Sign Of Torque Research Articles

Model Predictive Based Direct Torque Control for Induction Motor Drives by Sole-Evaluation of Two Parameter Independence Duty Ratios for Each Voltage Vector

Due to importance of duty cycle based model predictive torque control (MPTC), it has been accepted as an effective and common alternative control strategy for industry. Since its major drawback is great dependency on duty ratio parameter, the robustness and the complexity of control system has been respectively decreased and increased. A duty-ratio set considering limited members can be replaced with continuous and dependent parameters form duty cycle relationship. Hence, this paper proposes a new and applicable discrete duty cycle control strategy to reduce both the torque and flux ripples appeared in MPTC method. In the proposed method, after preselecting around half of all admissible voltage vectors based on the torque sign or speed variation and the stator flux position, two duty ratios have just been selected for the preselected active voltage vectors. These two duty ratios are achieved based on the equivalent voltage concept with independent motor parameter. Then, the model predictive control method is employed to select the optimum active voltage vector and its relevant duty ratio among the reduced feasible voltage vectors which reduces both the flux and torque ripples, especially in low speed ranges. The simulation results have confirmed the performance of the proposed method in order to reduce the torque and flux ripples, and the experimental results have accordingly validated its performance. Since the number of voltage vectors and duty ratios is significantly decreased, the execution time of the proposed method is further reduced, and virtually worked with a constant switching frequency for all speed ranges.

Collective spin dynamics under dissipative spin Hall torque

Current-induced spin torques in layered magnetic heterostructures have many commonalities across broad classes of magnetic materials. These include not only collinear ferromagnets, ferrimagnets, and antiferromagnets but also more complex noncollinear spin systems. We develop a general Lagrangian–Rayleigh approach for studying the role of dissipative torques, which can pump energy into long-wavelength magnetic dynamics, causing dynamic instabilities. While the Rayleigh structure of such torques is similar for different magnetic materials, their consequences depend sensitively on the nature of the order and, in particular, on whether there is a net magnetic moment. The latter endows the system with a unipolar switching capability, while magnetically compensated materials tend to evolve toward limit cycles, at large torques, with chirality dependent on the torque sign. Apart from the ferromagnetic and antiferromagnetic cases, we discuss ferrimagnets, which display an intricate competition between switching and limit cycles. As a simple case for compensated noncollinear order, we consider isotropic spin glasses and a scenario of their coexistence with a collinear magnetic order.

Interpretation of the Spin Torque Sign Change in F/N/F Structures in Terms of a Mechanical Analogy

A useful interpretation of the spin-accumulation and spin-current distributions in magnetic nanostructures with diffusive transfer has been discussed. A mathematically equivalent mechanical system was proposed that provides an intuitive understanding of the dependence of the spin-transfer torque values on various parameters. In particular, it gives a clear explanation for the sign change of the spin-transfer torque in asymmetric F/N/F structures.

Adjustable vector Airy light-sheet single optical tweezers: negative radiation forces on a subwavelength spheroid and spin torque reversal

Generalized solutions of vector Airy light-sheets, adjustable per their derivative order m, are introduced stemming from the Lorenz gauge condition and Maxwell’s equations using the angular spectrum decomposition method. The Cartesian components of the incident radiated electric, magnetic and time-averaged Poynting vector fields in free space (excluding evanescent waves) are determined and computed with particular emphasis on the derivative order of the Airy light-sheet and the polarization on the magnetic vector potential forming the beam. Negative transverse time-averaged Poynting vector components can arise, while the longitudinal counterparts are always positive. Moreover, the analysis is extended to compute the optical radiation force and spin torque vector components on a lossless dielectric prolate subwavelength spheroid in the framework of the electric dipole approximation. The results show that negative forces and spin torques sign reversal arise depending on the derivative order of the beam, the polarization of the magnetic vector potential, and the orientation of the subwavelength prolate spheroid in space. The spin torque sign reversal suggests that counter-clockwise or clockwise rotations around the center of mass of the subwavelength spheroid can occur. The results find useful applications in single Airy light-sheet tweezers, particle manipulation, handling, and rotation applications to name a few examples.

