Search

Wireless power transfer via magnetic resonant coupling is experimentally demonstrated in a system with a large source coil and either one or two small receivers. Resonance between source and load coils is achieved with lumped capacitors terminating the coils. A circuit model is developed to describe the system with a single receiver, and extended to describe the system with two receivers. With parameter values chosen to obtain good fits, the circuit models yield transfer frequency responses that are in good agreement with experimental measurements over a range of frequencies that span the resonance. Resonant frequency splitting is observed experimentally and described theoretically for the multiple receiver system. In the single receiver system at resonance, more than 50% of the power that is supplied by the actual source is delivered to the load. In a multiple receiver system, a means for tracking frequency shifts and continuously retuning the lumped capacitances that terminate each receiver coil so as to maximize efficiency is a key issue for future work. Index Terms--Microrobotics, resonant coupling, swarm robotics, wireless power.

An effective method has been developed to calculate the sensitivity of the resonance peak frequency and forced response level to variation of parameters of nonlinear friction contact interfaces and excitation. The method allows determination of the sensitivity characteristics simultaneously with the resonance peak frequency and response level calculated as a function of any parameter of interest and without significant computational expense. Capabilities of the method are demonstrated on examples of analysis of large-scale finite element models of realistic bladed disks with major types of the nonlinear contact interfaces: (i) a blisk with underplatform dampers, (ii) a bladed disk with friction damping at blade fir-tree roots, and (iii) a high-pressure bladed disk with shroud contacts. The numerical investigations show high efficiency of the method proposed. [DOI: 10.1115/1.2969094]

We have measured shape-induced high frequency properties of patterned submicrometer permalloy (Py) arrays. We sputtered and patterned Py films on gold (Au) transmission lines, using chromium (Cr) as adhesion layers for Au and Py deposition. Each Py bar in the arrays is 10 [micro]m long and 100 nm thick. The widths of the Py bars in two different arrays are 240 and 550 nm, respectively. Micromagnetic simulations indicate single domain magnetization distribution in these Py structures. The measured ferromagnetic resonance frequencies without bias field are approximately 11.5 and 8 GHz, respectively. We obtained the corresponding susceptibilities. The experimental results agree with theoretical predictions. Index Terms--Magnetic anisotropy, magnetic resonance, patterned thin film, permalloy, susceptibility.

Experimental characterization through electron paramagnetic resonance (EPR) and confocal luminescence microscopy (CML) of a Ge-doped glass (preform and fiber) reveals the generation of several point defects by 10 keV X-ray radiation-induced attenuation: GeE', Ge(1), Ge(2), and Ge-ODC. The generation mechanisms of Ge-ODC and charged defects like GeE' centers are studied through ab initio simulation. Our calculations used a 108 atom supercell with a glass composition comparable to the Ge-doped core or to the pure-silica cladding of the canonical sample. The large size of our cell allows us to study the influence of the local environment surrounding the X-ODC defect (X = Si or Ge) on its structure parameters (e.g., Si-X bond length) and its energy of formation. We found a statistical correlation between these two characteristics for pure- and Ge-doped silica-based glasses suggesting that the Si-ODC and Ge-ODC will be preferentially generated at sites leading to the shortest Si-X distances. We also evaluated the possible influence of the local environments of the defect on their generation mechanisms. From the whole set of possible X-ODC in the amorphous cells, we calculated the charged structures that can be obtained through the removing of one electron of the cell. For pure-silica glass, about 80% of the oxygen vacancies lead to a dimer structure and 20% to puckered ones. For the doped glass, the percentage of the final dimer structures is reduced to 42% while the puckered charged percentage increases to 36%. We also note the appearance of 22% of divalent centers. Further simulation shows that the presence of the Ge inside the glass strongly affects the generation mechanisms of Si-related centers. Index Terms--Ab initio calculations, defects, density functional theory, optical fibers, radiation effects, silica.

