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Dive into the research topics where Hassen M. Ouakad is active.

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Featured researches published by Hassen M. Ouakad.


Journal of Micromechanics and Microengineering | 2009

On the nonlinear resonances and dynamic pull-in of electrostatically actuated resonators

Fadi M. Alsaleem; Mohammad I. Younis; Hassen M. Ouakad

We present modeling, analysis and experimental investigation for nonlinear resonances and the dynamic pull-in instability in electrostatically actuated resonators. These phenomena are induced by exciting a microstructure with nonlinear forcing composed of a dc parallel-plate electrostatic load superimposed on an ac harmonic load. Nonlinear phenomena are investigated experimentally and theoretically including primary resonance, superharmonic and subharmonic resonances, dynamic pull-in and the escape-from-potential-well phenomenon. As a case study, a capacitive sensor made up of two cantilever beams with a proof mass attached to their tips is studied. A nonlinear spring‐mass‐damper model is utilized accounting for squeeze-film damping and the parallel-plate electrostatic force. Long-time integration and a global dynamic analysis are conducted using a finite-difference method combined with the Floquet theory to capture periodic orbits and analyze their stability. The domains of attraction (basins of attraction) for data points on the frequency‐response curve are calculated numerically. Dover cliff integrity curves are calculated and the erosion of the safe basin of attraction is investigated as the frequency of excitation is swept passing primary resonance and dynamic pull-in. Conclusions are presented regarding the safety and integrity of MEMS resonators based on the simulated basin of attraction and the observed experimental data. (Some figures in this article are in colour only in the electronic version)


Journal of Computational and Nonlinear Dynamics | 2010

Nonlinear Dynamics of Electrically Actuated Carbon Nanotube Resonators

Hassen M. Ouakad; Mohammad I. Younis

This work presents an investigation of the nonlinear dynamics of carbon nanotubes (CNTs) when actuated by a dc load superimposed to an ac harmonic load. Cantilevered and clamped-clamped CNTs are studied. The carbon nanotube is described by an Euler-Bernoulli beam model that accounts for the geometric nonlinearity and the nonlinear electrostatic force. A reduced-order model based on the Galerkin method is developed and utilized to simulate the static and dynamic responses of the carbon nanotube. The free-vibration problem is solved using both the reduced-order model and by solving directly the coupled in-plane and out-of-plane boundary-value problems governing the motion of the nanotube. Comparison of the results generated by these two methods to published data of a more complicated molecular dynamics model shows good agreement. Dynamic analysis is conducted to explore the nonlinear oscillation of the carbon nanotube near its fundamental natural frequency (primary-resonance) and near one-half, twice, and three times its natural frequency (secondary-resonances). The nonlinear analysis is carried out using a shooting technique to capture periodic orbits combined with the Floquet theory to analyze their stability. The nonlinear resonance frequency of the CNTs is calculated as a function of the ac load. Subharmonic-resonances are found to be activated over a wide range of frequencies, which is a unique property of CNTs. The results show that these resonances can lead to complex nonlinear dynamics phenomena, such as hysteresis, dynamic pull-in, hardening and softening behaviors, and frequency bands with an inevitable escape from a potential well.


IEEE\/ASME Journal of Microelectromechanical Systems | 2010

Nonlinear Dynamics of MEMS Arches Under Harmonic Electrostatic Actuation

Mohammad I. Younis; Hassen M. Ouakad; Fadi M. Alsaleem; Ronald N. Miles; Weili Cui

We present an investigation of the nonlinear dynamics of clamped-clamped micromachined arches when actuated by a dc electrostatic load superimposed on an ac harmonic load. The Galerkin method is used to discretize the distributed-parameter model of a shallow arch to obtain a reduced-order model. The static response of the arch due to a dc load actuation is simulated, and the results are validated by comparing them to experimental data. The dynamic response of the arch to a combined dc load and ac harmonic load is studied when excited near its fundamental natural frequency, twice its fundamental natural frequency, and near other higher harmonic modes. The results show a variety of interesting nonlinear phenomena, such as hysteresis, softening behavior, dynamic snap-through, and dynamic pull-in. The results are also shown demonstrating the potential to use microelectromechanical systems (MEMS) arches as bandpass filters and low-powered switches. An experimental work is conducted to test arches realized of curved polysilicon microbeams when excited by dc and ac loads. Experimental data are shown for the softening behavior and the dynamic pull-in of the curved microbeams.


