Electrical Degrees Of Freedom Research Articles

Dynamical electric characteristics of a quantum paramagnet

We consider the quantum paramagnet with the coupling between spin and electric degrees of freedom. The dynamical electric characteristics of the system under the action of the ac electric field are calculated. It is shown that for the closed system the quadrupole spin moment oscillates with the frequency of the ac field. The oscillations are modulated by the Rabi-like frequency, while the amplitude of the modulation is minimal at resonance, at which the frequency of the electric field is equal to the double energy of spin excitation of the paramagnet. The open system in the steady-state regime manifests only oscillations with the frequency of the ac field. The calculated dynamical electric susceptibility is nonzero only for nonzero dc magnetic field, and, depending on the values of the single-ion magnetic anisotropy, can manifest nonmonotonic dependence on temperature, dc electric and magnetic fields.

Multi-state data storage in a two-dimensional stripy antiferromagnet implemented by magnetoelectric effect

A promising approach to the next generation of low-power, functional, and energy-efficient electronics relies on novel materials with coupled magnetic and electric degrees of freedom. In particular, stripy antiferromagnets often exhibit broken crystal and magnetic symmetries, which may bring about the magnetoelectric (ME) effect and enable the manipulation of intriguing properties and functionalities by electrical means. The demand for expanding the boundaries of data storage and processing technologies has led to the development of spintronics toward two-dimensional (2D) platforms. This work reports the ME effect in the 2D stripy antiferromagnetic insulator CrOCl down to a single layer. By measuring the tunneling resistance of CrOCl on the parameter space of temperature, magnetic field, and applied voltage, we verified the ME coupling down to the 2D limit and probed its mechanism. Utilizing the multi-stable states and ME coupling at magnetic phase transitions, we realize multi-state data storage in the tunneling devices. Our work not only advances the fundamental understanding of spin-charge coupling, but also demonstrates the great potential of 2D antiferromagnetic materials to deliver devices and circuits beyond the traditional binary operations.

Nonlinear Dynamic Analysis of Hybrid Piezoelectric-Magnetostrictive Energy-Harvesting Systems

To progress the proficiency and broaden the action bandwidth of vibration energy harvesters, this paper presents a cantilever piezoelectric-magnetostrictive bistable hybrid energy harvester with a dynamic magnifier. The hybrid energy-harvesting system comprises two vibration degrees of freedom and two electrical degrees of freedom. It consists of a composite cantilever beam made of three layers, in which the magnetostrictive and piezoelectric layers are attached to the top and bottom of the base layer. The electromechanically coupled vibration equations of the whole hybrid structure were established with the lumped-parameter model while taking into account the magnetic interaction of two magnets. The nonlinear frequency-response of vibrations for the hybrid harvester is calculated using the harmonic balance method, and the model has been validated by literature. The time response and phase portraits of oscillation for the cantilever harvester and its performance in generating electrical power under different magnet distances, dynamic magnifier features, and excitation levels are analyzed. Numerical results have shown that the hybrid structure can harvest additional electrical power and operates at larger bandwidth than routine bistable piezoelectric or magnetostrictive energy harvesters.

Active vibration control of a piezoelectric functionally graded carbon nanotube-reinforced spherical shell panel

A finite-element model is presented based on the four-variable shear deformation refined theory for active vibration control of a functionally graded carbon nanotube-reinforced composite spherical panel with integrated piezoelectric layers, acting as an actuator and a sensor. The linear distribution of the electric potential across the thickness of the piezoelectric layer and different distribution types of carbon nanotubes through the thickness of the layers are considered. The weak form of the governing equation is derived using Hamilton's principle, and a four-node nonconforming rectangular element with eight mechanical and two electrical degrees of freedom per node is introduced for discretising the domain. A constant velocity feedback approach is utilised for the active control of the panel by closed-loop control with a piezoelectric sensor and actuator. The convergence and accuracy of the model are validated by comparing numerical results with data available in literature. Some new parametric studies are also discussed in detail.

Geometrically nonlinear analysis of CNT-reinforced functionally graded composite plates integrated with piezoelectric layers

The paper develops a geometrically nonlinear finite element model with large rotation based on the first-order shear deformation (FOSD) hypothesis for static and dynamic analyses of piezoelectric integrated carbon nanotube reinforced functionally graded (P-CNT-FG) composite structures. A constant electric field distribution through the thickness of plate is considered. An eight-node quadrilateral plate element with five mechanical degrees of freedom (DOFs) and one electric degree of freedom is developed for finite element analysis. Four typical forms of CNT distributions are included in the model, namely uniform, V-shaped, O-shaped, and X-shaped distributions. The nonlinear model considers fully geometrically nonlinear strain-displacement relations and large rotations of the shell direction of plate. Using the Hamilton’s principle, a nonlinear dynamic model including dynamic and sensory equations is obtained. The proposed nonlinear model is validated by a frequency analysis of a simply supported P-CNT-FG composite plate. Furthermore, the effects of various parameters on the static and dynamic behavior are investigated, e.g. CNT-reinforcement orientation, CNT distribution, the number of laminate layers and volume fraction.

