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ABSTRACT: A novel reconfigurable coupler with two operating modes is presented. The proposed structure can be electronically configured to operate as either a forward coupler or backward coupler, which is very useful in transceivers and diversity systems. Flat coupling in backward mode and high isolation in forward mode can be obtained, respectively, while the bandwidth is enhanced at the same time. For demonstration purposes, a 3 dB reconfigurable coupler at the centre frequency of 2.4 GHz is fabricated and examined. Both simulated and measured results are presented, and good agreement between them is observed.
Electronics Letters 07/2011; · 0.96 Impact Factor
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ABSTRACT: This study presents a smart energy management system (SEMS) to optimise the operation of the microgrid. The SEMS consists of power forecasting module, energy storage system (ESS) management module and optimisation module. The characteristic of the photovoltaics (PV) output in different weather conditions has been studied and then a 1-day-ahead power forecasting module is presented. As energy storage needs to be optimised across multiple-time steps, considering the influence of energy price structures, their economics are particularly complex. Therefore the ESS module is applied to determine the optimal operation strategies. Accordingly, multiple-time set points of the storage device, and economic performance of ESS are also evaluated. Smart management of ESS, economic load dispatch and operation optimisation of distributed generation (DG) are simplified into a single-object optimisation problem in the SEMS. Finally, a matrix real-coded genetic algorithm (MRC-GA) optimisation module is described to achieve a practical method for load management, including three different operation policies and produces diagrams of the distributed generators and ESS.
IET Renewable Power Generation 06/2011; · 1.74 Impact Factor
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ABSTRACT: A novel compact printed dipole antenna for wireless local area networks (WLAN) applications is presented. The proposed antenna consists of two radiating patches and four L-shaped slots etched on the patches, which can produce dual bands. Employing a unique tapered structure, good wide impedance matching can be implemented without an external matching circuit, and then wide bandwidths in the two working bands could be achieved conveniently. The proposed antenna yields an impedance bandwidth of 2.2-2.85 and 4.64-7.54-GHz with return loss less than -10-dB. In addition, the antenna has good omnidirectional radiation patterns in the H-plane and low cross-polarisation levels in both the E- and the H-planes. A comparison between measured and simulated results shows good agreement.
Electronics Letters 04/2011; · 0.96 Impact Factor
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ABSTRACT: A 0.9 V 58 μW 92 dB SNDR audio ΔΣ modulator is presented. Through combining the featured architecture with elaborately designed circuits, ultra-low-power operation is achieved. A power-efficient switched opamp (SO) with a new chopper stabilisation circuit for SO application is exploited to reduce power and minimise flicker noise. A novel data-weighted-averaging (DWA) technique is applied to sup press the harmonic distortion effectively.
Electronics Letters 03/2011; · 0.96 Impact Factor
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ABSTRACT: A Micro WEDM pulse generator is designed in this paper. It can adapt to the needs of various processing conditions. In additional, fuzzy control theory was applied to the pulse generator, which can automatically adjust the processing parameters to improve machining accuracy. So a more powerful Micro WEDM, which can achieve better processing results, is achieved.
Digital Manufacturing and Automation (ICDMA), 2010 International Conference on; 01/2011
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ABSTRACT: This paper, power optimization of two high performance ΔΣ modulators for portable measurement applications is presented. One modulator is a single-loop single-bit topology which achieves an 89.8dB peak SNDR and consumes 20μW with a 1.5V supply. Here, a new power efficient current mirror Class-AB OTA is introduced to reduce the power. The other modulator adopts both multi-bit technique and switched-opamp (SO) technique to realize the ultra-low power target. Its total power consumption is only 9μW at a 1.8V supply, and the peak SNDR reaches 80.5dB. Especially, a new fully-clocked SO is proposed in this modulator to achieve a 50% power saving and double Figure-of-Merit (FOM) over the traditional type. Besides, to realize a zero-optimization coefficient of 1/100 and improve the performance, a novel resonator idea applicable to SO technique is adopted with 75% power and 70% area reduction. Both modulators are fabricated in a low cost 0.35μm CMOS process with a bandwidth of 1 kHz. The measured results show high FOM of the designed modulators.
