Direction Of Static Magnetic Field Research Articles

유한요소해석을 이용한 이식형 골전도 보청기 트랜스듀서의 자기공명 안전성과 호환성 향상 연구

This study describes the design of transducer for bone conduction implants that minimize the effects from the magnetic resonance environments. To reduce torque and image artifacts magnitude generated from the magnetic resonance environments, a transducer with a three-pole structure was proposed by combining two permanent magnets with the same poles facing. A 1.5 T static magnetic field environment was modeled using finite element analysis software, and the torque and image artifact magnitude of the three-pole structure magnet were calculated according to the static magnetic field direction. And, to make sure that the proposed structure can reduce the effect in the magnetic resonance environment, the same analysis was performed for the two-pole structure magnet. Comparing the analysis results, the torque and image artifact magnitude of the proposed three-pole magnet were reduced by at least over 50% compared to the two-pole magnet. Through the results of finite element analysis, it was confirmed that the proposed three-pole bone conduction transducer structure can significantly reduce torque and image artifacts magnitude generated from the magnetic resonance environments.

Life on Magnet: Long-Term Exposure of Moderate Static Magnetic Fields on the Lifespan and Healthspan of Mice.

All living organisms on the Earth live and evolve in the presence of the weak geomagnetic field, a quasi-uniform static magnetic field (SMF). In the meantime, although the effects of moderate and high SMFs have been investigated on multiple aspects of a living organism, a long-term SMF exposure of more than 1 year has never been reported. Here, we investigated the influence of a moderate SMF (70-220 mT head-to-toe) long-term continuous exposure (1.7 years) to two different SMF directions on healthy male C57BL/6 mice. We found that not only was the lifespan of the mice prolonged, but their healthspan was also improved. The elevated plus maze test and open field test show that SMFs could significantly improve the exploratory and locomotive activities of the aged mice. The Morris water maze test shows that SMFs could improve their spatial learning ability and spatial memory. Tissue examinations reveal that SMFs have an ameliorative effect on oxidative stress in the brain of aged mice, which was reinforced by the cellular assays, showing that SMFs could protect the PC12 cells from D-gal-induced senescence by increasing superoxide dismutase, catalase, and reducing the malonaldehyde levels. Therefore, our data show that the 1.7-year SMF exposure can improve both the lifespan and healthspan of naturally aged mice due to reduced oxidative stress, which indicates that SMFs have the potential to be used as an adjuvant physical therapy to reduce the ageing-induced health risks to benefit animals, and even humans.

Magnetic properties of twisted plasmons

We consider the linear and nonlinear properties of twisted plasmons propagating in a magnetized plasma. Twisted plasmons are electron plasma waves with a finite amount of angular momentum. In contrast with plane plasma waves, which propagate along the static magnetic field direction with the same dispersion as in isotropic plasmas, the properties of twisted waves depend on the value of their angular momentum. A new dispersion relation is derived, using the fluid approximation. We also study nonlinear effects associated with twisted plasmons, and show that they introduce electromagnetic corrections. Of particular relevance is the excitation of a quasi-static magnetic field, which is associated with finite amplitude plasmon solutions.

Dust–ion acoustic solitary waves in a collisionless magnetized five components plasma

Abstract We have derived a Korteweg–de Vries–Zakharov–Kuznetsov (KdV-ZK) equation to study the nonlinear behavior of dust–ion acoustic waves in a collisionless magnetized five components dusty plasma consisting of warm adiabatic ions, nonthermal hot electrons, isothermal cold electrons, nonthermal positrons and static negatively charged dust particulates. It is found that the coefficient of the nonlinear term of the KdV-ZK equation vanishes along different family of curves in different compositional parameter planes. In this situation, to describe the nonlinear behavior of dust–ion acoustic waves, we have derived a modified KdV-ZK (MKdV-ZK) equation. When the coefficients of the nonlinear terms of both KdV-ZK and MKdV-ZK equations are simultaneously equal to zero, then we have derived a further modified KdV-ZK (FMKdV-ZK) equation which effectively describes the nonlinear behavior of dust–ion acoustic waves. Analytically and numerically, we have investigated the solitary wave solutions of different evolution equations propagating obliquely to the direction of the external static uniform magnetic field. We have seen that the amplitude of the KdV soliton strictly increases with increasing β e, whereas the amplitude of the MKdV soliton strictly decreases with increasing β e, where β e is the nonthermal parameter associated with the hot electron species. Also, there exists a critical value β r ( c ) ${\beta }_{\text{r}}^{(\text{c})}$ of β e such that the FMKdV soliton exists within the interval β r ( c ) < β e ≤ 4 7 ${\beta }_{\text{r}}^{(\text{c})}< {\beta }_{\text{e}}\le \frac{4}{7}$ , whereas the FMKdV soliton does not exist within the interval 0 < β e < β r ( c ) $0< {\beta }_{\text{e}}< {\beta }_{\text{r}}^{(\text{c})}$ . We have also discussed the effect of different parameters of the system on solitary waves obtained from the different evolution equations.