Negative optical radiation force and spin torques on subwavelength prolate and oblate spheroids in fractional Bessel-Gauss pincers light-sheets.

Fractional Bessel-Gauss light-sheets [J. Opt.19, 055602 (2017)JOOPDB0150-536X10.1088/2040-8986/aa649a], which correspond to finite optical "slices" in 2D and possess asymmetric slit openings and bending characteristics, are examined from the standpoint of optical radiation force and spin torque theories for a subwavelength spheroid with arbitrary orientation in space. The vector angular spectrum decomposition method in addition to the Lorenz gauge condition and Maxwell's equations are used to determine the Cartesian components of the incident radiated electric field of the Bessel-Gauss light-sheets. In the framework of the dipole approximation, the numerical results for the Cartesian components of the optical radiation force and spin torque vectors show that negative forces (oriented in the opposite direction of wave motion) and spin torques arise depending on the beam parameters, the orientation of the subwavelength spheroid in 3D space, and its aspect ratio (i.e., prolate versus oblate). The spin torque sign reversal reveals that counter-clockwise or clockwise rotations around the center of mass of the spheroid can occur. The results find important applications in the application of auto-focusing light-sheets in particle manipulation, rotation, and optical sorting devices.

Interaction of Bessel pincers light-sheets with an absorptive subwavelength sphere coated by a plasmonic layer

The interaction of Bessel pincers light-sheets (i.e., finite optical beam “slices” in 2D) with a light-absorptive subwavelength sphere coated by a plasmonic layer in vacuum is examined in the framework of the electric dipole approximation. The vector angular spectrum decomposition method in addition to the Lorenz gauge condition and Maxwell’s equations are used to determine the Cartesian components of the incident radiated electric field of the Bessel pincers light-sheets. Two main effects are thoroughly investigated from the standpoint of the optical radiation force and spin torque theories. The numerical results for the optical radiation force and spin torque components show that a plasmonic layer of optimal thickness coating a small sphere can enhance the longitudinal and transverse force components as well as the axial spin torque induced by Bessel pincers light-sheets at the plasmonic resonance. Moreover, sign reversal of the longitudinal force component is manifested off the plasmonic resonance, resulting in particle trapping in a confined region in space. An axial spin torque sign reversal also occurs, which induces counterclockwise or clockwise rotation around the center of mass of the coated absorptive sphere depending on its position in the cross-sectional transverse plane. Furthermore, based on Newton’s second law of motion, a particle dynamics numerical analysis is performed, which reveals the emergence of retrograde motions of the coated sphere off-resonance as well as complex non-rectilinear/wiggly trajectories depending on its position in the transverse cross-sectional plane. At the plasmonic resonance, the coated sphere is propelled away from the source in the transverse cross-sectional plane along quasi-rectilinear trajectories. The results find related applications using autofocusing Bessel pincers light-sheets in particle manipulation and optical sorting devices.

Pulling and spinning reversal of a subwavelength absorptive sphere in adjustable vector Airy light-sheets

In the framework of the electric dipole approximation, this work demonstrates the generation of a pulling/attractive longitudinal force and an axial spin torque sign reversal causing counterclockwise or clockwise rotation of a subwavelength absorptive sphere placed in adjustable Airy light-sheets. Based on the vector angular spectrum decomposition method, the Lorenz gauge condition and Maxwell's equations, the Cartesian components of the incident radiated electric field of the generalized adjustable solution are derived, for which the main maximum Airy-lobe (i.e. caustic) is translated in space. The results find potential applications in the design/manufacture of particle manipulation and optical sorting devices using adjustable Airy-light sheets.

