Directions of arrival estimation with planar antenna arrays in the presence of mutual coupling

Directions of arrival (DoAs) estimation of multiple sources using an antenna array is a challenging topic in wireless communication. The DoAs estimation accuracy depends not only on the selected technique and algorithm, but also on the geometrical configuration of the antenna array used during the estimation. In this article the robustness of common planar antenna arrays against unaccounted mutual coupling is examined and their DoAs estimation capabilities are compared and analysed through computer simulations using the well-known MUltiple SIgnal Classification (MUSIC) algorithm. Our analysis is based on an electromagnetic concept to calculate an approximation of the impedance matrices that define the mutual coupling matrix (MCM). Furthermore, a CRB analysis is presented and used as an asymptotic performance benchmark of the studied antenna arrays. The impact of the studied antenna arrays geometry on the MCM structure is also investigated. Simulation results show that the UCCA has more robustness against unaccounted mutual coupling and performs better results than both UCA and URA geometries. The performed simulations confirm also that, although the UCCA achieves better performance under complicated scenarios, the URA shows better asymptotic (CRB) behaviour which promises more accuracy on DoAs estimation.     

Processes involved during the production of Fe–W–Mo alloys by powder metallurgy

Sintering of Fe–W–Mo systems under a dynamic atmosphere of argon has been studied by different experimental techniques, including dilatometric trials, X-ray diffraction, optical microscopy and electron probe microanalysis. It has been found that sintering at 1300°C for only 10 min allows compacts to be obtained with a relative density close to 80%. The results also show an improvement in the final density by molybdenum addition. On the other hand, the structure of the sintered samples was, mainly, constituted of a soft matrix of (Fe–M) solid solutions (300 Hv) in which hard intermetallic compounds (1200 Hv) are dispersed. Furthermore, perturbing expansions have been observed during the sintering cycle. The first expansion occurred at about 620°C as a consequence of a Kirkendall effect. The second one arose at about 890°C in relation to Fe7M6 (where M is tungsten or molybdenum) formation. The latter expansion occurred at about 1200°C as a consequence of an increase in tungsten diffusion from indiffused areas to (Fe–M)a solid solutions and intermetallic compounds. © 1998 Chapman & Hall     

Extended reactance domain algorithms for DoA estimation onto an ESPAR antennas

Based on an extended reactance domain (RD) covariance matrix, this article proposes new alternatives for directions of arrival (DoAs) estimation of narrowband sources through an electronically steerable parasitic array radiator (ESPAR) antennas. Because of the centro symmetry of the classic ESPAR antennas, an unitary transformation is applied to the collected data that allow an important reduction in both computational cost and processing time and, also, an enhancement of the resolution capabilities of the proposed algorithms. Moreover, this article proposes a new approach for eigenvalues estimation through only some linear operations. The developed DoAs estimation algorithms based on this new approach has illustrated a good behaviour with less calculation cost and processing time as compared to other schemes based on the classic eigenvalues approach. The conducted simulations demonstrate that high-precision and high-resolution DoAs estimation can be reached especially in very closely sources situation and low sources power as compared to the RD-MUSIC algorithm and the RD-PM algorithm. The asymptotic behaviours of the proposed DoAs estimators are analysed in various scenarios and compared with the Cramer-Rao bound (CRB). The conducted simulations testify the high-resolution of the developed algorithms and prove the efficiently of the proposed approach.     

Three-dimensional antennas array for the estimation of direction of arrival

Direction of arrival (DOA) estimation of multiple sources using an antenna array becomes very important in wireless communications. It is well known that the quality of the DOA estimation depends on the selected technique and algorithm but it also depends on the geometrical configuration of the antenna array used during the estimation. The authors study the influence of the antenna array configurations on the Cramer?Rao bounds (CRB) of the 2D DOA estimation problem as well as on the performance of the well known MUSIC algorithm. For this we consider the most known planar arrays and we propose a 2-L shaped 3D antennas array. It appears that this 3D antennas array outperforms the other configurations as well as that already proposed in Tayem and Kwon (2005), in terms of both the CRB and the MUSIC root mean square estimation error and also removes ambiguities from the estimation MUSIC pseudo spectrum.     

A New and Economic Approach to Synthesize and Fabricate Bioactive Diopside Ceramics Using a Modified Domestic Microwave Oven. Part 1: Study of Sintering and Bioactivity

Diopside (CaMgSi₂O₆) ceramics was synthesized and fabricated by a simple solid‐state reaction rather than other used processes. This new and economic approach for diopside fabrication consists mainly of replacing the usually used starting materials by other more economic (activated CaO·MgO powders), using conventional sintering and microwave sintering. The P₂O₅ addition (0.5–5.0 wt%) promotes sintering, crystallization, and bioactivity. Additionally, a considerably low weight loss ratio (0.21%) was also obtained for these samples, after 2 days of soaking in lactic acid. Carbonated hydroxyapatite (CHA) formation in simulated body fluid was confirmed for all sintered samples. Both sintering and CHA formation mechanisms were proposed.     

Innovation Through Vertical Relations Between Firms,Suppliers And Customers: A Study Of German Firms

Interfirm cooperative R&D agreements are becoming more frequent, as firms seek to avoid market failures and exploit the competitive advantages of collaborating vertically with suppliers on the one hand and customers on the other. This paper investigates the phenomenon of vertical R&D linkages in the context of German manufacturing firms, based on a survey conducted at the Centre for European Economic Research, Mannheim. The major finding is that vertical linkages have high prevalence, and that the most common mode of linkage involves informal exchange of technical knowledge, with formal linkages such as joint development teams and contractual R&D cooperation being less common.     

Unknown Input Fault Detection and Isolation Observer Design for Neutral Systems

This paper deals with actuator fault diagnosis of neutral delayed systems with multiple time delays using an unknown input observer. The main purpose is to design an observer that guarantees the asymptotic stability of the estimate error dynamics and the actuator fault detection. The existence conditions for such an observer are established. The main problem studied in this paper aims at designing observer‐based fault detection and isolation. The designed observer enhances the robust diagnosis performance, including rapidity and accuracy, and generates residuals that enjoy perfect decoupling properties among faults. Based on Lyapunov stability theory, the design of the observer is formulated in terms of linear matrix inequalities, and the diagnosis scheme is based on a bank of unknown input observers for residual generation that guarantees fault detection and isolation in the presence of external disturbances. A numerical example is presented to illustrate the efficiency of the proposed approach.