Hollow Cylindrical Magnet Research Articles

On the magnetostatic scalar potential and magnetic field of a cylindrical magnet

Abstract The magnetostatic potential and magnetic field of a solid and hollow cylindrical magnet is calculated everywhere in space in terms of complete elliptic integrals. These expressions are calculated using an electromagnetic analogy with the electrostatic potential and electric field of two uniformly charged disks with opposite surface density. The analogy is employed to study intuitively the discontinuities and the dipolar approximation of the fields $\vec{H}$ and $\vec{B}$. The range of validity of the dipolar approximation has been studied along the cylinder axis and in the midplane perpendicular to the cylinder axis, comparing them with the obtained general expression.

Magnetic proximity sensor based on colossal magnetoresistance effect

Magnetic proximity sensors are widely used to determine the distance to ferromagnetic or highly conductive materials and to investigate their shape or to detect their motion. In this study, a magnetic proximity sensor incorporating a cylindrical permanent magnet and a scalar magnetic field sensor (measuring the magnitude of the field independently from its orientation) based on the phenomenon of colossal magnetoresistance in manganite films is presented. Two versions of the sensor, one with a solid cylindrical magnet and one with a hollow cylindrical magnet, were constructed and tested. A steel plate and a superconducting YBaCuO disk were used to investigate the static response. The measurements of the dynamic behavior were carried out with rotating steel and duralumin plates. The results of the static experiments and modelling showed that the output response (change of the magnetic field) of the sensor had a hyperbolic relationship with the distance between the sensor and the measured object. This change was positive for solid cylindrical magnet design and negative for hollow cylindrical magnet design when the target was steel. In contrast, the solid magnet-based sensor produced a negative signal for the superconducting material, while the hollow cylindrical magnet sensor showed a positive signal. It was found that the main features of the dynamic response of the proximity sensors can be explained by the magnetization of steel and the induction of eddy currents in duralumin. The present study demonstrates that the proposed magnetic proximity sensor can be successfully used to search for ferromagnetic objects, investigate the properties of superconductors and detect the motion of non-ferromagnetic conductive materials and can have advantages over conventional magnetic proximity sensors.

Micro-Solenoid Coil Design and Fabrication for Magnetic Labeled Cell and Antibody Detection

Introduction There has been considerable interest in developing techniques to create three-dimensional micro-solenoids for microfluidic devices for use with magnetic materials. Although micro-solenoids have been developed for miniaturization of inductors for on-chip power supplies and dc-dc voltage converters [1] there has been limited use in microfluidic devices [2]. Although photolithographically defined two-dimensional, planar micro solenoids have been developed, when a 3D geometry coils is required they are limited to larger scales in the millimeter range or the micro solenoids are not hollow and are filled with material, thus cannot be used with a microfluidic channel [3]. In our work we have developed a fabrication process for a 75-micron radius, vacuum micro solenoid embedded in PDMS channel for microfluidics applications [4].The applications for micro-solenoids in Bio-Micro-Fluidic systems which range from cell sorting and filtering, to the detection and analysis of individual cells. We have also demonstrated when particles in fluid pass through the coil they can be easily detected from the inducted current in the coil [4]. This approach requires much less power than a flow cytometry laboratory instrument, which requires a laser source to detect the cells and particles. Method and Results The construction of the prototype solenoid is as follows: A piece of optical fiber is held taught, and a coil of 20-30 turns of 46ga enameled wire is wound around it. A small, hollow cylindrical magnet is threaded around the coil and fiber, and the arrangement is placed in a 3d printed mold. Syringe needles are threaded onto the fiber and inserted into holes in the mold. Polydimethylsiloxane potting compound is mixed and poured into the mold. The mold and PDMS is placed in a vacuum chamber for 30 minutes to de-gas. The PDMS is cured on a hot plate on low for about 4 hours. The needles are removed and the fiber is pulled out of the PDMS using pliers wrapped in tape. Discussion and Conclusions The image in figure 1 shows a completed micro-solenoid and the induced current readings from beads injected into the channel. The motivation for developing micro-solenoid for sensing is to increase the sensitivity, by match the diameter of micro-coil to the size of the biological cell sorting, so that individual cells can be counted using a magnetic labels attached to the cells. Such micro-solenoids can be used for the detection of labelled cells with magnetic beads attached in an immunoassay. They can be used for counting magnetic particles, or measuring the size of magnetization intensity of particles, based upon the induced current in the micro-coil. Ultimately, the method could be developed for detection of individual pathogenic bacteria or even viruses in a biological sample.

Demagnetization Process Analysis and Numerical Simulation of Magnet with Shock Wave from Compact Explosively Driven Ferromagnetic Generator

For compact explosively driven ferromagnetic impulse source used in magnetic flux compression generators, the relations between the magnet’s demagnetization rate and the shock wave pressure are theoretically analyzed. A nonlinear finite element method is adopted to conduct numerical simulation on the magnet’s impact loading process. The propagation rules and pressure distributions of shock wave within hollow cylindrical NdFeB magnet caused by lateral impact of single-ended and double-ended initiating explosives are explored. The numerical simulation results show that, the pressures at both ends resulting from lateral impact of double-ended initiating explosives on hollow cylindrical magnet are low; double-ended initiating has faster demagnetization rate, swifter variation of flux and higher electromotive force of inductive output than single-ended initiating.

