Non-magnetic Objects Research Articles

Magnetic manipulation of unknown and complex conductive nonmagnetic objects with application in the remediation of space debris

This article extends recent work in magnetic manipulation of conductive, nonmagnetic objects using rotating magnetic dipole fields. Eddy-current-based manipulation provides a contact-free way to manipulate metallic objects. We are particularly motivated by the large amount of aluminum in space debris. We previously demonstrated dexterous manipulation of solid spheres with all object parameters known a priori. This work expands the previous model, which contained three discrete modes, to a continuous model that covers all possible relative positions of the manipulated spherical object with respect to the magnetic field source. We further leverage this new model to examine manipulation of spherical objects with unknown physical parameters by applying techniques from the online-optimization and adaptive-control literature. Our experimental results validate our new dynamics model, showing that we get improved performance compared to the previously proposed model, while also solving a simpler optimization problem for control. We further demonstrate the first physical magnetic manipulation of aluminum spheres, as previous controllers were only physically validated on copper spheres. We show that our adaptive control framework can quickly acquire useful object parameters when weakly initialized. Finally, we demonstrate that the spherical-object model can be used as an approximate model for adaptive control of nonspherical objects by performing magnetic manipulation of a variety of objects for which a spherical model is not an obvious approximation.

Probing with Each Step: How a Walking Crab-like Robot Classifies Buried Cylinders in Sand with Hall-Effect Sensors.

Shallow underwater environments around the world are contaminated with unexploded ordnances (UXOs). Current state-of-the-art methods for UXO detection and localization use remote sensing systems. Furthermore, human divers are often tasked with confirming UXO existence and retrieval which poses health and safety hazards. In this paper, we describe the application of a crab robot with leg-embedded Hall effect-based sensors to detect and distinguish between UXOs and non-magnetic objects partially buried in sand. The sensors consist of Hall-effect magnetometers and permanent magnets embedded in load bearing compliant segments. The magnetometers are sensitive to magnetic objects in close proximity to the legs and their movement relative to embedded magnets, allowing for both proximity and force-related feedback in dynamically obtained measurements. A dataset of three-axis measurements is collected as the robot steps near and over different UXOs and UXO-like objects, and a convolutional neural network is trained on time domain inputs and evaluated by 5-fold cross validation. Additionally, we propose a novel method for interpreting the importance of measurements in the time domain for the trained classifier. The results demonstrate the potential for accurate and efficient UXO and non-UXO discrimination in the field.

Position Regulation of a Conductive Nonmagnetic Object With Two Stationary Rotating-Magnetic-Dipole Field Sources

Position Regulation of a Conductive Nonmagnetic Object With Two Stationary Rotating-Magnetic-Dipole Field Sources

Asymmetric magnetic levitation for density-based measurement and analysis

BackgroundMagnetic levitation (MagLev) based on negative magnetophoresis represents a promising technology for density-based analysis and manipulation of nonmagnetic objects. This approach has garnered considerable interest across multiple fields, such as chemistry, materials science, and biochemistry, primarily due to its inherent simplicity, precision, and cost-effectiveness. However, it is essential to recognize that frequently used MagLev configurations, including standard MagLev and axial MagLev, are not without their limitations. These configurations often struggle to strike a balance between levitation performance, ease of operation, and visibility. Therefore, it is necessary to develop a new MagLev configuration to address the aforementioned issue. ResultsThis work describes the development of an innovative MagLev, termed “asymmetric MagLev”, achieved by combining a ring magnet and a cylinder magnet as up-down asymmetric magnetic field sources. The asymmetric design overcomes the physical obstacles along the centerline of the standard MagLev, offering unique open-structure advantages, including easy handling of samples, the ability to observe samples from the top or bottom, and no restrictions on the container height. Meanwhile, comparative analysis reveals a considerable enhancement in the working distance of the asymmetric MagLev without significantly sacrificing the measurement range compared to the axial MagLev. Notably, the asymmetric MagLev achieves a remarkable sensitivity of up to about 1.8 × 104 mm (g cm−3)−1, surpassing the axial MagLev by approximately 30 times. Furthermore, experimental results validate the successful application of the asymmetric MagLev in density measurement and quality detection of small-sized objects. SignificanceThis pioneering configuration represents the first utilization of up-down asymmetric magnets in the field of MagLev. Through the integration of an axially magnetized ring magnet and a cylinder magnet, the asymmetric MagLev design overcomes the limitations associated with conventional MagLev configurations. This innovative design exhibits outstanding operational capabilities and levitation performance, making it suitable for a wide range of applications in density-based measurement and analysis.