Optical torque on a magneto-dielectric Rayleigh absorptive sphere by a vector Bessel (vortex) beam

The optical torque exerted on an absorptive megneto-dielectric sphere by an axicon-generated vector Bessel (vortex) beam with selected polarizations is investigated in the framework of the dipole approximation. The total optical torque is expressed as the sum of orbital and spin torques. The axial orbital torque component is calculated from the z-component of the cross-product of the vector position r and the optical force exerted on the sphere F. Depending on the beam characteristics (such as the half-cone angle and polarization type) and the physical properties of the sphere, it is shown here that the axial orbital torque vanishes before reversing sign, indicating a counter-intuitive orbital motion in opposite handedness of the angular momentum carried by the incident waves. Moreover, analytical formulas for the spin torque, which is divided into spin torques induced by electric and magnetic dipoles, are derived. The corresponding components of both the optical spin and orbital torques are numerically calculated, and the effects of polarization, the order of the beam, and half-cone angle are discussed in detail. The left-handed (i.e., negative) optical torque is discussed, and the conditions for generating optical spin and orbital torque sign reversal are numerically investigated. The transverse optical spin torque has a vortex-like character, whose direction depends on the polarization, the half-cone angle, and the order of the beam. Numerical results also show that the vortex direction depends on the radial position of the particle in the transverse plane. This means that a sphere may rotate with different directions when it moves radially. Potential applications are in particle manipulation and rotation, single beam optical tweezers, and other emergent technologies using vector Bessel beams on a small magneto-dielectric (nano) particle.

Negative radiation torque using “acoustical sheets”

An interesting effect of negative acoustical radiation torque generation and direction reversal of the spinning of an absorptive cylinder is reported [F.G. Mitri, Wave Motion 66, 31-44 (2016)]. The emergence of the acoustic spin radiation torque experienced by the circular cylinder in a nonviscous host fluid is a consequence of acoustic attenuation inside its absorptive material. Depending on the direction of the shift from the center of a focused Hermite-Gaussian “acoustical-sheet” beam of first-order, the spin torque is negative or positive, causing the rotation of the cylinder in the polar plane in either the clockwise or the anticlockwise direction, respectively. Notice that at the center of the beam, the torque vanishes as required by symmetry. In the off-axial configuration, the spin torque sign reversal is dependent on the variation of absorption of both the longitudinal and shear waves inside the viscoelastic material. The effect of changing the non-dimensional size parameter ka (where k is the wa...

Magnetic and Transport Properties of π–d System κ-(BDH-TTP)2FeCl4

Resistance, magnetic susceptibility, magnetic torque, and ESR measurements have been performed to investigate the electronic state of the two-dimensional organic conductor κ-(BDH-TTP)2FeCl4. The temperature dependence of the resistance shows monotonic metallic behavior down to 30 mK, and the magnetic susceptibility, arising mainly from the Fe \(3d\) spins, follows the Curie–Weiss law down to 2 K. At low temperatures below 0.4 K, the magnetic torque steeply changes at low magnetic fields, associated with a sign change. The systematic measurements elucidate that the \(3d\) spins undergo an antiferromagnetic order at about 0.4 K and that the torque sign change is caused by a spin-flop transition. A rapid decrease of the magnetoresistance at the spin-flop field provides clear evidence of a finite π–\(d\) interaction. Characteristic temperature dependences of the magnetic susceptibility and ESR \(g\)-value are found in the paramagnetic phase, which are explained in terms of the single-ion anisotropy effect.

Identifying Leading Joint Strategies in a Bimanual Coordination Task: Does Coordination Stability Depend on Leading Joint Strategy?

