An optical wireless transmission technique represents an attractive choice for many indoor and outdoors applications within fixed and mobile networks. It has the advantage of providing a wide bandwidth that is unregulated worldwide, with availability to use it in a very dense fashion, and potentially very low cost. Due to the high attenuation suffered by Infrared radiation through the air, operating low power transmission sources, and generally adverse signal to the noise environment found by ambient background light, where the optical signal is typically at it is minimum power level when detected. A high sensitivity and high selectivity receiver will be imperative for such applications as subcarrier multiplex systems, millimetre-wave radio over fibre and other wireless optical system applications. The thesis details the research, design, and optimisation of a novel, low-noise frontend optical receiver concept using a photoparametric amplifier (PPA) technique, in which the detected optical baseband signal is electrically amplified and up-converted to upperside frequency, based on the nonlinear characteristic of the pin photodiode junction; the desired signal passes through a further signal processing stage, and the original baseband signal is recovered again, using the concept of the superheterodyne principle. The designed DCHPPA receiver acts in a parallel manner to a conventional double superheterodyne detector system, but without the noise penalty normally incurred in the first stage. The PPA is used instead of a resistive/transistor based mixer at the first stage. DCHPPAs have the properties to provide very high gain, with high selectivity, combined with a very low noise operation. The research is conducted from three aspects: theoretical analysis, modelling and simulation, and practical implementation and result analysis. The three approaches followed the same trend shown, and the results correspond closely with each other. Theoretically, a new non-degenerate PPA mode of operation is discussed, in which the applied dc bias to the pin photodetector is replaced by the applied ac pump signal. This is shown to be advantageous in terms of the desirable characteristics for PPA operation, leading to improved conversion efficiency and the potential for low noise operation. PPA was shown to behave more optimally with load resistance which was much lower than normally used in the common optical wireless receiver-amplifiers. A new PPA gain theory was derived and optimised accordance with the original gain theory, PPA input/output admittance power was analysed for optimum power transfer. More accurate DCHPPA circuit configurations were modelled and simulated using nonlinear simulator tools (AWR) which help to understand and optimise system performance, particularly device parameters and characteristics. The full DCHPPA system was implemented practically, and tested in VHF and UHF as a sequel to the simulation configuration, which subsequently exhibited a 34.9dB baseband signal over the modulated optical signal; by employing a chain gain DCHPPA cascaded configuration, 56.3 dB baseband signal gain was achieved. The PPA noise was also measured and analysed, which satisfied the tough front-end optical system requirements.

The intention of the work presented is to provide novel, accurate and time-efficient way of designing multi-sines stimulus signal to replace real-life modulated signals prevailing within telecommunication networks, hence providing a novel tool for the development of modern RF measurement and design solution. The work demonstrated that with 50 tones, the multi-sines stimulus excites almost the same level of nonlinearity as real modulated signals do. For this conclusion the investigation of nonlinear behaviour mechanism was taken and a real DUT was measured under designed multi-siness and various types of modulated signals. It is also demonstrated that this multi-sines stimulus is compatible with the advanced RF measurement systems which are capable of measuring the complete RF waveform including the harmonic and base-band frequencies but demanding a periodical stimulus signal. Furthermore, a novel and quick sub-sampling algorithm was proposed to efficiently use the memory of Sampling Oscilloscope and therefore allows for accurate multi-sines capturing. An averaging algorithm for multi-sines stimulus was proposed to “stabilize” the captured waveform and a PCA based phase compensating algorithm was also proposed to tackle the problem of frequency shift under multi-sines excitation.

Wireless communication systems require an efficient and broadband RF frontend. RF Power Amplifiers (PA) are the most critical component in the RF frontend and are considered the bottleneck in high efficient wideband transmitters. The research starts with an investigation of high efficient operation modes based on waveform engineering. The outcome of the research can be divided into two main parts: The first concerns an analysis of high efficient modes of operation. The second part builds on first part looking at the PA’s efficiency-bandwidth perspective to design a wide band high efficient PA. The first part of the thesis, introduces a novel linear high efficient PA mode termed Injection Power Amplifier (IPA) that exceeds drain efficiency of 90% without relying on the nonlinearity of a PA at the compression region. This is achieved by presenting appropriate negative harmonic impedances to a transistor to reduce the dissipated power, thus, increasing the efficiency of conversion of DC to fundamental RF power. The theoretical analysis of this mode is presented and a validation measurement has been carried out using an active load-pull system. The measured results confirmed the theoretical predictions of achieving high efficiency in a linear PA operation. Furthermore, a PA structure that is based on two parallel PAs (main PA and auxiliary PA) has been proposed along with the practical circuit realization of the IPA mode. In addition, a PA prototype has been designed following a methodology of nonlinear PA design based on waveform engineering. The PA prototype has been characterized and built operating at 0.9 GHz with an output power of 10 W showing a high linear efficient operation of 80% drain efficiency at only 1 dB compression level. The second part of this work aims to tackle today’s limitation of high efficient wideband PAs beyond octave bandwidth. A conceptual system based on multimode operation has been proposed to overcome the need for bandlimiting passive harmonic termination. This novel approach is based on combining passive termination with active harmonic injection to get around the theoretical limitation of one octave for high efficiency harmonically tuned power amplifiers. Furthermore, a proof of concept PA prototype has been designed and built for a two octave bandwidth (4:1 bandwidth) operating from 0.63-2.56 GHz and providing the rated output power of a 10 W GaN device with a PAE greater than 50% at only 1 dB compression point. This multi-mode approach shows a promising technique for future wideband high efficiency wireless transmitters.

