Small Permanent Magnet Research Articles

Electron-Spin-Resonance Dipstick.

Electron spin resonance (ESR) is a powerful analytical technique used for the detection, quantification, and characterization of paramagnetic species ranging from stable organic free radicals and defects in crystals to gaseous oxygen. Traditionally, ESR requires the use of complex instrumentation, including a large magnet and a microwave resonator in which the sample is placed. Here, we present an alternative to the existing approach by inverting the typical measurement topology, namely placing the ESR magnet and resonator inside the sample rather than the other way around. This new development relies on a novel self-contained ESR sensor with a diameter of just 2 mm and length of 3.6 mm, which includes both a small permanent magnet assembly and a tiny (∼1 mm in size) resonator for spin excitation and detection at a frequency of ∼2.6 GHz. The spin sensitivity of the sensor has been measured to be ∼1011 spins/√Hz, and its concentration sensitivity is ∼0.1 mM, using reference samples with a measured volume of just ∼10 nL. Our new approach can be applied for monitoring the partial pressure of oxygen in vitro and in vivo through its paramagnetic interaction with another stable radical, as well as for simple online quantitative inspection of free radicals generated in reaction vessels and electrochemical cells via chemical processes.

Effects of intergranular phase on the coercivity for MnBi magnets prepared by spark plasma sintering

MnBi magnets with a high content of low temperature phase (LTP) and excellent magnetic properties were prepared by spark plasma sintering (SPS) using ball milling powders as precursors without magnetic purification. A complicated intergranular phase, which contains Mn phase, Bi phase, MnO phase, and even amorphous phase in MnBi magnets, was characterized and reported systematically. It was found that the formation of intergranular phase which was contributed by ball milling precursors and sintering mechanism, jointly, had important influence on the magnetic properties. The appropriate content of intergranular phase was beneficial in improving the coercivity due to the strong magnetic isolation effects. The optimum magnetic properties with Mr=26.0 emu/g, Hci= 7.11 kOe and (BH)max=1.53 MGOe at room temperature, and a maximum value Hci= 25.37 kOe at 550 K can be obtained. Strongly favorable magnetic properties make SPSed MnBi magnets an attractive candidate material for small permanent magnets used in high-temperature applications.

Analysis of Magnetic Interaction in Remotely Controlled Magnetic Devices and its Application to a Capsule Robot for Drug Delivery

In this paper, we present the 3-D analysis of the torque transmitted to a small permanent magnet that is embedded in a capsule robot to achieve targeted drug delivery. This analysis is carried out by using analytical models and experimental results for the magnetic field created by multiple arc-shaped permanent magnets (ASMs), and the torque imparted to a magnetic capsule robot that has an arbitrary position and orientation. Our experimental results, which are in agreement with the analytical results, show that the on-board drug release mechanism can be actuated at any position and with large inclinations of the capsule robot without having to make positional adjustments in the external magnetic system. We have established analytical expressions describing the relationship between the rotating magnetic field created by the ASMs and the transmitted torque. Such relationships are essential to establish real-time control strategies for the actuation of magnetically articulated devices such as drug delivery in capsule robots.

Investigations into Internal Surface Finishing of Titanium (Grade 2) Pipe with Extended Magnetic Tool

Titanium pipes are being used in number of industrial application due to its superior strength to weight ratio, corrosion resistance, fatigue resistance and crack growth. Although Titanium has superior material properties but its machining and finishing is still a very difficult task. In present work, an extended magnetic tool has been used to finish internal surface of titanium (grade 2) pipe (Ø89.5 x Ø79.5 x 305 mm). An extended magnetic tool has been developed from small permanent magnet having its N-S poles made up of Nd-Fe-B permanent magnets (24 x 12 x 25 mm). Response surface methodology has been used to design the experiments. Effect of four major process parameters- processing time, pole-work gap, surface rotational speed and electrolytic iron particle size on percent improvement in surface finish has been analyzed. Microscopic images of processed surfaces also demonstrate the influence of selected process parameters.