Arbitrary amplitude ion acoustic solitons, double layers and supersolitons in a collisionless magnetized plasma consisting of non-thermal and isothermal electrons

Abstract Using Sagdeev pseudo-potential technique, we have studied the arbitrary amplitude ion acoustic solitons, double layers and supersolitons in a collisionless plasma consisting of adiabatic warm ions, non-thermal hot electrons and isothermal cold electrons immersed in an external uniform static magnetic field. We have used the phase portraits of the dynamical system describing the non-linear behaviour of ion acoustic waves to confirm the existence of different solitary structures. We have found that the system supports (a) positive potential solitons, (b) negative potential solitons, (c) coexistence of both positive and negative potential solitons, (d) negative potential double layers, (e) negative potential supersolitons and (f) positive potential supersolitons. Again, we have seen that the amplitude of the positive potential solitons decreases or increases with increasing n ch according to whether 0 < n c h < n c h ( c ) $0{< }{n}_{ch}{< }{n}_{ch}^{\left(c\right)}$ or n c h ( c ) < n c h ≤ 1 ${n}_{ch}^{\left(c\right)}{< }{n}_{ch}\le 1$ , where n c h ${n}_{ch}$ is the ratio of isothermal cold and non-thermal hot electron number densities, and n c h ( c ) ${n}_{ch}^{\left(c\right)}$ is a critical value of n ch . Also, we have seen that the amplitude of the positive potential solitons decreases with increasing β e , where β e is the non-thermal parameter. We have also investigated the transition of different negative potential solitary structures: negative potential soliton (before the formation of negative potential double layer) → negative potential double layer → negative potential supersoliton → negative potential soliton (after the formation of negative potential double layer) by considering the variation of θ only, where θ is angle between the direction of the external uniform static magnetic field and the direction of propagation of the ion acoustic wave.

Theoretical Study of the Frequency Multiplier Based on Irregular Quarter-Wavelength Microstrip Resonator with Thin Magnetic Film

The characteristics of a frequency doubler on a resonant microstrip structure with a thin magnetic film were studied theoretically. The electrodynamic calculation of the structure was performed within the quasi-static approximation. Nonlinear response of film magnetization was calculated taking into account the second-order terms in the Landau-Lifshitz equation. The frequency response of the microstrip resonator was calculated. It was shown that due to the use of the resonant circuit, high efficiency of the input signal energy conversion into the output signal at a doubled frequency was achieved. The optimal values of the magnitude and direction of an external static magnetic field, which ensure the maximum output power at a doubled frequency, were determined.

Experimental Study of the Guided Wave Directivity Patterns of Thin Removable Magnetostrictive Patches.

The characteristics of removable magnetostrictive thin patches are investigated for the generation of guided waves in plates. The directivity patterns of SH, S0 and A0 modes have been measured in a thin metallic plate for different combinations of static and dynamic magnetic field directions. This used different coil geometries such as racetrack and spiral coils to generate the dynamic magnetic field, as well as separate biasing static magnetic fields from permanent magnets. This arrangement generated signals via both Lorentz and magnetostrictive forces, and the resultant emitted guided waves were studied for different dynamic and static magnetic field directions and magnitudes. It is demonstrated that different guided wave modes can be produced by controlling these parameters.

SNR enhancement for the second harmonics in fluxgate sensor

The fluxgate sensor uses the nonlinear characteristics of soft magnetic materials to measure the geostationary magnetic field, which has the characteristics of high sensitivity, wide magnetic measurement range and easy portability, and is widely used in geological exploration, navigation, space technology and other fields. In this paper, the research is based on the second harmonic method of the development of fluxgate sensor, since the second harmonic contains static magnetic field direction and amplitude information, so the second harmonic signal to noise ratio enhancement can effectively improve the resolution of the fluxgate sensor. In this paper, the induction signal is first resonated to the second harmonic frequency using a resonant circuit, and then filtered after an amplification circuit, the second harmonic signal-to-noise ratio is significantly enhanced by 13 times.