Numerical and Experimental Analysis of the Dynamic Behavior of Piezoelectric Stiffened Composite Plates Subjected to Airflow

In this paper, the authors present results on dynamic behavior analysis of the stiffened composite plate with piezoelectric patches under airflow by finite element method and experimental study. The first-order shear deformation plate theory and nine-noded isoparametric piezoelectric laminated plate finite element with five elastic degrees of freedom at each node and one electric degree of freedom per element per piezoelectric layer were used in the dynamic analysis of plates by finite element method. The modern equipment was used in the dynamic behaviors analysis of plates subjected to airflow load by experimental method. In this study, the results of the theoretical method have been compared with experimental studies.

Multibeams energy harvester for rotational low-frequencies

The mechanical vibration induced by rotation speed is gaining interest in the last years. Comparing to other mechanical vibration sources, the excitation by rotational speed from low power wind turbines is really a challenge since the vibration frequency is lower than 10 Hz and it generates accelerations higher than 1 g. In this paper, a rotating piezoelectric energy harvester is designed and analysed. In order to achieve the best electrical power performance, the prototype is designed to have low natural frequencies varying the hub positions and dimensions of the multi-beams, decreasing the crossing-frequency (natural frequency/rotation speed) and finding the optimal electrical load resistance. The dynamic behaviour of the harvester is simulated using a nonlinear one-dimensional finite element formulation. The rotating piezoelectric beam is formulated by means of a geometrically nonlinear finite element with six mechanical degrees of freedom and one electrical degree of freedom per node. The simulations are performed from 1 to 4.5 Hz (60 – 270 rpm) rotation speeds. A performance assessment is done investigating the influence of the hub positions, crossing-frequencies, electrical resistance and rotation speeds over the voltage and power generation. Regarding harvester’s performance, promising results are obtained since the output power 3.72 mW @ 3.61 Hz. In this sense, this article provides a prototype at low rotational frequency capable to scavenge energy from low power wind turbines.

An Analytical Theory of Hall-Effect Devices with Three Contacts

Object:Vertical Hall-effect devices (VHalls) and split-drain MAG-FETs often have three contacts and a single mirror symmetry. We discuss the Equivalent Resistor Circuit (ERC) at small magnetic field, relate it to the electrical degrees of freedom, and compare it to traditional Hall plates with four contacts.Methods:In contrast to devices with four contacts, it is not possible to determine the sheet resistance of devices with three contacts by electrical measurements like the one of van der Pauw. However, for both types of devices, the output voltage over input current depends only on resistances of the ERC, the sheet resistance, and the Hall angle, irrespective of the exact shape of the devices and the size of the contacts.Result:This allows one to explore the maximum Signal-to-Noise Ratio (SNR) in a very general sense without consideration of any specific device geometry. It is shown how VHalls with all three contacts on the top face of the Hall tub can have electrical symmetry with maximum SNR.

OPTIMAL PLACEMENT AND ACTIVE VIBRATION CONTROL OF COMPOSITE PLATES INTEGRATED PIEZOELECTRIC SENSOR/ACTUATOR PAIRS

In this study, a finite element model based on first-order shear deformation theory is presented for optimal placement and active vibration control of laminated composite plates with bonded distributed piezoelectric sensor/actuator pairs. The model employs the nine-node isoparametric rectangular element with 5 degrees of freedom for the mechanical displacements, and 2 electrical degrees of freedom. Genetic algorithm (GA) is applied to maximize the fundamental natural frequencies of plates; and the constant feedback control method is used for the vibration control analysis of piezoelectric laminated composite plates. The results of this study can be used to aid the placement of piezoelectric sensor/actuator pairs of smart composite plates as well as for robust controller design.

