Research Seminars
Electronic Engineering seminars are talks by staff, visitors and research students about their research, pitched at a level any interested person should understand. The seminars are open to anyone to attend - undergraduate students are encouraged to attend, whilst postgraduate students and staff are expected to attend and contribute. For enquiries please contact the Department Administrator.
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2008 Seminars
Spiral Metamaterials
Speaker: Ozgur Isik
Time: 11 - 12nn, E6A Building, Room 357
Date: 13 November 2008
Abstract
"But I went to work—like a slave,” said the Invisible Man. “And I had hardly worked and thought about the matter six months before light came through one of the meshes suddenly—blindingly! I found a general principle of pigments and refraction—a formula, a geometrical expression involving four dimensions. Fools, common men, even common mathematicians, do not know anything of what some general expression may mean to the student of molecular physics. In the books—the books that tramp has hidden—there are marvels, miracles! But this was not a method, it was an idea, that might lead to a method by which it would be possible, without changing any other property of matter—except, in some instances colours—to lower the refractive index of a substance, solid or liquid, to that of air—so far as all practical purposes are concerned." – from Chapter 19, The Invisible Man by H.G. Wells (1897)
In this talk, I will briefly review the history and several selected topics associated with the fundamental properties of metamaterials. I will show how wave interaction with such materials can lead to interesting, unconventional features not observed in standard media. These physics characteristics can lead to exciting engineering concepts with future potential applications such as invisibility that is pictured above. After reviewing some of these concepts, I will present the novel building blocks of metamaterials, namely Archimedean Spiral Resonators, the structures that I have been working on since 2005.
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Analytic Non-linear Circuit Analysis for Resistive FET Mixers
Speaker: Lindsay Powles
Time: 11 - 12nn, E6A Building, Room 357
Date: 23 October 2008
Abstract
Resistive mixers present a difficult circuit analysis problem as they involve a small signal incident to
a time varying, weak non-linearity. The most widely used technique for this type of analysis is Harmonic Balance,
however, no analytic insight is gained from this technique. Other techniques exist, however, all the current
methods either involve numerically derived solutions or are only useful for conversion gain, not distortion prediction.
It is desirable to find an analytic expression to link individual circuit components to the output effect of concern.
This talk looks at double volterra analysis, including non-linearity extraction, and its range of accuracy for prediction of
LO leakage in resistive mixers. One potential method of improvement is shown from a simplification of theanalytic result.
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Future generation high-performance radio communications
circuits in gallium nitride technology
Speaker: Dr Peter Blockley
Time: 11 - 12nn, E6A Building, Room 357
Date: 2 October 2008
Abstract
Microwave transistors based on gallium nitride (GaN) are an exciting new technology that holds the promise of high power densities, high supply voltages and easy matching. GaN transistors have recently become commercially available with the industry poised to explode in the not too distant future. There are, however, a number of issues with this relatively immature technology that are limiting their uptake. These limitations include a high number of defects in the crystal lattice and difficulties in dissipating the heat generated by these devices. This presentation will give an overview of GaN transistors and present some of my recent results.
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Antenna Validation Scheme for MIMO Broadcast Wireless Channels with Linear Receivers
Speaker: M Arif Khan
Time: 11 - 12nn, E6A Building, Room 357
Date: 28 August 2008
Abstract
This seminar considers wireless broadcast systems with multi-antennas at base station and multiple users in the system. A typical wireless system usually has more users than the number of antennas at the base station. In this situation base station can not communicate to all users simultaneously. Therefore, base station has to select a set of users from all active users for communication. This selection process is known as user scheduling or user selection. We have discussed three practical user selection schemes in this talk. Once base station decides which users to serve, next step is to assign transmit antennas to each user. In traditional systems, base station selects a transmit antenna or a subset of transmit antennas for each user based on certain channel information from each user. We have proposed a new decentralized antenna selection scheme where each user selects a subset of transmit antennas for itself and sends this information back to the base station. This novel antenna selection approach reduces the interference among multiple users and increases the system throughput. We have analysed the performance of this approach with minimum mean square error (MMSE) and zero forcing (ZF) linear receivers. It is shown that the proposed scheme works better with both receivers.
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In Search of Scalable Models for FET and HEMT Structures
Speaker: Peter Vun
Time: 11 - 12nn, E6A Building, Room 357
Date: 14 August 2008
Abstract
FET and HEMT transistors designed to operate up to frequencies of 50GHz and beyond continue to be used for microwave and millimetre wave applications such as terrestrial and satellite communication, automotive radar and aerospace systems. These systems typically demand that the transistor based circuits have excellent wideband performance in terms of one or more of the following parameters – noise figure, linearity, power-added-efficiency, or saturated power handling. The optimal transistor geometry will vary widely for each scenario so circuit designers require transistor models for the full range of possible device sizes. Typically, a foundry will allow the unit-gate-width (UGW) and the number-of-gate-fingers (NOF) to be varied. In this context scalable models become very attractive as the measurement and characterisation of every possible geometry can be avoided. The following presentation will give an outline of some of the approaches that are proving to be successful in realising scalable models.
