Intrinsic Damping Research Articles

Theoretical Study of Fast Calculation of Damping Loss Factors for Rubber Polymers.

Rubber polymers as acoustic damping materials are widely used in industrial sectors. However, there is still no theoretical method to rapidly predict the damping properties of rubber polymers. Here we propose a theoretical method for the fast calculation of damping loss factors in rubber polymers. Molecular dynamics simulations were employed to construct the optimal configuration of internal polymer chains with density as the descriptor in order to calculate the mechanical properties and thus the damping loss factors. The acceptable difference between the calculated and experimental damping loss factors shows that the proposed method is efficient to predict the intrinsic damping properties of rubber polymers. Through studying the relationship among composition, microstructure, and the damping property, we found that the carbon-carbon skeletal chains with lateral methyl groups produce high damping properties.

Momentum-Dependent Magnon Lifetime in the Metallic Noncollinear Triangular Antiferromagnet CrB_{2}.

Noncollinear magnetic order arises for various reasons in several magnetic systems and exhibits interesting spin dynamics. Despite its ubiquitous presence, little is known of how magnons, otherwise stable quasiparticles, decay in these systems, particularly in metallic magnets. Using inelastic neutron scattering, we examine the magnetic excitation spectra in a metallic noncollinear antiferromagnet CrB_{2}, in which Cr atoms form a triangular lattice and display incommensurate magnetic order. Our data show intrinsic magnon damping and continuumlike excitations that cannot be explained by linear spin wave theory. The intrinsic magnon linewidth Γ(q,E_{q}) shows very unusual momentum dependence, which our analysis shows to originate from the combination of two-magnon decay and the Stoner continuum. By comparing the theoretical predictions with the experiments, we identify where in the momentum and energy space one of the two factors becomes more dominant. Our work constitutes a rare comprehensive study of the spin dynamics in metallic noncollinear antiferromagnets. It reveals, for the first time, definite experimental evidence of the higher-order effects in metallic antiferromagnets.

Effects of age and sex on trunk motor control

The goal of the present study was to assess the effects of age and sex on trunk motor control. Fifty healthy adults (aged between 19 and 67 years, 28 males) participated in this study. Trunk motor control was assessed using force-controlled perturbations directly applied to the trunk. Admittance (inverse of lumped intrinsic and reflexive impedance) decreased with age and tended to be lower in females than males. The age effect on admittance was due to increasing intrinsic stiffness and damping with age, while intrinsic damping and position- and velocity feedback gains were lower in females than males. Feedback delays were not dependent on age. The decrease of trunk admittance with age is most likely due to increasing levels of antagonistic co-activation. Trunk admittance was (just) not significantly different between females and males, in spite of lower feedback gains and damping, possibly due to differences in trunk mass between sexes. These results imply that age and sex differences should be considered when assessing the relationship between back pain and trunk motor control.

Dynamic magnetic properties of amorphous Fe80B20 thin films and their relation to interfaces

We present a ferromagnetic resonance study of the dynamic properties of a set of amorphous Fe-B films deposited on Corning Glass® and MgO (001) substrates, either with or without capping. We show that the in plane anisotropy of the MgO grown films contains both uniaxial and biaxial components whereas it is just uniaxial for those grown on glass. The angular dependence of the linewidth strongly differs in terms of symmetry and magnitude depending on the substrate and capping. We discuss the role of the interfaces on the magnetization damping and the generation of the anisotropy. We obtained values of the intrinsic damping parameters comparable to the lowest ones reported for amorphous films of similar compositions.

Nanoplasmonic Light Trapping Metascreen Encompassing Spectrally Dense Region of Solar Spectrum

An energy efficient nanoplasmonic metascreen is tailored to support near perfect absorption of sunlight around visible frequency range. To efficiently tap sunlight source, the metascreen is designed to perfectly absorb a spectrally dense region of solar spectrum. The absorption efficiency depends upon the choice of plasmonic material and optical thickness of the dielectric substrate between the metascreen and ground reflector. Alternative plasmonic materials including copper and aluminum are evaluated for their absorption characteristics, and their performance is compared to that of conventional gold and silver. Intrinsic surface plasmon resonance damping in copper-based metascreen platform is ideally suited to absorb an overall 72% of solar spectral irradiance between 400 and 1800 nm wavelength. The proposed polarization independent metascreen absorber can efficiently trap light to improve overall efficiency of solar cell.