A yttrium iron garnet/gadolinium gallium garnet-gallium arsenide (YIG/GGG-GaAs)-based magnetically-tunable wideband microwave band-pass filter with large tuning ranges for the center frequency (5.90-17.80 GHz) and the bandwidth (1.27-2.08 GHz) in the pass-band using a pair of cascaded band-stop filters is reported. The design and numerical simulation of the band-pass filter that incorporates multisegment microstrip meander-lines and 2-D nonuniform bias magnetic fields were first carried out using Ansoft High Frequency Structure Simulator (HFSS) software suite. The measured transmission characteristics of the band-pass filter at center frequency of 8.28 GHz, using 2-D nonuniform bias magnetic fields centered at 2,750 Oe and 4,150 Oe facilitated by Nd-Fe-B permanent magnets, shows a -3-dB bandwidth of 1.73 GHz, an out-of-band rejection of -33.5 dB, and an insertion loss of -4.2 dB. A good agreement between the simulation and experimental results for the band-pass filter in the center frequency and the bandwidths of the pass-band and the two guarding stop-bands has been accomplished. Index Terms--Bandpass filters, bandstop filters, ferromagnetic resonance (FMR), tunable filters, yttrium iron garnet (YIG) filters.

We present a study of magnetization dynamics at room temperature in periodic arrays of 50 nm thick FeNi (Py) circular magnetic dots of 500 nm radius and different center to center distance (1200 and 2500 nm), by using a broadband magnetometer based on Vector Network Analyzer which works between 300 kHz and 8.5 GHz. We also present a comparison between the dynamic response, ferromagnetic resonance (FMR) and its linewidth, with static magnetic characteristics such as magnetization curves. The FMR peak appears just above the nucleation field and is perfectly described by Kittel formula taking into account the demagnetizing factor of an individual magnetic dot. In addition to FMR we observed a spin wave resonance below the uniform mode, which could be attributed to spin waves in confined systems. The FMR linewidth shows a significant broadening close to the field region corresponding to nucleation of magnetic vortex. Index Terms--Magnetic devices, magnetic resonance, nanotechnology.

The free oscillations of a micromagnetic system around a saturated equilibrium are considered. Magnetization dynamics is described by the Landau--Lifshitz--Gilbert (LLG) equation. The LLG equation is linearized around the equilibrium and put in the form of a generalized eigenvalue problem for suitable self-adjoint operators connected to the micromagnetic effective field. The spectral properties of this problem are studied. The spatial discretization of the problem is analyzed and numerical computation of the resonant oscillations for a magnetic thin-film are performed. Index Terms--Ferromagnetic resonance, generalized eigenvalue problem, normal modes, resonant frequencies.

We investigated the high-frequency modes of 40 [micro]m wide, 160 nm thick [Fe.sub.70][Co.sub.8][B.sub.12][Si.sub.10] squares using time-resolved scanning Kerr microscopy. Two modes were identified using pulsed field excitation while the spatial character of the out-of-plane and in-plane magnetization component was investigated using harmonic field excitation. The field dependence of the two modes has been fitted using the Damon--Eshbach model. Index Terms--Ferromagnetic resonance, magnetooptic Kerr effect, spin dynamics, spin waves.

Nonlinear interactions of electromagnetic waves (EMW) in magnetic nanoparticle systems at microwave frequencies were numerically simulated using rigorous mathematical models to solve the nonlinear diffraction boundary problem. The transmission coefficients [absolute value of [S.sub.12]] of arrays of ferrite spheres, depending on the normalized frequency [omega]/[gamma] ([gamma] gyromagnetic ratio), for radii of 250 mm and 0.1 mm, and separation between the spheres from 600 to 3000 nm, were determined. The increase of the interaction effects upon decreasing separation is demonstrated. The instability regions of parametric generation in the nonlinear ferrite sphere array, depending on the magnitude of the pumping wave at frequency [omega]H, are simulated using our computational algorithm of the bifurcation points of the nonlinear Maxwell's operator. With decreasing separation, i.e., increasing interaction between the spherical elements of the array, the instabilities occur at lower inputs, revealing the power sensitivity of small particle systems. Index Terms--Electromagnetic propagation in magnetic media, magnetic resonance, nanomagnets, nonlinear magnetics.

