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This paper demonstrated the coupled surface effects of thermal Casimir force and squeeze film damping (SFD) on size-dependent electromechanical stability and bifurcation of torsion micromirror actuator. The governing equations of micromirror system are derived, and the pull-in voltage and critical tilting angle are obtained. Also, the twisting deformation of torsion nanobeam can be tuned by functionally graded carbon nanotubes reinforced composites (FG-CNTRC). A finite element analysis (FEA) model is established on the COMSOL Multiphysics platform, and the simulation of the effect of thermal Casimir force on pull-in instability is utilized to verify the present analytical model. The results indicate that the numerical results well agree with the theoretical results in this work and experimental data in the literature. Further, the influences of volume fraction and geometrical distribution of CNTs, thermal Casimir force, nonlocal parameter, and squeeze film damping on electrically actuated instability and free-standing behavior are detailedly discussed. Besides, the evolution of equilibrium states of micromirror system is investigated, and bifurcation diagrams and phase portraits including the periodic, homoclinic, and heteroclinic orbits are described as well. The results demonstrated that the amplitude of the tilting angle for FGX-CNTRC type micromirror attenuates slower than for FGO-CNTRC type, and the increment of CNTs volume ratio slows down the attenuation due to the stiffening effect. When considering squeeze film damping, the stable center point evolves into one focus point with homoclinic orbits, and the dynamic system maintains two unstable saddle points with the heteroclinic orbits due to the effect of thermal Casimir force.

Electronic skins are essential for real-time health monitoring and tactile perception in robots. Although the use of soft elastomers and microstructures have improved the sensitivity and pressure-sensing range of tactile sensors, the intrinsic viscoelasticity of soft polymeric materials remains a long-standing challenge resulting in cyclic hysteresis. This causes sensor data variations between contact events that negatively impact the accuracy and reliability. Here, we introduce the Tactile Resistive Annularly Cracked E-Skin (TRACE) sensor to address the inherent trade-off between sensitivity and hysteresis in tactile sensors when using soft materials. We discovered that piezoresistive sensors made using an array of three-dimensional (3D) metallic annular cracks on polymeric microstructures possess high sensitivities (> 10(7) Ω ⋅ kPa(−1)), low hysteresis (2.99 ± 1.37%) over a wide pressure range (0–20 kPa), and fast response (400 Hz). We demonstrate that TRACE sensors can accurately detect and measure the pulse wave velocity (PWV) when skin mounted. Moreover, we show that these tactile sensors when arrayed enabled fast reliable one-touch surface texture classification with neuromorphic encoding and deep learning algorithms.

Skin-like sensors that transduce tactile pressures and vibrations with minimal environment variation on performance are crucial in robotic sensing and prosthetic skins. However, sensor performance ...

Bonded structures are frequently adopted in structural connections and are highly prone to degradation or decrease of interfacial strength due to adhesive aging, poor quality of surface preparation, as well as the exposure to harsh environment and external loading. This study addresses the establishment of a framework in which a modally selective ultrasonic guided wave is used for disbond identification and sizing. In this framework, the propagating and evanescent modes of ultrasonic guided waves are first obtained, followed by the excitability analysis for each ultrasonic guided wave propagating mode, providing a theoretical basis for effective wave excitation in the experiment. Then the interaction of ultrasonic guided wave with disbond is interrogated analytically using a method combining semi-analytical finite element and normal mode expansion, whereby wave transmission, wave reflection, and mode conversion can be calculated quantitatively. Taking all these aspects into account, mode 11 at around 3.85 MHz features a high propagation velocity, large mode excitability, and increasing amplitude drop with the enlargement of disbond size, and is thus selected for disbond detection. Both numerical and experimental validations are performed, in which disbonds of different lengths from 10 to 40 mm are examined, and the results well corroborate the effectiveness of the proposed framework for ultrasonic guided wave–based disbond detection.

High-performance flexible pressure sensors are highly desirable in health monitoring, robotic tactile, and artificial intelligence. Construction of microstructures in dielectrics and electrodes is the dominating approach to improving the performance of capacitive pressure sensors. Herein, we have demonstrated a novel three-dimensional microconformal graphene electrode for ultrasensitive and tunable flexible capacitive pressure sensors. Because the fabrication process is controllable, the morphologies of the graphene that is perfectly conformal with the electrode are controllable consequently. Multiscale morphologies ranging from a few nanometers to hundreds of nanometers, even to tens of micrometers, have been systematically investigated, and the high-performance capacitive pressure sensor with high sensitivity (3.19 kPa–1), fast response (30 ms), ultralow detection limit (1 mg), tunable-sensitivity, high flexibility, and high stability was obtained. Furthermore, an ultrasensitivity of 7.68 kPa–1 was succ...

