Diamagnetic Objects Research Articles

Micromagnetic Manipulators - Ferromagnetic Microwire Systems for Diffusion and Separation of Para and Dia- magnetic Particles in GradientMagnetic Field

Micromagnetic manipulators to control and manage the dynamics of micro and nanoparticles are widely used in medicine, physics, and biology. In this paper, we proposed a number of concepts of targeted use of ferromagnetic microwires for para and dia-magnetic objects manipulation. The microwires are produced in a biocompatible glass shell by Taylor-Ulitovsky method and exhibit tunable magnetic properties. They have the ability to create high gradient magnetic fields due to specific composition of the ferromagnetic core, magnetic domain structure and micron dimensions. For various experimental tasks, the optimal configuration of ferromagnetic microwires in the system and the direction of the wire magnetization are selected. A point trap for paramagnetic particles is formed by an individual wire with an axial magnetization. The wires magnetized along diameter are a source of linearly situated magnetic poles and help to realize a fast redistribution of even weakly paramagnetic particles. Due to a camel-back profile of the magnetic potential, created by a pair of closely spaced wires with orthogonal magnetization they act as effective diamagnetic trapping system. There is also an interesting opportunity to realize a magnetic ratchet using a microwire with a circular domain structure. Thus, the magnetic manipulators based on systems of ferromagnetic microwires make it possible to organize fixation, redistribution and analysis of cell suspensions and magnetic nanoparticles. The biocompatibility of the glass shell of the microwires was demonstrated, hence, the possibility of their further using when working with living objects.

Magneto-Driven Gradients of Diamagnetic Objects for Engineering Complex Tissues.

Engineering complex tissues represents an extraordinary challenge and, to date, there have been few strategies developed that can easily recapitulate native-like cell and biofactor gradients in 3D materials. This is true despite the fact that mimicry of these gradients may be essential for the functionality of engineered graft tissues. Here, a non-traditional magnetics-based approach is developed to predictably position naturally diamagnetic objects in 3D hydrogels. Rather than magnetizing the objects within the hydrogel, the magnetic susceptibility of the surrounding hydrogel precursor solution is enhanced. In this way, a range of diamagnetic objects (e.g., polystyrene beads, drug delivery microcapsules, and living cells) are patterned in response to a brief exposure to a magnetic field. Upon photo-crosslinking the hydrogel precursor, object positioning is maintained, and the magnetic contrast agent diffuses out of the hydrogel, supporting long-term construct viability. This approach is applied to engineer cartilage constructs with a depth-dependent cellularity mirroring that of native tissue. These are thought to be the first results showing that magnetically unaltered cells can be magneto-patterned in hydrogels and cultured to generate heterogeneous tissues. This work provides a foundation for the formation of opposing magnetic-susceptibility-based gradients within a single continuous material.

Axial-Circular Magnetic Levitation: A Three-Dimensional Density Measurement and Manipulation Approach.

Magnetic levitation (MagLev) is a promising technology for density-based analysis and manipulation of diamagnetic objects of various physical forms. However, one major drawback is that MagLev can be performed only along the central axis (one-dimensional MagLev), thereby leading to (i) no knowledge about the magnetic field in regions other than the axial region, (ii) inability to handle objects of similar densities, because they are aggregated in the axial region, and (iii) objects that can be manipulated (e.g., separated or assembled) in only one single direction, that is, the axial direction. This work explores a novel approach called "axial-circular MagLev" to expand the operational space from one dimension to three dimensions, enabling substances to be stably levitated in both the axial and circular regions. Without noticeably sacrificing the total density measurement range, the highest sensitivity of the axial-circular MagLev device can be adjusted up to 1.5 × 104 mm/(g/cm3), approximately 115× better than that of the standard MagLev of two square magnets. Being able to fully utilize the operational space gives this approach greater maneuverability, as the three-dimensional self-assembly of controllable ring-shaped structures is demonstrated. Full space utilization extends the applicability of MagLev to bioengineering, pharmaceuticals, and advanced manufacturing.

