Distortion produced by RF MEMS varactors on digital communication signals

This paper presents a study of the nonlinear effects introduced by MEMS varactors when excited with digitally modulated RF signals (QPSK and 16 QAM). The study is based on simulating a nonlinear model of the MEMS device using harmonic-balance and envelope solvers, and on experimental measurements of the wave reflected by the on-wafer MEMS device. It is shown that the adjacent-channel power ratio (ACPR) and error-vector magnitude (EVM) of the digital signal suffer a degradation due to the device nonlinear distortion.Peer Reviewe

Study of intermodulation in RF MEMS variable capacitors

This paper provides a rigorous study of the causes and physical origins of intermodulation distortion (IMD) in RF microelectromechanical systems (MEMS) capacitors, its analytical dependence on the MEMS device design parameters, and its effects in RF systems. It is shown that not only third-order products exist, but also fifth order and higher. The high-order terms are mainly originated by the nonlinear membrane displacement versus applied voltage and, in the case considered in this study, with an additional contribution from the nonlinear dependence of the reflection coefficient phase on the displacement. It is also shown that the displacement nonlinear behavior also contributes to the total mean position of the membrane. In order to study these effects in depth, an analytical frequency-dependent IMD model for RF MEMS based on a mobile membrane is proposed and particularized to the case of a MEMS varactor-a device for which IMD can be significant. The model is validated, up to the fifth order, theoretically (using harmonic balance) and empirically (the IMD of a MEMS varactor is measured). To this end, a two-tone IMD reflection measurement system for MEMS is proposed.Peer Reviewe

Development of a wireless MEMS inertial system for health monitoring of structures

Health monitoring of structures by experimental modal analysis is typically performed with piezoelectric based transducers. These transducers are usually heavy, large in size, and require high power to operate, all of which reduce their versatility and applicability to small components and structures. The advanced developments of microfabrication and microelectromechanical systems (MEMS) have lead to progressive designs of small footprint, low dynamic mass and actuation power, and high-resolution inertial sensors. Because of their small dimensions and masses, MEMS inertial sensors could potentially replace the piezoelectric transducers for experimental modal analysis of small components and structures. To transfer data from MEMS inertial sensors to signal analyzers, traditional wiring methods may be utilized. Such methods provide reliable data transfer and are simple to integrate. However, in order to study complex structures, multiple inertial sensors, attached to different locations on a structure, are required. In such cases, using wires increases complexity and eliminates possibility of achieving long distance monitoring. Therefore, there is a need to implement wireless communications capabilities to MEMS sensors. In this thesis, two different wireless communication systems have been developed to achieve wireless health monitoring of structures using MEMS inertial sensors. One of the systems is designed to transmit analog signals, while the other transmits digital signals. The analog wireless system is characterized by a linear frequency response function in the range of 400 Hz to 16 kHz, which covers the frequency bandwidth of the MEMS inertial sensors. This system is used to perform modal analysis of a test structure by applying multiple sensors to the structure. To verify the results obtained with MEMS inertial sensors, noninvasive, laser optoelectronic holography (OEH) methodology is utilized to determine modal characteristics of the structure. The structure is also modeled with analytical and computational methods for correlation of and verification with the experimental measurements. Results indicate that attachment of MEMS inertial sensors, in spite of their small mass, has measurable effects on the modal characteristics of the structure being considered, verifying their applicability in health monitoring of structures. The digital wireless system is used to perform high resolution tilt and rotation measurements of an object subjected to angular and linear accelerations. Since the system has been developed based on a microcontroller, programs have been developed to interface the output signals of the sensors to the microcontroller and RF components. The system is calibrated using the actual driving electronics of the MEMS sensors, and it has achieved an angular resolution of 1.8 mrad. The results show viability of the wireless MEMS inertial sensors in applications requiring accurate tilt and rotation measurements. Additional results presented included application of a MEMS gyroscope and microcontroller to perform angular rate measurements. Since the MEMS gyroscope only generates analog output signals, an analog to digital conversion circuit was developed. Also, a program has been developed to perform analog to digital conversion with two decimal places of accuracy. The experimental results demonstrate feasibility of using the microcontroller and the gyroscope to perform wireless angular rate measurements

Automating Dynamic Decoupling in Object-Oriented Modelling and Simulation Tools

Abstract This manuscript presents a technique that allows Equationbased Object-Oriented Modelling Tools (EOOMT) to exploit Dynamic Decoupling (DD) for partitioning a complex model into "weakly coupled" submodels. This enhances simulation efficiency, and is naturally keen to parallel integration or co-simulation. After giving an overview of the problem and of related work, we propose a method to automate DD by means of a novel structural analysis of the system -called "cycle analysis" -and of a mixed-mode integration method. Also, some considerations are exposed on how the presented technique can be integrated in EOOMT, considering as representative example a Modelica translator. Simulation tests demonstrate the technique, and the realised implementation is released as free software

