Asymmetric Hysteresis Research Articles

Magnetic dynamics of NiMn2O4 spinel produced by a simple aqueous sol–gel route

Polycrystalline nickel manganite was prepared by a simple sol–gel method from an aqueous solution of metal chlorides containing sorbitol as a chelating agent. X-ray diffraction and Rietveld refinement show a spinel-type crystalline structure, space group Fd3¯m, and a minor (~3%) phase of rock salt structure assigned to NiO. XPS measurement shows a typical manganite electronic structure with Mn in the oxidation states Mn2+, Mn3+, and Mn4+. The zero-field-cooled and field-cooled magnetization curves measured under low magnetic fields display irreversibility and an asymmetric hysteresis evidencing some exchange bias. Field dependent DC susceptibility above Curie temperature put into evidence a competition of short ranged ferro and antiferromagnetic interactions. AC in-phase susceptibility shows a frequency independent sharp peak at the ferromagnetic phase transition (97 K) and a broad maximum at lower temperature. These maxima show a weak frequency dependence in the out-phase component. Cole–Cole plot reveals at least two magnetic relaxation processes.

Design, Fabrication, and Hysteresis Modeling of Soft Microtubule Artificial Muscle (SMAM) for Medical Applications

Robotic artificial muscles (RAMs) are promising power sources for medical fields such as surgical robotics. However, existing RAMs are challenged by scalability, material costs and fabrications. The nonlinear hysteresis in fluid-driven RAMs causes oscillations in open-loop systems. To circumvent these limitations, this letter introduces hydraulically soft microtubule artificial muscle (SMAM) that is low-cost and scalable, yet simple to fabricate. The SMAM, which only requires a flexible silicone microtube and a hollow micro-coil, is elongated or contracted under a fluid pressure. The SMAM presents an ideal candidate for flexible robotic systems such as endoscopic surgical robots. Experiments are conducted to characterize the SMAMs. Results show that the hysteresis profiles between the input syringe plunger position and output position are stable regardless of its configuration, as opposed to the highly variable responses for the tendon-sheath mechanisms. A new nonlinear model is developed to characterize the asymmetric hysteresis phenomena of the SMAM. Compared to the Bouc-Wen hysteresis models, the developed model presents a better capture of hysteresis. To demonstrate the muscle capability, a SMAMs-driven pulley and a flexible surgical arm are given. The new SMAM and its asymmetric hysteresis model are expected to provide a path for the development of rapidly efficient and low-cost soft actuators for use in flexible medical devices and surgical robotic systems.

Design and dynamic modeling of a continuum and compliant manipulator with large workspace

This paper focuses on the design and dynamic modeling of a novel multi-section continuum and compliant robotic manipulator with large workspace. In large scales, many of the design techniques and actuator types which have proved advantageous in creating continuum robots at smaller scales are not applicable. Fluidic muscles, a class of pneumatic muscle actuators (PMAs) with large scale movements, high actuation forces and compliant nature, are utilized in the design of the continuum manipulator. However, these actuators are capable of applying axial contracting forces and cannot produce bending movements. Moreover, their asymmetric hysteresis nonlinearity causes difficulties in the accurate control procedure. These drawbacks are addressed in the design and presented model of the manipulator. The presented model is based on constant curvature method and concentrated masses. The Bouc–Wen hysteretic function is modified to describe the asymmetric force/length hysteresis of the utilized PMAs in this model. Experimental results show that the proposed model has a proper performance to characterize the asymmetric hysteresis loop of the actuators. Finally, the design and dynamic model of the robot are validated experimentally on the implemented manipulator.

