Electromechanical Effects Research Articles

Experimental Research on Wind-Induced Flag-Swing Piezoelectric Energy Harvesters

Piezoelectric cantilever beams, which have simple structures and excellent mechanical/electrical coupling characteristics, are widely applied in energy harvesting. When the piezoelectric cantilever beam is in a wind field, we should consider not only the influence of the wind field on piezoelectric beam but also the electromechanical coupling effect on it. In this paper, we design and test a wind-induced flag-swing piezoelectric energy harvester (PEH). The piezoelectric cantilever beam may vibrate in the wind field by affixing a flexible ribbon to the free end as the windward structure. To fulfill the goal of producing electricity, the flexible ribbon can swing the piezoelectric cantilever in a wind-induced unstable condition. The experimental findings demonstrate that the flag-swing PEH performs well in energy harvesting when the wind field is excited. When the wind speed is 15 m/s, the peak-to-peak output AC voltage may reach 13.88 V. In addition, the voltage at both ends of the closed-loop circuit’s external resistance is examined. The maximum electric power of the PEH may reach 43.4 μW with an external resistance of 650 kΩ. After passing through the AC-DC conversion circuit, the flag-swing PEH has a steady DC voltage output of 1.67 V. The proposed energy harvester transforms wind energy from a wind farm into electrical energy for supply to low-power electronic devices, allowing for the creation and use of green energy to efficiently address the issue of inadequate energy.

Bifurcation and stability of resonance of electric vehicle powertrain: Focus on the influence of electromagnetic parameters

The influence of the electromagnetic parameters on the torsional dynamics of the electric vehicle powertrain is studied by considering the electromechanical coupling effect. By adding the electromagnetic torque on the drive side, the powertrain is simplified as nonlinear drive-shaft model. The number, stability, and bifurcation conditions of the equilibrium points of the nonlinear drive-shaft model are deduced. Based on the averaged equations and the amplitude-frequency response equation, the stability and bifurcation conditions, such as fold bifurcation and Hopf bifurcation, of the resonance curve are discussed. The influence of electromagnetic parameters on the torsional dynamics is studied by simulation. It is shown that with the change of the parameters, the number as well as the stability of the equilibrium points may be changed which is affected by fold bifurcation. It is also shown that the resonance curve may lose its stability when fold bifurcation happens. By limiting the parameters in the region without fold bifurcation, the unstable dynamics of the resonance curve can be controlled.

A Multi-Fidelity Model for Simulations and Sensitivity Analysis of Piezoelectric Inkjet Printheads.

The ink drop generation process in piezoelectric droplet-on-demand devices is a complex multiphysics process. A fully resolved simulation of such a system involves a coupled fluid–structure interaction approach employing both computational fluid dynamics (CFD) and computational structural mechanics (CSM) models; thus, it is computationally expensive for engineering design and analysis. In this work, a simplified lumped element model (LEM) is proposed for the simulation of piezoelectric inkjet printheads using the analogy of equivalent electrical circuits. The model’s parameters are computed from three-dimensional fluid and structural simulations, taking into account the detailed geometrical features of the inkjet printhead. Inherently, this multifidelity LEM approach is much faster in simulations of the whole inkjet printhead, while it ably captures fundamental electro-mechanical coupling effects. The approach is validated with experimental data for an existing commercial inkjet printhead with good agreement in droplet speed prediction and frequency responses. The sensitivity analysis of droplet generation conducted for the variation of ink channel geometrical parameters shows the importance of different design variables on the performance of inkjet printheads. It further illustrates the effectiveness of the proposed approach in practical engineering usage.

Flexoelectricity in composition-graded InGaN nanowires

Due to the electromechanical coupling effect, composition-graded InGaN nanowires (NWs) have promising potential application in piezotronics. However, as an inhomogeneous system at the nanoscale, the electromechanical response of InGaN NWs can be affected by some small-scale effects, e.g. the flexoelectric effect, which is almost unexplored. In this paper, the piezoelectric and elastic properties of composition-graded InGaN NWs are investigated by using molecular dynamics (MD) simulations, in which a power-law formula is introduced to describe the continuously varied composition in graded InGaN NWs. MD results show that the diameter, Young’s modulus and piezoelectric coefficient of graded InGaN NWs are dependent on the position of NWs. Moreover, the distribution of these structural and material parameters can be efficiently modified by changing the power-law exponent. The position-dependent diameter and Young’s modulus can be well described by Vegard’s law. However, as for the piezoelectric coefficient, a big discrepancy is observed between the results extracted from MD simulations and Vegard’s law. This discrepancy is attributed to the enhanced piezoelectricity in graded InGaN NWs induced by the flexoelectric effect. The flexoelectric effect is found to originate from the non-uniform strain in graded InGaN NWs majorly induced by the varied Young’s modulus along the NW axis, which becomes more significant as the length of NWs decreases. This work tries to present a comprehensive understanding of the electromechanical coupling of InGaN NWs, which can provide guidance for the design of graded InGaN NWs-based piezotronic nanodevices.