Nonlinear Systems

The editors of this book have incorporated contributions from a diverse group of leading researchers in the field of nonlinear systems. To enrich the scope of the content, this book contains a valuable selection of works on fractional differential equations.The book aims to provide an overview of the current knowledge on nonlinear systems and some aspects of fractional calculus. The main subject areas are divided into two theoretical and applied sections. Nonlinear systems are useful for researchers in mathematics, applied mathematics, and physics, as well as graduate students who are studying these systems with reference to their theory and application. This book is also an ideal complement to the specific literature on engineering, biology, health science, and other applied science areas. The opportunity given by IntechOpen to offer this book under the open access system contributes to disseminating the field of nonlinear systems to a wide range of researchers

Numerical analysis and performance improvement of nanostructured Cu2O/TiO2 pn heterojunction solar cells using SCAPS

Abstract: This paper reported numerical analysis and performance improvement of nanostructured Cu2O/TiO2 pn heterojunction solar cells. Metal oxides thin films including Copper oxides are promising materials for photovoltaic applications. Although, the efficiency is still lower than other solar cells materials. This paper focused on improving the efficiency of Cu2O/TiO2 solar cells using SCAPS simulation tool. This was done by varying the effect of film surface thickness and effect of varying deposition temperature on the solar cells. The aim of the study is to serve as a theoretical guide for laboratory research on the improvement of efficiency of Cu2O metal oxide solar cells. The solar cells equations were modelled and thereafter theoretical validation of the nanostructured metal oxides was performed. The model working points input power of 100 mW/m2 using an illumination of AM1.5 lamp. The modelled solar cell exhibits a short-circuit current (Jsc) of 26.57 mA/cm2, 0.7188 V open-circuit voltage (Voc), fill factor (FF) of 70, and 13.37% efficiency (η). A value of 2.30 eV was recorded for the band gap. Also, electron affinity and Nyquist plot were obtained for the solar cells. Solar cells with thin absorber surface thickness will result in lower fabrication cost. This will open a new frontier for modelling of metal oxide based thin films solar cells especially Cu2O thin films solar cells

Nonlinear stochastic vibration analysis for energy harvesting and other applications

With the rapid development of electronic technology, the power consumption of electronic devices has decreased significantly. Consequently, there is substantial interest in harvesting energy from ambient sources, such as vibration, in order to power small-scale wireless devices. To design optimal vibration harvesting systems it is important to determine the maximum power obtainable from a given vibration source. Initially, white noise base excitation of a general nonlinear energy harvester model is considered. The power input from white noise is known to be proportional both to the total oscillating mass of the system and the magnitude of the noise spectral density, regardless of the internal mechanics of the system. This power is split between undesirable mechanical damping and useful electrical dissipation, where the form of the stiffness profile and device parameters determine the relative proportion of energy dissipated by each mechanism. An upper bound on the electrical power is derived and used to guide towards optimal harvesting devices, revealing that low stiffness systems exhibit maximum performance. Many engineering applications will exhibit more complicated spectra than the flat spectrum of white noise. Expanding upon the white noise analysis, a method to investigate the power dissipation of nonlinear oscillators under non-white excitation is developed by extending the Wiener series. The relatively simple first term of the series, together with the excitation spectrum, is found to completely define the power dissipated. An important property of this first term, namely that the integral over its frequency domain representation is proportional to the oscillating mass, is derived and validated both numerically and experimentally, using a base excited cantilever beam with a nonlinear restoring force produced by magnets. Another form of excitation prevalent in many mechanical systems is a combination of deterministic and broadband random vibration. Lastly, the Duffing oscillator is used to illustrate the behaviour of a nonlinear system under this form of excitation, where the response is observed to spread around the attractor that would be seen if purely deterministic excitation was present. The ability of global weighted residual methods to produce the complex responses typical of nonlinear oscillators is assessed and found to be accurate for systems with weak nonlinearity

SISO Piezo based circuit development for active structural vibration control

This paper deals with the issue of developing a smart vibration control platform following an innovative model‐based approach. As a matter of fact, obtaining accurate information on system response in pre‐design and design phases may reduce both computational and experimental efforts. From this perspective, a multi‐degree‐of‐freedom (MDOF) electro‐mechanical coupled system has been numerically schematized implementing a finite element formulation: a robust simulation tool integrating finite element model (FEM) features with Simulink® capabilities has been developed. Piezo strain actuation has been modelled with a 2D finite element description: the effects exerted on the structure (converse effect) have been applied as lumped loads at the piezo nodes interface. The sensing (direct effect) has instead been modelled with a 2D piezoelectric constitutive equation and experimentally validated as well. The theoretical study led to the practical development of an integrated circuit which allowed for assessing the vibration control performance. The analysis of critical parameters, description of integrated numerical models, and a discussion of experimental results are addressed step by step to get a global overview of the engineering process. The single mode control has been experimentally validated for a simple benchmark like an aluminum cantilevered beam. The piezo sensor‐actuator collocated couple has been placed according to an optimization process based on the maximum stored electrical energy. Finally, a good level of correlation has been observed between the forecasting model and the experimental application: the frequency analysis allowed for characterizing the piezo couple behavior even far from the resonance peak