Study of the displacement of floating diamagnetic bodies by a magnetic field

The authors analyzed the motion of diamagnetic bodies that float on diamagnetic liquids. The motion was inspired by the deformation of the diamagnetic liquid surface by a magnetic field, called the ‘Moses effect’. The influence of the surface tension on the shape of the well pushed out by the steady magnetic field (B ≅ 0·35T) acting on the surface of the liquid was studied both experimentally and theoretically for water, silicone oil and aqueous surfactant solution. The suggested mathematical approach accurately predicted the shape of the well, depending on the surface tension of the liquid. Qualitative analysis is reported regarding the motion of floating diamagnetic polymers and metallic objects driven by the Moses effect. The impact of the bulk magnetic force on the motion is minor for all of the studied diamagnetic rafts. The influences of gravity and interfacial forces on the displacement of rafts may be of a comparable order of magnitude.

Magnetic confinement of diamagnetic objects for space utilization

Utilization of the space environment provides invaluable opportunities for researchers to fulfill challenging tasks that are impossible on Earth. Longtime sustainable containerless and simultaneously weightless condition is a desirable physical environment that can be easily obtained in outer space. However, in a space station, due to unpredictable disturbances, i.e., g-jitter, objects that are floating in containerless and weightless conditions may not be able to stay motionless at a specific location, making it difficult to conduct any investigation of the objects. In this study, we propose a method to confine objects without energy consumption using permanent magnets. Two types of confinement apparatuses made of permanent magnets were designed and manufactured. The apparatuses were used to demonstrate the capability of the magnetic field to confine diamagnetic objects without mechanical contact. We took confinement of a water droplet as an example and calculated the confinement performance of the two apparatuses. The results showed that the idea of using permanent magnets to confine diamagnetic objects without energy consumption in the space environment is feasible. Compared with other confinement methods, such as ultrasound and electrostatic confinement methods, the method proposed in this study is simple, efficient and inexpensive. Most importantly, the confined objects are restricted in a region with a low magnetic field. These advantages enable the method a potentially useful alternative for studying objects under containerless and weightless condition in space.

Magnetically inspired deformation of the liquid/vapor interface drives soap bubbles

The possibility of driving millimetrically scaled, soap and glycerol bubbles floating on a liquid, using a steady magnetic field of c. 0·5 T, is demonstrated. The bubbles are repelled by the magnet, starting from a threshold initial lateral distance of L0cr= 4 mm from the vertical axis of the magnet, and are attracted to the magnet when the initial lateral distance L0< L0cr. The displacement of bubbles is due to the deformation of the liquid/vapor interface by the magnetic field, known as the Moses effect. This deformation gives rise to the change in apparent contact angles driving the bubble. Switching of repulsion to attraction is explained in terms of a model of an interaction between two capillary charges, one of which represents the bubble and the second represents the well, produced by the magnet on the liquid/vapor interface. The experiments with bubbles demonstrate that the role of gravity in the displacement of floating diamagnetic objects driven by steady magnetic fields may be negligible. The mathematical model of the process is suggested. The experimental data are well explained by the proposed model.

Single-Ring Magnetic Levitation Configuration for Object Manipulation and Density-Based Measurement

Magnetic levitation is a recent research hot spot; however, most of the extant configurations use two magnets with like poles facing each other. This paper proposes a novel magnetic levitation configuration that is based on a single ring magnet, and this configuration opens a wide operational space that enables object manipulation and density-based measurement. We develop a mathematical model to calculate the magnetic field around the magnet and to numerically correlate the levitation height and density of the object. Experimental results prove that this novel configuration can achieve a high accuracy (±0.0005 to ±0.0078 g/cm3) in density measurement for small-sized (∼5 μL) samples. It can manipulate particles, powders, and oil droplets effectively without any direct contact, and it has high sensitivity in the separation of multiple diamagnetic objects with slight differences in densities as well. The accuracy and sensitivity of the proposed configuration are both higher than those of the extant configurations. All of these results are expected to promote deeper study and applications of the magnetic levitation configuration in the field of density-based characterizations and manipulations.

Toward an Understanding of Magnetic Displacement of Floating Diamagnetic Bodies, I: Experimental Findings.

Diamagnetic objects (polymer and metallic plates and spheres, ceramic beads, and liquid marbles), floating on water, and a variety of organic liquids may be driven by a steady magnetic field of 0.1 T, registered at the water-vapor surface. Diamagnetic bodies are attracted to the magnet, when the apparent contact angle at the solid/liquid interface is obtuse and repelled from the magnet, when the angle is acute. Cold plasma-treated polyolefin rafts and spheres, demonstrating underwater floating, are repelled by a permanent magnet. Addition of a surfactant to the water, as well as cold plasma treatment of the polyolefin bodies, can turn the attraction into the repulsion. We conjecture that the observed effects are caused by the interplay of two main phenomena. The first is the gravity, which induces sliding of the particle on the deformed liquid/vapor interface (the Moses effect). The second cause is the hysteresis of the contact angle at the bodies' boundaries.

