48,213 research outputs found
Reconfigurable tri-band H-shaped antenna with frequency selectivity feature for compact wireless communication systems
No full textThis is the post-print version of the Article. The published version can be accessed from the link below - Copyright @ 2011 IETThis study presents an H-shaped reconfigurable antenna for wireless applications. The antenna consists of an H-shape radiator and a CPW printed on a circuit board and a varactor diode connecting the upper and lower arms of the H-shape radiator for reconfigurability. The uniqueness of the antenna lies on the ability to select the operating mode and frequencies electronically using a varactor diode. By selecting the DC-bias voltages of 11.5, 10 and 8 V across the varactor diode, which in turn selects the corresponding varactor capacitances of 2, 4 and 6 pF, the antenna can be controlled to operate in three different modes, namely a single-band mode to cover the GSM1900, a dual-band mode at 1.88 and 2.4 GHz to cover the GSM1900 and Bluetooth/WLAN, respectively and a tri-band mode at 1.57, 1.88 and 2.4 GHz to cover the GSM1900, WLAN and GPS, respectively. Furthermore, by varying the varactor capacitance from 7 to 13 pF, the GPS and WLAN bands can be tuned by 11.44% (1.57-1.4 GHz) and 6.46% (2.4-2.25 GHz), respectively, yet keeping the 1.88-GHz band unchanged. Detailed studies on the antenna's performance are carried out to investigate the behaviour of the antenna at each resonant frequency in each operating mode.This work is supported by the Measurements for Innovators (MFI) program and the National Measurement Office, an Executive Agency of the Department for Business, Innovation and Skills
Stacking-dependent band gap and quantum transport in trilayer graphene
No full textGraphene is an extraordinary two-dimensional (2D) system with chiral charge carriers and fascinating electronic, mechanical and thermal properties. In multilayer graphene, stacking order provides an important yet rarely explored degree of freedom for tuning its electronic properties. For instance, Bernal-stacked trilayer graphene (B-TLG) is semi-metallic with a tunable band overlap, and rhombohedral-stacked trilayer graphene (r-TLG) is predicted to be semiconducting with a tunable band gap. These multilayer graphenes are also expected to exhibit rich novel phenomena at low charge densities owing to enhanced electronic interactions and competing symmetries. Here we demonstrate the dramatically different transport properties in TLG with different stacking orders, and the unexpected spontaneous gap opening in charge neutral r-TLG. At the Dirac point, B-TLG remains metallic, whereas r-TLG becomes insulating with an intrinsic interaction-driven gap ~6 meV. In magnetic fields, well-developed quantum Hall (QH) plateaux in r-TLG split into three branches at higher fields. Such splitting is a signature of the Lifshitz transition, a topological change in the Fermi surface, that is found only in r-TLG. Our results underscore the rich interaction-induced phenomena in trilayer graphene with different stacking orders, and its potential towards electronic applications
Multi-band antenna for different wireless applications
No full textA small multi-band compact antenna is presented. The antenna is designed on Roger RT/duroid 5880 with dielectric constant 2.2, multi-band operations is achieved by inserting a slot on the top patch. The antenna has wide impedance bandwidth at 1.2, 1.6, 2.4 and 2.6 GHz with Gain 4.2, 1, 5 and 2 dBi respectively. The bandwidth before adding the shorting wall and the slot was 3.72%, whereas after adding the shorting wall and the slot the bandwidth get wider to 31.9% at the centre of 1.4 GHz. The radiation pattern has acceptable response with low cross polarization at both E-plane and H-plane. The overall dimension of the ground plane is 70 X 70 X 1.5 m
On the Performance of Band-Limited Asynchronous DS-CDMA over Nakagami-m Channels
No full textIn this paper we investigated the BER performance of DS-CDMA using various chip-waveforms, which include three time-limited chip-waveforms and two band-limited chipwaveforms. Closed-form formulae were derived for evaluating the achievable bit-error rate performance with the aid of the standard Gaussian approximation, when communicating over a Nakagami-m channel. The time-limited waveforms impose a low implementational complexity, since they maybe oversampled and read from a look-up table. However, they are outperformed by the frequency-domain raised-cosine waveform as well as the optimum waveform specifically designed by Cho and Lehnert for achieving the lowest possible bit error rate. Index Terms—Code-division multiple-access, chip waveform, Gaussian approximation, Nakagami, band-limited, normalized bandwidth
Deficits in high- (>60 Hz) gamma-band oscillations during visual processing in schizophrenia
No full textCurrent theories of the pathophysiology of schizophrenia have focused on abnormal temporal coordination of neural activity. Oscillations in the gamma-band range (>25 Hz) are of particular interest as they establish synchronization with great precision in local cortical networks. However, the contribution of high gamma (>60 Hz) oscillations toward the pathophysiology is less established. To address this issue, we recorded magnetoencephalographic (MEG) data from 16 medicated patients with chronic schizophrenia and 16 controls during the perception of Mooney faces. MEG data were analysed in the 25–150 Hz frequency range. Patients showed elevated reaction times and reduced detection rates during the perception of upright Mooney faces while responses to inverted stimuli were intact. Impaired processing of Mooney faces in schizophrenia patients was accompanied by a pronounced reduction in spectral power between 60–120 Hz (effect size: d = 1.26) which was correlated with disorganized symptoms (r = −0.72). Our findings demonstrate that deficits in high gamma-band oscillations as measured by MEG are a sensitive marker for aberrant cortical functioning in schizophrenia, suggesting an important aspect of the pathophysiology of the disorder
Compact dual-band (2.4/5.2GHz) monopole antenna for WLAN applications
No full textCopyright ©2010 IEEE. Reprinted from Antenna Technology (iWAT), 2010 International Workshop. This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of Brunel University's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected] compact and optimized design of a rectangular printed monopole antenna with slits and truncated ground plane on FR-4 substrate is presented. The proposed antenna is designed for dual-band operation at 2.4 GHz and 5.2 GHz for Wireless Local Area Network (WLAN) applications with S11 < -10 dB. This antenna has good return loss and radiation characteristics in required frequency band. The proposed antenna gives omni-directional radiation pattern in the E Plane and H plane over the frequency range of 2.4 GHz and 5.2 GHz. The calculated and measured results in terms of return loss show good agreement and the results also show good wideband characteristics
Bandwidth enhancement for small patch antenna using PBG structure for different wireless applications
No full textA design strategy using Photonic Band Gap (PBG) structure on ground plane to achieve wider bandwidth for patch antenna is presented. It is found that, the impedance bandwidth has improved from 3.72% to 31.9% at centre frequency 9 GHz after adding PBG on the ground plane. The antenna has multi band operations at 5, 6 and 9 GHz. E-Plane and H-plane radiation patter is satisfied within this band
Stress in V-section band clamps
No full textThis paper presents an analysis of the stresses in V-section band clamps by examining the correlation between experimental work and theoretical models. Theoretical models incorporating traditional beam-bending theories and allowing for friction were developed to calculate the stress distribution and displacements within the clamps. The theoretical models demonstrated that the normal manufacturing tolerances associated with this type of component, combined with the uncontrolled operating parameters, will produce a wide variation in working stresses.
These theoretical models were validated using strain and displacement measurements from a test with a V-section band clamp positioned around rigid flanges. The experimental results all fell within the range of stresses predicted by the theoretical models. The paper provides a knowledge base for the rational design of V-section band clamp
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