Modelling and identification of the asymmetric hysteresis in the viscoelastic response of the fingertip under indentation: A multistate friction model with switching parameters

This paper presents a dynamic model for the identification of asymmetric hysteresis in the force response of the fingertip under cyclic local deformation of the fingertip soft tissues. Viscoelastic effects, marked anisotropy and nonlinearity contribute to the hysteretic behaviour of the force of the fingertip undergoing indentation. The fingertip force in response to an indentation stimulus varies along the loading and unloading cycles; the resulting hysteresis loops are asymmetric. The asymmetry arises from the simultaneous convexity of the branches of the hysteresis loop. The proposed model belongs to the class of multistate friction models that can effectively describe the hysteresis in the presliding regime of motion of general mechanisms with friction, by exploiting a mechanical analogy obtained through the concatenation of multiple elasto-plastic elements. The multistate model, which provides the mechanical representation of the fingertip response through a set of newly-conceived switching elements and viscoelastic blocks, can reproduce the convex and asymmetric hysteresis loops of the fingertip mechanical response, including the viscoelastic effects of stress relaxation and the influence of time interval between consecutive cycles of indentation.The model has been validated through the experimental identification of fingertip indentation tests performed on an optomechanical test-rig. This model potentially opens the way for efficient model-based control strategies of servomechanisms involved in tactile and haptic displays and interfaces.

Magnetization Reversal in Concave Iron Nano-Superellipses

Square magnetic nanodots can show intentional or undesired shape modifications, resulting in superellipses with concave or convex edges. Some research groups also concentrated on experimentally investigating or simulating concave nano-superellipses, sometimes called magnetic astroids due to their similarity to the mathematical shape of an astroid. Due to the strong impact of shape anisotropy in nanostructures, the magnetization-reversal process including coercive and reversibility fields can be expected to be different in concave or convex superellipses than that in common squares. Here, we present angle-dependent micromagnetic simulations on magnetic nanodots with the shape of concave superellipses. While magnetization reversal occurs via meander states, horseshoe states or the 180° rotation of magnetization for the perfect square, depending on the angle of the external magnetic field, more complicated states occur for superellipses with strong concaveness. Even apparently asymmetric hysteresis loops can be found along the hard magnetization directions, which can be attributed to measuring minor loops since the reversibility fields become much larger than the coercive fields.

Ultraviolet Light-Responsive Photorheological Fluid for Sensors and Actuators Realized by Phosphorescence Effects and LSTM RNN

A photo-rheological fluid (PRF) is a smart fluid which exhibits different viscosity under UV irradiation. A PRF is comprehensively presented in this work, with particular focus on its responses under UV off/on conditions. The isomeric conversion from SP to MC and vice versa under UV off and on, respectively, showed unequal rates of transformation. As a result, a complex non-linear hysteretic response was observed. To be used indifferent types of sensors and actuators which can exploit its rheological properties, it is essential the PRF have linearized hysteresis behavior. To minimize the asymmetric non-linear hysteresis characteristics under UV on and off conditions, the well-known long-lasting phosphor SAO (SrAl2O4:Eu2+, Dy3+) was incorporated. The incorporation of SAO in the PRF improved the linearity of the PRF response, although the conversion rate was not identical under UV off/on conditions. The SAO particles were observed to settle over time due to phase splitting, undermining the usefulness of the SAO-PRF composite. Instead of improving the PRF response by further adjusting the PRF composite, a software approach based on Long Short-Term Memory Recurrent Neural Networks (LSTM RNN) was employed to model and compensate the asymmetric non-linear hysteresis response, ensuring the realization of sensors and actuators that exploit PRF as hardware.

Symmetry and asymmetry induced dynamics in a memristive twin-T circuit

ABSTRACT The dynamics of memristor–based chaotic oscillators with perfect symmetry is very well documented. However, the literature is relatively poor concerning the behaviour of such types of circuits when their symmetry is perturbed. In this paper, we consider the dynamics of a memristive twin-T oscillator . Here, the symmetry is broken by assuming a memristor with an asymmetric pinched hysteresis loop characteristics. A variable disturbance term is introduced into the current-voltage relationship of the memristor in order to obtain an asymmetric characteristic. Phase portraits, bifurcations, basins of attraction, and Lyapunov exponents are used to illustrate various nonlinear patterns experienced by the underlined memristive circuit. It is shown that in the absence of the disturbance term, the characteristic of the memristor is perfectly symmetric which induces typical behaviours such as coexisting symmetric bifurcation and bubbles, spontaneous symmetry-breaking, symmetry recovering, and coexistence of several pairs of mutually symmetric attractors. With the perturbation term, the symmetry of the oscillator is destroyed resulting in more complex nonlinear phenomena such as coexisting asymmetric bubbles of bifurcation, critical transitions, and multiple coexisting (i.e. up to five) asymmetric attractors. Also, PSpice simulation studies confirm well the results of theoretical predictions.