High-Sensitivity Measurement of Density by Magnetic Levitation.

This paper presents methods that use Magnetic Levitation (MagLev) to measure very small differences in density of solid diamagnetic objects suspended in a paramagnetic medium. Previous work in this field has shown that, while it is a convenient method, standard MagLev (i.e., where the direction of magnetization and gravitational force are parallel) cannot resolve differences in density <10(-4) g/cm(3) for macroscopic objects (>mm) because (i) objects close in density prevent each other from reaching an equilibrium height due to hard contact and excluded volume, and (ii) using weaker magnets or reducing the magnetic susceptibility of the medium destabilizes the magnetic trap. The present work investigates the use of weak magnetic gradients parallel to the faces of the magnets as a means of increasing the sensitivity of MagLev without destabilization. Configuring the MagLev device in a rotated state (i.e., where the direction of magnetization and gravitational force are perpendicular) relative to the standard configuration enables simple measurements along the axes with the highest sensitivity to changes in density. Manipulating the distance of separation between the magnets or the lengths of the magnets (along the axis of measurement) enables the sensitivity to be tuned. These modifications enable an improvement in the resolution up to 100-fold over the standard configuration, and measurements with resolution down to 10(-6) g/cm(3). Three examples of characterizing the small differences in density among samples of materials having ostensibly indistinguishable densities-Nylon spheres, PMMA spheres, and drug spheres-demonstrate the applicability of rotated Maglev to measuring the density of small (0.1-1 mm) objects with high sensitivity. This capability will be useful in materials science, separations, and quality control of manufactured objects.

Combining Step Gradients and Linear Gradients in Density

Combining aqueous multiphase systems (AMPS) and magnetic levitation (MagLev) provides a method to produce hybrid gradients in apparent density. AMPS—solutions of different polymers, salts, or surfactants that spontaneously separate into immiscible but predominantly aqueous phases—offer thermodynamically stable steps in density that can be tuned by the concentration of solutes. MagLev—the levitation of diamagnetic objects in a paramagnetic fluid within a magnetic field gradient—can be arranged to provide a near-linear gradient in effective density where the height of a levitating object above the surface of the magnet corresponds to its density; the strength of the gradient in effective density can be tuned by the choice of paramagnetic salt and its concentrations and by the strength and gradient in the magnetic field. Including paramagnetic salts (e.g., MnSO4 or MnCl2) in AMPS, and placing them in a magnetic field gradient, enables their use as media for MagLev. The potential to create large steps in density with AMPS allows separations of objects across a range of densities. The gradients produced by MagLev provide resolution over a continuous range of densities. By combining these approaches, mixtures of objects with large differences in density can be separated and analyzed simultaneously. Using MagLev to add an effective gradient in density also enables tuning the range of densities captured at an interface of an AMPS by simply changing the position of the container in the magnetic field. Further, by creating AMPS in which phases have different concentrations of paramagnetic ions, the phases can provide different resolutions in density. These results suggest that combining steps in density with gradients in density can enable new classes of separations based on density.

Detecting breast microcalcifications with high-field MRI

The aim of this study was to detect microcalcifications in human whole breast specimens using high-field MRI. Four mastectomy specimens, obtained with approval of the institutional review board, were subjected to gradient-echo MRI acquisitions on a high-field MR scanner. The phase derivative was used to detect microcalcifications. The echo time and imaging resolution were varied to study the sensitivity of the proposed method. Computed tomography images of the mastectomy specimens and prior acquired mammography images were used to validate the results. A template matching algorithm was designed to detect microcalcifications automatically. The three spatial derivatives of the signal phase surrounding a field-perturbing object allowed three-dimensional localization, as well as the discrimination of diamagnetic field-perturbing objects, such as calcifications, and paramagnetic field-perturbing structures, e.g. blood. A longer echo time enabled smaller disturbances to be detected, but also resulted in shading as a result of other field-disturbing materials. A higher imaging resolution increased the detection sensitivity. Microcalcifications in a linear branching configuration that spanned over 8 mm in length were detected. After manual correction, the automatic detection tool identified up to 18 microcalcifications within the samples, which was in close agreement with the number of microcalcifications found on previously acquired in vivo mammography images. Microcalcifications can be detected by MRI in human whole breast specimens by the application of phase derivative imaging.