Solid State Circuits Conference (A-SSCC), 2010 IEEE Asian; 12/2010
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ABSTRACT: A new and simple calibration algorithm using general node equations is proposed in the calibration of the n -port vector network analyser (VNA). The crosstalk error term is considered in the error model to achieve high precision. With the general node equations deduced from the general flow graph, the S -parameters can be finally derived. The actual S -parameters of a four-port device can be corrected and compared with measurement results by Agilent VNA E5071B. The good agreement attests the precision of the calibration algorithm.
IET Science Measurement ? Technology 12/2010; · 0.60 Impact Factor
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ABSTRACT: A novel reconfigurable bandpass filter based on a net-type stepped-impedance resonator (SIR) is investigated. This work aims to demonstrate a new approach to implement the reconfigurable centre frequency of the bandpass filter. The approach controls the ratio of the two characteristic impedances of a quarter-wavelength microstrip SIR with pin diodes. The proposed filter is designed to be reconfigured in the three centre frequencies: 720 MHz, 900 MHz, 1 GHz. A comparison between measured and simulated results shows good agreement.
Electronics Letters 11/2010; · 0.96 Impact Factor
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ABSTRACT: The North Sea Super Grid (NSSG) will include several independently planned projects, comprising a variety of different AC and DC technologies. The offshore clusters will most likely be AC based. Long distance transmission will be HVDC and nowadays Voltage Source Converter (VSC) technology is applied for offshore projects. However in the future, Line Commutated Converter (LCC) technology could become an interesting option. Hybrid HVDC systems that combine VSC and LCC technology, Multiterminal HVDC systems (MTDC) and parallel HVDC links will gain importance for the development of the NSSG. In this paper an overview over possible technologies is given and it is discussed how these can be utilised to realise the North Sea Super Grid.
AC and DC Power Transmission, 2010. ACDC. 9th IET International Conference on; 11/2010
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ABSTRACT: A 9μW 88dB DR switched-opamp (SO) ΔΣ modulator is implemented in a low cost 0.35μm CMOS process. To evaluate the effects of finite voltage gain and 1/f noise clearly, two high efficient methods are introduced. And a new fully switched-off SO with a 50% power saving and double Figure-of-Merit (FOM) over the traditional type is proposed to reduce the total power. Besides, to improve the performance, a novel resonator idea applicable to SO technique is adopted to realize a coefficient of 1/100 with 75% power and 70% area reduction over the conventional design. The FOM of the designed modulator is highest among the collected recent low power modulators.
Custom Integrated Circuits Conference (CICC), 2010 IEEE; 10/2010
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ABSTRACT: A 9μW 88dB dynamic range (DR) switched-opamp (SO) μμ modulator is presented. A new SO with a fully switched-off scheme is proposed, which results in a 50μ power saving and double figure-of-merit over the traditional structure. Also, a novel resonator is applied to realise a zero-optimising coefficient of 1/100 with 75μ power and 70μ area reduction compared with the conventional one.
Electronics Letters 10/2010; · 0.96 Impact Factor
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ABSTRACT: A compact ultra-wideband (UWB) bandpass filter (BPF) with two sharply rejected notch-bands and wide stop-band is presented. The proposed UWB BPF is realised by cascading two interdigital hairpin resonator units, a coupled simplified composite right-left-handed (SCRLH) resonator, a semi-circle defected ground structure (S-DGS) and a semicircle stepped-impedance shunt stub (S-SISS). The SCRLH resonator is studied and employed to introduce two notched-bands. An S-DGS and an S-SISS are cascaded to suppress the spurious in the stop-band. Good insertion/return losses and high out-of-band rejections are achieved as demonstrated in both simulation and experiment.
