Journal articles on the topic 'Nano-force mechanical actuator'

The mechanical property is one of the important parameters for evaluating micro/nano-scale materials. The measurement of micro/nano-mechanical property usually involves measurements of small displacement and force. To provide a traceable force standard in micro/nano-newton level, we have developed a force measurement system based on electrostatic sensing and actuation techniques. The system mainly consists of a monolithic flexure stage, a three-electrode capacitor and a digital controller. The three-electrode capacitor is utilized as a position sensor, and at the same time an electrostatic force actuator. The force under measurement is balanced by a compensation electrostatic force which is traceable to electrical and length standards. A commercial cantilever-type micro-force probe was used in this calibration experiment. The force probe was brought to contact with and press into the load button (a ruby sphere) of the force measurement system by a closed-loop controlled z-scanner. The spring constant was obtained from the average slope determined from measured force-displacement curves and was found to be (2.26 ± 0.01) N/m where the given uncertainty is one standard deviation. We have successfully demonstrated the calibration of the microforce probe using our self-developed electrostatic sensing and actuating force measurement system. The measured spring constant is consistent with the manufacturer's specification, and the relative standard deviation is less than 0.5%. Note from Publisher: This article contains the abstract only.

Surface effect often plays a significant role in the pull-in performance of nano-electromechanical systems (NEMS) but limited works have been conducted for taking this effect into account. Herein, the influence of surface effect has been investigated on instability behavior of cantilever nano-actuator in the presence of van der Waals force (vdW). Three different methods, i.e. an analytical modified Adomian decomposition (MAD), Lumped parameter model (LPM) and numerical solution have been applied to solve the governing equation of the system. The results demonstrate that surface effect reduces the pull-in voltage of the system. Moreover, surface energy causes the cantilever nano-actuator with the assigned parameter to deflect as a softer structure. It is found that while surface effect becomes important for low values of the cantilever nano-actuator thickness, vdW attraction is significant for low initial gap values. Surprisingly, the increase in the initial gap, enhances the contribution of surface effect in pull-in instability of the system while reduces the contribution of vdW attraction. Furthermore, the minimum initial gap and the detachment length of the cantilever nano-actuator that does not stick to the substrate due to vdW force and surface effect has been approximated. A good agreement has been observed between the values of instability parameters predicted via these three methods. Whilst compared to the instability voltage predicted by numerical solution, the pull-in voltage obtained by MAD series and LPM method is overestimated and underestimated, respectively.

ABSTRACTIn this study, the pull-in phenomenon of a Nano-actuator is investigated employing a nonlocal Bernoulli-Euler beam model with clamped-clamped conditions. The model accounts for viscous damping, residual stresses, the van der Waals (vdW) force and electrostatic forces with nonlocal effects. The hybrid differential transformation/finite difference method (HDTFDM) is used to analyze the nonlocal effects on a graphene sheet nanobeam, which is electrostatically actuated under the influence of the coupling effect, the von Kármán nonlinear strains and the fringing field effect. The pull-in voltage as calculated by the presented model deviates by no more than 0.29% from previous literature, verifying the validity of the HDTFDM. Furthermore, the nonlocal nonlinear behavior of the electrostatically actuated nanobeam is investigated, and the effects of viscous damping, residual stresses, and length-gap ratio are examined in detail. Overall, the results reveal that small scale effects significantly influence the characteristics of the graphene sheet nanobeam actuator.

Piezoelectric bending actuators have been widely used in a variety of micro- and nano-applications, including atomic force microscopy, micro assembly, cell manipulation, and in general, micro electromechanical systems. However, their control algorithms at low frequencies suffer from nonlinearities such as hysteresis in high voltages and creep in long-time static applications. Also, in high-frequency applications, especially near the actuator natural frequencies, the actuator dynamic is greatly affected by the material nonlinearity. Therefore, the control approaches based on the linear dynamic modeling cannot be effective at high frequencies. Thus, the position control of the foregoing actuators become challenging, and it has been of researchers’ interests in the last decade. In this article, the robust position control of a bimorph piezoelectric bending actuators is investigated. In this regard, based on the nonlinear constitutive equations and the Euler–Bernoulli beam theory, a nonlinear dynamic model is presented. Then, to track a desired motion trajectory, an observer-based robust position control algorithm is proposed. The proposed control methodology is able to accommodate parametric uncertainties and other un-modeled dynamics. Also, it ensures the elimination of the position tracking error in the presence of the estimated states. Finally, the tracking ability of the controller is demonstrated in an experimental study. The experimental results show that the identification of the system is properly conducted with the average error of 5.5%. Also, the efficiency of the robust controller is proved with the error of 3.7% and 4.9% in the position tracking of the actuator inside and outside of the identified region, respectively.

