Méthode de mesure des impédances transitoires - Application aux puces RFID HF

International audienceCet article présente une méthode de mesure des impédances transitoires n'utilisant qu'un oscilloscope, un coupleur directionnel et un ordinateur. En plus d'obtenir des impédances comparables à celles obtenues avec un analyseur de réseaux standard, la méthode proposée permet également de visualiser l'évolution de l'impédance au cours du temps et ce, pour des puissances bien plus élevées que celles habituellement disponibles sur les analyseurs de réseaux. Appliquée à la RFID à 13,56MHz, cette méthode permet alors de mesurer les impédances en jeu lors de la communication entre un lecteur et une puce RFID, puis d'en déduire des informations telles que la consommation de la puce et les impédances de rétro-modulation, ces dernières permettant par exemple de vérifier la conformité d'une puce aux standards

Local polynomial modeling and variable bandwidth selection for time-varying linear systems

This paper proposes a local polynomial modeling (LPM) approach and variable bandwidth selection (VBS) algorithm for identifying time-varying linear systems (TVLSs). The proposed method models the time-varying coefficients of a TVLS locally by polynomials, which can be estimated by least squares estimation with a kernel having a certain bandwidth. The asymptotic behavior of the proposed LPM estimator is studied, and the existence of an optimal local bandwidth which minimizes the local mean-square error is established. A new data-driven VBS algorithm is then proposed to estimate this optimal variable bandwidth adaptively and locally. An individual bandwidth is assigned for each coefficient instead of the whole coefficient vector so as to improve the accuracy in fast-varying systems encountered in fault detection and other applications. Important practical issues such as online implementation are also discussed. Simulation results show that the LPM-VBS method outperforms conventional TVLS identification methods, such as the recursive least squares algorithm and generalized random walk Kalman filter/smoother, in a wide variety of testing conditions, in particular, at moderate to high signal-to-noise ratio. Using local linearization, the LPM method is further extended to identify time-varying systems with mild nonlinearities. Simulation results show that the proposed LPM-VBS method can achieve a satisfactory performance for mildly nonlinear systems based on appropriate linearization. Finally, the proposed method is applied to a practical problem of voltage-flicker-tracking problem in power systems. The usefulness of the proposed approach is demonstrated by its improved performance over other conventional methods. © 2006 IEEE.published_or_final_versio

Property Enhancements of Dielectric Nanoparticles via Surface Functionalization

This thesis describes the surface modification of barium strontium titanate nanoparticles for use in polymer/ceramic composite thin film capacitors with resultant improved dielectric and film-making properties. Phosphonic acid-type ligands proved to be most effective for surface conjugation to the surface of the barium strontium titanate nanoparticles. Amine-terminated ligands proved to be effective at removing surface adsorbed water before being almost entirely removed during the sample washing stage. Carboxylic acid terminated ligands proved to adhere less well to the nanoparticle than the phosphonic acid, but resulted in thin films with a higher dielectric constant, which was more stable in the measured frequency range than the phosphonic acid. This is seen via a systematic change in thin film variables, including ligand length, ligand reactive head, presence of polymer composite, and concentration of ligand. The nanoparticles were synthesized, ligands attached, then a series of thin film capacitors were fabricated to study the chang in dielectric properties. The results show a stabilized dielectric constant over a wide frequency range, a dramatically decreased loss, and better film-making properties. The new materials presented in this study are potentially useful as dielectrics for low-energy-density/low-loss capacitors