An experimentally validated finite element formulation for modeling 3D rotational energy harvesters

Piezoelectric energy harvesting devices convert mechanical energy into electrical energy due to the mechanical deformations of the structures. Energy harvesting prototypes are used to feed low-power electronic devices and sensors. In this work, a one-dimensional finite element is developed for modeling three-dimensional rotational energy harvesters. The rotating piezoelectric beam is formulated by means of a geometrically nonlinear finite element with six mechanical degrees of freedom and one electrical degree of freedom per node. Using Timoshenko beam theory for the mechanical domain and a first-order theory for the electrical field, the electromechanical equilibrium equations of motion are then derived using D’Alembert principle. In order to validate our finite element formulation, two energy harvesting devices are built and tested, getting insights into the generation of electrical power, natural frequencies and time responses of the dynamical variables. An Arduino board is implemented as the data acquisition system that transfers the voltage signal via Bluetooth, avoiding the complexity of slip-rings mechanisms for data transmission. Finally, the results of our formulation are compared with those obtained using a commercial software (Abaqus) and the experimental results. A good correlation between the three methods is obtained, providing evidence that our formulation accurately predicts the behavior of rotational energy harvesters.

A cubic spline layerwise time domain spectral FE for guided wave simulation in laminated composite plate structures with physically modeled active piezoelectric sensors

A novel theoretical framework is presented enabling enhanced simulation of guided waves generated by piezoelectric actuators in laminated composite plates. A new multi-field multi-physics layerwise theory is formulated for laminated plates with piezoelectric actuators and sensors which captures symmetric and anti-symmetric stress waves. Third-order Hermite splines are employed in the approximation of displacements and electric potential through the thickness. The piezoelectric actuators and sensors are physically modeled though coupled electromechanical governing equations. An explicit time-domain spectral finite element is formulated entailing displacement and electric degrees of freedom at the nodes which are further collocated with Gauss–Lobatto–Legendre integration points. The stiffness, consistent semi-diagonal mass, piezoelectric and electric permittivity matrices are calculated. Furthermore, an explicit time integration scheme is presented for the calculation of the coupled transient electromechanical response including the free sensor response. Numerical guided wave predictions of the developed multi-node time domain spectral finite elements are correlated with well established numerical tools and with experiments conducted on laminated carbon/epoxy plates with active piezoceramic sensor networks. Important effects introduced by the physical presence of the active actuator/sensor system on guided wave propagation, such as wave reflections, mode conversions and sensor signal attenuation, are successfully captured by the developed finite element and correlated and evaluated with numerical and experimental results.

Performance of consistent through-thickness electric potential distribution for Euler-Bernoulli piezoelectric beam finite elements

An accurate piezoelectric beam finite element analysis essentially requires appropriate assumptions of the field variables involved in the formulation. The conventional Euler-Bernoulli piezoelectric beam finite elements assume an independent linear through-thickness distribution of electric potential in a physical piezoelectric layer which is actually nonlinear due to induced potential effects. Here, a consistent through-thickness potential distribution in a physical piezoelectric layer derived from the electrostatic equilibrium equation is tested for its accuracy against the linear assumption. This consistent potential field contains, in addition to the conventional linear terms, a higher order term coupled with bending strain. Thus, this finite element, though employing higher order potential, does not increase the number of nodal electrical degrees of freedom. It is shown that the performance of the present formulation with consistent through-thickness potential is insensitive to the geometric configuration and material properties of the beam cross-section, unlike the conventional formulations.

Structure and Magnetism of EuTiO3

The tilting of the oxygen octahedra in cubic perovskites is known to induce structural phase transitions, which are often associated with the emergence of intriguing physical phenomena. While SrTiO3 is one of the most extensively studied perovskite oxides for its structural phase transition at 105 K, the discovery of magnetoelectric coupling in isostructural EuTiO3 has triggered many theoretical and experimental studies focused on this compound. I will present resonant ultrasound studies of the extremely subtle cubic to tetragonal structural phase transition at 288 K in EuTiO3 single crystals and the evolution of the physical properties upon chemical doping. The collective set of experimental data contributes to a better understanding of the link between lattice, magnetic, and electrical degrees of freedom in the EuTiO3 system, helps evaluate the similarities and differences between SrTiO3 and EuTiO3, and provides insight in the possible origin of the much higher structural transition temperature for EuTiO3 compared to SrTiO3.

A time domain spectral layerwise finite element for wave structural health monitoring in composite strips with physically modeled active piezoelectric actuators and sensors

A new explicit, two-dimensional plane strain, time domain spectral finite element is developed to enhance the simulation of guided waves generated by active piezoelectric sensors in laminated composite strips. A new multi-field layerwise theory is formulated for composite laminates with piezoelectric actuators and sensors which captures straight-crested symmetric and anti-symmetric Lamb waves. Third-order Hermite polynomial splines are employed for the approximation of displacements and electric potential through the thickness, and the piezoelectric actuators and sensors are physically modeled through coupled electromechanical governing equations. A multi-node finite element formulation is presented entailing displacement and electric degrees of freedom at nodes collocated with Gauss–Lobatto–Legendre integration points. Stiffness, diagonal mass, piezoelectric, and electric permittivity matrices are described, and the coupled transient electromechanical response is predicted by a properly formulated explicit time integration scheme. The numerical results of a nine-node time domain spectral finite element are correlated with the reported numerical results and with measured Lamb wave data generated by piezoceramic active sensor pairs in carbon/epoxy plate strips. Important effects introduced by the stiffness and mass of the active actuator/sensor system on Lamb wave propagation are captured by the developed finite element and quantified.