Harmonic resonances of graphene-reinforced nonlinear cylindrical shells: effects of spinning motion and thermal environment

This work investigates nonlinear harmonic resonance behaviors of graded graphene-reinforced composite spinning thin cylindrical shells subjected to a thermal load and an external excitation. The volume fraction of graphene platelets varies continuously in the shell’s thickness direction, which generates position-dependent useful material properties. Natural frequencies of shell traveling waves are derived by considering influences of the initial hoop tension, centrifugal and Coriolis forces, thermal expansion deformation, and thermal conductivity. A new Airy stress function is introduced. Harmonic resonance behaviors and their stable solutions for the spinning cylindrical shell are analyzed based on an equation of motion which is established by adopting Donnell’s nonlinear shell theory. The necessary and sufficient conditions for the existence of the subharmonic resonance of the spinning composite cylindrical shell are given. Besides the shell’s intrinsic structural damping, the Coriolis effect due to the spinning motion has a contribution to the damping terms of the system as well. Comparisons between the present analytical results and those in other papers are made to validate the existing solutions. Influences of main factors on vibration characteristics, primary resonance, and subharmonic resonance behaviors of the novel composite cylindrical shell are discussed. Furthermore, the mechanism of how the spinning motion affects the amplitude–frequency curves of harmonic resonances of the cylindrical shell is analyzed.

Three-dimensional vibrations of multilayered hollow spheres submerged in a complex fluid

Fluid–structure interaction is fundamental to the characteristics of the induced flows due to the motion of structures in fluids and also is crucial to the performance of submerged structures. This paper presents a three-dimensional analytical study of the intrinsic free vibration of an elastic multilayered hollow sphere interacting with an exterior non-Newtonian fluid medium. The fluid is assumed to be characterized by a compressible linear viscoelastic model accounting for both the shear and compressional relaxation processes. For small-amplitude vibrations, the equations governing the viscoelastic fluid can be linearized, which are then solved by introducing appropriate potential functions. The solid is assumed to exhibit a particular material anisotropy, i.e. spherical isotropy, which includes material isotropy as a special case. The equations governing the anisotropic solid are solved in spherical coordinates using the state-space formalism, which finally establishes two separate transfer relations correlating the state vectors at the innermost surface with those at the outermost surface of the multilayered hollow sphere. By imposing the continuity conditions at the fluid–solid interface, two separate analytical characteristic equations are derived, which characterize two independent classes of vibration. Numerical examples are finally conducted to validate the theoretical derivation as well as to investigate the effects of various factors, including fluid viscosity and compressibility, fluid viscoelasticity, solid anisotropy and surface effect, as well as solid intrinsic damping, on the vibration characteristics of the submerged hollow sphere. Particularly, our theoretically predicted vibration frequencies and quality factors of gold nanospheres with intrinsic damping immersed in water agree exceptionally well with the available experimentally measured results. The reported analytical solution is truly and fully three-dimensional, covering from the purely radial breathing mode to the torsional mode to any general spheroidal mode as well as being applicable to various simpler situations, and hence can be a broad-spectrum benchmark in the study of fluid–structure interaction.

High spin-wave propagation length consistent with low damping in a metallic ferromagnet

We report ultralow intrinsic magnetic damping in Co25Fe75 heterostructures, reaching the low 10-4 regime at room temperature. By using a broadband ferromagnetic resonance technique in out-of-plane geometry, we extracted the dynamic magnetic properties of several Co25Fe75-based heterostructures with varying ferromagnetic layer thicknesses. By measuring radiative damping and spin pumping effects, we found the intrinsic damping of a 26 nm thick sample to be α 0 ≲ 3.18 × 10-4. Furthermore, using Brillouin light scattering microscopy, we measured spin-wave propagation lengths of up to (21 ± 1) μm in a 26 nm thick Co25Fe75 heterostructure at room temperature, which is in excellent agreement with the measured damping.