An experimental setup to perform dynamic analysis of a micro- and nano-mechanical system in vacuum, gas, and liquid is presented. The setup mainly consists of a piezoelectric excitation part and the chamber that can be either evacuated for vacuum, or filled with gas or water. The design of the piezoelectric actuator was based on a Langevin transducer. The chamber is made out of materials that can sustain: vacuum, variety of gases and different types of liquids (mild acids, alkalies, common alcohols and oils). All the experiments were performed on commercial cantilevers used for contact and tapping mode Atomic Force Microscopy (AFM) with stiffness 0.2 N/m and 48 N/m, respectively, in vacuum, air and water. The performance of the setup was evaluated by comparing the measured actuator response to a finite element model. The frequency responses of the two AFM cantilevers measured were compared to analytical equations. A vacuum level of 0.6 mbar was obtained. The setup has a bandwidth of 10–550 kHz in vacuum and air, and a bandwidth of 50–550 kHz in liquid. The dynamic responses of the cantilevers show good agreement with theory in all media.

Electroplated nickel manufactured via the LIGA process, offers the possibility of stronger structure and connectors in a micro electro mechanical systems (MEMS). In this study, the mechanical properties of electroplated Nickel thin film were characterized using two methods; tension test and nano-indentation test. In tension test, a linear guided motor was used as actuator and the applied force was measured using a load cell. Strain was measured with a dual microscope that obtains the displacement of two separated zone by the tracking process of the image captured with CCD camera. In indentation test, elastic modulus was measured using a CSM(continuous stiffness measurement) module. Two types of specimen were prepared in the same wafer and tested after four months of aging, which reduces the variation of properties caused by fabrication condition and aging effect. The tension specimen is 15 µm thick and 300 µm wide. The indentation specimen is also 15 µm thick. Young's modulus were measured by two different testing methods and compared quantitatively.

AbstractThe article presents a redesigned sensor holder for an atomic force microscope (AFM) with an adjustable probe direction, which is integrated into a nano measuring machine (NMM-1). The AFM, consisting of a commercial piezoresistive cantilever operated in closed-loop intermitted contact-mode, is based on two rotational axes, which enable the adjustment of the probe direction to cover a complete hemisphere. The axes greatly enlarge the metrology frame of the measuring system by materials with a comparatively high coefficient of thermal expansion. The AFM is therefore operated within a thermostating housing with a long-term temperature stability of 17 mK. The sensor holder, connecting the rotational axes and the cantilever, inserted one adhesive bond, a soldered connection and a geometrically undefined clamping into the metrology circle, which might also be a source of measurement error. It has therefore been redesigned to a clamped senor holder, which is presented, evaluated and compared to the previous glued sensor holder within this paper. As will be shown, there are no significant differences between the two sensor holders. This leads to the conclusion, that the three aforementioned connections do not deteriorate the measurement precision, significantly. As only a minor portion of the positioning range of the piezoelectric actuator is needed to stimulate the cantilever near its resonance frequency, a high-speed closed-loop control that keeps the cantilever within its operating range using this piezoelectric actuator further on as actuator was implemented and is presented within this article.