Complementary analyses of hollow cylindrical unioriented permanent magnet (HCM) with high permeability external layer

In this article, several studies based on analytical expressions and computational simulations on Hollow Cylindrical Magnets with an external soft ferromagnetic material (HCM magnets) are presented. Electromagnetic configurations, as well as permanent-magnet-based structures, are studied in terms of magnetic field strength and homogeneity. Permanent-magnet-based structures are further analyzed in terms of the anisotropy of the magnetic permeability. It was found that the HCM magnets produce a highly homogeneous magnetic field as long as the magnetic material is isotropic. The dependency of the magnetic field strength and homogeneity in terms of the anisotropy of the magnetic permeability is also explored here. These magnets can potentially be used in medium-resolution NMR spectrometers and high-field NMR spectrometers.

The magnetic field of a permanent hollow cylindrical magnet

Based on the rational version of MAXWELL’s equations according to TRUESDELL and TOUPIN or KOVETZ, cf. (Kovetz in Electromagnetic theory, Oxford University Press, Oxford, 2000; Truesdell and Toupin in Handbuch der Physik, Bd. III/1, Springer, Berlin, pp 226–793; appendix, pp 794–858, 2000), we present, for stationary processes, a closed-form solution for the magnetic flux density of a hollow cylindrical magnet. Its magnetization is constant in axial direction. We consider MAXWELL’s equations in regular and singular points that are obtained by rational electrodynamics, adapted to stationary processes. The magnetic flux density is calculated analytically by means of a vector potential. We obtain a solution in terms of complete elliptic integrals. Therefore, numerical evaluation can be performed in a computationally efficient manner. The solution is written in dimensionless form and can easily be applied to cylinders of arbitrary shape. The relation between the magnetic flux density and the magnetic field is linear, and an explicit relation for the field is presented. With a slight modification the result can be used to obtain the field of a solid cylindrical magnet. The mathematical structure of the solution and, in particular, singularities are discussed.

Magnetic and electric bulge-test instrument for the determination of coupling mechanical properties of functional free-standing films and flexible electronics.

For the first time a novel multi-field bulge-test instrument which enables measurements of the biaxial mechanical properties and electro-magnetic-mechanical coupling effect of free-standing films in external magnetic/electric fields was proposed. The oil pressure was designed with two ranges, 0-1 MPa for elastic small deformation and 0-7 MPa for plastic/damage large deformation. A magnetic field that was horizontal and uniform in the film plane was supplied by a hollow cylindrical magnet. The magnitude could be changed from 0 to 10,000 Oe by adjusting the position of the testing film. Meanwhile, an electric field applied on the film was provided by a voltage source (Maximum voltage: 1000 V; Maximum current: 1 A). Various signals related to deformation, mechanical loading, magnetic field, and electric field could be measured simultaneously without mutual interference, which was confirmed by the coincidence of the measured P-H curves for titanium (Ti)/nickel (Ni) specimens with/without external fields. A hardening phenomenon under magnetic/electric fields was observed for Ni and lead zirconate titanate specimens. The multi-field bulge-test instrument will provide a powerful research tool to study the deformation mechanism of functional films and flexible electronics in the coupling field.

The Verdet constant of undoped Y3AL5O12 in the near infrared

The optical activity of an undoped Y3Al5O12 (YAG) crystal is measured in the near infrared at a fixed temperature. The crystal is located inside the bore of a hollow cylindrical magnet of uniform magnetization. By integrating the applied magnetic field along the cylindrical axis of the crystal, the Verdet constant is determined for wavelengths from 1300nm to 1350nm as well as at 1064nm. For the 1300nm range, the Verdet constant is found to be approximately 1.38rad/Tm while at 1064nm it is 2.12rad/Tm. From a fit to these measurements, we can extract values for the band gap energy and K-parameter of the crystal. For undoped YAG, we report a band gap value of 8.1eV±0.3eV and a K-parameter of 596rad/Tm±52rad/Tm, consistent with the previous measurements made with visible light.

5095271 Compact open NMR systems for in situ measurement of moisture, salinity, and hydrocarbons

A nuclear magnetic resonance device has a hollow cylindrical magnet that forms a void. The magnet has a plurality of south poles and an equal plurality of north poles, the poles being dimensioned and disposed on the magnet to establish a toroidal zone external to the magnet wherein the field of the magnet is of substantially constant strength. A solenoidal antenna is positioned within the void of the magnet. Electrical insulating material is positioned to cover the bases of the combined cylindrical structure and may also be disposed between the antenna and the magnet. Associated electronic power, signal processing, and indicating equipment may then be mounted adjacent the electrical insulator and the entire assembly contained in a suitable housing.