Piezostrain modulation of magnetic damping in MBE-grown epitaxial Co2FeAl/GaAs heterostructure

The electric voltage manipulated magnetic dynamic properties of Co2FeAl/GaAs heterostructure bonded on PbZr1−xTixO3 piezoelectric substrate were investigated using the time-resolved magneto-optical Kerr effect technique at room temperature. The butterfly-like response of precession frequency dependence on the applied electric field was observed with no external magnetic field applied, indicating efficient manipulation of precession frequency solely by piezostrain. The magnetic damping of Co2FeAl was observed to be enhanced (decreased) under the strengthened compressive (tensile) strain modulation. The observed efficient tuning of both precession frequency and extrinsic damping constant at low magnetic fields is attributed to piezostrain modulated magnetic anisotropy value and its inhomogeneous distribution. When the magnetic dynamics is governed by the external magnetic field at high-field regime, electric field tunability of precession frequency and damping constant becomes weaker and the intrinsic damping constant shows no modulation. The electric voltage tuning of magnetic damping and the associated physical mechanism presented in this work can help designing strain-mediated low-energy cost spintronic devices.

Study effect of the back irons in passive magnetic bearings with alternating radially magnetized rings by using 2D analytical method

PurposePermanent magnet passive magnetic bearings (PMBs) are used for suspension of rotating shafts in one direction. PMBs with alternating radially magnetized rings having back iron is one of the most optimum configurations among all configurations of PMBs. This paper aims to investigate the effect of the conductivity and permeability of these back irons on the stiffness and damping of the configuration.Design/methodology/approachThe stiffness and damping of the configuration will be calculated through a 2D dynamic analytical method and validated by FEM simulations.FindingsThe results of the paper show how the permeability and conductivity of the back irons can affect stiffness and damping of PMB. Furthermore, the size of the magnets and the air intervals between them are optimized for maximum stiffness and damping.Originality/valueThe results show that these bearings can have some intrinsic damping without any loss of stiffness, which can be useful for many applications.

Steady-State Error Suppression and Simplified Implementation of Direct Source Current Control for Matrix Converter With Model Predictive Control

A matrix converter (MC) with model predictive control based on the source reactive power control usually fails to show sinusoidal source currents. The analysis presented in this paper shows that this common combination of a converter and control has the inherent inability to suppress some harmonics in the source currents, even with additional passive or active damping control. Direct source current control can be implemented to give sinusoidal source currents and intrinsic active damping. However, the issue of steady-state error in output currents then arises, as the MC topology does not allow of the independent control of source and output currents. Therefore, feedback control of load active power is proposed to address this issue without degrading the fast dynamic performance. Benefiting from the direct source current control, a simplified implementation is also proposed to decrease the number of candidate switching states from 27 to 5, which significantly reduces the computational burden. Experimental results have verified the theoretical analysis and the effectiveness of the proposed control scheme.

Tuning of the intrinsic magnetic damping parameter in epitaxial CoNi(001) films : Role of the band-filling effect

The band-filling effect, which is due to tuning the electron occupation number near the Fermi level, on the intrinsic magnetic damping parameter is demonstrated by employing high-quality epitaxial ${\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}$ alloy films, in which the Fermi level and the density of states can be continuously tuned by varying the Ni concentration $x$. The intrinsic magnetic damping parameter, measured by the time-resolved magneto-optical Kerr effect, changes weakly at small $x$ and increases sharply for $x>0.80$. The experimental results are well reproduced by the density functional theory calculation. More interestingly, the magnetic damping parameter and the density of states near the Fermi level share similar variation trends, demonstrating their correlation. The band-filling effect in $3d$ magnetic transition metal alloys provides a way to tune the magnetic damping parameter as a key element in the controlg of energy loss and speed of spintronic devices.