Micro-Electro-Mechanical-Systems (MEMS) are miniaturized devices built at micro/nano-scales. At these scales, friction force is extremely strong as it resists the smooth operation and reduces the useful operating lifetimes of MEMS actuator devices. In order to reduce friction and wear in MEMS devices, we have undertaken a bio-inspired approach by applying the underlying principle of the “Lotus Effect”. Lotus leaf surfaces have small-scale protuberances and wax covered on them, which make the surfaces water-repellent in nature. By creating textured surfaces that mimic these bio-surfaces, surface energy and contact area can be reduced. This in turn reduces friction force and eventually increases the wear durability of surfaces. In our work, we have fabricated bio-inspired surfaces that resemble the texture on lotus leaf. The method includes oxygen plasma treatment of polymeric thin/thick films and application of a nanolubricant namely, perfluoropolyether (PFPE). When this method was applied to SU8 polymer thin/thick films spin coated on silicon wafers, friction reduced considerably, and simultaneously the wear durability increased by >1000 times. The method is time and cost effective, and is commercially viable.

We analyze, theoretically and by means of molecular dynamics (MD) simulations, the generation of mechanical force by a polyelectrolyte (PE) chain grafted to a plane and exposed to an external electric field; the free end of the chain is linked to a deformable target body. Varying the field, one can alter the length of the non-adsorbed (bulk) part of the chain and hence the deformation of the target body and the arising force. We focus on the impact of added salt on the magnitude of the generated force, which is especially important for applications. In particular, we develop a simple variational theory for the double layer formed near electrodes to compute the electric field acting on the bulk part of the chain. Our theoretical predictions agree well with the MD simulations. Next, we study the effectiveness of possible PE-based nano-vices, comprised of two clenching planes connected by PEs exposed to an external electric field. We analyze a novel phenomenon – two-dimensional diffusion of a nano-particle, clenched between two planes, and introduce a quantitative criterion for clenching efficiency, the clenching coefficient. It is defined as a logarithm of the ratio of the diffusion coefficients of a free and clenched particle. Using first a microscopic counterpart of the Coulomb friction model, and then a novel microscopic model based on surface phonons, with the vibration direction normal to the surface, we calculate the clenching coefficient as a function of the external electric field. Our results demonstrate a dramatic decrease of the diffusion coefficient of a clenched nano-particle for the range of parameters relevant for applications; this proves the effectiveness of the PE-based nano-vices.

This paper applies the homotopy perturbation method to the simulation of the static response of nano-switches to electrostatic actuation and intermolecular surface forces. The model accounts for the electric force nonlinearity of the excitation and for the fringing field effect. Using a mode approximation in the Galerkin projection method, the nonlinear boundary value differential equation describing the statical behavior of nano-switch is reduced to a nonlinear algebraic equation which is solved using the homotopy perturbation method. The number of included terms in the perturbation expansion for achieving a reasonable response has been investigated. Three cases have been specifically studied. These cases correspond to when the effective external force is the electrostatic force, the combined electrostatic and Casimir force and the combined electrostatic and van der Waals force. In all three cases the pull-in characteristics has been investigated thoroughly. Results have been compared with numerical results and also analytical results available in the literature. It was found that HPM modifies the overestimation of N/MEMS instability limits reported in the literature and can be used as an effective and accurate design tool in the analysis of N/MEMS.

Dispersion forces such as van der Waals and Casimir interactions become important when the size of structures shrinks. Therefore, the effective design of micro and nano-sized structures depends on appropriate consideration of these forces. In the current research, we analyzed the effect of dispersion forces on the dynamic behavior of a micro/nanobeam actuated by electrostatic forces subject to a mechanical shock. We used the Euler–Bernoulli beam theory including nonlinearities due to mid-plane stretching in our model. The equation of motion is solved using time-dependent finite element method, and pull-in forces are calculated. The stability regimes are evaluated as the set of three force parameters in which the beam elasticity overcomes the external forces, and the beam is able to vibrate without hitting the substrate. Results show that the design of the beam should be such that the three sets of non-dimensional parameters that determine the intensity of shock, dispersion, and electrostatic force do not fall above the stability limit to avoid pull-in instability. Our results have applications in the design of electrostatically actuated micro/nanobeams in mechanical shock environments such as accelerometers.