Precise dynamic modeling of pneumatic muscle actuators with modified Bouw–Wen hysteresis model

Pneumatic muscle actuators (PMAs) are frequently used in a wide variety of biorobotic applications, such as robotic orthoses and wearable exoskeletons, due to their high power/weight ratio and significant compliance. However, the asymmetric hysteresis nonlinearity reduces their fidelity and cause difficulties in the accurate control procedure. In this paper, Bouc–Wen hysteresis model is modified to describe the asymmetric force/length hysteresis of the PMA. The effect of muscle length on hysteretic restoring force is considered in this modified model and experimental results show that the proposed model has a better performance to characterize the asymmetric hysteresis loop of pneumatic muscles. The nonlinear pressure/force model of these actuators also is modeled precisely and its performance is experimentally verified for different muscle lengths.

Asymmetric Hysteresis Loops in Structured Ferromagnetic Nanoparticles with Hard/Soft Areas

Horizontally shifted and asymmetric hysteresis loops are often associated with exchange-biased samples, consisting of a ferromagnet exchange coupled with an antiferromagnet. In purely ferromagnetic samples, such effects can occur due to undetected minor loops or thermal effects. Simulations of ferromagnetic nanostructures at zero temperature with sufficiently large saturation fields should not lead to such asymmetries. Here we report on micromagnetic simulations at zero temperature, performed on sputtered nanoparticles with different structures. The small deviations of the systems due to random anisotropy orientations in the different grains can not only result in strong deviations of magnetization reversal processes and hysteresis loops, but also lead to distinctly asymmetric, horizontally shifted hysteresis loops in purely ferromagnetic nanoparticles.

Impact of concrete strength on seismic behavior of T-shaped double-skin composite walls

This study investigates the seismic performance of T-shaped double-skin composite walls (DSCWs), which are comprised of double-skin composite flange and web walls and concrete filled steel tubular (CFST) boundary elements, through experimental tests. Six T-shaped DSCW specimens, which are categorized into three groups, according to flange width and type of mechanical connectors (shear studs/tie bars), are tested under combined axial compressive loads and lateral cyclic loads. The DSCWs fail in a ductile flexural mode with similar damage patterns, characterized by buckling of steel tubes and faceplates, concrete crushing, and fracture of steel tubes at the wall base, and exhibit asymmetric hysteresis behaviors, with higher stiffness and strength but lower deformation capacities when the flange walls are under tension. Special focus should be placed on the design of CFST boundary element connected to the web wall, whose compressive failure triggers the loss of load carrying capacity of the specimens. The comparisons between the behaviors of two specimens in each group, which are infilled with high strength (C70) and normal strength concrete (C30) respectively, suggest that employment of high strength concrete improves the seismic behavior of T-shaped DSCW significantly regardless of the flange wall width when shear studs are used. Tie bars may impair the seismic behaviors of DSCWs by inducing premature local buckling of perforated steel faceplates. Numerical studies are conducted using detailed finite element models to investigate the buckling behaviors of steel faceplates which are connected to infilled concrete by tie bars and shear studs. The simulation results reveal that the former buckles earlier than the latter due to smaller critical stress. The slenderness ratio limits to prevent local buckling prior to yielding of steel faceplates are also suggested when these two types of mechanical connectors are used.

Evolution of electromechanical properties in Fe-doped (Pb,Sr)(Zr,Ti)O3 piezoceramics

Defects in acceptor-doped perovskite piezoelectric materials have a significant impact on their electrical properties. Herein, the defect mediated evolution of piezoelectric and ferroelectric properties of Fe-doped (Pb,Sr)(Zr,Ti)O3 (PSZT-Fe) piezoceramics with different treatments, including quenching, aging, de-aging, and poling, was investigated systematically. Oxygen vacancies with a cubic symmetry are preserved in the quenched PSZT-Fe ceramics, rendering them robust ferroelectric behaviors. In the aged PSZT-Fe polycrystals, defect dipole between Fe dopant and oxygen vacancy has the same orientation with spontaneous polarization PS, which enables the reversible domain switching and hence leads to the emergence of pinched polarization hysteresis and recoverable strain effect. And the defect dipoles can be gradually disrupted by bipolar electric field cycling, once again endowing the aged materials with representative ferroelectric properties. For the poled PSZT-Fe polycrystals, the defect dipoles are reoriented to be parallel to the applied poling field, and an internal bias field aligning along the same direction emerges simultaneously, being responsible for asymmetric hysteresis loops.

