Design considerations for tunnel diode non-linear transmission lines

A tunnel diode non-linear transmission line has been investigated for second and third harmonic generation purposes. Design criteria are given and performance predictions have been obtained simulating the single diode behavior by means of a polynomial expression. An optimization of the non-linear transmission line as a harmonic generator has been obtained as a function of the number of diodes, their separation distances and the bias voltage.     

Sur les méthodes de calcul de l’exposant linéique de propagation et d’impédance caractéristique des câbles aériens et enterrés

The propagation constant of a line or a cable, and its characteristic impedance represent two parameters which are needed in order to calculate the variation as a function of the time of a current induced by an emp.For the aerial lines expressions which take into account the presence of the soil could be developed but the case of the buried conductors is of a more difficult approach. The aim of this study is to present solutions introduced by different authors and to compare them with a calculation method for the propagation constant using iterations, proposed by the authors. If this value is known it is shown that the characteristic impedance calculation of buried cables can be improved by avoiding the necessity to compute with a reasonable precision the impedance of the ground.     

On a Thermodynamic Theory of Porous Cosserat Elastic Shells

This paper presents a theory for porous thermoelastic shells using the model of Cosserat surfaces and the Nunziato–Cowin theory for materials with voids. To describe the porosity of the thin body, we introduce two scalar fields: one field accounts for the changes in volume fraction along the middle surface of the shell, and the other field characterizes the porosity variations along the shell's thickness. First, we postulate the principles of thermodynamics for these two-dimensional continua and we obtain the equations of the nonlinear theory. Then, we consider the linearized theory and prove the uniqueness of solution to the boundary initial value problem with no definiteness assumption on the constitutive coefficients. Finally, we consider the deformation of isotropic and homogeneous shells and determine the constitutive coefficients for Cosserat surfaces, by comparison with the results obtained from the three-dimensional approach to shell theory.     

Coupled-field FEM nonlinear dynamics analysis of continuous microsystems by non-incremental approach

This paper deals with numerical prediction of the nonlinear dynamic behaviour of electromechanical continuous microsystems, in presence of large displacements. Finite Element Method (FEM) is applied, by following so-called “sequential” approach, based on the solution in series of coupled electromechanical problem. In spite of tested approaches available in the literature, a “non-incremental” method is developed to enhance the performances of numerical tools. In practice, for microelectrostatic beam actuators, the total voltage may be applied once, in only one step, instead of by small increments. Non-incremental approach is based on two features. A special non-incremental beam element is introduced to deal with so-called geometrical nonlinearity of microbeam, caused by large displacement. It allows computing the total displacement of a cantilever microbeam, by integrating local rotation and axial deformation of cross-section, by avoiding to refer to the assumption of small displacement. Proposed procedure includes a preliminary static nonlinear analysis, to find the equilibrium condition, then a computation of nodal voltages for the deformed shape and of electric load. Equations of motion are integrated in time, by Newmark's method, while at each step, Newton-Raphson approach finds the instantaneous equilibrium, by applying the total voltage, instead of a small incremental value. Results evidenced a fast convergence even for large initial deflection. Moreover, typical peculiarities of nonlinear dynamic system, like softening effect in frequency response and amplitude jumping are observed. The whole proposed approach is currently under experimental validation and improvement to include damping effects, to study the dynamic stability of the microsystem. Eugenio Brusa was born in Turin (Italy) on February 8th, 1969. Graduated aeronautical engineer (1993) and Ph.D. in Design and construction of machines (1997) at Politecnico di Torino (Technical University of Turin). Assistant professor at Politecnico di Torino, Dept. Mechanics, and head of the Spin Test Laboratory from 1998 to 2001, then at Università degli Studi di Udine (2001–2002). On 2002 he appointed Associate professor at Università degli Studi di Udine, chair of Machine Design. Since 2005 is Coordinator of the teaching staff of the Master on Project Management and System Engineering of the University of Udine. Research activity: Design of mechanical structures, rotors and structural mechatronic systems, for space applications (Italian Space Agency, INTAS), cold rolling mills (SKF), active magnetic suspension (ESA subcontract), motorvehicle dynamics (FIAT group) and MEMS. Teaching activity in international courses: TU Delft (2001), TU Helsinki (2003), Int. Centre for Mechanical Sciences CISM (2004), Italy, Université Blaise Pascal, Clermont Ferrand (2005), France. More than 80 scientific publications. Mircea Gh. Munteanu was born in Brasov (Romania), on April 5th, 1946. Graduated Mechanical Engineer (1968) and PhD in Applied Mechanics at Transilvania University of Brasov, Romania. Since 1979 in staff at Stress Analysis and Mechanical Vibrations Dept., Transilvania University of Brasov. Since 1993 full professor of Stress Analysis and Mechanical Vibrations, Transilvania University of Brasov. Invited professor at Università degli Studi di Udine, Italia, in the framework of a grant on microsystem mechanical design. Research activity on static and dynamic FEM analysis of mechanical structures, multi-body systems, precision engineering, microsystem design. More than 100 publications on national and international journals and congresses, several books.     

Two-step curing processes for coating application

Two novel two-stage cure processes will be described, both involving oxetane chemistry. In both processes, the two consecutive cure processes are completely separated from one another.     

Biased micromechanical cantilever arrays as optical image memory

We show that an array of optically actuated biased cantilevers can work as an optical data storage, able to encode data stored as arrays of optical pixels (images). Each of these optical pixels can, in addition, have a predetermined pixel depth, expressed as a certain number of gray levels. This new optical memory is able to work at a data rate of approximately 7 GB/s for an image with 128 x 128 pixels.     

Time-frequency signal processing of terahertz pulses

We demonstrate that some signal-processing techniques, such as the fractional Fourier transform and the spectrogram, which are known to be effective for optical signals, can be implemented at terahertz frequencies and with available terahertz devices. These techniques, contrary to the frequency-resolved optical-gating method for pulse characterization, do not require nonlinear media, which do not exist at terahertz frequencies. Thus the fractional Fourier transform or the spectrogram offers the only possibility of characterizing terahertz pulses simultaneously in time and frequency.     

Control of time delay linear systems with Gaussian white noise

Recurrence formulas are developed for finding mean, variances, and other statistics of the state vector of linear systems with random time delay and Gaussian white noise input. These statistics are used to define optimal control functions for these systems. Lyapunov exponents are used to evaluate the stability of the stationary solution when the control algorithm is based on the stationary statistics of the state vector. Two numerical examples are presented to illustrate the determination of the optimal control function and of the conditions required for the existence of the stationary solution for systems with random time delay.