Pull-in instability of carbon nanotube-reinforced nano-switches considering scale,surface and thermal effects

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.     

Fringing in tubular permanent-magnet Machines: part II. Cogging force and its minimization

In Part I of the paper, analytical field solutions, which account for the fringing flux associated with the finite length of the ferromagnetic armature core in tubular permanent-magnet machines, are established. In Part II, the technique is applied to both slotless and slotted machines, and the results are verified by finite-element calculations. The analytical field solutions enable the resultant cogging force associated with the finite length of the armature to be determined as a function of the armature displacement, for both radially and Halbach magnetized stators. Thus, they not only provide an effective means for evaluating the influence of leading design parameters on the cogging force waveform, but also facilitate its minimization.     

High-Fidelity Magnetic Equivalent Circuit Model for an Axisymmetric Electromagnetic Actuator

A computationally inexpensive magnetic equivalent circuit (MEC) improves axisymmetric electromagnet design and modeling tools by accurately capturing fringing and leakage effects. Lumped parameter MEC models are typically less accurate for modeling electromagnetic devices than distributed parameter finite-element models (FEMs). However, MEC models require significantly less computational time to solve than FEMs and therefore lend themselves to applications where solution time is critical, such as in optimization routines, dynamic simulation, or preliminary design. This paper describes how fringing permeances in axisymmetric electromagnetic devices can be derived and then included in a MEC model. Including fringing field effects significantly decreases error in the MEC model, creating a more accurate, or high fidelity, magnetic equivalent circuit (HFMEC). Eighty-nine electromagnets with unique geometries, coil currents, and materials were modeled with MEC, HFMEC, and FEM methods. The axisymmetric HFMEC developed in this work had 67% less average force error and 88% less average flux error compared to traditional MEC results while still being computationally inexpensive to solve.      

One-sided fluxes in planar, cylindrical, and spherical magnetizedstructures

In planar structures, magnetization patterns exist that have the surprising property that all the external fringing field of flux emerges from one side of the structure, with precisely none appearing on the other side. In the last 25 years, this fact has led to a number of useful applications. More recently, the same concept has been found to hold for both cylindrical and spherical hollow structures, where all the fringing flux emerges either inside or outside the structure, with precisely none appearing on the other side. Again, this has led to a number of important practical applications. While many of the concepts have been published previously, this paper contains, for the first time, a uniform mathematical analysis of these one-sided flux configurations. Additionally, the paper reviews the principal applications of one-sided flux structures     

Coral reefs of the Mascarenes, Western Indian Ocean

The reefs of the Mascarenes differ in structure and stage of development. Mauritius is the oldest island, bound by a discontinuous fringing reef and small barrier reef, with large lagoon patch reefs. Rodrigues has nearly continuous fringing reefs bounding an extensive lagoon with deep channels and few patch reefs. Reunion, the youngest island, has short stretches of narrow fringing reefs along southwestern coasts. The islets of St Brandon are bound to the east by an extensive arc of fringing reef. Reef mapping of the Mascarenes using satellite imagery provides an estimate of 705 km2 of shallow reef habitats. These areas have been modified over geological time by changes in sea level, ocean-atmosphere disturbances and biological and chemical forcing. Further modification has resulted from historical changes in land-use patterns. Recent economic development has placed many of these reefs at risk from anthropogenic impact. The reefs of the Mascarenes have escaped mass mortality from bleaching to date, which increases their conservation significance within the wider Indian Ocean. The reefs are poorly protected. A case study shows how a geographic information system incorporating reef-habitat maps can help formulate and demonstrate Marine Protected Area boundaries.     