Flexible pressure sensors have aroused tremendous attention, owing to their broad applications in healthcare, robotics, and prosthetics. So far, it remains a critical challenge to develop low-cost and controllable microstructures for flexible pressure sensors. Herein, a high-sensitivity and low-cost flexible piezoresistive sensor was developed by combining a controllable graphene-nanowalls (GNWs) wrinkle and a polydimethylsiloxane (PDMS) elastomer. For the GNWs-PDMS bilayer, the vertically grown GNWs film can effectively improve the interface strength and form delamination-free conformal wrinkles. More importantly, a controllable microstructure can be easily tuned through the thermal wrinkling method. The wrinkled graphene-nanowalls (WG) piezoresistive sensor has a high sensitivity (S = 59.0 kPa-1 for the 0-2 kPa region and S = 4.8 kPa-1 for the 2-20 kPa region), a fast response speed (

Power sources with good mechanical compliance are essential for various flexible and stretchable electronics. However, most of the current energy storage devices comprise of hazardous materials that may cause environmental pollution when improperly disposed. We show the first example of a stretchable, yet fully degradable battery made from nontoxic and environmentally friendly materials such as fruit‐based gel electrolytes and cellulose paper electrodes. The battery exhibits an areal capacity of 2.9 μAh cm−2 at 40 μA cm−2, corresponding to a maximum energy density around 4.0 μW h cm−2 at 56 μW cm−2 power density. The biomaterials constituted battery shows good mechanical tolerance to twisting, bending, and stretching while powering various electronic devices when combined with kirigami. Importantly, the entire battery disintegrates readily in phosphate buffered saline/cellulase solution. We integrate the “green” battery with various sensors in wearable healthcare devices for pulsation sensing and low‐noise surface electromyography applications.

Electronic skin (e-skin) has attracted much attention in smart wearables, prosthetics, and robotics. Capacitive-type pressure sensors are generally regarded as a good option for designing tactile sensing devices owing to their superior sensitivity in low-pressure regions, fast response time, and convenient manufacturing. Introducing microstructures on the electrode surface is an effective approach to achieve highly sensitive capacitive pressure sensors. In this work, an electromechanical model is proposed to build the relationship between capacitance change and compressive force. The present model can predict the sensitivity of the capacitive pressure sensor with microstructured electrodes, where each cellular microstructure is modeled using contact mechanics theory. It is the first time in the literature that, based on the Hertz theory framework, a rigorous electromechanical theory framework is established to model a flexible capacitive pressure sensor. In addition, the model can be extended to other microstructures, such as micro-pyramid, micro-pillar, and micro-dome array. The validation indicates that the analytical results agree well with the experimental data from our previous work and other literature. Moreover, the present model can effectively capture the sensitivity of the pressure sensor in the beginning range of small pressure. Sensitivity in this range is the most significant for the e-skin due to its robust linearity for a pressure sensor. Besides, we analyzed the compressive force–displacement relationship, the compressive force–contact radius relationship, and the influences of the geometrical and material parameters on the electromechanical coupling effect. The results show that the height and the Young’s modulus of the soft dielectric layer are regarded as the dominant influencing factors in the sensitivity of capacitive pressure sensors.

Stretchable electronics have advanced rapidly and many applications require high repeatability and robustness under various mechanical deformations. It has been described here that how a highly stretchable and reliable conductor composite made from helical copper wires and a soft elastomer, named eHelix, can provide mechanically robust and strain-insensitive electronic conductivity for wearable devices. The reversibility of the mechanical behavior of the metal-elastomer system has been studied using finite element modeling methods. Optimal design parameters of such helical metal-elastomer structures are found. The scaling of multiple copper wires into such helical shapes to form a Multi-eHelix system is further shown. With the same elastomer volume, Multi-eHelix has more conductive paths and a higher current density than the single-eHelix. Integrations of these eHelix stretchable conductors with fabrics showed wearable displays that can survive machine-washes and hundreds of mechanical loading cycles. The integration of the eHelix developed by us with a wearable optical heart rate sensor enabled a wearable health monitoring system that can display measured heart rates on clothing. Furthermore, Multi-eHelix conductors are used to connect flexible printed circuit boards and piezoresistive sensors on a tactile sensing glove for the emerging sensorized prosthetics.

