Home About us Contact
|
Home About us Contact | ||
|
|
||
Array Elements (array + element)
Selected AbstractsDesign of a high isolation dual-polarized slot-coupled microstrip antennaMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2005Xian-Ling Liang Abstract The design of a wideband dual-polarized slot-coupled stacked microstrip antenna with high isolation is introduced. The proposed stacked-patch antenna is excited by both open-ended and T-shaped microstrip lines via two H-shaped slots placed orthogonally so as to improve the isolation between the two polarization ports. The measured isolation is better than 40.5 dB over the bandwidth from 8.8 to 9.8 GHz with cross-polarization level of less than ,28.5 dB. The measured VSWR , 2 bandwidths reach 20.7% and 19.1% for the two polarization ports, respectively. This antenna is suitable as an array element for spaceborne synthetic aperture radar (SAR) and active phased-radar applications. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 212,215, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21126 [source] An efficient method for combining adaptive echo and noise canceller in hands-free systemsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 3 2009Jafar Ramadhan Mohammed Abstract Acoustic interferences severely degrade the quality and the intelligibility of the desired speech signal, thus posing a severe problem for many speech applications. Several acoustic echo cancellation (AEC) techniques have been proposed with a view to solving this problem. There are, however, few reports of AEC methods working under real noisy conditions. In this paper, we investigate the maximum positive synergies of the combination of acoustic echo canceller with a new adaptive beamformer. The proposed system achieves both the AEC and noise reduction of speech in an actual environment with real noise sources. Since the AEC is located behind the fixed beamformer of the new adaptive beamformer only one AEC is required for an arbitrary number of array elements, and the AEC does not feel any repercussions from the new adaptive beamformer. The proposed system was implemented in a real environment using National Instruments NI-PXI-1042Q controller system and data acquisition card PXI-4472. Experimental results show that the proposed system has successfully improved the performance of hands-free systems. Copyright © 2008 John Wiley & Sons, Ltd. [source] The performance analyses of multitarget CMA adaptive array considering mutual coupling and diffraction effectsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 7 2007Jin Xu Abstract The performance of a multitarget constant modulus algorithm (MU-CMA) adaptive array located on a regular conducting plate is studied in this paper. The effects of mutual coupling (MC) between array elements and diffraction caused by the conducting plate are taken into account. A hybrid method of equivalent edge current method (ECM) and moment method (MM) is employed in electromagnetic calculation to investigate the distortion of initial array pattern. We compare the capture property of three well-known MU-CMA arrays, respectively: multitarget least-squares constant modulus array (MT-LSCMA), multitarget decision-directed array (MT-DD) and least-squares despread respread multitarget constant modulus array (LS-DRMTCMA). Simulation result shows that: (i) the distorted initial pattern leads to the descending of the signal catch performance of MT-LSCMA and MT-DD; (ii) only the LS-DRMTCMA can work correctly due to its stronger anti-jamming ability in the presence of MC and diffraction. Copyright © 2006 John Wiley & Sons, Ltd. [source] Amplitude-only pattern nulling of linear antenna arrays with the use of an immune algorithmINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 5 2008Kerim Guney Abstract This article presents an optimization immune algorithm (opt-IA) for null steering of linear antenna arrays by controlling only the element amplitudes. Nulling of the pattern is also achieved by controlling the phase-only and the complex weights (both the amplitude and phase) of the array elements. The opt-IA is a new evolutionary computing algorithm based on the clonal selection principle of immune system. To show the accuracy and flexibility of the proposed opt-IA, several examples of Chebyshev array pattern with the imposed single, multiple, and broad nulls are given. It is found that the nulling technique based on opt-IA is capable of steering the array nulls precisely to the undesired interference directions. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008. [source] 96-Channel receive-only head coil for 3 Tesla: Design optimization and evaluationMAGNETIC RESONANCE IN MEDICINE, Issue 3 2009Graham C. Wiggins Abstract The benefits and challenges of highly parallel array coils for head imaging were investigated through the development of a 3T receive-only phased-array head coil with 96 receive elements constructed on a close-fitting helmet-shaped former. We evaluated several designs for the coil elements and matching circuitry, with particular attention to sources of signal-to-noise ratio (SNR) loss, including various sources of coil loading and coupling between the array elements. The SNR and noise amplification (g -factor) in accelerated imaging were quantitatively evaluated in phantom and human imaging and compared to a 32-channel array built on an identical helmet-shaped former and to a larger commercial 12-channel head coil. The 96-channel coil provided substantial SNR gains in the distal cortex compared to the 12- and 32-channel coils. The central SNR for the 96-channel coil was similar to the 32-channel coil for optimum SNR combination and 20% lower for root-sum-of-squares combination. There was a significant reduction in the maximum g -factor for 96 channels compared to 32; for example, the 96-channel maximum g -factor was 65% of the 32-channel value for acceleration rate 4. The performance of the array is demonstrated in highly accelerated brain images. