Ljubljana, Slovenia
Ljubljana, Slovenia

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Bratuz I.,Ams R and D | Vodopivec A.,Ams R and D | Trost A.,University of Ljubljana
IEEE Transactions on Wireless Communications | Year: 2014

The collision resolution mechanism is a key factor for successful communication in dense Radio-Frequency Identification (RFID) systems. One of such collision resolution mechanisms is the ALOHA protocol used in the EPCglobal Class-1 Gen-2 standard (EPCglobal). The success of the ALOHA-based protocols in RFID systems depends on the estimation of the number of tags in the electromagnetic field of an interrogator. The majority of the proposed optimization methods of the ALOHA-based protocols focus mainly on the estimation of the number of tags based on past slot results. Only few of the proposed methods try to determine the exact number of tags that involve an analysis of the received signal. One such method is the Radar Cross Section (RCS) method. We will show that RCS is not appropriate for RFID systems that include channel filtering as in the case of the EPCglobal standard. As a replacement for the RCS method, we propose a new anti-collision method to improve the anti-collision mechanism based on the utilization of the frequency analysis of the preamble. We will demonstrate that the method improves the existing anti-collision algorithm used in the EPCglobal and enhances the capture effect capability. © 2014 IEEE.

Mladenovic V.,Cetis | Pletersek A.,Ams R and D | Kavcic U.,Valkarton Rakek | Hladnik A.,University of Ljubljana | Muck T.,University of Ljubljana
Materiali in Tehnologije | Year: 2014

In this paper a novel design of UHF RFID antennas for smart cards is proposed. Smart cards usually include HF RFID antennas produced by means of hot foil stamping or etching - a subtractive process. Making HF antennas using printing - an additive process - is difficult, because it necessitates the printing of three layers: that of conductive lines (a coil), followed by a dielectric layer and once again a conductive layer. On the other hand, the printing of UHF antenna requires only the single-layer printing of conductive lines, i.e., antenna, thus enabling a more rational printing. After designing, simulating and testing a folded UHF dipole antenna for RFID applications, the impact of three different conductive printing inks, reading distance and card deformation on the backscattered signal power was studied. A three-way analysis of variance (ANOVA) was implemented to aid in the interpretation of the measurement results obtained on both non-laminated and laminated cards. It was demonstrated that smart cards with screen-printed UHF antennas can be fabricated using the proposed design optimization, so achieving good card readability.

Perschall M.,Karlsruhe Institute of Technology | Drevet J.B.,AMS R and D | Schenkel T.,Korea University | Oertel H.,Karlsruhe Institute of Technology
Artificial Organs | Year: 2012

This article describes the numerical fluid-structure interaction (FSI) validation of a new pumping concept and the possibility for application of a further developed type, as an implantable ventricular assist device (VAD). The novel principle of the so-called progressive wave pump is based on the interaction of an elastic membrane actuated by forced excitation with a surrounding fluid and the pump housing. By applying forced vibrations to one end of the membrane, a transversal wave builds up and progresses to the far end generating both a positive pressure gradient and flow rate. Among others, two axisymmetric geometrical configurations are possible, namely the discoidal and the tubular design. The first one has been built as a physical prototype and is experimentally investigated. In addition, a corresponding numerical FSI model is set up and validated against the experimental findings. Based on this validated numerical method, further numerical investigations are conducted focusing on the development of a tubular progressive wave pump concept with regard to its potential for application as a VAD in the future. To address VAD-relevant issues such as size, hydraulic performance, and blood trauma, corresponding numerical simulations involving macroscopic blood trauma models have been performed. Although being still in an early phase of development, the results are promising and indicate that the wave pump concept in its present state is feasible and can be further developed and investigated as a new type of blood pump. © 2012, International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

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