ABSTRACT The authors sought to determine if principles of the Leading Joint Hypothesis, when applied to a multijoint, bimanual coordination task, could provide insight into the contribution of intralimb dynamics to interlimb coordination. Participants repetitively traced ellipse templates with an isodirectional motion of the end effectors (both hands moving counterclockwise [CCW]) at two cycling frequencies. Ellipse templates were oriented either tilted right or tilted left, yielding a total of 4 left arm–right arm leading-joint combinations. Analysis of torque sign and impulse data indicated that the 4 ellipse-tracing conditions resulted in 4 distinct left arm–right arm leading-joint combinations: 2 conditions with similar leading joints and 2 conditions with different leading joints. Isodirectional CCW ellipse tracing was more stable when produced with similar leading joints compared with when produced with different leading joints. The authors discuss results within the context of intralimb control contributions to the stability of interlimb coordination patterns.

The co-orbital corotation torque in a viscous disk: Numerical simulations

The torque felt by a non-accreting protoplanet on a circular orbit embedded in a uniform surface density protoplanetary disk is analyzed by means of time-dependent numerical simulations. Varying the viscosity enables one to disentangle the Lindblad torque (which is independent of viscosity) from the corotation torque, which saturates at low viscosity and is unsaturated at high viscosity. The dependence of the corotation torque upon the viscosity and upon the width of the librating zone is compared with previous analytical expressions, and shown to be in agreement with those. The effect of the potential smoothing respectively on the Lindblad torque and on the corotation torque is investigated, and the question of whether 3D effects and their impact on the total torque sign and magnitude can be modeled by an adequate smoothing prescription in a 2D simulation is addressed. As a side result, this study shows that the total torque acting on a Neptune-sized protoplanet is positive in a sufficiently thin, viscous disk (H/r < 4%, \alpha > 10^-2), but the inward migration time of smaller bodies is still very short, making it unlikely that they reach the torque reversal mass before having migrated all the way to the central object.

Transverse vibration of a rotor system driven by Cardan joints. (3rd report. Influence of initial intersecting angle and sign of torque).

The torque-induced transverse vibration of rotor systems driven by Cardan joints with with initial intersecting angles is analyzed. Three systems, MR2, MR4, SR4 models are analyzed. MR2 and MR4 are models for working machines such as the compressor and SR4 is for transmission shafts. The analysis proves that the initial intersecting angle induces parametric terms of frequency 4ν(νis frequency of shaft rotation) in addition to 2ν, which is induced when there is no initial intersecting angle. The 4νterms make the system unstable especially in the low-speed range. MR2 and MR4 models are shown to have quite different instability boundaries, depending on the sign of torque. The parametric tems of SR4 have no principal parametric instability region. SR4 is more stable than MR4.

Torque exerted on anisotropic magnetic medium by electromagnetic wave

The possibility of exerting a torque with a nonzero time average value as a result of interaction of a plane electro-magnetic wave with anisotropic magnetic medium is discussed. The torque per unit volume produced by the action of the magnetic field on the magnetization of the medium is T = M \times H and it arises from the fact that the vector of magnetization M is in general not parallel to the magnetic field intensity H . Three cases of magnetic media are distinguished: 1) medium with a natural or static anisotropy, 2) gyrotropic medium, 3) medium with shape anisotropy. In the first case, the lossless medium having a permeability \mu x, \mu y in the x and y directions perpendicular to the direction of electromagnetic plane wave propagation, the maximum of the torque per unit area corresponds to the thickness of the section \Delta z = \lambda_{0}/2(nx - ny) , where nx,ny are the refraction constants of the medium, and the sign of torque is opposite in the neighboring sections. In the case of a gyrotropic medium characterized by Polder's permeability tensor, it can be shown that the average value of torque exerted on a lossless medium by a plane wave propagating in the direction of dc magnetic field is zero. The nonzero average value of torque exists in the case of gyrotropic medium with losses as in the third case when a plane linearly polarized wave propagates along a ferrite cylinder with elliptical cross section. The results of not yet finished experimental investigations, which had to confirm the possibility of utilization of the torque for the construction of a feed-through wattmeter for the measurement of microwave power in the X band, are shown at the end of the paper.