Stability analysis of shock response of EV powertrain considering electro-mechanical coupling effect

The main purpose of this manuscript is to analyze the stability of the shock response of the electric vehicle (EV) powertrain when considering the electro-mechanical coupling effect. The nonlinear drive-shaft model of the powertrain is built using the Lagrange method, based on which the shock response equation is also deduced. Meanwhile, the number and properties of the equilibrium points are studied. Two kinds of equilibrium points, saddle node and central point, which can induce different dynamic behaviors are found. The simulation results show that the trajectory of the shock response may be unstable if the parameters are chosen in the region that has a saddle node. If the parameters of the powertrain fall into the region that has only one central point, the trajectory of the shock response will be attracted by the stable limit cycle. Therefore, to ensure that the shock response is more stable, the parameters should be chosen in the region where only one central point is present.

Modelling of a direct‐driven electromechanical actuation system based on the Lagrange–Maxwell equation

This study proposes an integrated non-linear modelling method for an electromechanical actuation system directly driven by the switched reluctance motor (SDEMA). The mathematical model of the SDEMA system is established by energy analysis and calculation according to the proposed method, which omits the complex analysis of force or torque transmission in the cascade modelling method. By using the Lagrange–Maxwell equation and establishing the energy models of non-linear factors that include the friction, backlash, and flexibility, both the electromechanical coupling effects and the non-linear factors of the SDEMA system are considered simultaneously in the proposed method. To verify the feasibility and effectiveness of the proposed method, three modelling methods of the SDEMA system are comparatively studied through the simulations and experiments. The results of the simulations and experiments indicate that the proposed integrative non-linear model can reflect the dynamic performance of the SDEMA system more accurately.

Typical transient effects in a piezoelectric semiconductor nanofiber under a suddenly applied axial time-dependent force

Based on the mechanical motion equation, Gauss’s law, and the current continuity condition, we study a few typical transient effects in a piezoelectric semiconductor (PS) fiber to realize the startup and turning-off functions of common piezotronic devices. In this study, the transient extensional vibration induced by a suddenly applied axial time-dependent force is examined in a cantilevered n-type ZnO nanofiber. Neither the magnitude of the loadings nor the doping concentration significantly affects the propagation caused by disturbance of the axial displacement. However, both of the factors play an important role in the propagation caused by disturbance of the electron concentrations. This indicates that the electromechanical coupling effect can be expected to directly determine the electronic performance of the devices. In addition, the assumption of previous simplified models which neglect the charge carriers in Gauss’s law is discussed, showing that this assumption has a little influence on the startup state when the doping concentration is smaller than 1021 m−3. This suggests that the screening effect of the carriers on the polarized electric field is much reduced in this situation, and that the state is gradually transforming into a pure piezoelectric state. Nevertheless, the carriers can provide a damping effect, which means that the previous simplified models do not sufficiently describe the turning-off state. The numerical results show that the present study has referential value with respect to the design of newly multifunctional PS devices.

Electromechanical field effects in InAs/GaAs quantum dots based on continuum [formula omitted] and atomistic tight-binding methods

A comparison between k→·p→ and tight-binding methods for the analysis of InAs/GaAs quantum dot bandstructures is presented based on a fully coupled computation of electromechanical effects. Electromechanical effects are addressed using a continuum elastic model for the k→·p→ method and a pre-conditioned Valence Force Field algorithm for the tight-binding atomistic calculations. The Valence Force Field method allows the direct identification of the impact of internal strain. Results to ensure model parameter consistency between the two methods are also given by comparing bulk and unstrained quantum-well dispersion relations.The quantum dot size dependence of the bandstructure is investigated based on the models including electromechanical fields. Additionally, the effect of the electromechanical fields is studied for a specific dot size by comparing results with and without electromechanical fields. Good agreement is found for the confined energy levels but model differences show up in the symmetry of probability densities mainly due to the underlying crystal structure details taken into account by the tight-binding method but lacking in the k→·p→ formalism. The latter follows from not including bulk inversion-asymmetry effects in the k→·p→ method. Inclusion of piezoelectric field effects in the k→·p→ method, however, restores the correct symmetry in the k→·p→ model (in agreement with the tight-binding symmetry).Results are also given for oscillator strengths where both quantitative and qualitative differences are found in the comparison of k→·p→ and tight-binding models.

