Sharif Digital Repository

A Piezoelectric Energy Harvester (PEH) of cantilever beam type is developed to optimize the generated power by means of active control of moment of inertia of the beam. Distributed parameter equations of vibration of the beam are developed. Then the electromechanical response of the piezoelectric actuator is discussed. The harvester configuration is then described and it is shown that such a configuration can avoid the drastic power drop in presence of uncertainty around resonance frequency by applying voltage to the piezoelectric actuator. Finally the proposed harvester output power working frequency span is compared to conventional methods to show that the significant performance... 

We present fabrication, characterization, and experimental results describing electrical actuation and readout of the mechanical vibratory response of electrospun ZnO nanofibers. For a fiber with an approximate radius of 200 nm and a length of 70 ìm, a resonance frequency around 3.62 MHz with a quality factor (Q) of about 235 in air at ambient conditions is observed. It is shown that the measured frequency of the resonance is consistent with results from finite element simulations. Also, the measurements were performed in an enclosed chamber with controlled levels of ethanol vapor. The adsorption of ethanol causes a shift in the resonance frequency of the fibers, which can be related to the... 

The probability of occurrence of random cavities' resonance frequency in the Stokes bandwidth of the Raman active medium can cause Raman laser oscillation in the random structures. Due to the small bandwidth of Raman line shape, the probability of the simultaneous appearance of random cavity resonance frequencies in the cascade Stokes line shapes is small. As a result, the cascade Raman laser oscillation effects on the saturation behavior are negligible. The nonlinear transmission matrix method is employed to determine the statistical behavior of a Raman random laser. Our results showed that the statistical behavior depends on the position of the Stokes line shape relative to the center of... 

An efficient hybrid modal-molecular dynamics method is developed for the vibration analysis of large scale nanostructures. Using the reduced order method, presented in this paper, linear and nonlinear vibrations of a suspended graphene nanoribbon (GNR) carrying an electric current in a harmonic magnetic field are investigated. The resonance frequencies as well as the nonlinear vibration response obtained by the present technique and direct molecular dynamic simulations are in very good agreement. Also, the obtained results illustrate the hardening behavior of nonlinear vibrations which is diminished by stretching the GNR  

In recent years, there has been a growing interest in the simulation and analysis of piezoelectric transducers with the he help of equivalent electrical circuit simulations (EECS). This paper has been devoted to study of such approach for two designed and fabricated ultrasonic sandwich transducers. By using analytical analysis, the dimensions of components of the two piezoelectric transducers were determined for the assumed resonance frequencies of 30 kHz and 40 kHz. Then, by using a two dimensional finite element model, and regarding two different modeling techniques for the transducers and by application of a current source which was connected directly to the piezoelectric pieces of the... 

This paper presents an effective current injection method for a single phase grid-connected PV inverter with LCL filter. The main objective of the proposed control strategy is to compensate the resonance effect of the LCL filter. In the proposed control strategy, a resonance compensator is augmented to the conventional proportional resonance (PR) controller to attenuate current oscillations in resonance frequency of LCL filter. The proposed strategy robustly regulates the output current of grid connected inverter in various grid impedances and provides a high quality current injection capability for the PV inverter in harmonic polluted condition of the grid voltage. The performance of the... 

In this paper the free vibration of single walled carbon nanopeapods encapsulating C60 molecules is considered. The nanopeapod is embedded in an elastic medium and clamped at both ends. The Euler-Bernoulli beam model is used for the carbon nanotube and the C60 molecules are considered as lumped masses attached to the beam. Based on the nonlocal elasticity theory the governing equation of motion is derived and the resonance frequencies of the nanopeapod are obtained. The effects of small scale, foundation stiffness and ratio of the fullerenes' mass to the nanotube's mass on the frequencies are studied and some conclusions are drawn  

The analysis and design of a tunable low noise active inductor is presented. The noise performance of the proposed gyrator-based active inductor is improved without either degrading its quality factor or consuming more power using a linear Feed Forward Path (FFP). The proposed low noise active inductor has been designed and fabricated using standard 0.18-μm CMOS technology. The measurements show a 3 fold improvement in the input noise current compared to that of conventional active inductors. The active inductor was tuned and measured at the resonance frequency of 2.5 GHz, which could be extended as high as 5.5 GHz, with a quality factor of 30. The circuit draws 4.8 mA from a 1.8 V supply  

This paper aims at investigating the resonance frequencies and stability of a long Graphene Nano-Ribbon (GNR) carrying electric current. The governing equation of motion is obtained based on the Euler-Bernoulli beam model along with Hamilton's principle. The transverse force distribution on the GNR due to the interaction of the electric current with its own magnetic field is determined by the Biot-Savart and Lorentz force laws. Using Galerkin's method, the governing equation is solved and the effect of current strength and dimensions of the GNR on the stability and resonance frequencies are investigated  

This paper presents application of high-Q cavity resonator in phase-shifter less technique. A mathematical analysis is presented to show the dependency of the measured phase noise in terms of loaded quality factor and resonance frequency of the high-Q cavity resonator. Experimental measurements resulted from different methods for a synthesized oscillator at 9.976 GHz show great validity and accuracy of the proposed technique. This technique needs no tuning for the phase-shifter and can introduce better sensitivity compared to the setup that uses a delay-line as a frequency discriminator element due to much lower insertion loss particularly at high carrier frequencies. The sensitivity of -113... 

In this paper we present experimental results describing electrical readout of the mechanical vibratory response of graphene-doped fibers by employing electrical actuation. For a fiber resonator with an approximate radius of 850 nm and length of 100 m, we observed a resonance frequency around 580 kHz with a quality factor (Q) of about 2511 in air at ambient conditions. Through the use of finite element simulations, we show that the reported frequency of resonance is relevant. We also show that the resonance frequency of the fiber resonators decreases as the bias potential is increased due to the electrostatic spring-softening effect