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] Effects of inductive coupling on parallel MR image reconstructionsMAGNETIC RESONANCE IN MEDICINE, Issue 3 2004Michael A. Ohliger Abstract Theoretical arguments and experimental results are presented that characterize the impact of inductive coupling on the performance of parallel MRI reconstructions. A simple model of MR signal and noise reception suggests that the intrinsic amount of spatial information available from a given coil array is unchanged in the presence of inductive coupling, as long as the sample remains the dominant source of noise for the coupled array. Any loss of distinctness in the measured coil sensitivities is compensated by information stored in the measured noise correlations. Adjustments to the theory are described to account for preamplifier noise contributions. Results are presented from an experimental system in which preamplifier input impedances are systematically adjusted in order to vary the level of coupling between array elements. Parallel image reconstructions using an array with four different levels of coupling and an acceleration factor up to six show average SNR changes of ,7.6% to +7.5%. The modest changes in overall SNR are accompanied by similarly small changes in g-factor. These initial results suggest that moderate amounts of inductive coupling should not have a prohibitive effect on the use of a given coil array for parallel MRI. Magn Reson Med 52:628,639, 2004. © 2004 Wiley-Liss, Inc. [source] Ant colony based hybrid approach for optimal compromise sum-difference patterns synthesisMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2010P. Rocca Abstract Dealing with the synthesis of monopulse array antennas, many stochastic optimization algorithms have been used for the solution of the so-called optimal compromise problem between sum and difference patterns when sub-arrayed feed networks are considered. More recently, hybrid approaches, exploiting the convexity of the functional with respect to a sub-set of the unknowns (i.e., the sub-array excitation coefficients) have demonstrated their effectiveness. In this letter, an hybrid approach based on the ant colony optimization (ACO) is proposed. At the first step, the ACO is used to define the sub-array membership of the array elements, while, at the second step, the sub-array weights are computed by solving a convex programming problem. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 128,132, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24882 [source] An introduction to coil array design for parallel MRINMR IN BIOMEDICINE, Issue 3 2006Michael A. Ohliger Abstract The basic principles of radiofrequency coil array design for parallel MRI are described from both theoretical and practical perspectives. Because parallel MRI techniques rely on coil array sensitivities to provide spatial information about the sample, a careful choice of array design is essential. The concepts of coil array spatial encoding are first discussed from four qualitative perspectives. These qualitative descriptions include using coil arrays to emulate spatial harmonics, choosing coils with selective sensitivities to aliased pixels, using coil sensitivities with broad k -space reception profiles, and relying on detector coils to provide a set of generalized projections of the sample. This qualitative discussion is followed by a quantitative analysis of coil arrays, which is discussed in terms of the baseline SNR of the received images as well as the noise amplifications (g -factor) in the reconstructed data. The complications encountered during the experimental evaluation of coil array SNR are discussed, and solutions are proposed. A series of specific array designs are reviewed, with an emphasis on the general design considerations that motivate each approach. Finally, a set of special topics is discussed, which reflect issues that have become important, especially as arrays are being designed for more high-performance applications of parallel MRI. These topics include concerns about the depth penetration of arrays composed of small elements, the use of adaptive arrays for systems with limited receiver channels, the management of inductive coupling between array elements, and special considerations required at high field strengths. The fundamental limits of spatial encoding using coil arrays are discussed, with a primary emphasis on how the determination of these limits impacts the design of optimized arrays. This review is intended to provide insight into how arrays are currently used for parallel MRI and to place into context the new innovations that are to come. Copyright © 2006 John Wiley & Sons, Ltd. [source] Assessment of Finger Forces and Wrist Torques for Functional Grasp Using New Multichannel Textile NeuroprosthesesARTIFICIAL ORGANS, Issue 8 2008Marc Lawrence Abstract:, New multichannel textile neuroprotheses were developed, which comprise multiple sets of transcutaneous electrode arrays and connecting wires embroidered into a fabric layer. The electrode arrays were placed on the forearm above the extrinsic finger flexors and extensors. Activation regions for selective finger flexion and wrist extension were configured by switching a subset of the array elements between cathode, anode, and off states. We present a new isometric measurement system for the assessment of finger forces and wrist torques generated using the new neuroprostheses. Finger forces (from the middle phalanxes) were recorded using five load cells mounted on a "grasp handle" that can be arbitrarily positioned in space. The hand and the grasp handle were rigidly mounted to a 6-degree of freedom load cell, and the forces and torques about the wrist were recorded. A vacuum cushion was used to comfortably fixate the forearm. The position and orientation of the forearm, wrist, fingers, and handle were recorded using a new three-dimensional position measurement system (accuracy <±1 mm). The measurement system was integrated into the real-time multichannel transcutaneous electrode environment, which is able to control the spatiotemporal position of multiple activation regions. Using the combined system and textile neuroprosthesis, we were able to optimize the activation regions to produce selective finger and wrist articulation, enabling improved functional grasp. [source] | |||||||||||||