Development of device for quantifying magnetic nanoparticle tracers accumulating in sentinel lymph nodes

The developed device with electromagnetic coils and small permanent magnets quantifies the iron contents of superparamagnetic iron oxide nanoparticles for sentinel lymph node (SLN) biopsy. To remove diamagnetic and paramagnetic components and detect only superparamagnetic components, a 2nd harmonics signal is detected by a gradiometer under a moderate AC magnetic field (1–2 mT) with the fundamental frequency (2.944 kHz) of the coils and DC magnetic field (1–2 mT) of the magnets. The detection limit with a signal-to-noise ratio of 5 is approximately 0.28 μg of iron, and the device has a wide dynamic range of 104, 0.28 μg–2.8 mg. Additional coils and permanent magnets play an important role producing the optimum distribution of AC/DC magnetic fields for an iron distribution-independent and SLN size-independent quantification. We demonstrated the quantification of the iron in phantoms, which have a size of 3–20 mm with varied iron distributions and contain magnetic nanoparticles numerically. These results indicate that the developed device is useful for quantifying the magnetic nanoparticles accumulating in SLNs.

Desktop NMR and Its Applications From Materials Science To Organic Chemistry.

NMR spectroscopy is an indispensable method of analysis in chemistry, which until recently suffered from high demands for space, high costs for acquisition and maintenance, and operational complexity. This has changed with the introduction of compact NMR spectrometers suitable for small-molecule analysis on the chemical workbench. These spectrometers contain permanent magnets giving rise to proton NMR frequencies between 40 and 80 MHz. The enabling technology is to make small permanent magnets with homogeneous fields. Tabletop instruments with inhomogeneous fields have been in use for over 40 years for characterizing food and hydrogen-containing materials by relaxation and diffusion measurements. Related NMR instruments measure these parameters in the stray field outside the magnet. They are used to inspect the borehole walls of oil wells and to test objects nondestructively. The state-of-the-art of NMR spectroscopy, imaging and relaxometry with compact instruments is reviewed.

Magnetic Actuation of Drops and Liquid Marbles Using a Deformable Paramagnetic Liquid Substrate.

The magnetic actuation of deposited drops has mainly relied on volume forces exerted on the liquid to be transported, which is poorly efficient with conventional diamagnetic liquids such as water and oil, unless magnetosensitive particles are added. Herein, we describe a new and additive‐free way to magnetically control the motion of discrete liquid entities. Our strategy consists of using a paramagnetic liquid as a deformable substrate to direct, using a magnet, the motion of various floating liquid entities, ranging from naked drops to liquid marbles. A broad variety of liquids, including diamagnetic (water, oil) and nonmagnetic ones, can be efficiently transported using the moderate magnetic field (ca. 50 mT) produced by a small permanent magnet. Complex trajectories can be achieved in a reliable manner and multiplexing potential is demonstrated through on‐demand drop fusion. Our paramagnetofluidic method advantageously works without any complex equipment or electric power, in phase with the necessary development of robust and low‐cost analytical and diagnostic fluidic devices.

Magnetic Actuation of Drops and Liquid Marbles Using a Deformable Paramagnetic Liquid Substrate

AbstractThe magnetic actuation of deposited drops has mainly relied on volume forces exerted on the liquid to be transported, which is poorly efficient with conventional diamagnetic liquids such as water and oil, unless magnetosensitive particles are added. Herein, we describe a new and additive‐free way to magnetically control the motion of discrete liquid entities. Our strategy consists of using a paramagnetic liquid as a deformable substrate to direct, using a magnet, the motion of various floating liquid entities, ranging from naked drops to liquid marbles. A broad variety of liquids, including diamagnetic (water, oil) and nonmagnetic ones, can be efficiently transported using the moderate magnetic field (ca. 50 mT) produced by a small permanent magnet. Complex trajectories can be achieved in a reliable manner and multiplexing potential is demonstrated through on‐demand drop fusion. Our paramagnetofluidic method advantageously works without any complex equipment or electric power, in phase with the necessary development of robust and low‐cost analytical and diagnostic fluidic devices.