Unified nonlinear quasistatic and dynamic analysis of RF-MEMS switches

In this paper, the modified couple stress-based strain gradient theory is used to provide a unified nonlinear model of the quasistatic and dynamic behavior of an electrostatic microelectromechanical systems microbeam capacitive switch of the Euler–Bernoulli type. Our model not only accounts for the contact between the microbeam and the dielectric substrate using nonlinear springs and dampers, but also accounts for the system size by introducing an internal material length scale parameter. In view of the size of the microbeam and electrostatic gaps involved, Casimir and Van der Waals forces, damping force due to the squeeze membrane effect and electrostatic force with first-order fringing field effects were accounted for in our model. The resulting nonlinear system of PDEs was expanded into a coupled system using series expansion and integrated into ODEs using weighted residuals of the Galerkin type. To overcome the difficulties associated with the determination of the contact length, the Heaviside function for deflection was replaced with a Heaviside function for the contact length, and an iterative procedure was adopted to determine the contact length. To obtain the time variation of the microbeam, the dynamic system of equations was solved using Newmark’s integration scheme. The outcome of our work shows the dependence of the pull-in voltage upon the inertia force, slenderness ratios of the microbeam, the electrostatic gap and the initial boundary conditions of the switch. In addition, we were also able to provide the full history of the microbeam past the pull-in threshold.     

High-Frequency Fringing Fields Loss in Thick Rectangular and Round Wire Windings

This paper examines high-frequency losses of thick rectangular and round wire windings due to the fringing fields of an air-gap. It derives formulas for the losses and validates them numerically using the 2-D finite-element method (FEM). It also provides a procedure for including the effect of self and proximity fields in the loss calculations, using the principle of superposition and a one-dimensional model of self and proximity fields. The paper validates the latter procedure numerically, using a 2-D finite element model.      

High-efficiency, liquid-crystal-based, controllable diffraction grating

We propose a new reflective liquid-crystal diffraction grating design attained by combining the use of a polymer wall to reduce the detrimental effect of the fringing electric field in a high-resolution grating and a quarter-wave plate to make the device polarization independent. This design could offer significant performance advantages in a projection display system. Results of calculations are compared with experimental data.     

Design, Prototyping, and Analysis of a Novel Tubular Permanent-Magnet Linear Machine

In this paper, we present a new tubular permanent-magnet linear machine with square-shaped cross section and derive its corresponding analytical model by solving Maxwell equations and applying the superposition theorem. The analytical field solution is necessary for obtaining an analytic form of the machine parameters and variables such as the self- and mutual inductances of the windings, the thrust force, and the windings electromotive force (EMF). These provide a valuable tool for tubular machine analysis, design, and optimization. In order to achieve maximum force density, we optimized the design parameters of the proposed machine using the analytical model. We used finite-element analysis and experimental results to demonstrate the validity of the developed analytical model. Again using the Fourier series of the cogging force and its harmonic analysis, in this paper, we introduce two techniques for cogging force reduction in the new tubular linear permanent-magnet machine. The first technique reduces the cogging force due to interaction between the permanent magnets and the stator teeth, and the other reduces the cogging force due to finite length of the armature. These techniques are straightforward, and their implementations in the tubular linear permanent magnet machine with square cross section are easy. We investigated the effectiveness of the proposed techniques in cogging force reduction by 3-D finite-element analysis and experimental measurements.      

小型磁偏转质谱计磁场的分析计算

磁偏转质谱计是根据离子在磁分析器中运动时,不同质荷比的离子有不同的偏转半径原理来实现质量分离的。磁场大小和分布对质谱计的性能影响较大,因而设计时需要对质谱计磁场分布进行精确计算。应用有限元法建立了计算质谱计磁分析器磁场的物理模型,并利用这一模型计算了磁分析器磁感应强度在空间的分布情况。结果表明,在半径分别为20 mm和50 mm的1/4圆弧轨道上,其磁场分布规律类似。由于边缘磁场效应,在磁铁边界区域约3 mm范围内,磁感应强度基本呈直线下降,这一结果为磁分析器的结构优化和边缘场补偿提供了理论依据。     