Modulatory effects of magnetic vestibular stimulation on resting-state networks can be explained by subject-specific orientation of inner-ear anatomy in the MR static magnetic field

Strong static magnetic fields, as used in magnetic resonance imaging (MRI), stimulate the vestibular inner ear leading to a state of imbalance within the vestibular system that causes nystagmus. This magnetic vestibular stimulation (MVS) also modulates fluctuations of resting-state functional MRI (RS-fMRI) networks. MVS can be explained by a Lorentz force model, indicating that MVS is the result of the interaction of the static magnetic field strength and direction (called “B0 magnetic field” in MRI) with the inner ear’s continuous endolymphatic ionic current. However, the high variability between subjects receiving MVS (measured as nystagmus slow-phase velocity and RS-fMRI amplitude modulations) despite matching head position, remains to be explained. Furthermore, within the imaging community, an “easy-to-acquire-and-use” proxy accounting for modulatory MVS effects in RS-fMRI fluctuations is needed. The present study uses MRI data of 60 healthy volunteers to examine the relationship between RS-fMRI fluctuations and the individual orientation of inner-ear anatomy within the static magnetic field of the MRI. The individual inner-ear anatomy and orientation were assessed via high-resolution anatomical CISS images and related to fluctuations of RS-fMRI networks previously associated with MVS. More specifically, we used a subject-specific proxy for MVS (pMVS) that corresponds to the orientation of the individual inner-ear anatomy within the static magnetic field direction (also called “z-direction” in MR imaging). We found that pMVS explained a considerable fraction of the total variance in RS-fMRI fluctuations (for instance, from 11% in the right cerebellum up to 36% in the cerebellar vermis). In addition to pMVS, we examined the angle of Reid’s plane, as determined from anatomical imaging as an alternative and found that this angle (with the same sinus transformation as for pMVS) explained considerably less variance, e.g., from 2 to 16%. In our opinion, an excess variability due to MVS should generally be addressed in fMRI research analogous to nuisance regression for movement, pulsation, and respiration effects. We suggest using the pMVS parameter to deal with modulations of RS-fMRI fluctuations due to MVS. MVS-induced variance can easily be accounted by using high-resolution anatomical imaging of the inner ear and including the proposed pMVS parameter in fMRI group-level analysis.

Magnetically actuated bone scaffold: Microstructure, cell response and osteogenesis

Most of the existing scaffolds do not provide physical stimulation to cells in scaffold-guided bone regeneration. In this work, a superparamagnetic scaffold was fabricated using selective laser sintering with polyglycolic acid as matrix and Fe3O4 nanoparticles as internal magnetic source. Additionally, a self-developed external static magnetic field (SMF) was used to provide external magnetic source. In this case, the magnetic moment of the Fe3O4 nanoparticles rearranged along the direction of SMF, thereby generating a locally enhanced magnetic field. The enhanced magnetic field might directly stimulate cell surface receptors and activate downstream signaling pathways. As a consequence, the human umbilical cord-derived mesenchymal stem cells cultivated in the scaffold exhibited significantly enhanced gene expression of alkaline phosphatase, osteocalcin, type I collagen and runt-related transcription factor-2. In vivo tests revealed that the bone regeneration was accelerated with bone mineral density (with SMF: 515 ± 50 mg/cc, without SMF: 326 ± 15 mg/cc), percentage of bone volume/tissue volume (with SMF: 92 ± 3.5%, without SMF: 73 ± 5.2%) and new bone area fraction (with SMF: 86 ± 2.2%, without SMF: 70 ± 1.6%) after 8 weeks' implantation. The biodistribution and serum biochemistry analysis demonstrated that superparamagnetic scaffold possessed favorable biosafety.

Effect of Landau damping on ion acoustic solitary waves in a collisionless unmagnetized plasma consisting of nonthermal and isothermal electrons

We have used the Sagdeev pseudo-potential technique to investigate the arbitrary amplitude ion acoustic solitons, double layers and supersolitons in a collisionless magnetized plasma consisting of adiabatic warm ions, isothermal cold electrons and nonthermal hot electrons immersed in an external uniform static magnetic field. We have used the phase portraits of the dynamical system describing the nonlinear behaviour of ion acoustic waves to confirm the existence of different solitary structures. We have also investigated the transition of different solitary structures: soliton (before the formation of double layer) $\rightarrow$ double layer $\rightarrow$ supersoliton $\rightarrow$ soliton (soliton after the formation of double layer) by considering the variation of $\theta$ only, where $\theta$ is the angle between the direction of the external uniform static magnetic field and the direction of propagation of the wave.