Samarium (Sm) doped M-type strontium ferrite single crystals have been successfully grown from melts using a flux system of SrC[O.sub.3] and [Na.sub.2]C[O.sub.3]. The crystals exhibited the typical hexagonal ferrite growth habit with a plate-like geometry, and the largest crystals obtained are of 10 mm in length and 3-4 mm in thickness, respectively. It was observed that the saturation magnetization and anisotropy field are greatly affected by the doping concentration of Sm. A saturation magnetization ([[sigma].sub.s]) of 69.8 emu/g and an anisotropy field ([H.sub.k]) of 25 kOe was achieved. Room temperature FMR measurements show 85 Oe of linewidth ([DELTA]H) at 53 GHz. Index Terms--Ferrimagnetic resonance (FMR), hexagonal strontium ferrite, millimeter wave devices.

The magnetic properties of [La.sub.0.7][Ca.sub.0.3]Mn[O.sub.3] (LCMO) manganite thin films were studied with magnetometry and ferromagnetic resonance as a function of film thickness. They maintain the colossal magnetoresistance behavior with a pronounced metal-insulator transition around 150-200 K, except for the very thinnest films studied (3 nm). Nevertheless, LCMO films as thin as 3 nm remain ferromagnetic, without a decrease in saturation magnetization, indicating an absence of dead-layers, although below approximately 6 nm the films remain insulating at low temperature. Magnetization hysteresis loops reveal that the magnetic easy axes lie in the plane of the film for thicknesses in the range of 4-15 nm. Ferromagnetic resonance studies confirm that the easy axes are in-plane, and find a biaxial symmetry in-plane with two, perpendicular easy axes. The directions of the easy axes with respect to the crystallographic directions of the cubic SrTi[O.sub.3] substrate differ by 45 deg in 4- and 15-nm-thick LCMO films. Index Terms--Epitaxial layers, magnetic anisotropy, magnetic resonance, manganites, thin films.

To explore the size effect in electron-doped [La.sub.0.4] [Ca.sub.0.6]Mn[O.sub.3] (LCMO) compound, dc magnetic measurements and electron magnetic resonance were carried out with bulk and nano-grained LCMO in temperature ranges 5 K [less than or equal to] T [less than or equal to] 350 K and 5 K [less than or equal to] T [less than or equal to] 600 K, respectively. It appears that the antiferromagnetic, charge ordered state remains stable upon the reduction of the samples size down to nanometer scale. However, the low-temperature ferromagnetic (FM) component enhances in nano-grained LCMO as compared to its bulk counterpart, supposedly due to strong surface and inter-grain interaction effects. FM correlations in bulk and nano crystals are strong at paramagnetic (PM) state, which seems to be an electron-doping effect. The domination of ion-ion spin relaxation mechanism in PM state and drastic fading of the FM correlations upon cooling means that the doped electrons are localized in both bulk and nano-grained LCMO. The notable influence of the oxygen stoichiometry on magnetic ordering in LCMO, revealed in this work, may explain the contradictive data on the magnetic state of nano-crystalline LCMO reported in the literature. Index Terms--Magnetic resonance, magnetization processes, manganese compounds, nanotechnology.

FePt ferromagnetic polycrystalline thin films of equiatomic composition deposited on oxidized Si (100) substrates have been studied as a function of film thickness by means of dc magnetization and ferromagnetic resonance measurements. Films in the as- deposited state have a moderate texture along the [111] direction as confirmed by X-ray diffraction experiments. In-plane magnetic hysteresis loops show an increasing coercive filed and a decreasing remanent magnetization when the film thickness increases from 10 to 100 nm. Thicker films (t = 60 and 100 nm) reverse magnetization in a two step process, characteristic of samples that present stripe-like magnetic domains. Ferromagnetic resonance in thinner films (which have an almost square hysteresis loop) is characterized by a single resonance line related to the uniform precession of the magnetization, which correlates well with the static magnetic measurements. The two thicker films show an additional resonance line when the magnetic field is applied at, or very close to, the film plane normal. This line is shifted to lower fields from the main resonance by 400-700 Oe and is observed at both X and Q-bands with a field separation that depends on film thickness. These additional resonances, can be originated in the presence of standing spin waves in the thicker films which could not be observed in the thinner ones. Index Terms--FePt films, ferromagnetic resonance, stripe-like domains.