Using Magnetic Levitation for Three Dimensional Self‐Assembly

Magnetic levitation (MagLev) enables 3D self-assembly of diamagnetic objects with control over many aspects of position and orientation. This work demonstrates the ability of MagLev to position and align components, such as mirrors, filters, lenses, and soft objects, without mechanical support. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Deformation of Water by a Magnetic Field

After the discovery that superconducting magnets could levitate diamagnetic objects,1,2 researchers became interested in measuring the repulsion of diamagnetic fluids in strong magnetic fields,3–5 which was given the name “The Moses Effect.”5 Both for the levitation experiments and the quantitative studies on liquids, the large magnetic fields necessary were produced by superconducting magnets.

Diamagnetic repulsion—A versatile tool for label-free particle handling in microfluidic devices

We report the exploration of diamagnetic repulsion forces for the selective manipulation of microparticles inside microfluidic devices. Diamagnetic materials such as polymers are repelled from magnetic fields, an effect greatly enhanced by suspending a diamagnetic object in a paramagnetic Mn 2+ solution. The versatility of diamagnetic repulsion is demonstrated for the trapping, focussing and deflection of polystyrene particles for three example applications. Firstly, magnet pairs with unlike poles facing each other were arranged along a microcapillary to trap plugs of differently functionalised particles for a simultaneous surface-based assay in which biotin was selectively bound to a plug of streptavidin coated particles utilising only 22 nL of reagent. Secondly, by slightly modifying the magnetic field design, the rapid focussing of particles into a narrow central stream at a flow rate of 650 μm s −1 was accomplished for particle pre-concentration. In a third application, 5 and 10 μm polystyrene particles were separated from each other in continuous flow by passing the particle mixture through a microfluidic chamber with a perpendicular magnetic field, a method termed diamagnetophoresis. The separation was investigated between flow rates of 20–100 μL h −1, with full resolution of the particle populations being achieved at 20 μL h −1. These experiments show the potential of diamagnetic repulsion for simple, label-free manipulation of particles and other diamagnetic objects such as cells for a range of bioanalytical techniques.

Applications of bulk high-temperature Superconductors

Bulk high-temperature superconductors (HTSs) enable the opportunity to develop several unique applications in electrical power that are not feasible with superconducting or normal wires. The large current carrying capacity and low thermal conductivity of the HTSs allows relatively short lengths to carry large currents to low-temperature devices without introducing heat to the device. Such current leads can dramatically reduce the refrigeration requirements for devices such as SMES. The HTSs make a relatively sharp transition to a highly resistive state when the critical current density is exceeded, and this effect has suggested their use for resistive fault current limiters. The bulk HTSs may also take the form of large single-grained superconductors within which circulating currents may flow at large current density without loss. They are capable of developing magnetizations, similar to that of permanent magnets, but with much larger magnetic fields. In this case, they may be used as field-trapping components. Applications in this case include brushless synchronous motors, laboratory magnets, magnetic separation, and magnetron sputtering. The bulk HTSs may also be used as diamagnetic objects in magnetic circuits to provide new types of power devices. One application that uses this effect is an inductive fault current limiters, in which the HTS shields an iron core in an inductive circuit until some current level is exceeded. This transition increases the component from low impedance to high impedance. The diamagnetic property may also be used to create low-loss magnetic bearings for use in efficient energy-storage flywheel devices or sensitive instrumentation. The combination of diamagnetic shielding and field trapping has suggested their use in motor designs analogous to hysteresis motors. Laboratory prototypes for all of these devices have been constructed and tested, and in some cases the devices have been field tested in actual power systems. Improvements in HTS properties, such as flux pinning, mechanical strength, and the ability to grow large grains, have greatly improved the economics of applications that use bulk HTS.

A magnetic trap for living cells suspended in a paramagnetic buffer

This manuscript describes the fabrication and use of a three-dimensional magnetic trap for diamagnetic objects in an aqueous solution of paramagnetic ions; this trap uses permanent magnets. It demonstrates trapping of polystyrene spheres, and of various types of living cells: mouse fibroblast (NIH-3T3), yeast (Saccharomyces cerevisiae), and algae (Chlamydomonas reinhardtii). For a 40mM solution of gadolinium (III) diethylenetriaminepentaacetic acid (Gd·DTPA) in aqueous buffer, the smallest cell (particle) that could be trapped had a radius of ∼2.5μm. The trapped particle and location of the magnetic trap can be translated in three dimensions by independent manipulation of the permanent magnets. This letter a1so characterizes the biocompatibility of the trapping solution.