A scale-dependent analytical model is presented to solve the nonlinear pull-in instability of functionally graded carbon nanotubes (CNTs) reinforced nano-actuator with piezoelectric layer considering high order-corrected electrostatic pressure and finite temperature and conductivity corrections of Casimir force. Based on Eringen’s nonlocal elasticity theory considering the long range forces among atoms, and geometrical nonlinearity, the electro-thermo-mechanical coupling governing equation of nano-actuator is derived, and solved by utilizing natural mode function and Galerkin’s decomposition method. The higher-order corrected model of electrostatic force with fringing field effect accounting for large gap and geometrical nonlinearity is employed. The results indicate that pull-in voltage decreases with increase of positive piezoelectric effect but increases with increment of negative piezoelectric effect. Pull-in voltage declines as the piezoelectric layer thickness of nano-actuator increases. Casimir force appears in more significant effect on the pull-in voltage of nano-actuator than that of van der Waals force, which shows that the analysis of nanoscale devices cannot neglect the influences of intermolecular forces within sub-micron separations. Finally, the coupling influences of van der Waals force and Capillary force on pull-in voltage are compared.

This paper aims to investigate the coupling influences of thermal loading and surface effects on pull-in instability of electrically actuated circular nanoplate based on Eringen's nonlocal elasticity theory, where the electrostatic force and thermally corrected Casimir force are considered. By utilizing the Kirchhoff plate theory, the nonlinear equilibrium equation of axisymmetric circular nanoplate with variable coefficients and clamped boundary conditions is derived and analytically solved. The results describe the influences of surface effect and thermal loading on pull-in displacements and pull-in voltages of nanoplate under thermal corrected Casimir force. It is seen that the surface effect becomes significant at the pull-in state with the decrease of nanoplate thicknesses, and the residual surface tension exerts a greater influence on the pull-in behavior compared to the surface elastic modulus. In addition, it is found that temperature change plays a great role in the pull-in phenomenon; when the temperature change grows, the circular nanoplate without applied voltage is also led to collapse.

A size-dependent model of functionally graded carbon nanotubes (FGCNTs) reinforced microbeam with piezoelectric layer is presented based on unifying nonlocal stress and strain gradient framework. Nonlinear dynamic characteristics of the microbeam arise from electrostatic, piezoelectric actuation and thermal loading, with consideration of quantum and thermal fluctuations induced Casimir force. The nonlinearly dynamic frequency and pull-in instability of FGCNTs reinforced microbeam with damping effect are investigated by perturbation technique and verified by numerical method, where the coupling effects of nonlocal stress gradient and strain gradient parameters on fundamental frequency are described. The results show that the frequency of piezoelectric laminated microbeam-damping system declines with the growth of nonlocal stress gradient parameter while increases with the increment of strain gradient parameter. The pull-in voltage of micro- piezoelectric laminated beam can be tuned by excitation voltage exerted on piezoelectric layer, and the frequency and pull-in voltage decrease with the increase of the excitation voltage exerted on piezoelectric layer. In addition, dissipative effects originating from viscous and structural damping are evaluated. It is found that the pull-in voltage of micro-structures with damping system is higher than that of undamped system.

Architected materials consisting of periodic unit cells are desirable for many engineering applications. Characterizing the elastic isotropy is of great significance for the mechanical design of architected materials. However, prevailing experimental and numerical approaches are normally too costly and time-consuming to screen out isotropic architected materials in the large design space. Here, a deep learning-based approach is developed as a highly efficient and portable tool to identify the elastic isotropy of architected materials directly from images of their unit cells with arbitrary component distributions. The measure of elastic isotropy for heterogeneous architected materials is derived firstly in this paper to construct a database with associated images of unit cells. Then a convolutional neural network is fully trained with the database, performing well on the isotropy identification with about 90% accuracy and milliseconds processing time per sample. Meanwhile, it exhibits enough robustness to maintain its performance under the fluctuating material properties in test sets. Moreover, the transfer learning of the convolutional neural network is successfully implemented among architected materials with different numbers of material components, which further promotes the efficiency of the deep learning-based approach without scarifying its identification performance. This study gives new inspirations on the rapid mechanical characterization of architectured materials, which holds promising applications in the big-data driven topological design and nondestructive testing of architected materials.