Enhanced converse flexoelectricity in piezoelectric composites by coupling topology optimization with homogenization

We demonstrate that large apparent converse flexoelectric properties can be obtained in piezoelectric composites using theoretical approaches. To do so, we first present a numerical homogenization method accounting for all electromechanical terms related to strain and the electric field gradient. We then evaluate the coefficients of the model by numerical simulations on periodic piezoelectric composites. After combining the homogenization approach with topology optimization to enhance the converse properties of the composite, we present numerical results that reveal that the apparent converse flexoelectric coefficients, as well as those associated with the higher order coupling terms involving the electric field gradient, are of the same order as the direct flexoelectric properties of the local constituents. These results suggest that both converse and higher order electromechanical coupling effects may contribute strongly to the flexoelectric response and properties of piezoelectric composites. Finally, we show that it is theoretically possible to obtain optimized designs of composites with apparent converse flexoelectric properties 1–2 orders of magnitude larger than ones obtained with naïve guess designs.

Dynamics of piezoelectric structures with geometric nonlinearities: A non-intrusive reduced order modelling strategy

A reduced-order modelling to predictively simulate the dynamics of piezoelectric structures with geometric nonlinearities is proposed in this paper. A formulation of three-dimensional finite element models with global electric variables per piezoelectric patch, and suitable with any commercial finite element code equipped with geometrically nonlinear and piezoelectric capabilities, is proposed. A modal expansion leads to a reduced model where both nonlinear and electromechanical coupling effects are governed by modal coefficients, identified thanks to a non-intrusive procedure relying on the static application of prescribed displacements. Numerical simulations can be efficiently performed on the reduced modal model, thus defining a convenient procedure to study accurately the nonlinear dynamics of any piezoelectric structure. A particular focus is made on the parametric effect resulting from the combination of geometric nonlinearities and piezoelectricity. Reference results are provided in terms of coefficients of the reduced-order model as well as of dynamic responses, computed for different test cases including realistic structures.

Mechanically induced Shapiro steps: Enormous effect of vibrations on the charge-density wave transport

Charge-density wave (CDW) transport is studied in the whiskers of orthorhombic TaS3 suspended between piezoelectric actuators. It is found that when the frequency of rf voltage applied to the actuators coincides with a vibration resonance of the whisker, the I–V curves show Shapiro-step-like features, similar with those under rf voltage applied directly to the sample. We provide evidence that the features observed are coupled with the periodic lattice deformation. The effect of vibrations appears surprisingly strong: a time-dependent strain not exceeding 10−4 results in a periodic stop of the CDW. The result suggests an area of electromechanical effects inherent to sliding CDWs.

Fuzzy Logic-Based and Nondestructive Concrete Strength Evaluation Using Modified Carbon Nanotubes as a Hybrid PZT–CNT Sensor

Concrete strength and factors affecting its development during early concrete curing are important research topics. Avoiding uncertain incidents during construction and in service life of structures requires an appropriate monitoring system. Therefore, numerous techniques are used to monitor the health of a structure. This paper presents a nondestructive testing technique for monitoring the strength development of concrete at early curing ages. Dispersed carbon nanotubes (CNTs) were used with cementitious materials and piezoelectric (PZT) material, a PZT ceramic, owing to their properties of intra electromechanical effects and sensitivity to measure the electromechanical impedance (EMI) signatures and relevant properties related to concrete strength, such as the elastic modulus, displacement, acceleration, strength, and loading effects. Concrete compressive strength, hydration temperature, mixture ratio, and variation in data obtained from the impedance signatures using fuzzy logic were utilized in the comparative result prediction method for concrete strength. These results were calculated using a fuzzy logic-based model considering the maturity method, universal testing machine (UTM) data, and analyzed EMI data. In the study, for data acquisition, a hybrid PZT–CNT sensor and a temperature sensor (Smart Rock) were embedded in the concrete to obtain the hydration temperature history to utilize the concrete maturity method and provide data on the EMI signatures. The dynamic changes in the medium caused during the phase in the concrete strengthening process were analyzed to predict the strength development process of concrete at early curing ages. Because different parameters are considered while calculating the concrete strength, which is related to its mechanical properties, the proposed novel method considers that changes in the boundary condition occurring in the concrete paste modify the resonant frequency response of the structure. Thus, relating and analyzing this feature can help predict the concrete strength. A comprehensive comparison of the results calculated using the proposed module, maturity method, and cylindrical specimens tested using the UTM proved that it is a cost-effective and fast technique to estimate concrete strength to ensure a safe construction of reinforced cement concrete infrastructures.