On Stability of SDOF Systems with Asymmetric Bi-Linear Hysteresis Subjected to Seismic Excitations

This technical note presents a numerical study on the stability of single degree of freedom (SDOF) systems with asymmetric bi-linear hysteretic restoring force, subjected to earthquake excitations. The aim is to report: (a) the existence of an unstable behavior in the response of such systems, under a specific ground motion, given small modifications of the yielding conditions of the hysteresis model, and (b) the introduction of a novel three-dimensional graphic visualization of the problem. The modifications of the yielding conditions were introduced via the symmetry-breaking produced by very small variations of the static equilibrium position of the system, equivalent to having an initial position and restoring force different from zero and symmetric yielding. The concise study comprises of nonlinear dynamic analyses of three system cases, one of them with symmetric (reference) and two with asymmetric yielding conditions. The results show that the system presented a stable response and severe ratcheting toward the weakest yielding direction for the symmetric and asymmetric cases, respectively. Differences as large as [Formula: see text]% between the asymmetric and reference cases were obtained for the residual displacement of the systems, due to variations as small as [Formula: see text]% in the static-equilibrium position, and consequent [Formula: see text]% variations of the positive/negative yielding displacements and forces. In turn, negligible variations of the velocity between the three cases were predicted. To conclude, the paper introduces novel three-dimensional representations of the solution-curve and of the hysteresis cycles of the systems, deepening the discussion on the identified bifurcation. The 3D hysteresis curve, in particular, can be of much use for seismic engineering and mechanical studies, either numerical or experimental, as it allows visualizing the sequence of events in the hysteresis plots in a much clearer fashion compared to the traditional two-dimensional counterparts.

Development of Hybrid Prandtl–Ishlinskii and Constitutive Models for Hysteresis of Shape-Memory-Alloy-Driven Actuators

SUMMARY Prandtl–Ishlinskii (PI) model has an excellent compromise to characterize an asymmetric saturated hysteresis behavior of shape-memory-alloy (SMA)-driven systems, but it cannot consider thermomechanical relations between components of SMA-driven systems. On the other hand, constitutive models are composed of these relations, but their precision needs to be improved. In this paper, PI model is proposed to boost constitutive models in two cases. In the first case, PI model is used to characterize martensite volume fraction (MVF) called hybrid model. In the second case, the model is applied as a regulator in the output of a constitutive model called PI-based output (PIO) regulator. Due to simplicity and ability of Liang–Rogers (LR) model in transformation phases, it is considered as an MVF in the original constitutive model. The performance of both proposed models is compared with the original LR-based constitutive model. Unknown parameters of all three models are identified using genetic algorithm in MATLAB Toolbox. The performance of the three models is investigated at three different frequencies of \[\frac{{2\pi }}{8}\] , \[\frac{{2\pi }}{{15}}\] , and \[\frac{{2\pi }}{{30}}\] Hz because the excitation frequency changes the hysteresis behavior. Results show that the proposed hybrid model keeps the precision of the original constitutive model at different frequencies. In addition, the proposed PIO model shows the best performance to predict hysteresis behavior at different frequencies.

Dynamic exponential model of ferromagnetic hysteresis

We introduce a dynamic exponential model of ferromagnetic hysteresis that unifies the cooperative exponential model with the Néel fluctuating field, Jiles-Atherton approach to the anhysteretic and a Preisach convolution integral over a field distribution function. Dynamic effects such as viscous field advance and eddy current field delay are modeled directly by the model parameters. The dynamic effect of creeping in the direction of the previous maximum susceptibility due to viscosity as predicted by Street is observed and is modeled using the proposed method. Negative tilting of asymmetric minor hysteresis loops (lower susceptibility) with cycling is also observed and is also modeled using the proposed model as increased Néel's “opposition” in our cooperative field, Hcoop. Shearing of hysteresis loops is modeled as an averaging of the exponential model <Xexp> over viscous advance and eddy current delay fields, causing truncation and broadening. Detailed measurement procedures are described for a hollow cylinder and thin and thick rings of Fe94Ni3Cr2Mo1 steel with variable frequency sine, triangle and step field waveforms.

