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Conventional Designs (conventional + design)
Selected AbstractsSchallfeldsimulation mit Spiegelquellen , Eine Planungshilfe für reflexionsarme RäumeBAUPHYSIK, Issue 4 2009Xueqin Zha Prof. Schall; Berechnungsverfahren; sound protection and acoustics; calculation methods Abstract Konventionelle Auslegungen von akustischen Freifeldräumen nach ISO 3745 sind häufig mit Risiken behaftet, weil die übliche Annahme eines Absorptionsgrades bei senkrechtem Schalleinfall von 99 % herkömmlicher faseriger oder poröser Auskleidungen von Fall zu Fall weder notwendig noch ausreichend sein kann. Es wird ein Simulationsprogramm vorgestellt, das mit der phasenrichtigen Überlagerung der Schallwellen einer realen Punkt- und einer Serie von Spiegelquellen arbeitet, welche die unvollständig absorbierenden Begrenzungsflächen des Raumes ersetzen. Damit werden verschiedene Einflüsse aufgezeigt, die die Freifeldeigenschaften ebenso stark beeinflussen können wie der Absorptionsgrad der Auskleidung. So lässt sich bereits in einem frühen Planungsstadium mehr Sicherheit über die Qualität eines Akustik-Prüfstandes zur Bestimmung von Schallleistung, Spektrum und Richtcharakteristik technischer Schallquellen gewinnen. Sound field simulation by image sources , A design tool for anechoic rooms. Conventional designs of anechoic rooms according to ISO 3745 often bear risks since the usual assumption of an absorption coefficient at normal incidence of 99 % of traditional fibrous or porous claddings may be not necessary in one case but insufficient in another. A simulation program is presented which is based on the wave interferences of the sound from a real point source and a number of image sources which replace imperfectly absorbing bounding surfaces. Its application demonstrates various effects which can influence the free-field characteristics to the same extent as the absorption of the cladding. By this one may gain more confidence , at an early stage of the planning process , in the quality of an acoustic test facility for the determination of sound power, spectrum and directivity of technical sound sources. [source] A compact wideband parallel-strip 180° hybrid couplerMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 12 2008L. Chiu Abstract In this study, a wideband compact parallel-strip 180° hybrid coupler with the center frequency of 2 GHz is presented. By replacing the 270° section in the 180° hybrid coupler with a parallel-strip phase reversal swap, the total circuit size is reduced by half. In this structure, the phase gradients of the four arms of the coupler are equalized; therefore, the operation bandwidth is dramatically enhanced. S-parameters of the coupler are simulated and measured with good agreement. As predicted from the measured data, the bandwidth of the 90% combining efficiency is increased from 45 to 124%. The proposed design achieves more than ,25 dB signal suppression within the whole measured frequency range (0,4 GHz) as opposed to 1.8 to 2.2 GHz of the conventional design. The proposed 180° hybrid coupler can serve as a wideband in-phase/differential power divider/combiner, which are essential for many RF and microwave subsystem designs. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3271,3274, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23926 [source] Current density mapping approach for design of clinical magnetic resonance imaging magnetsCONCEPTS IN MAGNETIC RESONANCE, Issue 3 2002Stuart Crozier Abstract Novel current density mapping (CDM) schemes are developed for the design of new actively shielded, clinical magnetic resonance imaging (MRI) magnets. This is an extended inverse method in which the entire potential solution space for the superconductors has been considered, rather than single current density layers. The solution provides an insight into the required superconducting coil pattern for a desired magnet configuration. This information is then used as an initial set of parameters for the magnet structure, and a previously developed hybrid numerical optimization technique is used to obtain the final geometry of the magnet. The CDM scheme is applied to the design of compact symmetric, asymmetric, and open architecture 1.0,1.5 T MRI magnet systems of novel geometry and utility. A new symmetric 1.0-T system that is just 1 m in length with a full 50-cm diameter of the active, or sensitive, volume (DSV) is detailed, as well as an asymmetric system in which a 50-cm DSV begins just 14 cm from the end of the coil structure. Finally a 1.0-T open magnet system with a full 50-cm DSV is presented. These new designs provide clinically useful homogeneous regions and have appropriately restricted stray fields but, in some of the designs, the DSV is much closer to the end of the magnet system than in conventional designs. These new designs have the potential to reduce patient claustrophobia and improve physician access to patients undergoing scans. © 2002 Wiley Periodicals, Inc. Concepts in Magnetic Resonance (Magn Reson Engineering) 15: 208,215, 2002 [source] Magnetic field of high-phase order and compact transmission linesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2002Hanafy M. IsmailArticle first published online: 14 DEC 200 Abstract Research has been conducted in high phase order (HPO) power transmission wherein 6 or 12 phases are used to transmit power in less physical space and with reduced environmental effects than conventional designs. In this paper, existing 3-phase double circuit transmission lines (TL) are reconfigured to 6-phase systems for the purpose of calculating and comparing the magnetic field of both systems. The magnetic field of several single-phase configurations; flat, vertical, delta and inverted-delta with the same degree of compaction is calculated and analysed at 1m height above the ground level. The magnetic field of the inverted-delta arrangement, which showed the lowest field profile, is compared with the magnetic field of 6- and 12-phase TLs having the same degree of line compaction and current loading conditions. The three systems are analysed when their lowest conductors had the same clearance to ground in one case and when their highest conductor positions were matched in another case. A comparison between 12-, 6- and 3-phase double circuit TLs having the same degree of compaction, the same phase voltage, the same clearance to ground and the same current per conductor is made to demonstrate if HPO lines reduce fields or not. The 6- and 12-phase lines are raised while keeping their conductors within the space, which would be taken by the conductors of the double circuit line. In this case, the highest conductor positions of the two systems are matched and the magnetic field is recomputed to conclude the results. The vector magnetic field potential concept, as extended to HPO transmission lines, together with a flexible developed computer program are used to calculate and present the magnetic flux density components profiles around the mentioned systems. Copyright © 2002 John Wiley & Sons, Ltd. [source] Joint design of trajectory and RF pulses for parallel excitationMAGNETIC RESONANCE IN MEDICINE, Issue 3 2007Chun-Yu Yip Abstract We propose an alternating optimization framework for the joint design of excitation k-space trajectory and RF pulses for small-tip-angle parallel excitation. Using Bloch simulations, we show that compared with conventional designs with predetermined trajectories, joint designs can often excite target patterns with improved accuracy and reduced total integrated pulse power, particularly at high reduction factors. These benefits come at a modest increase in computational time. Magn Reson Med 58:598,604, 2007. © 2007 Wiley-Liss, Inc. [source] The resonant behavior of the Fibonacci fractal tree antennasMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2008Basak Ozbakis Abstract An investigation of a novel fractal tree antenna with the application to two different geometries is presented. The antenna is designed by using the special Fibonacci number sequence which leads to nonuniform branch length ratios to form the fractal tree. This new approach gives better performance, especially in the miniaturization of the antenna, when compared with the conventional designs. The results obtained from the experiments are also compared with the computed ones and there is a very good agreement between the numerical and measured data. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1046,1050, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23299 [source] | |||||||||||||