The unique capability of rendering opaque specimens transparent with atomic resolution makes transmission electron microscopy (TEM) an indispensable toolfor microstructural and crystallographic analysis of materials. Conventional TEM specimens are placed on grids about 3 mm in diameter and 10–100 μm thick. Such stringent size restriction has precluded mechanical testing inside the TEM chamber.So far, in situ testing of nanoscale thin foils has been mostly qualitative. Micro-electro-mechanical systems (MEMS) offer an unprecedented level of miniaturization to realize sensors and actuators that can add TEM visualization to nano-mechanical characterization. We present a MEMS-based uniaxial tensile experiment setup that integrates nanoscale freestanding specimens with force and displacement sensors, which can be accommodated by a conventional TEM straining stage. In situ TEM testing on 100-nm-thick freestanding aluminum specimens (with simultaneous stress measurement) show limited dislocation activity in the grain interior and consequent brittle mode of fracture. Plasticity at this size scale is contributed by grain boundary dislocations and partial dislocations.

In this article, a nonlocal thermoelastic model that illustrates the vibrations of nanobeams is introduced. Based on the nonlocal elasticity theory proposed by Eringen and generalized thermoelasticity, the equations that govern the nonlocal nanobeams are derived. The structure of the nanobeam is under a harmonic external force and temperature change in the form of rectified sine wave heating. The nonlocal model includes the nonlocal parameter (length-scale) that can have the effect of the small-scale. Utilizing the technique of Laplace transform, the analytical expressions for the studied fields are reached. The effects of angular frequency and nonlocal parameters, as well as the external excitation on the response of the nanobeam are carefully examined. It is found that length-scale and external force have significant effects on the variation of the distributions of the physical variables. Some of the obtained numerical results are compared with the known literature, in which they are well proven. It is hoped that the obtained results will be valuable in micro/nano electro-mechanical systems, especially in the manufacture and design of actuators and electro-elastic sensors.

AbstractA nonlocal elasticity theory is a popular growing technique for mechanical analysis of the micro- and nanoscale structures which captures the small-size effects. In this paper, a comprehensive study was carried out to investigate the influence of the nonlocal parameter on the bifurcation behavior of a capacitive clamped-clamped nano-beam in the presence of the electrostatic and centrifugal forces. By using Eringen’s nonlocal elasticity theory, the nonlocal equation of the dynamic motion for a nano-beam has been derived using Euler–Bernoulli beam assumptions. The governing static equation of motion has been linearized using step by step linearization method; then, a Galerkin based reduced order model have been used to solve the linearized equation. In order to study the bifurcation behavior of the nano-beam, the static non-linear equation is changed to a one degree of freedom model using a one term Galerkin weighted residual method. So, by using a direct method, the equilibrium points of the system, including stable center points, unstable saddle points and singular points have been obtained. The stability of the fixed points has been investigated drawing motion trajectories in phase portraits and basins of attraction set and repulsion have been illustrated. The obtained results have been verified using the results of the prior studies for some cases and a good agreement has been observed. Moreover, the effects of the different values of the nonlocal parameter, angular velocity and van der Waals force on the fixed points have been studied using the phase portraits of the system for different initial conditions. Also, the influence of the nonlocal beam theory and centrifugal forces on the dynamic pull-in behavior have been investigated using time histories and phase portraits for different values of the nonlocal parameter.