A novel method for dynamic characterization of angular displacement-dependent viscoelastic properties of magnetorheological elastomer under torsional loading conditions

The dynamic properties of magnetorheological elastomers are predominantly affected by variation in the input displacements. The displacement-dependent characteristics have been extensively studied under lateral shear, but the property variations under torsional shear have not been explored. The present study focuses on developing a novel method to study the influence of angular displacement on the dynamic properties of magnetorheological elastomers under torsional loading conditions. The experimental setup is developed according to the ISO 10846-2 standard to evaluate the variations in the dynamic torsional stiffness and loss factor. Experiments are conducted for input angular displacements ranging from 0.002 to 0.016 rad for an input frequency between 10 and 30 Hz. Results highlight the effectiveness of the developed method in capturing the rheological properties under torsion. Variations in the dynamic torsional stiffness suggest the dominant behaviour of the input angular displacement. The bound rubber theory is used to interpret the angular displacement dependent variations on the torsional stiffness. Further, the effect of input frequency and magnetic field on the dynamic torsional stiffness is also examined. It is also observed that the damping capacity of the MRE is dependent on the angular displacement and the dissipation capacity of the elastomer is evaluated in terms of loss factor. Results indicate a significant contribution of the interfacial damping over the intrinsic and magneto-mechanical hysteresis damping.

Effect of Ga composition on the static and dynamic magnetic properties of Fe100-Ga films (18.5 ≤ x ≤ 33.4)

Abstract This paper describes the effect of Ga composition (x) on the static and dynamic magnetic properties of 50-nm-thick Fe100-xGax films (18.5 ≤ x ≤ 33.4). The in-plane damping constant (α//), the perpendicular (out-of-plane) damping constant (α⊥), the saturation magnetostriction (λs) and the maximum piezomagnetic coefficient ((dλ/dH)max) of these films are dependent on x, whereas the tendencies of α// and α⊥ for x are quite opposite to those of λs and (dλ/dH)max for x. For every x, the value of α// is much larger than that of α⊥, suggesting that both the intrinsic damping and the extrinsic damping coexists in the in-plane dynamics of each Fe100-xGax film because of magnetic inhomogeneities such as two magnon scattering, anisotropy dispersion and so on. These results also demonstrate that only the intrinsic damping contributes to the out-of-plane dynamics of each Fe100-xGax film.

Enhancement of intrinsic magnetic damping in defect-free epitaxial Fe3O4 thin films

We have investigated the magnetic damping of precessional spin dynamics in defect-controlled epitaxial grown Fe3O4(111)/Yttria-stabilized Zirconia nanoscale films by all-optical pump-probe measurements. The intrinsic damping constant of the defect-free Fe3O4 film is found to be strikingly larger than that of the as-grown Fe3O4 film with structural defects. We demonstrate that the population of the first-order perpendicular standing spin wave (PSSW) mode, which is exclusively observed in the defect-free film under sufficiently high external magnetic fields, leads to the enhancement of the magnetic damping of the uniform precession (Kittel) mode. We propose a physical picture in which the PSSW mode acts as an additional channel for the extra energy dissipation of the Kittel mode. The energy transfer from the Kittel mode to the PSSW mode increases as in-plane magnetization precession becomes more uniform, resulting in the unique intrinsic magnetic damping enhancement in the defect-free Fe3O4 film.

Abnormal anticrossing effect in photon-magnon coupling

We report the experimental demonstration of an abnormal, opposite anti-crossing effect in a photon-magnon-coupled system that consists of an Yttrium Iron Garnet film and an inverted pattern of split-ring resonator structure (noted as ISRR) in a planar geometry. It is found that the normal shape of anti-crossing dispersion typically observed in photon-magnon coupling is changed to its opposite anti-crossing shape just by changing the position/orientation of the ISRR's split gap with respect to the microstrip line axis along which ac microwave currents are applied. Characteristic features of the opposite anti-crossing dispersion and its linewidth evolution are analyzed with the help of analytical derivations based on electromagnetic interactions. The observed opposite anti-crossing dispersion is ascribed to the compensation of both intrinsic damping and coupling-induced damping in the magnon modes. This compensation is achievable by controlling the relative strength and phase of oscillating magnetic fields generated from the ISRR's split gap and the microstrip feeding line. The position/orientation of an ISRR's split gap provides a robust means of controlling the dispersion shape of anti-crossing and its damping in a photon-magnon coupling, thereby offering more opportunity for advanced designs of microwave devices.