Electronics Letters 09/2010; · 0.96 Impact Factor
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ABSTRACT: There is an increasing demand for network devices to perform deep packet inspection (DPI) to enhance network security. In DPI the packet payload is compared against a set of predefined patterns which can be specified using regular expressions (regexes). It is well-known that mapping regexes to deterministic finite automata (DFA) will suffer from the state explosion problem. Through observation, we attribute DFA explosion to the necessity of remembering matching history. In this paper, we investigate how to record the matching history efficiently and propose an extended DFA approach for regex matching called fcq-FA, which can make a memory size reduction of about 1000 times with a fully automated approach. In fcq-FA, we use pipeline queues and counters to help recording the matching history. Hence, state explosion caused by Kleene closure and repetitions can be definitely avoided. Further, it achieves a fully automated signature compilation with polynomial running time and space.
Communications (ICC), 2010 IEEE International Conference on; 06/2010
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ABSTRACT: To achieve satisfying user experiences of diverse applications, quality of service (QoS) guaranteed mechanisms such as per-flow queuing are required in routers. However, deployment of per-flow queuing in high-speed routers is considered as a great challenge since its industrial brute-force implementation is not scalable with the increase of the number of flows. In this study, the authors propose a dynamic queue sharing (DQS) mechanism to enable scalable per-flow queuing. DQS keeps isolation of each concurrent active flow by sharing a small number of queues instead of maintaining a dedicated queue for each in-progress flow, which is novel compared to the existing methods. According to DQS, a physical queue is created and assigned to an active flow upon the arrival of its first packet, and is destroyed upon the departure of the last packet in the queue. The authors combine hash method with binary sorting tree to construct and manage the dynamic mapping between active flows and physical queues, which significantly reduces the number of required physical queues from millions to hundreds and makes per-flow queuing feasible for high-performance routers.
IET Communications 04/2010; · 0.83 Impact Factor
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ABSTRACT: L1<sub>0</sub> FePt – Ta <sub>2</sub> O <sub>5</sub> films with (001) texture were synthesized by cosputtering FePt and Ta <sub>2</sub> O <sub>5</sub> targets and in situ heated at 350 ° C . The (001) preferred orientation was preserved even when doped with 20 vol % Ta <sub>2</sub> O <sub>5</sub> . The out-of-plane coercivity, H<sub>c</sub> , increased from 6.7 kOe (for pure FePt film) to 8.8 kOe when doped with 20 vol % Ta <sub>2</sub> O <sub>5</sub> . Further increase in the dopant content to 25 and 30 vol % caused H<sub>c</sub> to decrease significantly to below 3 kOe. Well-isolated FePt grains of tall column structures were observed for the 12 nm thick FePt film when doped with 20 vol % . The loop slope parameter, α , of such FePt film approached 1.
Journal of Applied Physics 05/2009; · 2.17 Impact Factor
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ABSTRACT: The conjugated polyelectrolyte (CPE) poly{9,9'-bis[6 ''-(N,N,N-trimethylammonium)-hexylfluorene-alt-co-phenylene] dibromide} (PFPN+Br-) demonstrates a high solubility in methanol in comparison to other more hydrophilic or hydrophobic solvents. We have employed a combination of pulsed-field-gradient-NMR, photoluminescence (PL), and Raman spectroscopy to establish the conformation and aggregation behavior of PFPN+Br- in methanol, with the aim to attain information on how to design CPEs with a high solubility in a preferred solvent. We find that the diffusion coefficient and PL spectrum of PFPN+Br-, as well as the Raman-active methyl rocking mode of methanol, all exhibit a strong dependence on PFPN+Br- concentration. We rationalize our findings with a model in which PFPN+Br- forms aggregates via pi-pi interactions between main-chain segments, while the ionic side chains are surrounded and electrostatically screened by the methanol solvent. Accordingly, the notably high solubility of PFPN+Br- in methanol is rationalized by favorable interactions between the ionic side chains and the methanol molecules. We propose that an appropriate design of a high-solubility CPE should consider a matching of the mixed hydrophobic/hydrophilic character of the ionic side chain with that of the preferred solvent. (C) 2009 Elsevier Ltd. All rights reserved.