Combined action of Casimir and electrostatic forces on nanocantilever arrays

Cantilever arrays with nearest-neighbor interactions are considered to obtain the pull-in parameters. The interactions between the neighboring beams are a combination of the Casimir force and the electrostatic force with the first-order fringing field correction. A set of coupled nonlinear boundary value problems and a set of coupled nonlinear equations arise in the distributed and lumped parameter modeling of the array, respectively. The models are simulated numerically to obtain the pull-in parameters of the arrays with different number of beams. The pull-in parameters of large arrays converge to constant values, which are independent of the number of beams in the array. The constants obtained by the distributed and lumped parameter models are compared. The verification of the proposed models is performed by comparing the simulation results with the corresponding ones in the literature.     

Effect of mechanical force,rotation and moving internal heat source on a two-temperature fiber-reinforced thermoelastic medium with two theories

In the present paper, the three-phase-lag model and Green–Naghdi theory without energy dissipation are used to study the effect of a mechanical force and a rotation on the wave propagation in a two-temperature fiber-reinforced thermoelastic problem for a medium with an internal heat source that is moving with a constant speed. The methodology applied here is the use of the normal mode analysis to solve the problem of a thermal shock problem to obtain the exact expressions of the displacement components, force stresses, thermal temperature, and conductivity temperature. Numerical results for the considered variables are given and illustrated graphically in the absence and presence of a rotation as well as a mechanical force. A comparison is made with the results in the context of the two theories in the absence and presence of a moving internal heat source.     

Fringing-field effect in liquid-crystal beam-steering devices: an approximate analytical model

An approximate analytical model was developed that links the fringing-field broadening of the phase profile of a liquid-crystal (LC) beam-steering device, and the resulting diffraction efficiency, to the physical parameters of the device including the cell thickness as well as the dielectric, optical, and geometrical constants of the device. The analysis includes a full solution of the Laplace equation for the LC device in which the broadening of the initial voltage profile into an effective voltage-drop profile, due to the fringing-field effect, is derived. It is shown that within the linear approximation used, the broadening of the phase profile is identical to the broadening of the effective voltage profile in the presence of the fringing field. On the basis of this model, the resulting broadening kernel of the phase profile is found to be proportional to the LC cell thickness. These results are found to be in an excellent agreement with high-precision computer simulations performed on the LC beam-steering structure, thereby validating this approximate linear model.     

Suction force of vibrating suction method based on pi theorem: Analysis and experiment

This paper presents an analysis method for calculating the suction force generated by the vibrating suction method, which is used for mini wall-climbing robots. Using this analysis method, an empirical equation based on the pi theorem was deduced. To verify the validity and feasibility of the empirical equation, an experimental platform was developed, and a series of vibrating experiments were performed. In the experiments, the sine vibration mode was chosen as a special case to determine the two coefficients of the empirical equation in the experimental condition of a certain suction cup and working plane. Then, the calculated suction force and the real suction force were compared and analysed. The results indicate that the empirical equation will satisfy the engineering application with a small margin of error if the amplitude and angular frequency of the vibrating suction method are not too small. In addition, the effect of amplitude and frequency on the average suction force of the sine vibration mode was also analysed and tested.     

Tubular modular permanent-magnet machines equipped with quasi-Halbach magnetized magnets-part I: magnetic field distribution, EMF, and thrust force

This paper describes the analysis, design, and experimental characterization of three-phase tubular modular permanent-magnet machines equipped with quasi-Halbach magnetized magnets. It identifies feasible slot/pole number combinations and discusses their relative merits. It establishes an analytical expression for the open-circuit magnetic field distribution, formulated in the cylindrical coordinate system. The expression has been verified by finite-element analysis. The analytical solution allows the prediction of the thrust force and electromotive force in closed forms, and provides an effective tool for design optimization, as will be described in Part II of the paper.     