Microstructural and magnetic properties of rGO/MnFe2O4 nanocomposites; relaxation dynamics

In the present investigation, nanocomposite (NC) of reduced graphene oxide (rGO) and manganese ferrite (MnFe2O4) with three different (rGO/MnFe2O4) weight-ratio of rGO have been synthesized using a simple and efficient one-step hydrothermal route. The crystallinity, morphology and magnetic studies were conducted using X-ray diffraction (XRD), confocal Raman imaging and vibrating sample magnetometry (VSM).Detailed ferromagnetic resonance (FMR) studies were performed in the field-sweep mode at different applied frequencies ranging from 5 to 30 GHz using a vector network analyzer (VNA). We have realized a nano-composite layer of rGO/MnFe2O4 NC on top of coplanar waveguide (CPW) transmission lines to perform FMR experiments. The largest ferromagnetic resonance (FMR) absorption of −28 dB was observed for 0.06 g GO doped MnFe2O4 at the 22 GHz frequency. This absorption at FMR is found to be tunable by rGO concentration in manganese ferrite. We have also evaluated various relaxation/damping parameters of the nanocomposites. The experimental values of FMR linewidths were fitted using two micromagnetic models, and hence intrinsic and extrinsic damping parameters were obtained for nanocomposite samples. The damping parameters were observed to influenced by the rGO weight ratio. Therefore the developed nanocomposite can find various applications in the area of microwave monolithic devices and circuits like filters, phase shifters, circulators, etc.

Novel liner concepts

Modern, low-emission aero-engine concepts, such as, for instance, Ultrahigh-Bypass Ratio (UHBR) designs, claim higher demands on the damping performance of acoustic wall treatment, called liner, installed in the engine. New liner concepts are needed providing a more broadband damping efficiency ranging explicitly to the low-frequency range. However, space and weight constrains are still also one of the crucial criteria which need to be fulfilled by the liner structure. To overcome this challenge, two novel liner concepts are presented here. One concept, the hybrid ZML, combines the classical Single-Degree-of-Freedom (SDOF) liner with a Zero-Massflow-Liner (ZML) principle. The other one, the FlexiS concept, takes advantage of the intrinsic material damping of flexible walls within the liner structure. A proof of concepts study of both novel concepts is provided highlighting the enhanced damping performance with respect to broadband capacity and low-frequency damping.

Tunable specific-loss power of magnetic nano-spheres in vortex state for high-efficiency hyperthermia bio-applications: A theoretical and simulation study

We explored the reliable control of high-efficiency specific-loss power (SLP) using magnetic nanoparticles in the vortex state, where the value of power is one order of magnitude higher than those of the conventional mechanisms of SLP reported thus far. The underlying mechanism is based on the precession of a single vortex core and subsequent dissipation due to the intrinsic damping when the vortex-state spheres are resonantly excited. Owing to the dynamic characteristics of vortex-state nanoparticles, the resonant excitation of vortex-core precession is variable with particle size as well as tunable by the size-specific resonant frequency and strength of ac magnetic fields applied to the particles. The ac magnetic-field energy absorbed by the particles can be converted very efficiently to other energy forms such as heat. We derived, semi-analytically and by micromagnetic simulations, the quantitative relationships of the SLP quantity with the particle size and intrinsic damping constant of nanoparticles, and with externally controllable parameters including the frequency and strength of ac magnetic fields and dc magnetic-field strength. This work provides a reliable means of control as well as an optimal design of high-value SLPs for high-efficiency hyperthermia bio-applications.

Perfect absorption of water waves by linear or nonlinear critical coupling

We report on experiments of perfect absorption for surface gravity waves impinging a wall structured by a subwavelength resonator. By tuning the geometry of the resonator, a balance is achieved between the radiation damping and the intrinsic viscous damping, resulting in perfect absorption by critical coupling. Besides, it is shown that the resistance of the resonator, hence the intrinsic damping, can be controlled by the wave amplitude, which provides a way for perfect absorption tuned by nonlinear mechanisms. The perfect absorber that we propose, without moving parts or added material, is simple and robust and presents a deeply subwavelength ratio wavelength/thickness of ≃18.