The paper reports a result of investigation on the dynamic pull-in instability of functionally graded carbon nanotubes (FGCNTs) reinforced nano-actuator considering damping behavior. Here, the nonlocal stress gradient and strain gradient theories are jointly utilized to capture the size effects of nanoscale structures. The material properties of FGCNTs reinforced nano-actuator are temperature-dependent, and the influences of geometrical nonlinearity and intermolecular forces such as van der Waals interaction and Casimir force are also considered. The results indicate that the fundamental frequency decreases with the increase of initial amplitude and electrostatic voltage until drops to zero when the dynamic pull-in occurs. It is shown that the frequencies of nano-actuator decline with the increment of nonlocal stress gradient parameter whereas increasing the strain gradient parameters enlarges the frequencies. In addition, it is observed from the time history and phase portrait that the dynamic pull-in voltage of system with damping behavior is larger than that without damping system, since the dissipative effect of damping requires more energy injected into the system.

An analytical model of investigating the pull-in characteristics of CNTs reinforced nano-actuator with temperature-dependency subjected to coupled electrostatic loading, dispersion forces as van der Waals and thermally corrected Casimir force, and surface stress are derived based on von Karman׳s geometric nonlinearity and surface elasticity. The results illustrate that increment of volume fraction of CNTs enhances the structural stiffness and leads to the increases of pull-in voltage of CNTs reinforced nano-actuator; the growth of temperature increases the axial compression stress and thus decreases the pull-in voltage; and free-standing behavior depends on the characteristic scale of the CNTs reinforced nano-actuator. The doubly-clamped and doubly-supported configuration of nano-actuator are considered and the pull-in voltage of doubly-clamped nano-actuator is larger than that of doubly-supported type. Casimir force with thermal correction significantly depends on the temperature and initial gap between electrodes. The results show the difference between Casimir force with and without thermal correction is small within couples of nanometers gap but the effect of Casimir force on pull-in instability of CNTs reinforced nano-actuator cannot be neglected.

In this paper, an analytical method is presented to investigate the effect of surface characteristic and temperature change on the pull-in instability of electrically actuated nano-switches reinforced by carbon nanotubes (CNTs) based on Eringen's nonlocal beam theory. An extremely nonlinear fourth-order governing equation for the doubly clamped nano-switches made of CNTs/Si composites nanobeam is derived and solved by using the principle of virtual work, where Van der Waals force as atomic interactions and Casimir force as macro effects of quantum field fluctuation of vacuum are combined as an electrostatic force with fringing field effects. The results show that both the pull-in voltage and pull-in deflection of CNTs/Si composite nanobeam increase with the increase of CNTs volume ratio but decrease with the increase of temperature change. The coupling influences of small scale parameter, geometric behavior, surface characteristic and thermal effect on the pull-in instability of electrostatically actuated CNTs/Si nanobeam are detailedly discussed.

This paper proposes a scale-dependent model to investigate the dynamic-pull-in characteristics of a functionally graded carbon nanotubes (FGCNTs) reinforced nanodevice with a piezoelectric ...

The electromechanical coupling characteristics of carbon nanotubes (CNTs) reinforced cantilever nano-actuator are investigated by considering surface effect, nonlocal scale effect containing the long-range forces among atoms, van der Waals force as molecular interaction, and Casimir force as macro effect of quantum field fluctuation. The extremely nonlinear governing equation is derived by utilizing energy methods based on Eringen's nonlocal elasticity theory and Young–Laplace's surface effect model. Some useful finding and results show that the pull-in voltage and deflection of nano-actuator increase with the increase of CNTs volume ratio, the increase of the nonlocal scale parameter enhances the pull-in voltage, but declines the pull-in deflection, and the surface effect becomes gradually significant as the thickness of CNTs reinforced nano-actuator decreases. In addition, it is found that van der Waals force and Casimir force could lead to the collapse of nano-actuator without applied voltage, where the influence of Casimir force is more significant than that of van der Waals force on the electromechanical coupling behavior of CNTs reinforced nano-actuator.

In this paper, a nonlocal phase field method is presented to solve anisotropic diffusion-driven morphological evolution and migration of void defects in finite metallic film interconnects by utilizing a nonlocal phase field model considering a small scale effect. The nonlocal elastic theory is used to describe a small scale effect on the morphological evolution and migration of the void. In example calculations, the effects of the stress field, the electric field, and the anisotropic diffusion characteristic on the evolution of void defects in finite metallic film interconnects are described and discussed. The result in comparison with literature shows that the small scale effect based on nonlocal elastic model induces the migration diffusion of the crack tip to decrease.

