RF-MEMS switches with AlN dielectric and their applications

This paper reports on the potential of RF-MEMS technology based on aluminum nitride capacitive dielectric and nickel-suspended membranes to provide RF circuit functions in reconfigurable front-end radios. The RF performance of capacitive switches, distributed MEMS transmission lines (DMTLs) phase shifters for beam steering and tunable filters, including center frequency and bandwidth tuning of bandpass and band-stop filters are presented. Detailed characterization based on S-parameter data demonstrates very promising figures of merit of all fabricated demonstrators from 5 to 40GH

Hybrid modeling and control of mechatronic systems using a piecewise affine dynamics approach

This thesis investigates the topic of modeling and control of PWA systems based on two experimental cases of an electrical and hydraulic nature with varying complexity that were also built, instrumented and evaluated. A full-order model has been created for both systems, including all dominant system dynamics and non-linearities. The unknown parameters and characteristics have been identi ed via an extensive parameter identi cation. In the following, the non-linear characteristics are linearized at several points, resulting in PWA models for each respective setup. Regarding the closed loop control of the generated models and corresponding experimental setups, a linear control structure comprised of integral error, feed-forward and state-feedback control has been used. Additionally, the hydraulic setup has been controlled in an autonomous hybrid position/force control mode, resulting in a switched system with each mode's dynamics being de ned by the previously derived PWA-based model in combination with the control structure and respective mode-dependent controller gains. The autonomous switch between control modes has been de ned by a switching event capable of consistently switching between modes in a deterministic manner despite the noise-a icted measurements. Several methods were used to obtain suitable controller gains, including optimization routines and pole placement. Validation of the system's fast and accurate response was obtained through simulations and experimental evaluation. The controlled system's local stability was proven for regions in state-space associated with operational points by using pole-zero analysis. The stability of the hybrid control approach was proven by using multiple Lyapunov functions for the investigated test scenarios.publishedVersio

Investigation into the use of active frequency selective surfaces to extend the absorption bandwidth of a conventional Salisbury screen absorber

It is well accepted that the absorption bandwidth of a metal back-plane absorber, built with either dielectric or magnetic materials, is inherently narrow. It is also well known that in order to increase the absorption bandwidth, the absorber thickness must be increased through decreasing the permittivity or permeability of its spacer. This improved performance, however, comes at a cost. The absorption bandwidth is increased at the expense of not only an increase of absorber thickness, specially at lower frequencies, but also the yielding of a mechanically weaker structure. The most important implication of the former is that there is a tradeoff between absorber thickness and absorption bandwidth. These two conflicting absorber properties are, however, of equal importance since the optimum absorber is one which has a small thickness as well as a wideband absorption response. This inherent trade-off is due to the fundamental frequency limitations imposed by the constitutive parameters of materials and is more detrimental at microwave frequencies.The aim of the research programme described in this thesis was thus to investigate the use of adaptive complex impedance structures, in the form of active frequency selective surfaces (AFSSs), to extend the absorption bandwidth of a small thickness Salisbury screen absorber, thus addressing directly the aforementioned by minimizing the trade-off that exists between absorber thickness and absorption bandwidth

Identification of high-level functional/system requirements for future civil transports

In order to accommodate the rapid growth in commercial aviation throughout the remainder of this century, the Federal Aviation Administration (FAA) is faced with a formidable challenge to upgrade and/or modernize the National Airspace System (NAS) without compromising safety or efficiency. A recurring theme in both the Aviation System Capital Investment Plan (CIP), which has replaced the NAS Plan, and the new FAA Plan for Research, Engineering, and Development (RE&D) rely on the application of new technologies and a greater use of automation. Identifying the high-level functional and system impacts of such modernization efforts on future civil transport operational requirements, particularly in terms of cockpit functionality and information transfer, was the primary objective of this project. The FAA planning documents for the NAS of the 2005 era and beyond were surveyed; major aircraft functional capabilities and system components required for such an operating environment were identified. A hierarchical structured analysis of the information processing and flows emanating from such functional/system components were conducted and the results documented in graphical form depicting the relationships between functions and systems

Compact simulated countercurrent chromatography for downstream processing of (bio)pharmaceuticals

Dissertação para obtenção do Grau de Doutor em Engenharia Química e BioquímicaFundação para a Ciência e Tecnologia - PhD gran

Nonlinear switching and solitons in PT-symmetric photonic systems

One of the challenges of the modern photonics is to develop all-optical devices enabling increased speed and energy efficiency for transmitting and processing information on an optical chip. It is believed that the recently suggested Parity-Time (PT) symmetric photonic systems with alternating regions of gain and loss can bring novel functionalities. In such systems, losses are as important as gain and, depending on the structural parameters, gain compensates losses. Generally, PT systems demonstrate nontrivial non-conservative wave interactions and phase transitions, which can be employed for signal filtering and switching, opening new prospects for active control of light. In this review, we discuss a broad range of problems involving nonlinear PT-symmetric photonic systems with an intensity-dependent refractive index. Nonlinearity in such PT symmetric systems provides a basis for many effects such as the formation of localized modes, nonlinearly-induced PT-symmetry breaking, and all-optical switching. Nonlinear PT-symmetric systems can serve as powerful building blocks for the development of novel photonic devices targeting an active light control.Comment: 33 pages, 33 figure

Control Theory: On the Way to New Application Fields

Control theory is an interdisciplinary field that is located at the crossroads of pure and applied mathematics with systems engineering and the sciences. Recently, deep interactions are emerging with new application areas, such as systems biology, quantum control and information technology. In order to address the new challenges posed by the new application disciplines, a special focus of this workshop has been on the interaction between control theory and mathematical systems biology. To complement these more biology oriented focus, a series of lectures in this workshop was devoted to the control of networks of systems, fundamentals of nonlinear control systems, model reduction and identification, algorithmic aspects in control, as well as open problems in control

NASA patent abstracts bibliography: A continuing bibliography. Section 1: Abstracts (supplement 38)

Abstracts are provided for 132 patents and patent applications entered into the NASA scientific and technical information system during the period July 1990 through December 1990. Each entry consists of a citation, an abstract, and in most cases, a key illustration selected from the patent or patent application