Nakul Haridas

ESPACENET: A Framework of Evolvable and Reconfigurable Sensor Networks for Aerospace–Based Monitoring and Diagnostics

There is an increasing need to develop flexible, reconfigurable, and intelligent multi-spacecraft sensing networks for aerospace-based monitoring and diagnostics. Technical advancements in ad hoc networking, MEMS devices, low-power electronics, adaptive and reconfigurable hardware, micro-spacecraft, and micro-sensors have enabled the design and development of such highly integrated space wireless sensor networks. This paper proposes the framework for an evolvable sensor network architecture, investigated as part of the ESPACENET project, collocated at the University of Edinburgh, Essex, Kent and Surrey. The aim is to design a flexible and intelligent embedded network of reconfigurable piconodes optimised by a hierarchical multi-objective algorithm. Although the project is targeted at aerospace applications, the same intelligent network can be used for many earth bound applications such as environmental and medical diagnostics

A smart antenna array for brain cancer detection

A smart antenna array is designed and fabricated for brain cancer detection. The smart antenna array is composed of three ultra-wideband vivaldi antennas. A brain model with 4 layers is created and simulated with the CST Microwave Studio. A radius of 5mm tumour model is placed into the white matter close to the skull. A short pulse is transmitted into the brain and the reflected signals are detected by one or more receiver antennas placed in different positions. Analysis of the reflected signals shows that using a smart antenna array based imaging system can be used for brain cancer detection.

Uniform circular arrays for phased array antenna

This paper compares the performances of a number of uniform circular array (UCA) configurations for phased array antennas. A UCA geometry is targeted due to its symmetrical configuration which enables the phased array antenna to scan azimuthally with minimal changes in its beam width and sidelobe levels. Each UCA configuration consists of 19 isotropic elements. Particle Swarm Optimization (PSO) is used to calculate the complex weights of the antenna array elements in order to adapt the antenna to the changing environments. Comparisons are made in the context of adaptive beamforming properties and Signal to Interference Ratio (SIR). The results obtained suggest that a planar uniform hexagonal array PUHA (1:6:12) is suitable for high resolution applications as its sidelobe levels are the lowest compared to the other geometries.

Single-feed polarization reconfigurable patch antenna

A novel single-feed design of a patch antenna with polarization reconfigurability is proposed in this paper. Four identical notches with parasitic elements are embedded into the design. The antenna can switch between linear polarization (LP), left hand circular polarization (LHCP) and right hand circular polarization (RHCP). The results show that the proposed antenna demonstrates an impedance bandwidth of 50 MHz (S11 <;-10 dB), and a polarization bandwidth of 44.3 MHz (axial ratio <; 3 dB). Also, the axial ratio is obtained in a broad angular range when the antenna is in LHCP and RHCP mode. The structure of the proposed antenna is simple and suitable for antenna array applications that require circular polarization and polarization diversity properties.

An evaluation of 2-phase charge pump topologies with charge transfer switches for green mobile technology

The development of charge pumps has been motivated by the power supply requirements of portable electronic devices. Charge pumps are inductorless DC-DC converters that are small size and high integration. The quality of the charge pump greatly depends on the effectiveness of switches to turn on and off at the designated clock phases. However, to date, no analysis has been carried out on the overall performance of charge pumps based on switch components in practice. This work demonstrates the characteristics of transistors as charge transfer switches and their effects on the performance of a charge pump. Three most common charge pump topologies are evaluated in terms of voltage drop due to on-resistance and charge loss per switch. Simulations are performed in 0.35µm Austriamicrosystems (AMS) technology for Dickson, Voltage Doubler and Makowski charge pump topologies in steady and dynamic states. In addition, the effect of switch parameters for different charge pump topologies are compared and analysed. We demonstrate that the Makowski charge pump is the topology for future green mobile technology.

Analysis of DOA estimation for directional and isotropic antenna arrays

A comparison analysis between two different types of antenna arrays in direction-of-arrival (DOA) estimation is presented. This study was undertaken to point out any difference in the process of DOA estimation between isotropic and directional antenna array. To the best of our knowledge, there is no previous work that analysed the DOA estimation between these two antenna arrays. The approach taken was to estimate all predetermined angle-of-arrival (AOA) correctly by using MUSIC, a spectral-based DOA algorithm. Results obtained show that, to perform the DOA estimation, isotropic antenna array depends entirely on DOA algorithm, whereas directional antenna array required both the DOA algorithm and the position of the main beam at any instant. This work concludes that, in practical application, it is essential to consider both the performance of DOA algorithm and the beam pattern to ensure the DOA estimation is carried out correctly.

Practical design strategy for two-phase step up DC-DC Fibonacci Switched-Capacitor converter

The Fibonacci Switched-Capacitor (SC) converter demonstrates the highest performance by using minimum number of capacitors. However, as the Fibonacci SC requires a wide range of voltage rating of the devices, its implementation is difficult. This paper presents two gate driving techniques for designing and implementing two-phase Fibonacci SC converter for both low and high step-up conversion ratios. The proposed gate driving techniques only require few auxiliary transistors to provide the required boosted voltages for turning the charge transfer switches in the converter on and off. As a result, the proposed gate driving techniques reduce the design complexity and increase the reliability of the Fibonacci SC converter. Practical 8X and 5X Fibonacci SC converters are simulated and constructed based on the proposed techniques. The high conversion efficiencies achieved prove the effectiveness of the proposed techniques.

Fault Tolerant and Adaptive GPS Attitude Determination System

In this paper a fault tolerant platform for the GPS attitude determination is proposed. The algorithm encompasses speed, adaptability and performance as its key objectives and also deals with Single Hard Errors (SHE) from the fault tolerance perspective. The technique is based on the Ambiguity Function Method (AFM) but overcomes restrictions and computational overheads incurred by existing techniques such as AFM. The adaptation of the GPS architecture is done by using fine-grained or cellular Parallel Genetic Algorithm to compute more efficiently the attitude parameters in terms of speed and performance. The algorithm also has the ability to efficiently search the complex search space imposed by the problem in addition to being immune to cycle slips compared to other conventional methods.

Capon-like DOA estimation algorithm for directional antenna arrays

This work proposes a new direction-of-arrival (DOA) estimation algorithm for directional antenna arrays. Most of the existing DOA algorithms are difficult to work with directional antenna arrays due to the characters of directional elements and thus proper modification is required. The proposed algorithm is based on Capon algorithm through the introduction of a new optimisation problem, which aims to maintain the array gain in the ‘look direction’, so that the DOA can be estimated correctly using a directional antenna array. To verify the performance of the proposed algorithm, computer simulations are performed and then the results obtained are compared with the Capon algorithm. The results show that the proposed algorithm outperforms the Capon algorithm.

Multiobjective Optimal Design of MEMS-Based Reconfigurable and Evolvable Sensor Networks for Space Applications

In this paper, the multiobjective optimal design of space-based reconfigurable sensor networks with novel adaptive MEMS antennas is investigated by using multiobjective evolutionary algorithms. The non-dominated sorting genetic algorithm II (NSGA-II) is employed to obtain multi-criteria Pareto-optimal solutions, which allows system designers to easily make a reasonable trade-off choice from the set of non-dominated solutions according to their preferences and system requirements. As a case study, a cluster-based satellite sensing network is simulated under multiple objectives. Most importantly, this paper also presents the application of our newly designed adaptive MEMS antennas together with the NSGA-II to the multiobjective optimal design of space-based reconfigurable sensor networks.