压电陶瓷在叠加式力标准机上的应用研究

指出了叠加式力标准机力源施力精度和力值维持时问取决于它所能实现的最小位移量及其控制精度。提出并建立了利用“逆压电效应”原理产生可控制的精密变形,直接作用于力源的传力系统中调节力值的理论和方法。使用压电陶瓷材料研制了施力装置及其控制器,并进行了实验研究。理论分析和实验结果表明,用压电陶瓷材料及其控制技术作叠加式力标准机力值控制装置,使力源具有高精度、高性能、自动化和低成本的特点。     

A Low-Cost Centrifugal Force Type Flow Sensor for Measuring the Flow Rate of a Fluid Through a Pipeline

In this paper, attempts have been made to develop a very simple low-cost flow sensor by using the effect of centrifugal force of a fluid on circular pipe section. The theoretical analysis of the sensor is reported in this paper. The centrifugal force developed by the flowing fluid on one end of a common balance has been sensed by an inductive pickup placed in a bridge network. The output of the bridge network has been found to vary with flow rate. Experiments have been carried out to find the static characteristic of the sensor and the experimental results are reported in this paper. From these experiments, it has been observed that the experimental graph follows the theoretically predicted characteristic with very good repeatability.     

Fringing field directed assembly of nanomaterials

This letter reports on a new gas-phase printing approach to deposit nanomaterials into addressable areas on a surface with 50 nm lateral accuracy. Localized fringing fields that form around conventional resist patterns (PMMA and SiO2) with openings to a silicon substrate are used to direct the assembly of nanomaterials into the openings. Directed assembly was observed due to a naturally occurring inbuilt charge differential at the material interface that was further enhanced by corona charging to yield a field strength exceeding 1 MV/m in Kelvin probe force microscopy (KFM) measurements. The assembly process is independent of the nanomaterial source and type: an evaporative, plasma, and electrospray source have been tested to deposit silicon and metallic nanoparticles. The results suggest a potential route to form nanolenses on the basis of charged resist structures; a 3-fold size reduction has been observed between the structures and the assembled particles. Applications range from the integration of functional nanomaterial building blocks to the elimination of lift-off steps in semiconductor processing.     

Inelastic behaviour in steel wire pull-out from Portland cement mortar

This paper describes a study of the factors influencing the pull-out force of stainless steel wires embedded in Portland cement mortar. The first part provides a theoretical elastic analysis of the pull-out force in terms of the misfit between wire and matrix, the coefficient of friction at the wire-matrix interface and the elastic constants of the materials. The resulting equation shows that the behaviour is greatly influenced by the Poisson contraction of the wire during pull-out. Since the elastic modulus of the mortar is only five or six times smaller than that of the wire this can lead to a large reduction in stress-transfer across the wire-matrix interface and a corresponding reduction in pull-out force. In general the pull-out force is extremely sensitive to the wire-matrix misfit. The second part deals with an experimental study of the effect of surface finish of the wire and the effect of an externally applied confining pressure. The results show that when a pressure is applied the pull-out force increases, as expected, due to the increase in stress-transfer across the interface. However, a very small amount of movement of the wire leads to a large reduction in pull-out force. This is not due to wear of the matrix; it is due to densification of the cement mortar near the wire surface and is produced by the combined effect of the normal pressure and the tangential traction. This compaction in turn leads to a non-reversible reduction in the fibre-matrix misfit and a fall in pull-out force. The paper concludes with a discussion of the significance of this non-elastic behaviour in the practical performance of fibre reinforced mortars and the role of mechanical deformations of the fibres.     

Deformation and strength of cracked member under bending moment and axial force

This paper presents the analysis of the deformation and the strength of a cracked body, emphasizing a superimposed effect of multiple toads on elastic and plastic deformation of an edge-cracked beam or column under two kinds of loads, bending and axial toads. The analysis has been done about the effect of axial force on the elastic angular deformation, including the effect of half-closure of crack, and also on the angular deformation of a cracked plastic hinge. Finally as a practically important example, the above analyses are applied to the problem of the deformation and the load carrying capacity of the cracked column under an eccentric axial force.