Active vibration control of FGM plates with piezoelectric layers based on Reddy’s higher-order shear deformation theory

Literature researching the active vibration control of functionally graded material (FGM) plates with piezoelectric layers using Reddy’s higher-order shear deformation theory (HSDT) using any of the element-free methods does not exist. To the best of the authors’ knowledge, this paper is the first to use Reddy’s HSDT with the element-free IMLS-Ritz method to investigate this problem. In this study, seven mechanical degrees of freedom (DOF) and one additional electrical DOF are considered for each node of the discretized domain. The natural frequency results of two FGM plates with top and bottom piezoelectric layers are compared with the literature in terms of various electrical and mechanical boundary conditions, volume fraction exponent (n) and dimension ratios, with obvious agreement. Furthermore, parametric studies are performed, for the first time, to study the effects of mechanical boundary conditions, n value, FGM plate thickness-to-width ratio and piezoelectric layer thickness to FGM plate thickness ratio on the natural frequency increment between open and closed circuit conditions. For the purpose of active vibration control, a constant velocity feedback approach is utilized. The effectiveness of two proposed positions, of piezoelectric sensor and actuator layers, to control the vibration of FGM plates is investigated.

Detection of Zeptojoule Microwave Pulses Using Electrothermal Feedback in Proximity-Induced Josephson Junctions.

We experimentally investigate and utilize electrothermal feedback in a microwave nanobolometer based on a normal-metal (Au_{x}Pd_{1-x}) nanowire with proximity-induced superconductivity. The feedback couples the temperature and the electrical degrees of freedom in the nanowire, which both absorbs the incoming microwave radiation, and transduces the temperature change into a radio-frequency electrical signal. We tune the feedback insitu and access both positive and negative feedback regimes with rich nonlinear dynamics. In particular, strong positive feedback leads to the emergence of two metastable electron temperature states in the millikelvin range. We use these states for efficient threshold detection of coherent 8.4GHz microwave pulses containing approximately 200 photons on average, corresponding to 1.1×10^{-21} J≈7.0 meV of energy.

ChemInform Abstract: Structure and Properties of Magnetoelectric Gallium Ferrite: A Brief Review

AbstractReview: 40 refs.

Experimental and Simulation Investigations of the Cantilever Beam Energy Harvester

Machines, cars suspensions, buildings steel constructions etc. usually generate vibrations, which can be the excitement signal for piezoelectric energy harvesters. The piezoelectric patches attached to the vibrating construction have ability to convert mechanical energy of harmful vibrations into electrical energy.The goal of the study was to verify a finite element model of the piezoelectric beam energy harvester by comparing results of numerical simulations with those obtained experimentally. The stand used in the experiment consists of the cantilever beam with piezoelectric elements attached, which is excited by the base harmonic movement. The transverse displacements of the selected beam’s point and the base, and also the frequency of vibrations were observed and measured using an accelerometer and a B&K Pulse platform. A portable data acquisition module was used to quantify the voltage generated by the piezoelectric layers.The finite element model was built in ANSYS software. The beam and piezoelectric layers were modeled by twenty node elements with an additional electric degree of freedom for piezoelectric elements. A full piezoelectric matrix was used in the finite element analysis instead of a one-dimensional piezoelectric effect, which dominates in many analytical approaches. It allowed building a more accurate model of the system. The experimental tests and finite element method simulations were performed and acquired results were compared. The characteristics of voltage amplitude in the time and frequency domain were shown and discussed.

ChemInform Abstract: Magnetoelectrics for Magnetic Sensor Applications: Status, Challenges and Perspectives

AbstractReview: 92 refs.

Robust Optimal Control Applied to a Composite Laminated Beam

This paper proposes an active vibration control technique, which is based on linear matrix inequalities, that is applied to a piezoelectric actuator bonded to a composite structure, forming a so-called smart composite structure. Serendipity-type finite element, based on first-order shear deformation theory with rectangular shape, eight nodes, five mechanical degrees of freedom (DOF) per node and eight electrical DOF per piezoelectric layer, is established for the composite structural model. Additionally, a mixed theory that uses a single equivalent layer for the discretization of the mechanical displacement field and a layerwise representation of the electrical field is adopted. Temperature effects are neglected. Simulation results illustrate the effectiveness of the proposed vibration control methodology for composite structures.