Stator Shape Design Method for Improving Power Density in PM Motor

In this paper, we propose a stator shape design method for improving power density in a small permanent magnet motor. In order to calculate iron loss correctly, we analyze a motor by using 2-D finite element method (FEM) in which an E&S model is introduced. Moreover, external circuit equations are solved coupled with equations in electromagnetic field by FEM to calculate copper loss correctly. It is possible to calculate power density correctly by evaluating loss and weight of a motor correctly whether stator shape is changed. As a result, we show that our analysis technique is useful as a shape design method of a motor’s stator for improving power density.

An Improved 6-D Pose Detection Method Based on Opposing-Magnet Pair System and Constraint Multiple Magnets Tracking Algorithm

Magnetic tracking method is mainly based on sensing of the magnetic field generated by the magnetic source. Usually a small permanent magnet is used as the magnetic source, and magnetic dipole model is used to estimate the magnetic field. The disadvantage of this approach is that only 5-D pose information can be estimated, but the spin rotation with respect to the direction of magnetic moment cannot be detected. In our previous work, we proposed a novel 6-D (3-D position and 3-D orientation) pose detection method, which was based on an opposing-magnet pair system. The disadvantage is that different rotational parameters may lead to the same pose result due to the symmetric structure of object magnets. In order to solve this problem, we propose an improved 6-D pose detection method in this paper, which is based on a novel constraint multiple magnets tracking algorithm. Two magnets of different sizes with opposite magnetic directions have been combined together to serve as the tracking target. By applying the constraint multi-magnet tracking algorithm, 5-D pose of each magnet can be obtained. Therefore, we can estimate the missing spin rotational information according to the relative movement between these two magnets. Experimental results verified the feasibility of the proposed method. The average position error is 2.3 mm and the orientation error is 4.36°, when the volume ratio between these two magnets is 1:1.5.

A new contactless magneto-LC resonance technology for real-time respiratory motion monitoring

Monitoring the rate of respiration and its pattern is crucial to assessing an individual’s health or progression of an illness, creating a pressing need for fast, reliable and cost-effective monitors. We present here a novel respiratory monitoring technology based on a magnetic microwire coil (MMC) magneto-LC resonance sensor. The 3mm diameter coil is wound from a melt-extracted amorphous Co69.25Fe4.25Si13B12.5Nb1 microwire. Unlike typical solenoids, the MMC is sensitive to small magnetic fields due to a significant change in an impedance attributed to the high-frequency giant magneto-impedance (GMI) effect. We propose an application of the MMC sensor to detect a position-varying source of a small magnetic field (∼0.01–10Oe) for real-time respiratory monitoring of a human patient. We simulate this application by mounting a small permanent magnet to a mechanical vibrator and vibrating the magnet at different frequencies, amplitudes, and waveforms ∼3–15cm above the MMC. This newly developed MMC magneto-LC resonance technology is highly promising for active respiratory motion monitoring and other biomedical field sensing applications.

Thermoanalytical (TG/DSC/EVG–GC–MS) characterization of the lanthanide (Ho) iron garnet formation in sol–gel

In the present study, the investigation of formation mechanism of holmium iron garnet (Ho3Fe5O12, HoIG) prepared by an aqueous sol–gel method was reported. We specifically focused on the identification of species released during the thermal decomposition of the Ho–Fe–O precursor gel using thermal analysis method. The formation of holmium iron garnet phase and some magnetic properties were investigated by X-ray diffraction analysis, Mossbauer spectroscopy and TG–DSC measurements. Evolved gas analysis of the decomposition products of gel precursor was performed by coupled TG–GC–MS method. In addition, the Curie temperatures of series of rare earth iron garnets were measured using thermal analyser with the small permanent magnet. The influence of the transition temperature from ferrimagnetic to paramagnetic state on the nature of lanthanide element in the iron garnets has been also investigated.