Based on an effective model of multi-walled carbon nanotubes and Donnell-shell theory, an analytical method is presented to study dynamic stability characteristics of multi-walled carbon nanotubes reinforced composites considering the surface effect of carbon nanotubes. From obtained results it is seen that carbon nanotubes composites, under combined static and periodic axial loads, may occur in a parametric resonance, the parametric resonance frequency of dynamic instability regions of CNTs reinforced composites under axially oscillation loading enhances as the stiffness of matrix surrounding CNTs increases, and the surface effective modulus and residue stress of carbon nanotubes make the parametric resonance frequency and the region breadth of dynamic instability of carbon nanotubes reinforced composites increase.

In this paper, an analytical method is presented to solve the influence of initial stress and scale effect on the dynamic behaviors of bioliquid-filled microtubule, utilizing the non-local elastic theory containing long-range forces among atoms and the surface characteristics of nonstructural materials. Results show that the influences of surface characteristics on the couple vibration frequency of bioliquid-filled microtubule with initial axial stress is larger than that of long-range forces among atoms when the density of bioliquid is larger the density of microtubule, the influences of initial stress on the kth order vibration frequency of individual microtubule gradually become stables when the surface modulus is larger than a given value, and the influence of surrounding cytosol on the transverse vibration of an individual microtubule immersed cytosol increases as axially compressed loading exerted on the individual microtubule increases.

In this paper, an analytical method is presented to investigate the nonlinear buckling and expansion behaviors of local delaminations near the surface of functionally graded laminated piezoelectric composite shells subjected to the thermal, electrical and mechanical loads, where the mid-plane nonlinear geometrical relation of delaminations is considered. In examples, the effects of thermal loading, electric field strength, the stacking patterns of functionally graded laminated piezoelectric composite shells and the patterns of delaminations on the critical axial loading of locally delaminated buckling are described and discussed. Finally, the possible growth directions of local buckling for delaminated sub-shells are described by calculating the expanding forces along the length and short axis of the delaminated sub-shells.

An analytical method is presented to study the non-linear buckling characteristic of rectangular local delamination near the surface of fiber-reinforced piezoelectric lamination shells under coupled mechanical and electric loads. The stacking sequence of fiber reinforced lamination shells with piezoelectric layers is considered as symmetry, but the stacking sequence of rectangular local delamination sub-shells is arbitrary. Based on the nonlinear displacement mode of delaminated sub-shells, the effects of electric fields, the geometrical, physical parameters and stacking sequences of piezoelectric laminated shells on the non-linear local buckling for rectangular delamination near the surface of piezoelectric laminated base-shells are solved.

In this study, we report a new energy dissipation mechanism of nanomechanical resonators due to the Casimir effect originating from quantum fluctuation of the vacuum electromagnetic field at the nanoscale. An analytical study on the evaluation of the Casimir effect-induced energy loss in nanobeam resonators undergoing in-plane flexural vibration is presented. Two-dimensional elastic wave theory is employed to determine the energy transmission from the vibrating resonator to the substrate. Fourier transform and Green's function technique are adopted to solve the problem of wave motions on the surface of the substrate excited by the Casimir force. Analytical expressions of the Casimir effect-induced energy loss in terms of the quality factor, taking into account both pressure wave propagation in the noncontact substrate and shear wave propagation in the supporting substrate, as well as linear and nonlinear terms of time-varying Casimir force, have been derived. Effects of beam geometry, initial separation gap, and structural boundary conditions on energy loss are examined. Results of the present study demonstrate that the Casimir effect-induced energy loss plays an important role in the dissipation of the nanobeam resonators, in which the influence of shear wave propagation is remarkable. Also, as reflected by our results, the influence of nonlinear terms of time-varying Casimir force on the energy dissipation cannot be neglected for large-amplitude vibration, which is obviously a feature of nonlinear damping. Furthermore, we propose a possible way to experimentally measure the Casimir force by using the energy dissipation mechanism due to the Casimir force.

Stretchable conductors are critical building blocks for enabling new forms of wearable and curvilinear electronics. In this paper, we introduce a new method using the interfacial design to enable stretchable conductors with ultra-high conductivity and robustness to strain using three-dimensional helical copper micro-interconnects embedded in an elastic rubber substrate (eHelix-Cu). We studied the interfacial mechanics of the metal-elastomer to achieve highly reversible conductivities with strains. The stretchable eHelix-Cu interconnect has an ultra-high conductivity (∼105 S cm−1) that remains almost invariant when stretched to 170%, which is significantly higher than in other approaches using nanomaterials. The stretchable conductors can withstand strains of 100% for thousands of cycles, demonstrating remarkable durability for exciting potential wearable electronic applications.