I have been the chairman of the technical committee of ultraprecision positioning at the Japan Society of Precision Engineers (JSPE) from 1993 to 1997. In November 2008, the 3rd International Conference on Positioning Technology (ICPT) was held in Shizuoka, Japan. After the conference I together with Dr. Sadaji Hayama, an adviser of the journal editorial board, asked by mail the most significant presenters and members of the technical committee of ultraprecision positioning if they are willing to contribute their papers for this special issue. As a result, we received more than 20 manuscripts, among which 2 development reports, 2 reviews, and 14 papers have been selected for publication in this journal. The contents of these papers relate mainly to the nano/subnanometer positioning technology, new control methods for ultraprecision positioning, guide way for precision positioning, positioning for ultraprecision machining, new hard disk drive method, etc. I would like to express my sincere gratitude to the authors for their interesting papers on this issue and I also would like to deeply thank all the reviewers and editors for their invaluable effort.1. Demarcation Between Precision Positioning and Ultraprecision Positioning The Technical Committee of Ultraprecision Positioning (TCUP) has had a poll on Ultraprecision and Ultraprecision technology to the randomly selected members of Japan Society for Precision Engineers (JSPE) every four years since 1986 [1]. Results indicate that most respondents felt that the maximum allowable positioning error and image resolution was 1 µm for precision positioning and 10 nm for ultraprecision positioning. After 2004, most respondents appeared to view 0.1 nm as the demarcation line between the precision positioning and ultraprecision positioning.2. Know-How for Achieving Ultraprecision Positioning The champion device in ultraprecision positioning is always the stages of demagnification exposure devices for semiconductors. The exposure method using stages have advanced from 1980s steppers shown in Fig. 1(a) to today's scanning stages with the increasement of LSI capacity in achieving higher processing as shown in Fig. 1(b). The stepper consists of X and Y stages.The XY stages in the 1980s consisted of a DC servomotor, either a ball or sliding screw plus a linear guide way consisting of either rollers or a slide guide. Current scanning type consists of a linear motor and pneumatic hydrostatic guide way (Fig. 1(b)). Reticle and wafer stages travel in opposite directions and the relative positioning error is about 1 nm.Ultraprecision positioning of sub-µm accuracy is now achieved either by an AC servomotor and a ball screw or by using a linear motor. subsection2.1. Achieving high positioning resolution and accuracy with less than 0.1 µm generally depends on three factors: newpage(1) Displacement sensors for feed-back(2) Mechanical structure(3) Control, including software Ultraprecision positioning is possible only when these three factors are well coordinated.(1) Displacement Sensors Ultra-precision positioning requires high-performance displacement sensors. About 10 sensor manufacturers in Japan alone currently achieve resolution under 1 nm [3]. To achieve higher resolution, laser interferometers must operate in thermostatic chambers controlling or monitoring temperature, humidity, and atmospheric pressure. Great effort is required to minimize or eliminate air turbulence and inhomogeneous atmosphere temperatures in the laser beam path. To achieve nm level resolution, operations must be conducted in a vacuum.Linear encoders, although somewhat less accurate than laser interferometers, are used in over 50% for ultraprecision positioning devices in Japan and their market share continues to grow, according to the 2006 TCUP poll. Analog sensor performance in detecting microscopic displacement is steadily improved. The technical level of precision positioning device is often assessed by how the designer considers Abbe's principle.(2) Mechanical Structure Overall structural rigidity should be maximized to ensure monolithic construction. Semiconductor aligners used in exposure are made from ceramics with a high specific rigidity, i.e., the quotient of Young's modulus divided by specific gravity.1990s arguments pitting linear actuators against ball screws subsided as their specific advantages and domains of preferred use became established. Linear guide ways using steel balls or rollers are becoming cheaper, and their accuracy and other aspects of performance are improving.When stage movement is reversed, friction generated by preloads as nonlinear spring behavior which is caused by elastic deformation of balls and race ways over the moving stroke of several tens of µm, stage vibration is easy to generate. Another disadvantage, called waving, occurs when the table moves up and down at the sub-µm level perpendicular to the stage travel direction at twice the spacing of the roller separation. It is found out that waving is minimized by crowning roller guide race way. Error due to waving is reduced to less than one tenth of the original error margin [4]. Nonlinear spring behavior is minimized by modifying control method of the positioning device. For longitudinal travel, pneumatic-hydrostatic devices virtually unaffected by friction are an alternative but are prohibitively expensive.(3) Control, Including Software In precision positioning, control devices and systems have advanced significantly in the last two decades [5], changing from analog to digital with higher sampling frequency. Current digital control enables devices to be operated in conceptually the same way as analog control. TCUP respondents [1] stated that 70% of positioning devices in Japan still depend on conventional control, PID control, with innovative contemporary control theory, fuzzy control, and neural nets, etc. yet to be fully implemented.2.2. Higher Positioning Speed Higher positioning speed is required, as well as higher positioning accuracy. In scanning Fig. 1(b), maximum stage speed exceeds 2 m/s second and maximum acceleration ranges from 3G to 5G. The corresponding speed and acceleration of the wafer stage is one fourth of these values. At such high acceleration, reaction dampers are used to prevent vibration [2].About ten years ago, the maximum velocities of positioning stages tended to be limited by the speed of the displacement sensor for feed-back, however at present, it is possible to operate at the range of speed mentioned above. Note that the velocity exceeding 2 m/s is possible even with ball-screw, but noise and microvibration remain a problem.3. Nanometer and Subnanometer Positioning [3, 5-7, 10] We are pursuing the convergence of the positioning resolution to the fullest extent of the resolution of the displacement sensor for the feed-back. Bulletins [3, 6] have carried reports on experiments attaining resolution for positioning with maximum error below 0.1 nm. We introduce cases of positioning device development at nm and sub-nm resolution using both ball screw [7] and linear motor drives [8]. I would like to introduce a commercialized ball screw drive production of 1 nm resolution [7].3.1. Combination of Ball-Screw and Stepping Motors [7] The positioning devices have the resolution respectively at 1 nm and 5 nm (the lengths of travelling strokes for the stage are 20 m and 50 mm respectively). Both compensate for the rolling frictions between the ball screw and the roller guide way and for the nonlinear spring behavior at the micro-displacement range through the control of the stepping motors at high, medium and low ranges of speeds. As the dimension of detector of the displacement sensor is very small, we can make the positioning devices smaller. So, it is very strong to external disturbances.3.2. New type of Linear Motor Drive [8] The latest new type of linear actuators, generally referred to as tunnel actuators (TAs) used in ultraprecision positioning devices with a stage stroke of 200 nm (Fig. 2) are free from magnetic attractive force between stator magnets and armatures, generating less heat and having other advantages over conventional linear motors with cores.In experiments using a displacement sensor to adjust feed-back with 0.034 nm resolution and a maximum velocity of 400 mm/s, we use ball guide ways to reduce cost and still achieved a positioning resolution of 0.2 nm (Fig. 3) [8]. Experiments confirmed that, to achieve more higher resolution, electric current linear amplifiers are 10 times more effective than PWM as the current amplifier.4. Conclusions We have discussed how nanometer- and sub-nm level positioning resolution and accuracy became possible, greatly contributing to advances in nanotechnology. Nanometer and subnanometer positioning resolution are currently verified by signals from displacement sensors for feed-back. Considering changes in the positioning of stages, however, such positioning and resolution should be verified by using displacement sensors which are more accurate.If possible, verification on the resolution and accuracy must be done using a laser interferometer in a vacuum in a temperature-controlled chamber. We feel that positioning resolution should be indicated by signals directly received from sensors without low pass filter.