Exchange Bias in Thin Films—An Update

The exchange bias (EB) is an effect occurring in coupled ferromagnetic/antiferromagnetic materials of diverse shapes, from core–shell nanoparticles to stacked nanostructures and thin films. The interface coupling typically results in a horizontal—often also vertical—shift of the hysteresis loop, combined with an increased coercivity, as compared to the pure ferromagnet, and the possibility of asymmetric hysteresis loops. Several models have been developed since its discovery in 1956 which still have some drawbacks and some unexplained points, while exchange bias systems are at the same time being used in hard drive read heads and are part of highly important elements for spintronics applications. Here, we give an update of new theoretical models and experimental findings regarding exchange bias phenomena in thin films during the last years, including new material combinations in which an exchange bias was found.

Adaptive Pseudo Inverse Control for a Class of Nonlinear Asymmetric and Saturated Nonlinear Hysteretic Systems

This paper aims at eliminating the asymmetric and saturated hysteresis nonlinearities by designing hysteresis pseudo inverse compensator and robust adaptive dynamic surface control (DSC) scheme. The “pseudo inverse” means that an on-line calculation mechanism of approximate control signal is developed by applying a searching method to the designed temporary control signal where the true control signal is included. The main contributions are summarized as: 1) to our best knowledge, it is the first time to compensate the asymmetric and saturated hysteresis by using hysteresis pseudo inverse compensator because the construction of the true saturated-type hysteresis inverse model is very difficult; 2) by designing the saturated-type hysteresis pseudo inverse compensator, the construction of true explicit hysteresis inverse and the identifications of its corresponding unknown parameters are not required when dealing with the saturated-type hysteresis; 3) by combining DSC technique with the tracking error transformed function, the “explosion of complexity” problem in backstepping method is overcome and the prespecified tracking performance is achieved. Analysis of stability and experimental results on the hardware-in-loop platform illustrate the effectiveness of the proposed adaptive pseudo inverse control scheme.

Modeling of the dynamic hysteresis in DEAP actuator using an empirical mode decomposition based long-short term memory network

As a smart material-based actuator, the dielectric electro-active polymer (DEAP) actuator is widely considered to be a potential driving mechanism for many applications, especially in intelligent bio-inspired robotics. However, the DEAP actuator demonstrates rate-dependent and asymmetrical hysteresis phenomenon which leads to great tracking inaccuracy and even oscillatory response, severely limiting its further development. Feedforward Neural Network (FNN) model has already become a widely used method to describe this kind of strong hysteresis nonlinearity in recent years. However, the FNN has no ability to remember the historical state of long period of time which is also a very important factor to restrict hysteresis phenomenon. In this paper, a novel hybrid model, Long-Short Term Memory (LSTM) network combined with Empirical Mode Decomposition (EMD), is proposed to model the dynamic hysteresis nonlinearity in DEAP actuator. At first, the original control signal sequence is preprocessed into a series of sub-sequence by the EMD method and is reshaped by one-sided dead-zone operator. Then the input space of LSTM is conducted using the original control signal, the sub-sequence, and reshaped signal. Finally, the input space and the displacement signal are applied to train the long-short term memory network. In order to verify the performance of the proposed model, the traditional artificial back propagation neural network (BPNN) model, rate-dependent Prandtl-Ishlinskii (RPI) model, and nonlinear electromechanical (NEM) model are compared from prediction accuracy. The results demonstrate that: (1) the proposed model has a higher prediction accuracy than the traditional artificial BPNN, RPI, and NEM model; and (2) the prediction accuracy of LSTM network is significantly improved by using EMD. Therefore, the long-short term memory network combined with empirical mode decomposition is a competitive method compared to the existing state-of-the-art approach.

Modeling and Compensation for Asymmetrical and Dynamic Hysteresis of Piezoelectric Actuators Using a Dynamic Delay Prandtl-Ishlinskii Model.