A dense plane periodical array of cylindrical magnetic nanodots has been fabricated using a lithographic mask formed by self-organization of polystyrene nanospheres. In this paper, we study collective static and dynamic magnetic behavior of this array. We find that this technique produces samples with reasonably small dispersion of magnetic parameters of individual dots. This is evidenced by magnetometry and well-resolved discrete frequencies of standing spin waves measured with cavity and coplanar-waveguide ferromagnetic resonance. The standing spin wave resonances could be reliably observed in a large range of frequencies (4-15 GHz). However the measured linewidth of resonances is about ten times larger than for unpatterned Permalloy. This may be due to some variation in shape and magnetic parameters from dot to dot resulting in inhomogeneous broadening of the resonance lines. Index Terms--Ferromagnetic resonance, magnetic nanodot, self-organized structures.

The line width of the ferromagnetic resonance (FMR) spectrum of Cu/CoFeB/Cu/Co/Cu is studied. Analyzing the FMR spectrum by the theory of spin pumping, we determined the penetration depth of the transverse spin current in the Co layer. The obtained penetration depth of Co is 1.7 nm. Index Terms--Ferromagnetic resonance, spin pumping, transverse spin current, Gilbert damping.

Troubleshooting resonance problems within alternating current induction motor systems has always presented difficult challenges for motor manufacturers and end users alike. Often, the changes in structural stiffness from a motor manufacturer's rigid foundation to a less stiff field base can produce drastically different vibration performance. In most cases, a structural natural frequency of a motor or foundation that coincides with a motor forcing function will provide detrimental results to the motor vibration. Many times the effects of undesirable system resonances may be detected after the motor has been installed, causing costly down time, or even motor failure if the problem remains undetected. Additionally, natural frequencies of motor components, such as fans, may cause a catastrophic fatigue failure when the motor is subjected to forcing functions with frequencies in the vicinity of these localized resonances. This paper will provide insight on motor system resonances and localized resonances that may be damaging to an induction motor's operation. Index Terms--Induction motor, local resonance, structural resonance.

The results of an unfocused capacitive micromachined ultrasonic transducer (CMUT) monitored by magnetic resonance (MR)-temperature maps are discussed. Findings reveal the successful heating of a high intensity focused ultrasound (HIFU) phantom by the unfocused CMUT by 14 degree Celsius in 2.5 minutes.

The article presents a novel algorithm based on the Mumford-Shah model for simultaneous detection of the edge features of two images and for joint estimation of a consistent set of transformations to match them. The algorithm helps in the determination of one-to-one correspondences between the edge features of two images.

The extension of well-known scalar image bilateral filtering technique to diffusion tensor magnetic resonance images is examined. Results suggest that diffusion tensor (DT) bilateral filtering is successful in the preservation of diffusion tensor interfaces.

Magnetic resonance energy (MRE) is interpreted as a kind of aromatic stabilization energy and it is calculated for typical heterocyclic cmolecules. The MRE concept is established as a reliable indicator of aromaticity, which has mediated the magnetic criteria of aromaticity with energetic ones.

We present the design of miniaturized resonant inclusions to be employed in the practical realization of metamaterial samples with anomalous values of the real part of the permeability. Such inclusions, in fact, can be employed in the design of both [micro]-negative (MNG) materials and artificial magnetodielectrics (with negative and high-positive values of the real part of the permeability, respectively). The inclusions here considered are the multiple split-ring resonators (MSRRs), that represent a straightforward extension of the commonly used split-ring resonators (SRRs), and the spiral resonators (SRs) that enable a greater miniaturization rate. Some physical insights on the resonance mechanism and on the inherent saturation of the resonant frequency when increasing the number of the rings of the MSRRs and the number of the turns of the SRs are given in the paper. New and accurate analytical design formulas, based on a quasi-static model, for both MSRRs and SRs are derived and tested through a proper comparison with the existing formulas and full-wave numerical results. Both MSRRs and SRs are shown to be useful to reduce the electrical dimensions of the resonant inclusions when synthesizing artificial metamaterials. Index Terms--Metamaterials, [micro]-negative (MNG) metamaterials, resonant magnetic inclusions, split ring resonators.

A density functional theory study was carried out for magnetic resonance of internally trapping water anions and the study the structure of the hydrated electron. It was shown that hyperfine coupling tensors of H/D nuclei in the water molecules are defined mainly by the cavity size and the coordination number of the electron and the water molecules in the second solvation shell play a relatively minor role.

