Electrical & Computer Engineering

The growth of interactive multimedia (IMM) applications is one of the major driving forces behind the swift evolution of next-generation wireless networks where the traffic is expected to be varying and widely diversified. The amalgamation of multimedia applications on high-speed wireless networks is somewhat a natural evolution. Wireless local area network (WLAN) was initially developed to carry non-real time data. Since this type of traffic is bursty in nature, the channel access schemes were based on contention. However real time traffic (e.g. voice, video and other IMM applications) are different from this traditional data traffic as they have stringent constraints on quality of service (QoS) metrics like delay, jitter and throughput. Employing contention free channel access schemes that are implemented on the point coordination function (PCF), as opposed to the numerous works on the contending access schemes, is the plausible and intuitive approach to accommodate these innate requirements. Published researches show that works have been done on improving the distributed coordination function (DCF) to handle IMM traffic. Since the WLAN traffic today is a mix of both, it is only natural to utilize both, DCF and PCF, in a balanced manner to leverage the inherent strengths of each of them. We saw a scope in this technique and develop a scheme that combines both contention and non-contention based phases to handle heterogeneous traffic in WLAN. Standard access scheme, like 802.11e, improves DCF functionality by trying to emulate the functions of PCF. Researchers have made a multitude of improvements on 802.11e to reduce the costs of implementing the scheme on WLAN. We explore improving the PCF, instead, as this is more stable and implementations would be less costly. The initial part of this research investigates the effectiveness of the point coordination function (PCF) for carrying interactive multimedia traffic in WLAN. The performance statistics of IMM traffic were gathered and analyzed. Our results showed that PCF-based setup for IMM traffic is most suitable for high load scenarios. We confirmed that there is a scope in improving IMM transmissions on WLAN by using the PCF. This is supported by published researches on PCF related schemes in carrying IMM traffic on WLAN. Further investigations, via simulations, revealed that partitioning the superframe (SF) duration according to the need of the IMM traffic has considerable impact on the QoS of the WLAN.

An updated version of a 1985 tutorial paper on active filters using operational transconductance amplifiers (OTAs) is presented. The integrated circuit issues involved in active filters (using CMOS transconductance amplifiers) and the progress in ths field in the last 15 years is addressed. CMOS transconductance amplifiers, nonlinearised and linearised, as well as frequency limitations and dynamic range considerations are reviewed. OTA-C filter architectures, current-mode filters, and other potential applications of transconductance amplifiers are discussed.

This research involves the design and fabrication of micro-scale electrodes and optimisation of image reconstruction techniques. It aims to explore the use of bioimpedance tomography techniques in extracting some structured information on three-dimensional (3D) cell growth for the purpose of identifying cancer development, such as, cancer cell spheroids. Electrical impedance tomography (EIT) is a non-invasive imaging technique that maps the variation in conductivity of a sample, in the form of two or three dimensions. This technique has been successfully used in many clinical applications, for example, in detection of breast cancer, acute stroke differentiation, detection of bleeding due to traumatic brain injury, and detection of bacterial infection during surgery. The capability of EIT to spatially map biological development process enables it to be used in monitoring cell growth in three-dimensional formation. The work presented in this thesis includes miniaturising the electrode...

Electrical impedance tomography (EIT) is an imaging technique that reconstructs the conductivity distribution of an inhomogeneous medium and is capable of monitoring physiological changes in biological materials. This paper focuses on comparison of state-of-the-art regularisation methods in solving the image reconstruction problem in micro-scale EIT for biomedical applications. Since the quality of image reproduction is weak for micro-scale phantoms, it is vital to study the image reconstruction algorithm. Hence, we present three regularisation methods in this paper — Tikhonov, Gaussian-Laplace and L1 — for the image reconstruction of 700 pm diameter test samples. We verified our method using 500 μm × 250 μm rectangular Pt electrodes and compared the performance of these regularisation methods. The results suggest that Gaussian-Laplace regularisation provides better image reconstruction than L1 and Tikhonov algorithms.

A 250MHz Surface-Transverse Wave (STW) resonator is employed as a sensor element for the detection of DF-1 cells. STWs are horizontally polarized shear waves which are generated and detected by the interdigitated transducers (IDTs) similar to surface-acoustic wave (SAW) resonators. Detection of chemical and biological agents in aqueous solutions is a difficult problem, especially when the detection technique has to be sensitive, power-efficient and very handy. This paper presents the biosensor prototype utilizing STW resonator. The two-dimensional finite element (FEM) modeling of the STW resonator was performed using COMSOL Multiphysics™. 200MHz operating frequency was applied in the simulation. The FEM simulations results are equal with the theoretical results where an operating frequency of 200MHz will produce a resonance frequency of 200MHz.

Electrical impedance tomography (EIT) is an imaging technique that reconstructs the conductivity distribution of an inhomogeneous medium and is capable of monitoring physiological changes in biological materials. This paper focuses on comparison of state-of-the-art regularisation methods in solving the image reconstruction problem in micro-scale EIT for biomedical applications. Since the quality of image reproduction is weak for micro-scale phantoms, it is vital to study the image reconstruction algorithm. Hence, we present three regularisation methods in this paper-Tikhonov, Gaussian-Laplace and L1-for the image reconstruction of 700 µm diameter test samples. We verified our method using 500 µm × 250 µm rectangular Pt electrodes and compared the performance of these regularisation methods. The results suggest that Gaussian-Laplace regularisation provides better image reconstruction than L1 and Tikhonov algorithms.

Real-time quantitative imaging is becoming highly desirable to study nondestructively the biological behavior of three dimensional cell culture systems. In this work, we investigate the feasibility of quantitative imaging/monitoring of 3D cell culture processes via Electrical Impedance Tomography (EIT), which is capable of generating conductivity images in a non-destructive manner with high temporal resolution. To this end, a planar miniature EIT sensor amenable to standard cell culture format is designed and a 3D forward model for the sensor is developed for 3D imaging. Furthermore, a novel 3D-Laplacian and sparsity joint regularization algorithm is proposed for enhanced 3D image reconstruction. Simulation phantoms with spheres at various vertical and horizontal positions were imaged for 3D performance evaluation. In addition, experiments on human breast cancer cell spheroid and a triangular breast cancer cell pellet were carried out for experimental verification. The results have shown that stable measurement on high conductive cell culture medium and significant improvement of image quality based on the proposed regularization method are achieved. It demonstrates the feasibility of using the miniature EIT sensor and 3D image reconstruction algorithm to visualize 3D cell cultures such as spheroids or artificial tissues and organs. The established work would expedite real-time quantitative imaging of 3D cell culture for assessment of cellular dynamics.