Banafsheh Sajadi
Delft University of Technology
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Publication
Featured researches published by Banafsheh Sajadi.
Journal of Applied Physics | 2017
Banafsheh Sajadi; Farbod Alijani; Dejan Davidovikj; J.F.L. Goosen; Peter G. Steeneken; Fred van Keulen
In the last decade, graphene membranes have drawn tremendous attention due to their potential application in Nano-Electro-Mechanical Systems. In this paper, we show that the frequency response curves of graphene resonators are powerful tools for their dynamic characterization and for extracting their equivalent Youngs modulus. For this purpose, vibrations of an electrostatically actuated circular graphene membrane are studied both experimentally and numerically. The experiments reveal the dependency of the linear and nonlinear resonance frequency of the nano-resonator on the driving DC and AC voltages. A numerical model is proposed based on the nonlinear membrane theory, and by fitting the numerically calculated change in resonance frequency due to the DC voltage to those of the experimental observations, the Youngs modulus is determined. It is shown that by using the obtained equivalent Youngs modulus, the numerical model can accurately describe the nonlinear dynamics of the graphene membrane in other...
Applied Physics Letters | 2017
Banafsheh Sajadi; J.F.L. Goosen; Fred van Keulen
The electrostatic instability (pull-in) of a flat electrode in a parallel plate capacitor has been shown to be highly sensitive to external mechanical loads such as pressure. In this paper, we substantiate the possibility of prompting additional unstable configurations in such a system, with a remarkable sensitivity to the applied pressure. This additional instability has significant advantageous properties for sensing purposes. In addition to the high sensitivity and robustness of the pull-in voltage measurements, it can be adjusted so that after the unstable configuration is met, a snap-through to a new stable configuration occurs. As a result of this bi-stable behavior, the contact between the electrodes, which is the main drawback of pull-in phenomena, will be easily avoided. The results of this paper particularly suggest the suitability of this mechanism for two different methods of pressure measurements.
IEEE Sensors Journal | 2017
Banafsheh Sajadi; Hans Goosen; Fred van Keulen
Surface stress-based measurement is a relatively new mechanism in biological and chemical sensing. The viability of this mechanism depends on the maximum sensitivity, accuracy, and precision that can be achieved with these sensors. In this paper, an analytical approximate solution and a finite-element model are employed to describe the electromechanical behavior of a surface stress-based sensor with capacitive measurements. In the proposed model, a circular membrane is assumed as the sensing component, while only a smaller concentric circular area of its surface is subjected to a change in surface stress. The presented approximate analytical solution has a good correspondence with the finite-element model and is computationally fast and accurate enough to be an effective design tool. Based on this modeling study, we can determine the optimum design of the sensor to obtain the maximum capacitive sensitivity. Moreover, we study the effect of this optimization on the precision of the system in surface stress sensing. This paper shows that the ratio of sensing area to the whole membrane plays a key role in the overall performance of such a sensor.
ASME 2016 International Mechanical Engineering Congress and Exposition | 2016
Banafsheh Sajadi; Farbod Alijani; Hans Goosen; Fred van Keulen
Micro-Electro-Mechanical devices have shown enormous popularity in engineering devices as sensors and actuators. In this paper, the instability, i.e. the dynamic pull-in behavior, of an electrically actuated circular micro-membrane is studied. In order to investigate the periodic solutions, detect bifurcations and follow branches of the solution, the non-linear equation of motion is derived using an energy approach, and, is solved by using a pseudo arc-length continuation and collocation technique. It has been shown that, both hardening and/or softening nonlinear responses could emerge depending on the applied DC voltage. The results indicate that the critical load parameters, namely DC and AC voltages and the excitation frequency, have a major influence on the pull-in characteristics of the micro-membrane. The results reveal different dynamic pull-in mechanisms. In addition, they accurately show the decrease of the pull-in voltage due to dynamic loading.The proposed approximate solution is very fast and robust for detecting the pull-in instability. It allows observation of both global and local softening behavior even close to dynamic pullin, where the resonance frequency is almost equal to zero.Copyright
Carbon | 2018
Banafsheh Sajadi; Simon van Hemert; Behrouz Arash; Pierpaolo Belardinelli; Peter G. Steeneken; Farbod Alijani
The bending rigidity of two-dimensional (2D) materials is a key parameter for understanding the mechanics of 2D NEMS devices. The apparent bending rigidity of graphene membranes at macroscopic scale differs from theoretical predictions at micro-scale. This difference is believed to originate from thermally induced dynamic ripples in the atomically thin membrane. In this paper, we perform modal analysis to estimate the effective macroscopic bending rigidity of graphene membranes from the frequency spectrum of their Brownian motion. Our method is based on fitting the resonance frequencies obtained from the Brownian motion in molecular dynamics simulations, to those obtained from a continuum mechanics model, with bending rigidity and pretension as the fit parameters. In this way, the effective bending rigidity of the membrane and its temperature and size dependence, are extracted, while including the effects of dynamic ripples and thermal fluctuations. The proposed method provides a framework for estimating the macroscopic mechanical properties at high frequencies in other two-dimensional nano-structures at finite temperatures.
International Journal of Solids and Structures | 2017
Banafsheh Sajadi; Hans Goosen; Fred van Keulen
Nonlinear Dynamics | 2018
Banafsheh Sajadi; Farbod Alijani; J.F.L. Goosen; A. van Keulen
Journal of The Mechanics and Physics of Solids | 2019
Banafsheh Sajadi; Sander Wahls; Simon van Hemert; Pierpaolo Belardinelli; Peter G. Steeneken; Farbod Alijani
arxiv:physics.app-ph | 2018
Banafsheh Sajadi; Simon van Hemert; Behrouz Arash; Pierpaolo Belardinelli; Peter G. Steeneken; Farbod Alijani
International Journal of Mechanical Sciences | 2018
Banafsheh Sajadi; Hans Goosen; Fred van Keulen