite, goethite and lepidocrocite have also been used as catalysts in their pure forms, doped with other cations, and as composites with carbon, alumina and zeolites among others.In this review we report on the use of synthetic and natural Fe (hydr)oxides as catalysts in environmental remediation procedures using an advanced oxidation process, more specifically the Fenton-like system, which is highly efficient in generating reactive species such as hydroxyl radicals, even at room temperature and under atmospheric pressure. The catalytic efficiency of Fe (hydr)oxides is strongly affected by factors such as the Fe oxidation state, surface area, isomorphic substitution of Fe by other cations, pH and temperature.