English

Tongue drive system (TDS) is a tongue operated unobtrusive assistive technology,which can potentially provide people with severe disabilities with effective access and environment control.It translate user’s intentions into control commands by detecting and classifying their voluntary tongue motion utilizing a small permanent magnet,secured on the tongue and an array of magnetic sensors mounted on the mouth the magnetic sensor are nothing but hall effect sensors. a hall effect sensor is a transducerthat varies its output voltage in response to changes in magnetic field.in its simplest form the sensor operates as an analogue transducer, directly returning a voltage. With a known magnetic field, its distance from the hall plate can be determined. Wheel chair is made up of high torque geared DC motors, the motors direction can be changed through the set of instructions given from the hall effect sensor and the action of these instructions is already loaded into the microcontroller using embedded C programming. Complete system proposed in this paper has been designed around PIC microcontroller and a RF module. The design has been tested and result achieved confirms the design approach illustrated.

On the motion of linked spheres in a Stokes flow

The results of an experimental investigation into the motion of linked spheres at low Reynolds number are presented. Small permanent magnets were embedded in the spheres and torques were generated by application of an external magnetic field. Pairs of neutrally buoyant spheres, connected by either glass rods or thin elastic struts, move in a reciprocal orbit when driven by an oscillatory field. An array of three spheres linked by elastic struts buckles in a periodic, non-reciprocal manner. The induced magneto-elastic buckling propels the elemental swimmer and we find that the geometrical asymmetry of the device, introduced by the struts of different lengths, determines the swimming direction. We propose that this novel method of creating movement remotely is suitable for miniaturization.

Direct measurement and microscale mapping of nanoNewton to milliNewton magnetic forces

This paper describes the direct measurement and mapping of magnetic forces/fields with microscale spatial resolution by combining a commercial microforce sensing probe with a thin-film permanent micromagnet. The main motivation of this work is to fill a critical metrology gap with a technology for direct measurement of magnetic forces from nN to 10’s of mN with sub-millimeter spatial resolution. This capability is ideal for measuring forces (which are linked to magnetic field gradients) produced by small-scale magnetic and electromagnetic devices including sensors, actuators, MEMS, micromotors, microfluidics, biomedical devices. This new measuring technique is validated by comparison of measured forces from small permanent magnets with the analytical models.

A magnetic rod interfacial shear rheometer driven by a mobile magnetic trap

The magnetic rod interfacial shear rheometer has been successfully used over the past years to measure mechanical properties of fluid-fluid interfaces. However, the resolution is limited due to the finite system compliance and the probe mass and size. Here, we propose a new design that modifies the way in which the magnetic force is imposed on the probe by substituting the usual coils by a pair of small permanent magnets forming a magnetic trap. Suitably displacing the magnet pair imposes a longitudinal force on the probe that depends on the probe-trap displacement. We show that the relative importance of the surface drag to the rest of the forces acting on the probe is increased, allowing more precise measurements. We have checked our dynamical model on a clean air-water interface, showing that the device response depends only on the elastic constant of the magnetic trap. We have made a full characterization of the performance of several trap-probe combinations showing that the new configuration yields a null system compliance and a stable probe positioning. We have checked the rheometer performance on silicone oil thin films and pentadecanoic acid Langmuir monolayers, showing that surface viscosities as low as 10−9 N · s/m are measurable.