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Beamforming for Focal Plane Arrays
Speaker: Douglas Hayman
Time: 3 - 4pm E6A Building, Room 357
Date: 22 July 2008
Abstract
A new generation of radiotelescopes is being developed using dishes with dense focal plane arrays to achieve a wide field of view. This PhD project has involved ways of investigating beamforming solutions for focal plane arrays. It has made use of a two dish interferometer at Marsfield for experimental results and looked at some of the theory. This talk will describe aspects of the project.
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Actively Q-switched Fibre Laser: Experiment and Analysis
Speaker: Matthew Fellew
Time: 3 - 4pm E6A Building, Room 357
Date: 24 June 2008
Abstract
In this talk, the speaker will review progress and results from an actively Q- switched fibre laser. I will also review an analysis of the rise times of various mechanical switching methods in an effort to overcome multiple pulsing as is common with mechanical switching.
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Nonlinear Effects in an OFDM-RoF Link
Speaker: Razibul Islam
Time: 3 - 4pm E6A Building, Room 357
Date: 10 June 2008
Integration of orthogonal frequency division multiplexing (OFDM) and radio over fiber (RoF) technique emerged the possibility of cost-effective and high data rate ubiquitous wireless networks. As because OFDM is a combination of few subcarriers; resulting OFDM signal contains large peak to average power ratio (PAPR). The level of non-linear distortions largely depends on PAPR of an input signal led to a power amplifier (PA). RF power amplifier over a large dynamic range is also desired as high PAPR ratio reduces the power efficiency of the system. Hence, this work investigates the distortion effects of OFDM signals fed via an RF amplifier integrated with an RoF link employing electro absorption modulators (EAM) as a receiver for broadband in-building network applications. Firstly, adjacent channel power ratio (ACPR) (which estimates the degree of spectral re-growth due to the in-band and out-of-band interference resulting from distortion effects upon nonlinear amplification) is observed for the proposed system. Later, the dependence of PAPR and SFDR on the number of subcarriers of OFDM signals over RoF links integrated with an RF amplifier is examined. A complete analytical model of the OFDM-RoF system is also simulated and a closer agreement is reported for the distortion effects experienced in the system. To the best of knowledge, until now, the distortion effects of OFDM signals over RoF links integrated with an RF amplifier and EAM have not been reported with consideration of the distortion parameters as mentioned above. Therefore, this research will be helpful to determine design requirements for suitable picocell and microcell RoF applications in the future.
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MM-Wave Circuit Design in Deep Sub-Micron CMOS
Speaker: Michael Boers
Time: 3 - 4pm E6A Building, Room 357
Date: 13 May 2008
Next generation wireless systems at mm-wave frequencies require implementation in low-cost silicon technologies. This talk will discuss the implementation of building blocks and circuitsin SiGe and CMOS, look at the trade-offs between these two technologies and present recent research.
Fabrication Process Dependency of Local Oscillator Breakthrough in Sub-Harmonic Mix
Speaker: Venkata Gutta
Time: 3 - 4pm E6A Building, Room 357
Date: 29 April 2008
Abstract
The fabrication process-specific dependency of diode asymmetry and resulting local oscillator breakthrough in anti-parallel diode pair mixers is investigated. Statistical analysis of two anti-parallel diode pair mixers, fabricated on processes using different structure, lithographic techniques and feature sizes are compared to identify their asymmetry inducing aspects.
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Integrated Receiver Systems for Next Generation Telescopes
Speaker: Suzy Jackson
Time: 3 - 4pm E6A Building, Room 357
Date: 18 March 2008
Abstract
Transmission Improvement of Useful Signals through Energy Saving Glass Windows Using Frequency Selective Surfaces
Speaker: Ghaffer Kiani
Time: 3 - 4pm E6A Building, Room 357
Date: 11 March 2008
Abstract
Energy saving glass windows are becoming very popular in building design due to their effective shielding against infrared signals. These windows mainly help in providing thermal insulation to the buildings keeping them cold in summer and hot in winter. This effective shielding is obtained by depositing multiple layers of metallic oxides on glass surface using special processes. Besides providing effective thermal insulation, the presence of such coating also attenuates the transmission of mobile phone signals, GPS signals etc. To overcome this drawback, we propose a solution to this problem by employing bandpass frequency selective surfaces on two types of energy saving glass windows.