Background:: Tribological issues severely confound smooth operation of moving elements in actuators-based miniaturized devices e.g. micro-electro-mechanical systems. At micro/nano scales, surface forces namely adhesion and friction manifest strongly and oppose relative mechanical motion of actuator elements. Topographical modification of sur-faces via surface patterning has emerged as a potential route to mitigate surface forces at small-scales. Methods:: Capillary force lithography is a simple yet robust technique to fabricate polymer nanostructures with varying shapes/sizes. This paper presents a brief review on the capillary force lithography technique, its salient features and tribo-logical performance of nanostructures fabricated by the technique. Conclusion:: Capillary force lithography has several attractive salient features, in particular the ability of the technique to create polymer nanopatterns of varying shapes/sizes without the need for molds with different shapes/sizes. Polymer nanostructures fabricated by the technique effectively reduce surface forces at micro/nano-scales, and are of interest for tribological application in small-scale devices.

ABSTRACTThis paper reports a NEMS (Nano Electro Mechanical Syetems) tunable color filter based on subwavelength grating with high color uniformity and low drive voltage. We newly proposed a GVG (Ground-Voltage-Ground) type tunable color filter deployed with a parallel-plate actuator with three pairs of electrode to decrease a crosstalk of an electrostatic attraction force between each actuator. The proposed structure was fabricated using an SOI wafer. The color tuning using was demonstrated by applying the drive voltage of 6.7 V. The reflected light intensity was decreased by 34 % at 680 nm wavelength. The color uniformity was also obtained in the filter area by reducing the variation of the displacement on one-dimensional arrayed actuators.