Pulsation of chemically peculiar stars

AbstractThis paper reviews our current knowledge about pulsating chemically peculiar (CP) stars. CP stars are slowly rotating upper main-sequence objects, efficiently employing diffusion in their atmospheres. They can be divided into magnetic and non-magnetic objects. Magnetic activity significantly influence their pulsational characteristics. Only a handful of magnetic, classical pulsating objects are now known. The only exceptions are about 70 rapidly oscillating Ap stars, which seem to be located within a very tight astrophysical parameter space. Still, many observational and theoretical efforts are needed to understand all important physical aspects and their interrelationships. The most important steps to reach these goals are reviewed.

Attracting Conductive Nonmagnetic Objects With Rotating Magnetic Dipole Fields

Recent research has shown that eddy currents induced by rotating magnetic dipole fields can produce forces and torques useful for dexterous manipulation of conductive nonmagnetic objects. This control paradigm shows promise for application in the remediation of space debris. However, the resulting force from each field source always includes a repulsive component, suggesting that the object should be surrounded by field sources to some degree to ensure the object does not leave the dexterous workspace during manipulation. In this letter, we describe the ability of multiple field sources working together in a coordinated fashion to attract conductive nonmagnetic objects that are not surrounded, reminiscent of a tractor beam. This enables an object to be pulled into a dexterous manipulation workspace. We explicitly describe the nominal attractive force on spherical objects, serving as an approximation for other object geometries, as a function of the properties of the object and the field-generation system. We perform experimental verification using a water-based microgravity simulator.

Exact Solution of New Magnetic Current Based Surface-Volume-Surface EFIE and Analysis of Its Spectral Properties

A novel magnetic current based Surface-Volume-Surface Electric Field Integral Equation (SVS-EFIE-M) is presented for the problem of scattering on homogeneous non-magnetic dielectric objects. The exact Galerkin Method of Moments (MoM) utilizing both the rotational and irrotational vector spherical harmonics as orthogonal basis and test functions according to the Helmholtz decomposition is implemented to solve SVS-EFIE-M analytically for the case of dielectric sphere excited by an electric dipole. The field throughout the sphere is evaluated and compared against the exact classical Mie series solution. The two are shown to agree to 12 digits of accuracy upon a sufficient number of basis/test functions taken in the MoM solution and the Mie series expansion. This exact solution validates the rigorous nature of the new SVS-EFIE-M formulation. It also reveals the spectral properties of its individual operators, their products and their linear combination. The spectrum of the MoM impedance matrix is also obtained. It is shown that upon choosing basis and test functions in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$L^{2}(S)$</tex-math></inline-formula> space and evaluating testing inner products in the same space, the MoM impedance matrix features bounded condition number with increasing order of discretization and/or at low frequencies. This makes the proposed SVS-EFIE-M formulation free of oversampling and low-frequency breakdowns giving it advantage both over its SVS-EFIE-J predecessor and classical double-source integral equations such as PMCHWT, Muller, and others suffering from this type of numerical instabilities inherent to their inferior spectral properties.

Dexterous magnetic manipulation of conductive non-magnetic objects

Dexterous magnetic manipulation of ferromagnetic objects is well established, with three to six degrees of freedom possible depending on object geometry1. There are objects for which non-contact dexterous manipulation is desirable that do not contain an appreciable amount of ferromagnetic material but do contain electrically conductive material. Time-varying magnetic fields generate eddy currents in conductive materials2-4, with resulting forces and torques due to the interaction of the eddy currents with the magnetic field. This phenomenon has previously been used to induce drag to reduce the motion of objects as they pass through a static field5-8, or to apply force on an object in a single direction using a dynamic field9-11, but has not been used to perform the type of dexterous manipulation of conductive objects that has been demonstrated with ferromagnetic objects. Here we show that manipulation, with six degrees of freedom, of conductive objects is possible by using multiple rotating magnetic dipole fields. Using dimensional analysis12, combined with multiphysics numerical simulations and experimental verification, we characterize the forces and torques generated on a conductive sphere in a rotating magnetic dipole field. With the resulting model, we perform dexterous manipulation in simulations and physical experiments.