Theory of Magnetostatic Force Inspection Method for Monitoring the Oscillation Marks of Continuous Casting

We report an investigation of magnetostatic force of a permanent magnet passing by casting slab in order to monitor oscillation marks on its surface. This problem represents a highly simplified yet enlightening version called magnetostatic force inspection method (MFIM). Our investigation is a combination of analytic theory, numerical simulation and experimental validation [1]. The method allows a prediction of the relationship between profile of the oscillation marks and the change in magnetostatic force. We test our predictions by performing a series of experiments and numerical simulation to overcome difficulty inherent to the analytic theory. We conclude that MFIM has ability of capturing the characteristics of oscillation marks although a refinement of responding theory is necessary to reduce the discrepancy to the predictions. The present results can serve as a prototype for research on magnetostatic inspection. This paper formulates the MFIM through computing the reaction force of the ferromagnetic material. The magnetic field of the small cubic permanent magnet is modeled by an exponential function together with Gauss distribution possibility density function and this approach makes magnetostatic force by various ferromagnetic oscillation marks solved analytically. Cases of regular profile, triangular, rectangular and circular mimicking marks, provide the key scaling laws of the method and illustrate relation between magnetostatic force and the geometric properties of oscillation marks. It provides a theoretical framework for the prediction of the sensitivity of MFIM in laboratory experiments and implementation in industrial practice.

Design and Simulation of Three Degrees-of-Freedom Tracking Systems for Capsule Endoscope

Wireless capsule endoscopes (WCE) are a new technology for inspection of the intestines, which offer many advantages over conventional endoscopes, while devices currently in use are passive and can only follow the natural transit of the intestines. There is a considerable interest in methods of controlled actuation for these devices. In this paper, an actuation system based on magnetic levitation is proposed, utilizing a small permanent magnet within the capsule and an arrangement of digitally controlled electromagnet placed on a movable frame. The objective of this paper is to design a multi-input multi-output (MIMO), three degrees-of-freedom (3DOF) tracking system for capsule endoscope. Two techniques, entire eigenstructure assignment (EEA) and linear quadratic regulator (LQR), are presented to design the controller of the system. The performance of the EEA and LQR controllers was compared based on the stability parameters to validate the proposed actuation system. Finally, simulation results suggest that the LQR approach can be used to synthesize a suitable and simple controller for this application.

Novel Structure of Three-Axis Active-Control-Type Magnetic Bearing for Reducing Rotor Iron Loss

Magnetic bearings (MBs) are useful for suspending the rotor shaft of a high-speed, high-output motor because they can do so without mechanical contact. In [2] , we have proposed a three-axis active-control-type MB (3-axis AMB) with a cylindrical rotor whose diameter is equal to that of the rotor of a radial MB (RMB) or a motor. The proposed 3-axis AMB integrates an RMB and a thrust MB in one unit. However, the assembly of the conventional 3-axis AMB is complex, and the rotor iron loss is large. Thus, in order to simplify the assembly of the 3-axis AMB and to reduce rotor iron loss, this paper discusses a novel structure for the 3-axis AMB in which small auxiliary permanent magnets (PMs) are inserted in the radial winding slots. The suspension force and the rotor iron loss of the proposed device are evaluated by 3-D finite-element analysis in comparison with a 3-axis AMB without small auxiliary PMs.

Improving the efficiency of a reconfigurable microstrip patch using magneto‐static field responsive structures

A new approach on improving the efficiency of a frequency reconfigurable rectangular microstrip patch antenna using magneto-static responsive structures (MRSs) is proposed. In particular, a 1.5 mm × 1.5 mm × 0.508 mm volumetric structure consisting of two parallel conducting plates separated by a dielectric material summarises the overall MRS embodiment. The dielectric material has a cylindrical cavity (i.e. drilled cavity) with a diameter of 0.9 mm and is partially filled with conducting particles (i.e. silver-coated nickel-based cores) that respond to magneto-static fields. Then, when a small permanent magnet is placed close to the MRS, the conducting particles form columns orientated in the direction of the field lines and connect the two conducting plates, acting as an RF switch. Next, to demonstrate the benefits of the MRS, the efficiency of a reconfigurable patch antenna is investigated. Finally, for comparison, the MRS-based reconfigurable antenna is compared with the measured and simulated efficiency of a reconfigurable patch antenna with the same geometry that uses P-region Intrinsic-region N-region (PIN) diodes. It was shown that the MRS-based design had a much better efficiency (50% larger).