ABSTRACTBy use of excellent properties of bulk metallic glasses, some industrial products were practically prepared and their performances were investigated. Linear actuator constructed by a set of Fe-based BMG yokes generates large Lorentz force due to the large permeability and saturation magnetization of the BMG. Ni-based BMG microgear prepared by injection casting exhibits nano-imprintability against the surface roughness of mold. The newly developed alloy with a nominal atomic composition of Ti52Cu23Ni11Mo7Fe7 exhibits high yield strength of 1250 MPa, high fracture strength of 2740 MPa and large plastic elongation of over 20 %. These results for the industrial products made of BMGs are promising for future developments as industrial materials with high performance.

Two-dimensional (2D) equations of piezoelectric bimorph nano-actuators are presented which take account of the surface effect. The surface effect of the bimorph structure is treated as a surface layer with zero thickness. The influence on the plate's overall properties resulted from the surface elasticity and piezoelectricity is modeled by a spring force exerting on the boundary of the bulk core. Using the derived 2D equations, the anti-parallel piezoelectric bimorph nano-actuators of both cantilever and simply supported plate type are investigated theoretically. Numerical results show that the effective properties and the deflections of the antiparallel bimorph nano-actuators are size-dependent. The deflection at the resonant frequency achieves nearly 50 times as that under the static driving voltage.

This paper deals with the investigation of nonlinear static pull-in instability of smart Nano-switches regarding the new size-dependent phenomenon, known as flexoelectricity, together with the surface effects. It is noteworthy that the coupling effect of the flexoelectricity and surface elasticity on nonlinear static pull-in instability of electrostatically-actuated Nano-switches has not been studied before. Euler-Bernoulli beam assumptions in conjunction with the von-Karman nonlinearity are considered to formulate the problem. The Nano-switch is subjected to electrostatic actuation force with fringing field effect as well as Casimir force. Refined constitutive relations for piezoelectric materials capturing the flexoelectric effects are taken into consideration for mathematical modeling. Additionally, a surface elasticity approach is employed to reach an accurate model for the system. Considering the imposed electric boundary conditions, Gauss’s equation is solved to acquire the electric potential distribution along with the thickness of the Nano-switch. Thereafter, Hamilton’s principle is hired to derive the coupled nonlinear governing equations of the system. Utilizing the differential quadrature method (DQM), the nonlinear ordinary differential equations are transformed into a system of nonlinear algebraic equations. Consequently, Newton-Raphson method is exploited as a numerical method to solve the obtained algebraic equations which leads to the pull-in voltage. Investigating the maximum displacement of the Nano-switch in response to the applied electrostatic force, the effects of various involved parameters such as flexoelectricity and surface elasticity on pull-in instability are explored in detail. Furthermore, the size-dependent behavior of the pull-in instability against the flexoelectric, surface effects and applied piezoelectric voltage is analyzed. Totally, it is revealed that the flexoelectricity may exhibit a substantial influence on the pull-in behavior of smart Nano-switches, especially for some cases with small thicknesses. Therefore, this effect should be taken into account to reach an accurate, reliable and optimized design for Nano-switches.

ABSTRACTBasic recent results, properties and characteristics of ionic polymer conductor nano-composites (IPCNC) as biomimetic distributed nanosensors, nanoactuators and artificial muscles are briefly discussed in this paper. Some fundamental considerations on biomimetic distributed nanosensing and nanoactuation are first presented and then expanded to cover some recent advances in manufacturing techniques, force optimization, 3-D fabrication of IPMC's, recent modeling and simulations, sensing and transduction and product development. This paper also covers some recent industrial and medical applications including a multi-fingered grippers (macro, micro, nano), biomimetic robotic fish and caudal fin actuators, diaphragm micropump, multi-string musical instruments, linear actuators made with IPMNC's, IPMNC-based data glove and attire, IPMNC-based heart compression/assist devices and systems, wing flapping flying system made with IPMNC's and a host of others.