Of flying frogs and levitrons

Diamagnetic objects are repelled by magnetic fields. If the fields are strong enough, this repulsion can balance gravity, and objects levitated in this way can be held in stable equilibrium, apparently violating Earnshaw's theorem. In fact Earnshaw's theorem does not apply to induced magnetism, and it is possible for the total energy (gravitational + magnetic) to possess a minimum. General stability conditions are derived, and it is shown that stable zones always exist on the axis of a field with rotational symmetry, and include the inflection point of the magnitude of the field. For the field inside a solenoid, the zone is calculated in detail; if the solenoid is long, the zone is centred on the top end, and its vertical extent is about half the radius of the solenoid. The theory explains recent experiments by Geim et al, in which a variety of objects (one of which was a living frog) was levitated in a field of about 16 T. Similar ideas explain the stability of a spinning magnet above a magnetized base plate. Stable levitation of paramagnets is impossible.Samenvatting. Magnetische velden stoten diamagnetische voorwerpen af. Zulke velden kunnen zo sterk zijn dat zij de zwaartekracht opheffen. Het is op deze wijze mogelijk zulke voorwerpen te laten zweven. Dit vormt een stabiel evenwicht, wat in tegenspraak schijnt te zijn met Earnshaw's Theorema. Echter Earnshaw's Theorema is niet langer geldig als het magnetisme veld geinduceerd is. De totale energie (bevattende bijdragen van het magnetisme en de zwaartekracht) kan toch een lokaal minimum vertonen. Algemene criteria voor zo'n minimum zullen worden opgesteld. Verder zal worden aangetoond dat voor een cilindrisch symmetrisch veld, langs zijn symmetrie as altijd een zone gevonden kan worden waarin een stabiel evenwicht bestaat. Voor het veld binnen een solenoïde zal deze zone in detail bepaald worden. Als deze spoel voldoende land is bevindt deze zone zich aan het uiteinde van de spoel. De lengte van deze zone langs de symmetrie as van het veld is ongeveer de helft van de straal van de spoel. Deze theorie geeft een goede verklaring voor de experimenten van Geim et al. In deze experimenten werden een grote verscheidenheid aan verschillende voorwerpen (waaronder een levende kikker) tot zweven gebracht in velden van ongeveer 16 T. Analoge theoriën verklaren de stabiliteit van een roterend permanent magneetje boven een magneetische grondplaat. Het is onmogelijk om paramagnetische voorwerpen stabiel te doen zweven.

Magnetic susceptibility tomography for three-dimensional imaging of diamagnetic and paramagnetic objects

A tomographic technique for reconstructing the three-dimensional distribution of magnetic susceptibility in an object is described, A SQUID magnetometer may be used to measure the perturbations imposed by the object on an applied magnetic field and these data contain information about the susceptibility distribution. To assess the technique, a model object was defined, simulated magnetic field data were generated, and a matrix inversion was carried out with singular value decomposition to yield a least-squares solution for the susceptibility distribution. Various relative geometries of the three interacting physical systems (the applied field, the object and the measurement space) were used and the algorithm's performance was investigated for each of the cases in which one of the systems was moved while keeping the other two fixed. With either strategy involving relative motion between the object and the measurement space, accurate, convergent solutions were obtained, but the algorithm failed when only the direction of the uniform applied field was varied. A suitable nonuniform applied field may make the algorithm robust. Applications for a tomographic imaging susceptometer in biomedical imaging, nondestructive evaluation, and geophysics are envisaged.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A high resolution imaging susceptometer

A high-resolution, MicroSQUID (superconducting quantum interference device)-based susceptometer has been constructed for imaging the susceptibility distribution in diamagnetic and paramagnetic objects. The maximum available applied field, produced by the Helmholtz pair, is 300 mu T, which provides an adequate signal-to-noise ratio for common susceptible materials. The calculated variation in the applied field within 20 mm of the center is less than 0.1% of the field at the center. In a 100-Hz bandwidth, the minimum detectable susceptibility-induced field change, (limited by SQUID noise) is 3*10/sup -9/ of the applied field. The sensitivity of the system may be improved by increasing the applied field, for instance by incorporating a superconducting magnet into the magnetometer dewar, and by using lower-noise SQUIDs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>