New Magnetic Current Based Surface-Volume-Surface Electric Field Integral Equation For Solution of Scattering Problems on Dielectric Objects

New Surface-Volume-Surface Electric Field Integral Equation (SVS-EFIE) based on magnetic current single source field representation (SVS-EFIE-M) is proposed for the problems of scattering on homogeneous non-magnetic dielectric objects. It's analytic MoM solution for a dielectric sphere is compared against the Mie series expansion to validate the exact nature of this new magnetic current based SVS-EFIE formulation. This analytic solution also allows to rigorously study spectral properties of the SVS-EFIE- M operators and to determine proper functional spaces in which MoM solutions of it should be sought in order to maintain bounded condition number of the pertinent matrix equation.

Ferrofluidic Manipulator: Automatic Manipulation of Nonmagnetic Microparticles at the Air–Ferrofluid Interface

Manipulation of small-scale matter is a fundamental topic in micro and nanorobotics. Numerous magnetic robotic systems have been developed for the manipulation of microparticles in an ambient environment, liquid, as well as on the air-liquid interface. These systems move intrinsically magnetic or magnetically tagged objects by inducing a magnetic torque or force. However, most of the materials found in nature are nonmagnetic. Here, we report a ferrofluidic manipulator for automatic 2-D manipulation of nonmagnetic objects floating on top of a ferrofluid. The manipulation system employs 8-cm-scale solenoids, which can move nonmagnetic particles by deforming the air-ferrofluid interface. Using linear programming, we can control the motion of the nonmagnetic particles with a predefined trajectory of a line, square, and circle with a precision of 25.1 ± 19.5, 34.4 ± 28.4, and 33.4 ± 26.6 μm, respectively. The ferrofluidic manipulator is versatile with the materials and the shapes of the objects under manipulation. We have successfully manipulated particles made of polyethylene, polystyrene, a silicon chip, and poppy and sesame seeds. This article shows a promising venue for the manipulation of living and nonliving matter at the air-liquid interface.

ОСОБЕННОСТИ ЭЛЕКТРОПОТЕНЦИАЛЬНЫХ ИЗМЕРЕНИЙ ГЛУБИНЫ ПОВЕРХНОСТНЫХ ТРЕЩИН НА ПЕРЕМЕННОМ ТОКЕ В НЕМАГНИТНЫХ ОБЪЕКТАХ

The paper presents the results of the study of electropotential signals when measuring surface cracks on alternating current in magnetic and non-magnetic objects. Electropotential signals in the frequency range in the form of hodographs of the initial and fractured stress complexes, as well as in the form of calibration characteristics. Problems of measurement features in non-ferromagnetic objects. The analysis of the influence of specific electrical conductivity and current frequency when measuring the depth of cracks in non-ferromagnetic objects

Implementation of Demonstration Methods to Improve Science Learning Results for Violent Students of Sdn 01 Simpur

&lt;p&gt;&lt;em&gt;The purpose of the classroom action research in this study was to improve the learning outcomes of Kalas VI students in science learning basic competence to identify magnetic and non-magnetic objects through the demonstration method. This research was conducted in two cycles, with each cycle consisting of one meeting. The procedures in classroom action research include planning, acting, observing, reflecting. Based on the data analysis of the research results, it can be concluded that the use of the demonstration method in science learning basic competence to identify magnetic and non-magnetic objects, is proven to improve learning outcomes of class VI SDN 01 Simpur students with an average value of 60 up to 75 and the percentage of students who have completed from 45% to 88%. The use of the Demonstration method can also increase student learning activeness in science learning, from 18 active students to 29 active students and the percentage of active students from 58% to 92%.&lt;/em&gt;&lt;em&gt;&lt;/em&gt;&lt;/p&gt;

Application of Project Based Learning Models to Improve Student Learning Outcomes in Science Material