The study results shows that SQUID systems originally designed for biomagnetic applications like magnetoterolaxometry and magnetoencephalography could easily be modified for high resolution NMR at very low field by adding polarization and detection coils and SQUID electronics.

We present a method for designing single-sided magnets suitable for unilateral magnetic resonance (UMR) measurements. The method uses metal pole pieces to shape the field from permanent magnets in a target region. The pole pieces are shaped according to solutions to Laplace's equation, and can be designed using a combination of analytical methods and numerical optimization. The design leads to analytical expressions for the pole piece shapes and magnetic field. Here, we develop the method in Cartesian, polar, and spherical coordinates, and discuss the merits of each system. Finite magnet size has a substantial effect on the field quality in many cases, according to our simulations. We found that in order to achieve a compact magnet in which the static field closely matches that specified, a full 3-D design approach is necessary. A magnet designed by our method produces a static field with a constant gradient over a region 2 cm in diameter and 2 mm thick. This leads to a compact cylindrical magnet just over 11 cm in diameter, topped with a single metal pole piece. The design is validated through simulation. The simulated field is found to agree closely with that specified analytically through the design procedure. Index Terms--Magnetic resonance, scalar potential, static magnetic fields, unilateral magnetic resonance.

A new type of divergence measure is described for the registration of medical images, which has exploited the properties of the modified Bessel functions of the second kind. The new divergence measure is used in the registration of computed tomography (CT) to magnetic resonance (MT) medical images in order to validate the improvement in registration accuracy.

A biomechanical-model constrained state-space analysis framework is described for the multiframe estimation of the periodic cardiac motion and deformation. The results are obtained from estimated displacement fields and strain maps by using in vivo left ventricular magnetic resonance tagging and phase contrast image sequences.

It is important to detect and extract the major cortical sulci from brain images, but manually annotating these sulci is a time-consuming task and requires the labeler to follow complex protocols. This paper proposes a learning-based algorithm for automated extraction of the major cortical sulci from magnetic resonance imaging (MRI) volumes and cortical surfaces. Unlike alternative methods for detecting the major cortical sulci, which use a small number of predefined rules based on properties of the cortical surface such as the mean curvature, our approach learns a discriminative model using the probabilistic boosting tree algorithm (PBT). PBT is a supervised learning approach which selects and combines hundreds of features at different scales, such as curvatures, gradients and shape index. Our method can be applied to either MRI volumes or cortical surfaces. It first outputs a probability map which indicates how likely each voxel lies on a major sulcal curve. Next, it applies dynamic programming to extract the best curve based on the probability map and a shape prior. The algorithm has almost no parameters to tune for extracting different major sulci. It is very fast (it runs in under 1 min per sulcus including the time to compute the discriminative models) due to efficient implementation of the features (e.g., using the integral volume to rapidly compute the responses of 3-D Haar filters). Because the algorithm can be applied to MRI volumes directly, there is no need to perform preprocessing such as tissue segmentation or mapping to a canonical space. The learning aspect of our approach makes the system very flexible and general. For illustration, we use volumes of the right hemisphere with several major cortical sulci manually labeled. The algorithm is tested on two groups of data, including some brains from patients with Williams Syndrome, and the results are very encouraging. Index Terms--Cortical sulci, discriminative models, dynamic programming, learning, magnetic resonance (MR) images, probability boosting tree.

The magnetic hysteresis phenomenon plays an important role in the ferroresonance behavior of a transformer. However, most existing transformer models for the analysis of the ferroresonance phenomenon either ignore the hysteresis effects or represent it based on the hysteresis major loop and scale it for lower current levels. Such a modeling approach does not reflect the actual physical behavior of the magnetic core with respect to the ferroresonance phenomenon. This paper, based on Preisach theory, introduces an accurate model of hysteretic inductor to represent a single-phase transformer for the investigation of the ferroresonance phenomenon. Based on the developed model, time-domain simulation studies show that even in the case of a single-phase transformer where no magnetic coupling exists between the three-phases, all known types of ferroresonance, including fundamental, sub-harmonic, quasi-periodic and chaotic modes, may occur. The effects of hysteresis and its initial conditions, grading capacitors and transformer winding capacitance on occurrence of ferroresonance and its change of mode are also discussed. Index Terms--Ferroresonance, grading capacitor, hysteresis, initial conditions, power transformer, Preisach theory.