Electro-structural analysis and optimization studies of laminated composite beam energy harvester

Modern ambient energy harvesters meet the micropower demands of the industrial sensors and communication hardware. Optimum design of such systems to maximize the power output is, therefore, of vital importance. This paper presents a multi-objective optimization methodology of smart laminated composite beam energy harvester by considering different geometric parameters. A typical multilayer carbon-epoxy composite beam with unimorph piezoelectric configuration is analyzed with finite element model. The coupled electro-mechanical effects are considered and the resultant free vibration solution is validated with that of a three-dimensional model. The structural response and power density of the base excited beam are obtained by varying thickness ratio of piezo layer, composite lamination sequence, number of layers, circuit resistance, piezoelectric materials, and so on. The most influencing design variables are identified using analysis of variance (ANOVA). By minimization of the frequency band gap between first two modes and maximization of output power density simultaneously, optimum solution is obtained from grey relation analysis technique. The results are validated with a surrogate model employing multilayer perceptron (MLP) neural network in conjunction with multi-objective genetic algorithms. The structural dynamic response and electrical power output characteristics of optimized configuration are found to be improved.

Electromechanical coupling effect in the detection of nanomechanical motion

The electromechanical coupling in the nanomechanical detection experiment is important as people forever pursue the higher sensitivity. In this work, we have studied theoretically the electromechanical coupling effect on the sensitivity of nanomechanical motion with the mixing current detection method under monostable and bistable regime, respectively. To obtain the sensitivity, the response function, the shot noise and the backaction noise with the coupling in the nanomechanical system consists of the oscillator coupled to a quantum dot are present. It is found that for the monostable state, the higher coupling means higher sensitivity. Both the contributions of shot noise and the backaction noise to the sensitivity are the decreasing function of the coupling. Once the system enters the bistability regime, the telegraph noise dominates instead of the resonance frequency noise, that due to the electron hopping in the bistable regime contributes more noise for the detection, its value is 3 orders of magnitude larger than the contribution of shot noise. As a result, one could find that there is a optimal value of the coupling corresponding to the phase transition point where the sensitivity is the best. Our results provide the pioneer and useful approach for the detection experiment.

Orientation control of phase transition and ferroelectricity in Al-doped HfO2 thin films

Binary ferroelectric materials such as hafnium oxide have been intensively studied, which are expected to exhibit robust ferroelectricity comparable to the perovskite-based ferroelectrics at nanoscale. Here, using the combination of X-ray diffraction (XRD) associate with Transmission Electron Microscope (TEM), we reveal the epitaxial growth of Al-doped HfO2 possessing various phase structures on different oriented SrTiO3 substrates. The well-oriented films show different ferroelectricity indicated by piezoresponse force microscopy (PFM). The film grown on the (111) SrTiO3 substrate shows the largest electromechanical effect. These results, with the analyses of structural characterizations, demonstrate the orientation control of phase transitions and ferroelectricity in Al-doped HfO2 thin films.

Hemodynamic and electromechanical effects of paraquat in rat heart.

Paraquat (PQ) is a highly lethal herbicide. Ingestion of large quantities of PQ usually results in cardiovascular collapse and eventual mortality. Recent pieces of evidence indicate possible involvement of oxidative stress- and inflammation-related factors in PQ-induced cardiac toxicity. However, little information exists on the relationship between hemodynamic and cardiac electromechanical effects involved in acute PQ poisoning. The present study investigated the effects of acute PQ exposure on hemodynamics and electrocardiogram (ECG) in vivo, left ventricular (LV) pressure in isolated hearts, as well as contractile and intracellular Ca2+ properties and ionic currents in ventricular myocytes in a rat model. In anesthetized rats, intravenous PQ administration (100 or 180 mg/kg) induced dose-dependent decreases in heart rate, blood pressure, and cardiac contractility (LV +dP/dtmax). Furthermore, PQ administration prolonged the PR, QRS, QT, and rate-corrected QT (QTc) intervals. In Langendorff-perfused isolated hearts, PQ (33 or 60 μM) decreased LV pressure and contractility (LV +dP/dtmax). PQ (10-60 μM) reduced the amplitudes of Ca2+ transients and fractional cell shortening in a concentration-dependent manner in isolated ventricular myocytes. Moreover, whole-cell patch-clamp experiments demonstrated that PQ decreased the current amplitude and availability of the transient outward K+ channel (Ito) and altered its gating kinetics. These results suggest that PQ-induced cardiotoxicity results mainly from diminished Ca2+ transients and inhibited K+ channels in cardiomyocytes, which lead to LV contractile force suppression and QTc interval prolongation. These findings should provide novel cues to understand PQ-induced cardiac suppression and electrical disturbances and may aid in the development of new treatment modalities.