&lt;p&gt;&lt;em&gt;This study aims to determine the increase in learning outcomes in science learning through the application of the PjBL model. This research is a classroom action research with 21 students of grade VI SD Margadana 5 Tegal as the subject. This research was conducted in 3 cycles, each cycle of 2 meetings. Each meeting consists of 4 stages, namely planning, implementing, observing and reflecting. Based on the results of the research, in the first cycle, it was obtained an average of 68.09 classical student learning outcomes with 52% student completeness success, and in the second cycle the classical student learning outcomes were 70.47 with the completeness success increasing to 67% and still under the indicators of success. In cycle III, the classical average of student learning outcomes was 83.33 with the success of student completeness increasing to 86% in this case it was more than the 75% achievement indicator. So from cycle I, cycle II and cycle III there is an increase in student learning outcomes. So, in this study it can be concluded that using the PjBL model can improve student learning outcomes in science subjects magnetic and non-magnetic objects.&lt;/em&gt;&lt;/p&gt;

Improving Student Learning Outcomes in Energy Materials and Their Changes through Demonstrations, Concrete Media in Class V

&lt;p&gt;&lt;em&gt;Based on the formulation of the problem, the research objective to be achieved through the application of concrete media-based methods is to improve science learning outcomes regarding the grouping of magnetic and non-magnetic objects in class V. This research was conducted at SDN 3 Jangkungharjo. The research was conducted in 2 cycles, where each cycle consisted of 4 stages of planning, implementing, observing / observing, and reflecting. The results of the pre-cycle research stated that: out of 32 students, only 10 students (31.25%) obtained complete learning. After the learning improvement process in cycle I, students who obtained learning completeness increased to 20 students (62.50%). The process of improving learning in Cycle II can improve students' understanding with learning outcomes reaching 30 students (93.75%). This increase shows that the methods used in the learning improvement process can be used as a means to improve student learning outcomes.&lt;/em&gt;&lt;/p&gt;

Comparative study of the surface potential of magnetic and non-magnetic spherical objects in a magnetized radio-frequency discharge

We report measurements of the time-averaged surface floating potential of magnetic and non-magnetic spherical probes (or large dust particles) immersed in a magnetized capacitively coupled discharge. In this study, the size of the spherical probes is taken greater than the Debye length. The surface potential of a spherical probe first increases, i.e. becomes more negative at low magnetic field ( $B &lt; 0.05\ \textrm {T}$ ), attains a maximum value and decreases with further increase of the magnetic field strength ( $B &gt; 0.05\ \textrm {T}$ ). The rate of change of the surface potential in the presence of a $B$ -field mainly depends on the background plasma and types of material of the objects. The results show that the surface potential of the magnetic sphere is higher (more negative) compared with the non-magnetic spherical probe. Hence, the smaller magnetic sphere collects more negative charges on its surface than a bigger non-magnetic sphere in a magnetized plasma. The different sized spherical probes have nearly the same surface potential above a threshold magnetic field ( $B &gt; 0.03\ \textrm {T}$ ), implying a smaller role of size dependence on the surface potential of spherical objects. The variation of the surface potential of the spherical probes is understood on the basis of a modification of the collection currents to their surface due to charge confinement and cross-field diffusion in the presence of an external magnetic field.

Chemically-engineered multipurpose spin selection in a double-level molecular device with spinterface

Molecular spintronics has triggered a tremendous revolution in the fields of information storage, transport, and processing, within which the exploitation of multipurpose spintronic devices is one of the key challenges. In this paper, based on a nonmagnetic molecular object with two transport-active orbits connected parallelly to two magnetic electrodes, we reveal such structure behaves as an electronically-controllable multifucntional spin device. Dual and bipolar spin selectors are realized, without need to repeat the operation or reverse the spin state of the electrodes. The selection schemes could be engineered by tuning the distance between two orbits, which essentially stems from the inter-correlation between the spinterface and the local exchange interactions. Through a detailed design of the interfacial and local parameters, we disclose these behaviors are robust in the strongly correlated limit, but may be affected significantly by the strength of the spin imbalance of the electrode and the local energy level. Our results may afford an important guideline for a competitive magnetoelectronics molecular device, which could be easily manipulated through purely chemical technologies.