Modulation instability of obliquely propagating ion acoustic waves in a collisionless magnetized plasma consisting of nonthermal and isothermal electrons

We have studied the modulation instability of obliquely propagating ion acoustic waves in a collisionless magnetized warm plasma consisting of warm adiabatic ions and two different species of electrons at different temperatures. We have derived a nonlinear Schr{\"o}dinger equation using the standard reductive perturbation method to describe the nonlinear amplitude modulation of ion acoustic wave satisfying the dispersion relation of ion acoustic wave propagating at an arbitrary angle to the direction of the external uniform static magnetic field. We have investigated the correspondence between two nonlinear Schr{\"o}dinger equations $-$ one describes the amplitude modulation of ion acoustic waves propagating along any arbitrary direction to the direction of the magnetic field and other describes the amplitude modulation of ion acoustic waves propagating along the direction of the magnetic field. We have derived the instability condition and the maximum growth rate of instability of the modulated ion acoustic wave. We have seen that the region of existence of maximum growth rate of instability decreases with increasing values of the magnetic field intensity whereas the region of existence of the maximum growth rate of instability increases with increasing $\cos \theta$, where $\theta$ is the angle of propagation of the ion acoustic wave with the external uniform static magnetic field. Again, the maximum growth rate of instability increases with increasing $\cos \theta$ and also this maximum growth rate of instability increases with increasing $\beta_{e}$ upto a critical value of the wave number, where $\beta_{e}$ is the parameter associated with the nonthermal distribution of hotter electron species.

In-vivo and numerical analysis of the eigenmodes produced by a multi-level Tic-Tac-Toe head transmit array for 7 Tesla MRI.

Radio-frequency (RF) field inhomogeneities and higher levels of specific absorption rate (SAR) still present great challenges in ultrahigh-field (UHF) MRI. In this study, an in-depth analysis of the eigenmodes of a 20-channel transmit Tic-Tac-Toe (TTT) RF array for 7T neuro MRI is presented. The eigenmodes were calculated for five different Z levels (along the static magnetic field direction) of the coil. Four eigenmodes were obtained for each Z level (composed of 4 excitation ports), and they were named based on the characteristics of their field distributions: quadrature, opposite-phase, anti-quadrature, and zero-phase. Corresponding finite-difference time-domain (FDTD) simulations were performed and experimental B1+ field maps were acquired using a homogeneous spherical phantom and human head (in-vivo). The quadrature mode is the most efficient and it excites the central brain regions; the opposite-phase mode excites the brain peripheral regions; anti-quadrature mode excites the head periphery; and the zero-phase mode excites cerebellum and temporal lobes. Using this RF array, up to five eigenmodes (from five different Z levels) can be simultaneously excited. The superposition of these modes has the potential to produce homogeneous excitation with full brain coverage and low levels of SAR at 7T MRI.

Additional Nonreciprocity Effects in the Magneto-Optics of Asymmetric Layer Structures

It has been shown that space–time inversion symmetry breaking at the normal incidence of a quasiplane wave on an asymmetric multilayer structure in the Voigt geometry can result in the formation of the angular Goos–Hanchen effect at reflection and transmission, as well as the spatial Goos–Hanchen effect at transmission. The effects are characterized by nonreciprocity not only with respect to the inversion of direction of static magnetic field but also with respect to the permutation of nongyrotropic layers surrounding a gyrotropic layer.

On some optical properties of magnetic photonic crystals

ABSTRACTThe features of the eigen polarizations of magnetic photonic crystals for large values both of the parameter of magneto-optical activity and the depth of modulation are investigated. The case when the angle between the direction of the external static magnetic field and the normal to the boundary of the layer is zero is considered. The light transmission through the magnetic photonic crystal layer is solved by Ambartsumian's layer addition modified method. The influence of the depth of modulation, the parameter of magneto-optical activity, and the angle of incidence on the eigen polarizations is studied. A simple geometric method for determination of the Bragg frequencies and the widths of forbidden bands is proposed.

