We present a study of the dynamic behavior of a microelectromechanical systems (MEMS) device consisting of an imperfect clamped–clamped microbeam subjected to electrostatic and electrodynamic actuation. Our objective is to develop a theoretical analysis, which is able to describe and predict all the main relevant aspects of the experimental response. Extensive experimental investigation is conducted, where the main imperfections coming from microfabrication are detected, the first four experimental natural frequencies are identified and the nonlinear dynamics are explored at increasing values of electrodynamic excitation, in a neighborhood of the first symmetric resonance. Several backward and forward frequency sweeps are acquired. The nonlinear behavior is highlighted, which includes ranges of multistability, where the nonresonant and the resonant branch coexist, and intervals where superharmonic resonances are clearly visible. Numerical simulations are performed. Initially, two single mode reduced-order models are considered. One is generated via the Galerkin technique, and the other one via the combined use of the Ritz method and the Padé approximation. Both of them are able to provide a satisfactory agreement with the experimental data. This occurs not only at low values of electrodynamic excitation, but also at higher ones. Their computational efficiency is discussed in detail, since this is an essential aspect for systematic local and global simulations. Finally, the theoretical analysis is further improved and a two-degree-of-freedom reduced-order model is developed, which is also capable of capturing the measured second symmetric superharmonic resonance. Despite the apparent simplicity, it is shown that all the proposed reduced-order models are able to describe the experimental complex nonlinear dynamics of the device accurately and properly, which validates the proposed theoretical approach.
Remote areas are usually fed from generators that run on diesel. Recently, there is an increasing interest on hybrid renewable energy sources, especially wind and solar energies for their availability and competitive running cost in the Middle East region. The hybrid renewable energy generation systems usually have two or more different generation (or storage) sources of different types to secure a continuous supply for the electrical loads.The paper presents a case study of a remote health center which operates 24 hours a day, and shows the importance of relying on renewable energy systems. The system considered consists of Wind Turbine, Batteries, photovoltaic, and conventional diesel generator to feed a load variable at a rate of 55 kWh/day with 5.9 kW peak load. The study is based on real data of wind speed and solar radiation obtained from official authorities. The various available options are compared technically and economically using a HOMER software package. The optimal reliable system is selected and the capacity of the system components is specified.
We present an investigation into the static and dynamic behavior of an electrostatically actuated clamped-clamped polysilicon microbeam resonator accounting for its fabrication imperfections, which are commonly encountered in similar microstructures. These are mainly because of the initial deformation of the beam due to stress gradient and its flexible anchors. First, we show experimental data of the microbeam when driven electrically by varying the amplitude and frequency of the voltage loads. The results reveal several interesting nonlinear phenomena of jumps, hysteresis, and softening behaviors. Theoretical investigation is then conducted to model the microbeam, and hence, interpret the experimental data. We solve the Eigen value problem governing the natural frequencies analytically. We then utilize a Galerkin-based procedure to derive a reduced order model, which is then used to simulate both the static and dynamic responses. To achieve good matching between theory and experiment, we show that the exact profile of the deformed beam needs to be utilized in the reduced order model, as measured from the optical profiler, combined with a shooting technique simulation, which is capable of tracing the resonant frequency branches under very-low damping conditions.
In this study we present a theoretical and experimental investigation of a microelectromechanical system (MEMS). The device is constituted of a clamped-clamped polysilicon microbeam electrostatically and electrodynamically actuated. The microbeam has imperfections in the geometry, which are related to the microfabrication process. Using a laser Doppler vibrometer, experimental testing based on forward and backward sweeps is conducted in a neighborhood of the first symmetric natural frequency. Our aim is that of introducing a simple mechanical model, which, despite the inevitable approximations, is able to catch and predict the most relevant aspects of the device response. Many parameters of the microbeam are unknown. Their values are identified by developing a parametric analysis, which is based on matching the experimental natural frequencies and the experimental frequency response diagrams. Extensive simulations are performed. Theoretical and experimental frequency responses are analyzed in detail at increasing values of electrodynamic excitation. A satisfactory concurrence of results is achieved, not only at low electrodynamic loads, but also at higher ones, when the escape (dynamic pull-in) becomes impending. This confirms that, despite the apparent simplicity, the proposed theoretical model is able to simulate the complex dynamics of the device accurately and properly.
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