The Experts below are selected from a list of 12588 Experts worldwide ranked by ideXlab platform
Pedro Ribeiro - One of the best experts on this subject based on the ideXlab platform.
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non linear modes of vibration of timoshenko nanobeams under Electrostatic Actuation
International Journal of Mechanical Sciences, 2017Co-Authors: Marco Alves, Pedro RibeiroAbstract:Abstract The non-linear dynamical behaviour of Electrostatically actuated nanobeams of rectangular cross section is investigated using a p -version finite element derived by Galerkin’s method, where the partial differential equations of motion are reduced into a finite dimensional system of non-linear ordinary differential equations in the time domain. Timoshenko’s beam theory is applied, as well as the beam analogue of von Karman’s plate theory in order to take into account the geometrical non-linearity. The formulation considers non-local effects which affect the inertia of the system, the non-linear stiffness terms and the Electrostatic force. Considering several harmonics for the periodic solution, the harmonic balance method is used to transform the ordinary differential equations into algebraic equations of motion in the frequency domain, which are then solved by an arc-length continuation method. Convergence studies show that accurate results are achieved with a reasonably low number of degrees of freedom, and the different terms related to the effects considered in the proposed model are validated with results published in the literature. The importance of the shear deformation and the rotary inertia in this problem is investigated, as well as the influence on the dynamic response of the Electrostatic force, fringing fields and non-local effects, combined with the geometrical non-linearity. It is found that different combinations of these effects lead to different outcomes in the system dynamics, changing the natural frequencies and, to a smaller extent, the mode shapes, and leading to hardening, softening or even the combination of both. Furthermore, non-linear phenomena such as internal resonances and bifurcations are studied.
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non local effects on the non linear modes of vibration of carbon nanotubes under Electrostatic Actuation
International Journal of Non-linear Mechanics, 2016Co-Authors: Pedro RibeiroAbstract:Abstract Carbon nanotubes (CNTs) based NEMS with Electrostatic sensing/Actuation may be employed as sensors, in situations where it is fundamental to understand their dynamic behaviour. Due to displacements that are large in comparison with the thickness and to the non-linearity of the Electrostatic force, these CNT based NEMS operate in the non-linear regime. The knowledge of the modes of vibration of a CNT provides a picture of what one may expect from its dynamic behaviour not only in free, but also in forced vibrations. In this paper, the non-linear modes of vibration of CNTs actuated by Electrostatic forces are investigated. For that purpose, a p-version finite element type formulation is implemented, leading to ordinary differential equations of motion in the time domain. The formulation takes into account non-local effects, which influence the inertia and the stiffness of CNTs, as well as the Electrostatic Actuation. The ordinary differential equations of motion are transformed into algebraic equations of motion via the harmonic balance method (HBM) and then solved by an arc-length continuation method. Several harmonics are considered in the HBM. The importance of non-local effects, combined with the geometrical non-linearity and with the action of the Electrostatic force, is analysed. It is found that different combinations of these effects can result in alterations of the natural frequencies, variations in the degrees of softening or hardening, changes in the frequency content of the free vibrations, and alterations in the mode shapes of vibration. It is furthermore found that the small scale, here represented by the non-local theory, has an effect on interactions between the first and higher order modes which are induced by the geometrical and material non-linearities of the system.
Yael Nemirovsky - One of the best experts on this subject based on the ideXlab platform.
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Novel micromachined vibrating rate-gyroscope with optical sensing and Electrostatic Actuation
Sensors and Actuators A: Physical, 2000Co-Authors: O. Bochobza-degani, D J Seter, Eran Socher, Yael NemirovskyAbstract:This paper reports the fabrication and preliminary characterization of a novel vibratory rate-sensor. The sensor employs the modulated integrative differential optical sensing (MIDOS) to detect the output mode amplitude. The mechanical part of the sensor is fabricated by bulk micromachining using a double side anisotropic wet etching process. A CMOS chip containing the detecting photodiodes and their readout electronics is fabricated through MOSIS. Electrical and mechanical integration of the two parts is achieved by using the indium bumps technology. The proof mass is aligned with the detecting photodiodes, so that when at rest, equal portions of the two photodiodes are exposed. Several prototypes have been fabricated and tested on a rotating table. Good linearity (
Adriano Cola - One of the best experts on this subject based on the ideXlab platform.