Shock and Vibration | 2013

An electrostatically actuated MEMS arch band-pass filter

Hassen M. Ouakad

This work presents an investigation of the dynamics of micromachined arches resonators and their potential to be uti- lized as band-pass filters. The arches are actuated by a DC electrostatic load superimposed to an AC harmonic load. The dynamic response of the arch is studied analytically using a Galerkin-based reduced-order model when excited near its fundamental and third natural frequencies. Several simulation results are presented demonstrating interesting jumps and snap-through behavior of the arches and their attractive features for uses as band-pass filters, such as their sharp roll-off from pass bands to stop bands and their flat response.


Mathematical Problems in Engineering | 2009

Modeling and Simulations of Collapse Instabilities of Microbeamsdue to Capillary Forces

Hassen M. Ouakad; Mohammad I. Younis

We present modeling and analysis for the static behavior and collapse instabilities of doubly-clamped and cantilever microbeams subjected to capillary forces. These forces can be as a result of a volume of liquid trapped underneath the microbeam during the rinsing and drying process in fabrication. The model considers the microbeam as a continuous medium, the capillary force as a nonlinear function of displacement, and accounts for the mid-plane stretching and geometric nonlinearities. The capillary force is assumed to be distributed over a specific length underneath the microbeam. The Galerkin procedure is used to derive a reduced-order model consisting of a set of nonlinear algebraic and differential equations that describe the microbeams static and dynamic behaviors. We study the collapse instability, which brings the microbeam from its unstuck configuration to touch the substrate and gets stuck in the so-called pinned configuration. We calculate the pull-in length that distinguishes the free from the pinned configurations as a function of the beam thickness and gap width for both microbeams. Comparisons are made with analytical results reported in the literature based on the Ritz method for linear and nonlinear beam models. The instability problem, which brings the microbeam from a pinned to adhered configuration is also investigated. For this case, we use a shooting technique to solve the boundary-value problem governing the deflection of the microbeams. The critical microbeam length for this second instability is also calculated.


International Journal of Bifurcation and Chaos | 2014

Analysis of Bifurcation Behavior of a Piecewise Linear Vibrator with Electromagnetic Coupling for Energy Harvesting Applications

A. El Aroudi; Hassen M. Ouakad; L. Benadero; Mohammad I. Younis

Recently, nonlinearities have been shown to play an important role in increasing the extracted energy of vibration-based energy harvesting systems. In this paper, we study the dynamical behavior of a piecewise linear (PWL) spring-mass-damper system for vibration-based energy harvesting applications. First, we present a continuous time single degree of freedom PWL dynamical model of the system. Different configurations of the PWL model and their corresponding state-space regions are derived. Then, from this PWL model, extensive numerical simulations are carried out by computing time-domain waveforms, state-space trajectories and frequency responses under a deterministic harmonic excitation for different sets of system parameter values. Stability analysis is performed using Floquet theory combined with Filippov method, Poincare map modeling and finite difference method (FDM). The Floquet multipliers are calculated using these three approaches and a good concordance is obtained among them. The performance of the system in terms of the harvested energy is studied by considering both purely harmonic excitation and a noisy vibrational source. A frequency-domain analysis shows that the harvested energy could be larger at low frequencies as compared to an equivalent linear system, in particular, for relatively low excitation intensities. This could be an advantage for potential use of this system in low frequency ambient vibrational-based energy harvesting applications.


international symposium on mechatronics and its applications | 2009

The static and dynamic behavior of MEMS arches under electrostatic actuation

Mohammad I. Younis; Hassen M. Ouakad

In this paper, we investigate the static and dynamic behavior of electrostatically actuated clamped-clamped micromachined arches. The Galerkin method is used to discretize the distributed-parameter model of the considered shallow arch, and thus approximate it by a set of nonlinear algebraic equations and ordinary-differential equations describing its statics and dynamics. Five symmetric mode shapes of either a straight beam or a deformed arch is found to be sufficient to simulate the static and dynamic behavior of the arch. The natural frequencies and mode shapes of the arch are calculated for various values of DC voltages and initial rises of the arch. The forced vibration response of the arch to a combined DC and AC harmonic load is determined when excited near its fundamental natural frequency. The results show various nonlinear behaviors, such as hysteresis, softening behavior, and dynamic pull-in. Several scenarios of snap-through and pull-in are shown, which found depend on the initial rise of the arch.