Piezoelectric actuators are widely used in micro- and nano-manufacturing and precision machining due to their superior performance. However, there are complex hysteresis nonlinear phenomena in piezoelectric actuators. In particular, the inherent hysteresis can be affected by the input frequency, and it sometimes exhibits asymmetrical characteristic. The existing dynamic hysteresis model is inaccurate in describing hysteresis of piezoelectric actuators at high frequency. In this paper, a Dynamic Delay Prandtl–Ishlinskii (DDPI) model is proposed to describe the asymmetrical and dynamic characteristics of piezoelectric actuators. First, the shape of the Delay Play operator is discussed under two delay coefficients. Then, the accuracy of the DDPI model is verified by experiments. Next, to compensate the asymmetrical and dynamic hysteresis, the compensator is designed based on the Inverse Dynamic Delay Prandtl–Ishlinskii (IDDPI) model. The effectiveness of the inverse compensator was verified by experiments. The results show that the DDPI model can accurately describe the asymmetrical and dynamic hysteresis, and the compensator can effectively suppress the hysteresis of the piezoelectric actuator. This research will be beneficial to extend the application of piezoelectric actuators.

Spin Canting in Silica-Coated Nickel Ferrite (NiFe2O4@SiO2) Nanoparticles: a Mössbauer Spectroscopy Study

We present a comparative study on superparamagnetic uncoated and silica-coated NiFe2O4@SiO2 nanoparticles with identical NiFe2O4 cores and two different silica coating thicknesses, focusing on the surface spin arrangement on NiFe2O4. For the investigation of surface spin dynamics, in addition to the SQUID magnetometry experiments which probe the macroscopic behaviour of particle magnetization, Mossbauer spectroscopy was utilized as being a local technique with superior characteristic measurement time. It was revealed that two common aspects observed in nanoscaled magnetic particles, namely the surface spin canting and interparticle dipolar interactions, are intertwined with respect to their contributions to the total magnetic anisotropy, where the latter is significantly decreased with silica coating thickness and allowed surface effects to manifest itself in Mossbauer spectra. The reduced saturation magnetization of uncoated NiFe2O4 nanoparticles with respect to their bulk counterparts indicated the existence of a “magnetically dead” layer on NiFe2O4 surface. In opposite to some assumptions in the literature, the Mossbauer spectra confirmed that such reduced magnetization arises from spin disorder, rather than a change in coordination from inverse spinel to the mixed spinel structure. On the other side, emergence of broad sextet peaks at room temperature Mossbauer spectra showed that for NiFe2O4@SiO2 samples, silica coating further enhanced the spin canting on NiFe2O4 surface. Similarly, for NiFe2O4@SiO2 sample, an unusual asymmetric hysteresis loop at spin freezing temperature was observed as a signature of the existence of disordered spins in the SiO2/NiFe2O4 interface. It was shown that the sextet components in Mossbauer spectra can be reproduced with a continuous hyperfine field distribution due to the frustrated local spin arrangement at the surface. The thickness of the “magnetically dead” disordered surface spin layer was estimated for uncoated NiFe2O4, and average spin canting angle was calculated for NiFe2O4@SiO2 nanoparticles.

Accessing nanoscopic polarization reversal processes in an organic ferroelectric thin film.

Towards eliminating toxic substances from electronic devices, Croconic Acid (CA) has great potential as a sublimable organic ferroelectric material. While studies on CA thin films are just beginning to emerge, its capability to be integrated in nanodevices remains unexplored. We demonstrate at the laterally nanoscopic scale robust ferroelectric switching of a stable enduring polarization at room temperature in CA thin films, without leakage. The challenging ferroelectric characterization at the nanoscale is performed using a unique combination of piezoresponse force microscopy, polarization switching current spectroscopy and concurrent strain response. This helps rationalize the otherwise asymmetric polarization-voltage hysteresis due to background noise limited undetectable switching currents, which are statistically averaged in macrojunctions but become prevalent at the nanoscale. Apart from successfully estimating the nanoscopic polarization in CA thin films, we show that CA is a promising lead-free organic ferroelectric towards nanoscale device integration. Our results, being valid irrespective of the ferroelectrics' nature; organic or inorganic, pave the way for fundamental understandings and technological applications of nanoscopic polarization reversal mechanisms.