European Polymer Journal 01/2009; 45(11):3228-3233. · 2.74 Impact Factor
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ABSTRACT: For high-quality synthetic aperture radar (SAR) processing, Doppler centroid ambiguity resolving is an essential procedure. A novel method for the resolution of Doppler ambiguity is presented which exploits the fact that, in the compressed azimuth time and range frequency domain, all targets span the same range frequency bandwidth and exhibit the same slope which is just proportional to the Doppler ambiguity number. The slope is removed by interpolation so that a simplified Radon transform can be applied. The use of entropy to find the maximum concentration of the Radon-transformed image can improve the robustness of the method. The proposed method directly gives a reliable estimate of the Doppler ambiguity number and is not affected by the azimuth partially covered targets. Experimental results show that the proposed method works well in medium- to high-contrast scenes.
IEEE Transactions on Geoscience and Remote Sensing 12/2008; · 2.89 Impact Factor
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ABSTRACT: Magnetic hard and soft phases FePtC thin films based exchange coupling assisted (ECA) perpendicular recording media were prepared. The coercivity of the FePtC film decreased after introducing a top magnetic soft FePtC layer. The cross-sectional transmission electron microscopy image illustrated that the soft FePt grains were located both on top of the bottom FePt grains and the grain boundaries, where the hard and soft grains were separated by a C layer accumulated on the hard FePtC layer surface. The reduction of coercivity was attributed to the exchange coupling between FePt hard and soft grains. For hard and soft grains separated by the accumulated C layer, the strength of the exchange coupling depended on the carbon layer thickness.
IEEE Transactions on Magnetics 12/2008; · 1.36 Impact Factor
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ABSTRACT: FePt–SiO2 films with different volume percentage (0–20%) of SiO2 were prepared by a co-sputtering process at a substrate temperature of 350 °C. The microstructure and magnetic properties of the composite films were investigated. Inhomogeneous SiO2 segregation in the composite films was observed. It was found that the SiO2 segregation depended on the sputter power used for FePt and SiO2 deposition. For low sputter power, most of the SiO2 was located at the film surface. As the sputter power increased, a two-layer film composed of a continuous FePt layer on the bottom and a FePt–SiO2 composite layer on the top was observed. The possible reasons for SiO2 accumulation on the surface and the two-layer film growth are proposed. The results suggested that the SiO2 segregation at high temperature was very sensitive to the dynamic film growth process. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Physica Status Solidi (A) Applications and Materials 07/2008; 205(10):2458 - 2463. · 1.46 Impact Factor
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ABSTRACT: Chemically ordered L10 FePt layer was obtained at temperature as low as 280 °C by in situ heating by using MgO buffer layer on CrRu (200) underlayer. The chemical ordering and magnetocrystalline anisotropy, Ku, increased with increasing deposition temperature from 280 to 400 °C. The out-of-plane coercivity Hc⊥ also increased significantly from 2.7 to 9.0 kOe. All the films showed perpendicular anisotropy. The reason for the increase in the coercivity was investigated by reducing the thickness of the FePt layer to 4 nm and varying the thickness of the MgO buffer layer at 1, 2, and 4 nm. Well isolated FePt islands were formed. When the MgO layer was 1 nm, the Hc⊥ of the 4 nm FePt layer was as high as 12 kOe. However, it reduced to 6.3 kOe when the MgO was 4 nm. The change in Hc⊥ was due to the improved chemical ordering and thus higher magnetocrystalline anisotropy.
Journal of Applied Physics 03/2008; 103(7):07E143-07E143-3. · 2.17 Impact Factor