Journal of Vibration and Control | 2015

The response of a micro-electro-mechanical system (MEMS) cantilever-paddle gas sensor to mechanical shock loads

Hassen M. Ouakad

This work presents an investigation into the effect of nonlinearities on the response of a micro-electro-mechanical system gas sensor under mechanical shock and electrostatic loading. The gas sensor consists of a cantilever microbeam with a rigid microplate (micro-paddle) attached to its tip. A nonlinear Euler-Bernoulli beam theory is used to model the system, accounting for both geometric and inertia nonlinearities, in addition to the nonlinear electrostatic force used to actuate the system. The system of integro-partial-differential equations is discretized using a Galerkin procedure to extract a reduced-order model, which is then used for dynamic simulations of the system responses. The influences of the different components of nonlinearity such as geometric and inertia nonlinearities are examined. The results of the nonlinear model are compared to results obtained from linear beam theory and finite element simulations. For mechanical shock loading, both quasi-static and dynamic responses of a microbeam are considered. The effect of nonlinearity is found to be significant when the deflection of the microbeam exceeds around 30% of its length. The consequence of the large deflection is that the geometric nonlinearity has a much stronger influence on the response in comparison to the inertia nonlinearity. It is also apparent that the effect of the paddle is to enhance the dynamic, as opposed to the quasi-static, response of the microbeam to mechanical shock. For electrostatic actuation, it is found that using a nonlinear beam model to predict the pull-in and the deflection produces a slight improvement over using a linear beam model.


Journal of Vibration and Control | 2015

Nonlinear feedback controller of a microbeam resonator

Hassen M. Ouakad; Ali H. Nayfeh; Slim Choura; Fehmi Najar

This paper is concerned with the modeling, nonlinear dynamic analysis and control design of an electrostatically actuated clamped-clamped microbeam. The model accounts for the mid-plane stretching and nonlinear form of the electrostatic force actuated along the microbeam span. A reduced-order model is constructed, using the method of multiple scales, to examine the microsystem static and dynamics behaviors. To improve the microbeam behavior, a nonlinear feedback controller is proposed. The main control objective is to make it behave like commonly known one-degree-of-freedom self-excited oscillators, such as the van der Pol and Rayleigh oscillators, which depict attractive filtering features in their dynamic frequency responses. For this, a review of the nonlinear dynamics of one of these oscillators is first provided to gain insight into its appealing filtering characteristics. We then present a novel control design that regulates the pass band of the considered microbeam and derive analytical expressions that approximate the nonlinear resonance frequencies and amplitudes of the periodic solutions when it is subjected to one-point then to fully distributed feedback forces. We apply Floquet theory to ascertain the stability of the limit cycles. We finally suggest an electronic circuitry made of six analog devices AD633JN for the implementation of the proposed feedback controller.


Archive | 2016

NONLINEAR STRUCTURAL MECHANICS OF MICRO AND NANO SYSTEMS

Hassen M. Ouakad

Recently, the use of micro- and nanoelectromechanical systems (MEMS and NEMS) has seen a dramatic increase observed especially with the increasing interest of wide spectrum of technologies such as mass/gas sensors, filters, switches, and resonators. Adding to that, their simple fabrication process makes them easy to be fabricated at a low cost and hence commercialized easily. The basic structures that are used numerously to build MEMS and NEMS devices are principally made of cantilever or clamped-clamped beams. For example, they are employed in mass sensors for bio and gas sensing, as switching elements in RF microswitches and optical fibers, and probe elements in atomic force microscope (AFM). Also, they form a basic element in nanoscale devices such as carbon nanotubes (CNTs).

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Mohammad I. Younis

King Abdullah University of Science and Technology

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Fadi M. Alsaleem

University of Nebraska–Lincoln

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Fehmi Najar

Tunisia Polytechnic School

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Iswan Pradiptya

King Fahd University of Petroleum and Minerals

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Jihad E. Alqasimi

King Fahd University of Petroleum and Minerals

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Hussain M. Al-Qahtani

King Fahd University of Petroleum and Minerals

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Muhammad A. Hawwa

King Fahd University of Petroleum and Minerals

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Mohammad H. Hasan

University of Nebraska–Lincoln

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