Electrical and Microstructural Characterization of TiO2 Thin Films for Flexoelectric Devices

This work investigates the flexoelectric potential of titanium oxide thin films regarding their microstructural and electrical properties to be integrated into nanoscaled resonators. Flexoelectricity is an electromechanical effect that can result in deformation of a material due to a polarization gradient and can outperform piezoelectric effects at the nanoscale. The flexoelectric constant is linearly dependent on the permittivity and therefore we determined TiO2 as a suitable flexoelectric material because of its high permittivity, its CMOS compatability and its linearity with respect to polarization. TiO2 capacitors with various electrode materials are evaluated in order to achieve the c-axis oriented (110) rutile growth, thus to exploit the highest permittivity. The permittivity ranges from 65 to 95, with TiO2 on IrO2 electrodes representing the highest value achieved in this study. As expected, the IrO2/TiO2/IrO2 capacitors show an almost constant impedance up to 200 kHz and have leakage current density values of ∼10−3 A/cm2 at 0.5 MV/cm at room temperature.

Superconducting Nanoelectromechanical Transducer Resilient to Magnetic Fields.

Nanoscale electromechanical coupling provides a unique route toward control of mechanical motions and microwave fields in superconducting cavity electromechanical devices. However, conventional devices composed of aluminum have presented severe constraints on their operating conditions due to the low superconducting critical temperature (1.2 K) and magnetic field (0.01 T) of aluminum. To enhance their potential in device applications, we fabricate a superconducting electromechanical device employing niobium and demonstrate a set of cavity electromechanical dynamics, including back-action cooling and amplification, and electromechanically induced reflection at 4.2 K and in strong magnetic fields up to 0.8 T. Niobium-based electromechanical transducers operating at this temperature could potentially be employed to realize compact, nonreciprocal microwave devices in place of conventional isolators and cryogenic amplifiers. Moreover, with their resilience to magnetic fields, niobium devices utilizing the electromechanical back-action effects could be used to study spin-phonon interactions for nanomechanical spin-sensing.

Flexophotovoltaic Effect in Potassium Sodium Niobate/Poly(Vinylidene Fluoride-Trifluoroethylene) Nanocomposite.

Flexoelectricity is an electromechanical coupling effect in which electric polarization is generated by a strain gradient. In this investigation, a potassium sodium niobite/poly(vinylidene fluoride‐trifluoroethylene) (KNN/PVDF‐TrFE)‐based nanocomposite is fabricated, and the flexoelectric effect is used to enhance the photovoltaic current (I pv) in the nanocomposite. It is found that both a pyroelectric current and photovoltaic current can be generated simultaneously in a light illumination process. However, the photovoltaic current (I pv) in this process contributes ≈85% of the total current. When assessing the effect of flexoelectricity with a curvature of 1/20, the I pv of the curved KNN/PVDF‐TrFE (20%) (K/P‐20) composite increased by ≈13.9% compared to that of the flat K/P‐20 nanocomposite. Similarly, at a curvature of 1/20, the I pv of the K/P‐20 nanocomposite is 71.6% higher than that of the PVDF‐TrFE film. However, the photovoltaic effect induced by flexoelectricity is much higher than the increased polarization from flexoelectricity, so this effect is called as the flexophotovoltaic effect. Furthermore, the calculated energy conversion efficiency of the K/P‐20 film is 0.017%, which is comparable to the previous research result. This investigation shows great promise for PVDF‐based nanocomposites in ferroelectric memory device applications.

Competing anticlastic and piezoelectric deformation at large deflections

In bending of a purely elastic beam or plate, it is well established that the cross-sectional shape changes character with decreasing bending radius-of-curvature and that the transition can be characterized by the Searle parameter. In a piezoelectric structure, the cross-sectional deformation is affected by the opposite anticlastic and electromechanical bending curvatures. The behavior is consequently more complicated and it is an open question how the cross-sectional shape develops with increasing bending. In this paper, analytical solutions are used to study the cross-sectional deformation of piezoelectric cantilever-actuators taking both anticlastic and electromechanical bending effects into account. We consider unimorph and bimorph actuators. In the case of electrical actuation, as for the purely mechanical case, we find that the Searle parameter is an important parameter characterizing the shape of the cross-section. A load scaling rule gives a criterion for fixed cross-section-deflection for different actuator widths. Using this scaling rule, the Searle parameter is kept unchanged. The analytical results are verified by non-linear finite element analysis using electric potential and mechanical moment as applied loads.