Sound absorption properties of natural fiber-reinforced sandwich structures based on the structure of the fabrics were investigated in this work. The sound absorption coefficients of the sandwich structures were measured by the impedance tubes with the aid of the transfer function. Effects of yarn sizes, fiber diameters and hybrid stacking of different fibers on the sound absorption properties were studied. The flow resistance and characteristic impedance of the reinforcing fabrics which were correlated with the fabric structures were calculated and compared. It was concluded that the thicker the fabric yarn and the bigger the fiber diameter were, the better the sound absorption properties were for natural fiber-reinforced sandwich structures.

This paper reports a novel, cost-effective, scalable, and simple method for preparing poly(3-hexylthiophene)/multiwalled carbon nanotube (P3HT/MWCNT) nanocomposite films. The P3HT/MWCNT films were prepared by oxidative polymerization of 3-hexylthiophene in chloroform solution containing dispersed MWCNT. The phase composition and microstructure of the composite films were analyzed by x-ray diffraction (XRD), Fourier-transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and field-emission scanning electron microscopy. The composite films were smooth, dense, and uniform. The thermoelectric properties of the composite films were measured at room temperature. The electrical conductivity and Seebeck coefficient of the films with MWCNT content of 5 wt.% were ~1.3 × 10−3 S/cm and 131.0 μV/K, respectively.

Ignition-proof magnesium alloy is obtained in Mg–Y–Ce system, which can be melted at 1173 K in air without any protections. A dense and compact oxide film is obtained on the surface of molten Mg–Y alloys when the concentration of Y is greater than 10 wt%. With the addition of Ce the critical concentration of Y in Mg–Y alloys for forming a protective film is decreased significantly from 10 wt% to 3 wt%. AES and XRD analysis reveal that the oxide film formed on the surface of Mg–3Y–4.5Ce alloy is mainly composed of Y 2 O 3 and Ce 0.202 Y 0.798 O 1.601 . Based on the theoretic analysis and experimental results, a selective oxidation model of Mg–Y alloys at high temperatures is developed, and the third-element effects of Ce in Mg–Y alloys are discussed in detail.

Genetic transformation is useful for basic research and applied biotechnology. However, genetic transformation of microalgae is usually quite difficult due to the technical limitations of existing methods. We cloned the promoter and terminator of the nitrate reductase gene from the microalga Phaeodactylum tricornutum and used them for optimization of a transformation system of the microalga Chlorella vulgaris. This species has been used for food production and is a promising candidate as a bioreactor for large-scale production of value-added proteins. A construct was made containing the CAT (chloramphenicol acetyltransferase) reporter gene driven by the nitrate reductase promoter. This construct was transferred into the C. vulgaris genome by electroporation. Expression of CAT in transgenic Chlorella conferred resistance to the antibiotic chloramphenicol and enabled growth in selective media. Overall efficiency for the transformation was estimated to be approximately 0.03%, which is relatively high compared with other available Chlorella transformation systems. Expression of CAT was induced in the presence of nitrate and inhibited in the presence of ammonium as a sole nitrogen source. This study presented an inducible recombinant gene expression system, also providing more gene regulation elements with potential for biotechnological applications.

An analytical method is presented to investigate the pull-in instability of a carbon nanotube (CNT)-reinforced variable cross-section nanoswitch with a piezoelectric effect. Governing equations with variable coefficients are derived based on the nonlocal beam model with geometrical nonlinearity and are solved using the shooting method. All the nonlinear effects of the piezoelectric voltage, van der Waals force, Casimir force, CNT volume fraction, nonlocal parameters and width ratio on the pull-in instability are investigated. The pull-in electrostatic voltage increases with the increment of nonlocal parameters, which exhibits the significant scale-dependent behavior of nanostructures. The results show that the variable cross-section improves the flexural rigidity of the cantilever-type nanoswitch effectively, and that the piezoelectric effect of the piezoelectric layer is utilized to control the electrostatic force induced by the voltage exerted on the elastic layer, owing to piezoelectric materials' advantages of rapid response, light weight and low energy consumption.

Concerned with a 3 phase to ground permanent fault occurred at the two terminal of the 500 kV Luohe-Yingzhou transmission line in the Anhui power grid, the instability mechanism of the Anhui power grid when such a fault occurred is analyzed from the conventional point of view and also with the EEAC theory. The qualitative and quantitative explanations are also given to the cause of the stability difference when the fault occurs at different locations on the concerned line.