AbstractWe report a novel tunable nanophotonic device concept based on Mechanically Controlled Photonic Crystal (MCPC), which is comprised of a periodic array of high index dielectric material and a low index polymer. Tunability is achieved by applying mechanical force with nano-/micro-electron-mechanical system actuators. The mechanical stress induces changes in the periodicity of the photonic crystal, to which the photonic band structure is extremely sensitive. This consequently produces tunability much greater than that achievable by electro-optic materials such as liquid crystal. Our theoretical investigations revealed that we could achieve dynamic beam steering over a wide range of angles up to 75° with only 10% mechanical stretching. We also predicted tunable sub-wavelength imaging in which we could tune the frequency response and focal length of negative index PC lens. For experimental demonstration, we fabricated the PC structures on Si-on-insulator substrates. Optical characterizations clearly showed the anticipated negative refraction in which the incident beam was refracted back to the side it was incident. The experimental demonstration of negative refraction at optical frequencies in a Si-based photonic crystal structure is a significant step toward the next-generation nanophotonics.

AbstractThe surface wrinkling of biological tissues is ubiquitous in nature. Accumulating evidence suggests that the mechanical force plays a significant role in shaping the biological morphologies. Controlled wrinkling has been demonstrated to be able to spontaneously form rich multiscale patterns, on either planar or curved surfaces. The surface wrinkling on planar substrates has been investigated thoroughly during the past decades. However, most wrinkling morphologies in nature are based on the curved biological surfaces and the research of controllable patterning on curved substrates still remains weak. The study of wrinkling on curved substrates is critical for understanding the biological growth, developing three-dimensional (3D) or four-dimensional (4D) fabrication techniques, and creating novel topographic patterns. In this review, fundamental wrinkling mechanics and recent advances in both fabrications and applications of the wrinkling patterns on curved substrates are summarized. The mechanics behind the wrinkles is compared between the planar and the curved cases. Beyond the film thickness, modulus ratio, and mismatch strain, the substrate curvature is one more significant parameter controlling the surface wrinkling. Curved substrates can be both solid and hollow with various 3D geometries across multiple length scales. Up to date, the wrinkling morphologies on solid/hollow core–shell spheres and cylinders have been simulated and selectively produced. Emerging applications of the curved topographic patterns have been found in smart wetting surfaces, cell culture interfaces, healthcare materials, and actuators, which may accelerate the development of artificial organs, stimuli-responsive devices, and micro/nano fabrications with higher dimensions.

AbstractAluminum nitride (AlN) is a promising material for a number of applications due to its temperature and chemical stability. Furthermore, AlN maintains its piezoelectric properties at higher temperatures than more commonly used materials, such as Lead Zirconate Titanate (PZT) [1, 2], making AlN attractive for high temperature micro and nano-electromechanical (MEMs and NEMs) applications including, but not limited to, high temperature sensors and actuators, micro- channels for fuel cell applications, and micromechanical resonators.This work presents a novel AlN micro-channel fabrication technique using Metal Organic Vapor Phase Epitaxy (MOVPE). AlN easily nucleates on dielectric surfaces due to the large sticking coefficient and short diffusion length of the aluminum species resulting in a high quality polycrystalline growth on typical mask materials, such as silicon dioxide and silicon nitride [3,4]. The fabrication process introduced involves partially masking a substrate with a silicon dioxide striped pattern and then growing AlN via MOVPE simultaneously on the dielectric mask and exposed substrate. A buffered oxide etch is then used to remove the underlying silicon dioxide and leave a free standing AlN micro-channel. The width of the channel has been varied from 5 ìm to 110 ìm and the height of the air gap from 130 nm to 800 nm indicating the stability of the structure. Furthermore, this versatile process has been performed on (111) silicon, c-plane sapphire, and gallium nitride epilayers on sapphire substrates. Reflection High Energy Electron Diffraction (RHEED), Atomic Force Microscopy (AFM), and Raman measurements have been taken on channels grown on each substrate and indicate that the substrate is influencing the growth of the AlN micro-channels on the SiO2 sacrificial layer.