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on the Electrostatic Actuation of capacitive rf mems switches on gaas substrate
Sensors and Actuators A-physical, 2015Co-Authors: Anna Persano, M C Martucci, Fabio Quaranta, Pietro Siciliano, Adriano ColaAbstract:Abstract The Electrostatic Actuation behaviour of the gold bridge in capacitive radio frequency microelectromechanical system switches, fabricated on GaAs substrate, is investigated. An unconventional imaging technique, based on the out-of-focus reflection, was used to evaluate the topographic profile of the suspended bridge and its lowering as a function of the voltage. Important parameters for the switch Actuation, such as the pull-down voltage and the air gap between the bridge and the actuator, are estimated. Capacitance-voltage curves allow to evaluate the capacitance associated to the bridge in the up and down states as well as the dielectric constant of the Si 3 N 4 layer, which covers the actuator. The experimental values of the pull-down voltage and the dielectric constant are used to extract from the theoretical equations the residual stress of the fabricated gold membrane. Finally, the current through the dielectric Si 3 N 4 layer was measured as a function of the voltage applied to the actuator, finding that the Poole–Frenkel effect is the dominant conduction mechanism when the switch is actuated.
M T Ahmadian - One of the best experts on this subject based on the ideXlab platform.
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non linear behaviors of carbon nanotubes under Electrostatic Actuation based on strain gradient theory
International Journal of Non-linear Mechanics, 2014Co-Authors: Abbas Rastgoo, Mir Masoud Seyyed Fakhrabadi, M T AhmadianAbstract:Abstract The paper deals with studying the deflection and pull-in voltages of the carbon nanotubes under Electrostatic Actuation with various dimensions and boundary conditions. The size-dependent behaviors of the carbon nanotubes (CNTs) are considered via application of the strain gradient theory. The results obtained from the strain gradient theory are compared to those estimated using the classical elasticity. The outcomes reveal that the classical elasticity theory underestimates the pull-in voltages of the carbon nanotubes and strain gradient theorem results in stiffer nano-structures with higher pull-in voltages. Increasing of the deflection due to the higher voltages increases the differences between the results of the strain gradient theory and classical elasticity. Thus, in order to design CNT-based nano-electromechanical systems, researchers should consider the size-dependent theories such as the theorem used in this paper. In addition, the influences of different dimensions on the pull-in voltages are studied in detail. The results proved that longer CNTs with smaller diameters possess lower pull-in voltages than shorter ones with larger diameters.
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a new efficient approach for modeling and simulation of nano switches under the combined effects of intermolecular surface forces and Electrostatic Actuation
International Journal of Applied Mechanics, 2009Co-Authors: Mahdi Mojahedi, Hamid Moeenfard, M T AhmadianAbstract: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 th...
Mir Masoud Seyyed Fakhrabadi - One of the best experts on this subject based on the ideXlab platform.
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non linear behaviors of carbon nanotubes under Electrostatic Actuation based on strain gradient theory
International Journal of Non-linear Mechanics, 2014Co-Authors: Abbas Rastgoo, Mir Masoud Seyyed Fakhrabadi, M T AhmadianAbstract:Abstract The paper deals with studying the deflection and pull-in voltages of the carbon nanotubes under Electrostatic Actuation with various dimensions and boundary conditions. The size-dependent behaviors of the carbon nanotubes (CNTs) are considered via application of the strain gradient theory. The results obtained from the strain gradient theory are compared to those estimated using the classical elasticity. The outcomes reveal that the classical elasticity theory underestimates the pull-in voltages of the carbon nanotubes and strain gradient theorem results in stiffer nano-structures with higher pull-in voltages. Increasing of the deflection due to the higher voltages increases the differences between the results of the strain gradient theory and classical elasticity. Thus, in order to design CNT-based nano-electromechanical systems, researchers should consider the size-dependent theories such as the theorem used in this paper. In addition, the influences of different dimensions on the pull-in voltages are studied in detail. The results proved that longer CNTs with smaller diameters possess lower pull-in voltages than shorter ones with larger diameters.