Nutation-like-mode excitation of coupled vortex cores in magnetic spherical shells

We performed micromagnetic numerical calculations to explore the novel dynamics of two vortex cores magnetically coupled via long-range dipolar interactions and short-range exchange interactions in a single element of spherical nano-shells. One vortex core is located in the upper half-shell and the other in the lower half-shell. Under a given static magnetic field, they show unique coupled dynamic motions that have yet to be reported so far. For the parallel core orientations, they show slow and large-amplitude orbital motions around the static field direction, and both cores' positions on the surface are out-of-phase with each other. This motion resembles the precession motion of a single vortex core around the static magnetic field direction in a nanosphere. In addition to such a precession-like motion, each core simultaneously shows relatively fast and small-amplitude gyration-like motions that move along with the precession-like motion. The superposition of the two distinct dynamic modes results in an overall nutation-like motion as observed in other non-linear systems such as gyroscopes and geodynamics. For the anti-parallel configuration of both cores, further complex fast decaying, irregular motions are shown, because their opposite core orientations show an almost null surface-normal component of the average magnetization of both cores as well as the opposite rotational senses of their gyration motions. This work provides not only a further understanding of dynamic-coupled motions of magnetic vortices in 3D nano-structures but also an efficient way to utilize nano-spherical shells in other possible applications related to novel dynamic-modes excitation.

Optical properties of magnetic photonic crystals with an arbitrary magnetization orientation

We have studied the peculiarities of diffraction of light in magnetic photonic crystals at large values of magnetooptical activity parameter and modulation depth. We have considered the case of an arbitrary angle between the directions of the external static magnetic field and the normal to the layer. The problem has been solved by the modified Ambartsumyan layer summation method. It has been shown that the given system is nonreciprocal with respect to not only circular, but linear polarizations also. In this case, a new type of nonreciprocity is observed (namely, the relation R(α) ≠ R(–α) holds, where R is the reflection coefficient and α is the angle of incidence). It has been demonstrated that in the case of oblique incidence, there appears a new photonic forbidden band that is not selective relative to the polarization of incident light. We have detected strong dependences of reflectance, absorbance, transmittance nonreciprocity, and other characteristics on the angle between the direction of the external static magnetic field and the normal to the layer boundary. Such a system can be used as a controllable polarization filter and a mirror, as well as a source of circular (elliptic) polarization, a controllable optical diode, and so on.

Band structure peculiarities of magnetic photonic crystals

In this work we studied light diffraction in magneto-photonic crystals (MPC) having large magneto-optical activity and modulation large depth. The case of arbitrary angles between the direction of the external static magnetic field and the normal to the border of the MPC layer is considered. The problem is solved by Ambartsumian’s modified layer addition method. It is found that there is a new type of non-reciprocity, namely, the relation R(α)≠R(-α) takes place, where R is the reflection coefficient, and α is the incidence angle. It is shown the formation of new photonic band gap (PBG) at oblique incidence of light, which is not selective for the polarization of the incident light, in the case when the external magnetic field is directed along the medium axis. Such a system can be used as: a tunable polarization filter, polarization mirror, circular (elliptical) polarizer, tunable optical diode, etc.

Coherent manipulation of dipolar coupled spins in an anisotropic environment

We study coherent dynamics in a system of dipolar coupled spin qubits diluted in solid and subjected to a driving microwave field. In the case of rare earth ions, anisotropic crystal background results in anisotropic g tensor and thus modifies the dipolar coupling. We develop a microscopic theory of spin relaxation in transient regime for the frequently encountered case of axially symmetric crystal field. The calculated decoherence rate is nonlinear in Rabi frequency. We show that the direction of static magnetic field that corresponds to the highest spin g-factor is preferable in order to obtain higher number of coherent qubit operations. The results of calculations are in excellent agreement with our experimental data on Rabi oscillations recorded for a series of CaWO4 crystals with different concentrations of Nd3+ ions.

Effects of high static magnetic field on crystal orientation and magnetic property of Bi-5 wt.% Zn alloys

Orientation behavior and magnetic property of Bi-5wt.% Zn alloys were investigated under various magnetic fields. The c-axes of Zn crystals in eutectic BiZn structure, which have a maximum magnetic susceptibility, were completely parallel to the direction of 6T high static magnetic field (HSMF). The alloys solidified at 0T and 6T showed a near-magnetic isotropic behavior whereas alloys solidified at 2T and 4T showed a magnetic anisotropic behavior. Magnetic properties at different directions of alloys were strictly dependent on the dimensions of Zn plates and value of angle between c-axis of Zn and a- or b-axis of Bi. These phenomena were explained by a mechanism known as rotation to orientation.