Abstract: Non-integrability of planar oscillation of a satellite in an elliptic orbit under the influence of magnetic torque has been studied. The amplitude of the oscillation remains constant upto the [...]

A new class of magnetic resonance (MR) contrast agents that uses a self-immolative mechanism for activation in the presence of an enzyme is reported. A Gd(III) agent that is activated by the oncologically significant beta-glucuronidase is synthesized in nine steps.

In magnetic resonance (MR), imaging methods that use a non-Cartesian (e.g., spiral) sampling grid in k-space are becoming increasingly important. Reconstruction is then usually performed by resampling the data on a Cartesian grid, followed by fast Fourier transform (gridding). In gridding, the weighting of the data to compensate for the varying density of the sampling scheme can lead to a degradation of image quality. An iterative approach that avoids this problem is proposed. The two methods were compared using spiral k-space trajectories. Simulations were performed and showed better image quality and higher signal-to-noise ratio in comparison to gridding based reconstruction. Index Terms--Iterative image reconstruction, magnetic resonance imaging (MRI), pseudo inverse, system matrix.

The favorable spin arrangement between adjacent layers of CuO(sub)2 ribbon chains in the Cu(sub)2O(sub)3 spin lattice of paramelaconite forces the CuO(sub)2 chains to adopt an infinite opposing spin exchange arrangement. Data indicate that the calculated spin exchange parameters suggest a low-dimensional magnetic character determines the magnetic properties of paramelaconite.

We present a new algorithm for the nonrigid registration of three-dimensional magnetic resonance (MR) intraoperative image sequences showing brain shift. The algorithm tracks key surfaces of objects (cortical surface and the lateral ventricles) in the image sequence using a deformable surface matching algorithm. The volumetric deformation field of the objects is then inferred from the displacements at the boundary surfaces using a linear elastic biomechanical finite-element model. Two experiments on synthetic image sequences are presented, as well as an initial experiment on intraoperative MR images showing brain shift. The results of the registration algorithm show a good correlation of the internal brain structures after deformation, and a good capability of measuring surface as well as subsurface shift. We measured distances between landmarks in the deformed initial image and the corresponding landmarks in the target scan. Cortical surface shifts of up to 10 mm and subsurface shifts of up to 6 mm were recovered with an accuracy of 1 mm or less and 3 mm or less respectively. Index Terms--Brain modeling, finite element method, intraoperative image registration, tetrahedral mesh generation.

In this paper, the problem of retrospective correction of intensity inhomogeneity in magnetic resonance (MR) images is addressed. A novel model-based correction method is proposed, based on the assumption that an image corrupted by intensity inhomogeneity contains more information than the corresponding uncorrupted image. The image degradation process is described by a linear model, consisting of a muitiplicative and an additive component which are modeled by a combination of smoothly varying basis functions. The degraded image is corrected by the inverse of the image degradation model. The parameters of this model are optimized such that the information of the corrected image is minimized while the global intensity statistic is preserved. The method was quantitatively evaluated and compared to other methods on a number of simulated and real MR images and proved to be effective, reliable, and computationally attractive. The method can be widely applied to different types of MR images because it solely uses the information that is naturally present in an image, without making assumptions on its spatial and intensity distribution. Besides, the method requires no preprocessing, parameter setting, nor user interaction. Consequently, the proposed method may be a valuable tool in MR image analysis. Index Terms--Information minimization, intensity inhomogeneity, magnetic resonance imaging, nonuniformity correction, segmentation.

The first demonstration of a sandwich-type ferromagnetic RF integrated spiral inductor for the 2-GHz range is reported. Two ferromagnetic CoNbZr films were set to sandwich the spiral in order to enhance the amount of magnetic flux linkage across the coil current. The stresses given from the insulator to the ferromagnetic film were studied. The inductance L of 7.9 nH and the qualify factor Q of 12.7 were obtained for a 200 [micro]m x 400 [micro]m size four-turn rectangular spiral at f = 2 GHz. The inductance was better than that of an air core of the same coil size by 19%, and the Q was better by 23%. Comparison with the on-top magnetic film type was also discussed. Index Terms--Inductors, integrated circuit fabrication, magnetic films, magnetic resonance, magnetic susceptibility.