Slippery and magnetically responsive micropillared surfaces for manipulation of droplets and beads

Stimuli-responsive surfaces are of practical importance for applications ranging from enhanced mixing of reagents in lab-on-a-chip systems until probing cellular traction forces. Non-destructive reversible bending of cilia-inspired magnetic pillars can be used for controlled transportation of non-magnetic objects and bio-inspired sensing. Magnetic actuation of micropillars suspended in liquids allows controlled mixing, propelling, and stirring of fluids as well as droplet manipulation, which are important for various applications including generation of cell spheroids and droplet coalescence in microfluidic systems. In order to expand their practical applications, fabrication processes capable of rapid prototyping have to be developed. Inspired by biological cilia and their functionalities, actuating hairy surfaces are herein fabricated and implemented to manipulate both microbeads and droplets. The artificial cilia are based on microscale magnetic pillar arrays made of flexible polydimethylsiloxane functionalized with magnetic microparticles. The arrays are fabricated by a new method using patterned molds that relies on cryogenic separation to produce transparent cilia-inspired arrays without requiring manual interference to clean the templates during the process. Magnetic actuation of the pillar arrays is demonstrated in isopropanol and silicone oil. Filling with oil yields magnetically responsive slippery lubricated surfaces allowing directional motion of droplets by repetitive bending and recovery of the flexible magnetic pillars. The achieved structures allow manipulation of microbeads and droplets which is uncommon even at the sub-mm scale; directional motion is demonstrated for 250 μm–550 μm sized droplets. Droplet transportation is facilitated by extremely low hysteresis and a high degree of omnidirectional bending of the pillar array.

Switchable adhesion of soft composites induced by a magnetic field.

Switchable adhesives have the potential to improve the manufacturing and recycling of parts, and to enable new modes of motility for soft robots. Here, we demonstrate magnetically-switchable adhesion of a two-phase composite to non-magnetic objects. The composite's continuous phase is a silicone elastomer, and the dispersed phase is a magneto-rheological fluid. The composite is simple to prepare, and to mold into different shapes. When a magnetic field is applied, the magneto-rheological fluid develops a yield stress, which dramatically enhances the composite's adhesive properties. We demonstrate up to a nine-fold increase of the pull-off force of non-magnetic objects in the presence of a 250 mT field.

Biped Walking of Magnetic Microrobot in Oscillating Field for Indirect Manipulation of Non-Magnetic Objects

Magnetic microrobots have been developed for various biomedical applications, such as microswimmers for indirect manipulation and assembly of objects. When non-magnetic targets fall or adhere to the substrate by gravity, the indirect manipulation is required to move objects on substrate surface. Inspired by human walking, a novel magnetic microrobot with two pseudopods was designed. Driven by a periodic magnetic field, the structure can subtly lift and move two feet alternately to walk forward. The amplitude and frequency of oscillation were optimized and the controllability of the system was evaluated through performing the motion along planned paths with a velocity of 3.5 mm/s. Finally, microbeads and cell aggregates were pushed and arranged together by the microrobot, which shows potential application in flexible microassembly on substrate surface.

Energy budget and optical theorem for scattering of source-induced fields

We provide rigorous definitions of various components of the energy budget for scattering of source-induced electromagnetic fields by a finite nonmagnetic object. We use the classical volume-integral-equation (VIE) framework and define power rates in terms of integrals of the Poynting vector over various surfaces, enclosing some or all of the impressed sources, scatterer, and environment (such as a planar multilayered substrate). Thus, we generalize the conventional cross sections and obtain new interrelations analogous to the well-known optical theorem. We rigorously treat the strong singularity of the VIE kernel, but keep derivations accessible to a wide audience. The defined power rates are further related to the decay rate enhancement and apparent quantum yield of an arbitrary emitter, which are the core concepts in nanophotonics, surface-enhanced Raman scattering, and electron energy-loss spectroscopy. We also discuss the practical calculation of the power rates and decay rate enhancements in the framework of the discrete dipole approximation (DDA). In particular, we derive the volume-integral expression for the scattered power and use it to prove the automatic satisfaction of the optical theorem irrespective of the discretization level. Thus, the optical theorem cannot be used as an internal measure of the DDA accuracy.