The research work presented in this thesis aims to achieve high-power, high-efficiency amplification across substantial bandwidths at microwave frequencies. The push-pull topology was identified as a promising possible solution which had previously not been considered for this application. The key component in the push-pull power amplifier is the balun, which converts between balanced and unbalanced signal environments. The novel use of ferrite materials allowed the half-wavelength resonance of a coaxial-cable transmission line balun to be suppressed, greatly extending its bandwidth. This was done by utilising the resistive properties of the ferrite material at frequencies greater than 1 GHz, at which these materials are not usually studied. The multi-decade performance of the transmission line baluns opened up the possibil- ity of realising push-pull power amplifiers across similar bandwidths. The measurement of these baluns revealed that they present a resistive impedance to the odd-harmonic frequencies, and an open circuit to the even-harmonic frequencies. This is a significant departure from the conventional view of the push-pull mode, and led to the modes of operation inside a microwave push-pull power amplifier being reconsidered. Factorised waveform expressions were used to describe the new modes of operation, and these were verified through load-pull simulations and measurements. The wave- forms were found to resemble the inverted modes of operation, with similar desirable characteristics such as high efficiency and an increase in output power compared to Class A. The viability of the push-pull amplifier topology was demonstrated through two pro- totype amplifiers, which achieved high output power levels and efficiencies over multi- octave bandwidths. Measurement systems for characterising and analysing these amplifiers were developed, which should lead to improved understanding and better performance in future.

As the range of transmission voltage increases, the pollution severity of the site becomes the most important factor in determining the insulation level of the system. Flashover on polluted insulators poses a serious threat to the reliability of the system and leads to system outages. There are many remedial measures to minimize the flashover of a porcelain insulator under pollution conditions. One such method is the application of hydrophobic coatings such as Room Temperature Vulcanizing Silicone Rubber (RTV- SiR) and Grease coatings on the surface of ceramic insulators. A recently proposed solution for contaminated outdoor insulators consists of the application of the Nanocoating “Voltshield” onto the surface of the insulator. This thesis reports a comparative assessment of the performance of these coating systems. Laboratory testing of coated porcelain insulators has been undertaken based on the solid layer method of IEC 60507 (artificial pollution- clean fog testing) and IEC 60587 (the inclined plane tests and constant voltage-liquid contaminants) to evaluate the coatings’ resistance against tracking and erosion. The performance of these coatings was assessed by monitoring the leakage current on the insulator surfaces. The applied voltage and the leakage current signals were acquired throughout the tests and saved for further analysis. The effect of UV radiation on the coatings has also been investigated. In addition, hydrophobicity tests were performed on the coated insulators. It was found that the Nanocoating reduces the leakage current by 90% whilst the energy absorbed on the insulator surface is reduced by 98% when compared to an uncoated insulator. The Nanocoating showed good resilience to sand blasting, but under long exposure to sand blasting, the surface began to degrade and showed pockmarks. The Nanocoated insulator showed good stability under UV exposure in terms of leakage current suppression. However, Nanocoated insulator lost its hydrophobicity on exposure to fog, and has lower flashover voltage than the uncoated insulator by 12.5%. Similar observations were made for the RTV coatings, where the current magnitude reduced by 92%, the energy absorbed on the insulator surface is reduced by 99% when compared to uncoated insulator and the flashover voltage is increased by 50%. RTV coating materials showed good resistance against tracking and erosion even after UV exposure. The electric field and voltage distribution along the leakage surface of coated and uncoated ceramic insulators under clean and polluted conditions were studied using finite element analysis COMSOL Multiphysics®. The electric field peaked at both the HV electrode and the ground electrode, and the presence of pollution in the form of water droplets on the coated insulator increased the electric field at the HV electrode. This study shows that the application of protective coatings to HV outdoor insulators significantly improves their performance. A reduction in surface current and power dissipation is observed, and a reduction in surface heating results in less dry-band arcing. A reduction in dissipated energy can make a contribution to reducing the total loss on the power system. In addition it showed the ability of coatings to resist tracking and erosion which leads to longer coating life under severe weather conditions. The coatings also increased the flashover voltage of the insulators which leads to more stable power system.

In this project an investigation of a wireless power transmission method utilising ultrasonic Lamb waves travelling along plates was performed. To the author’s knowledge, this is the first time such a system was investigated. The primary application for this method is the supply of power to wireless structural health monitoring (SHM) sensor nodes located in remote areas of the aircraft structure. A vibration generator is placed in a location where electricity supply is readily available. Ultrasonic waves generated by this device travel through the aircraft structure to a receiver in a remote wireless sensor node. The receiver converts the mechanical vibration of the ultrasonic waves back to electricity, which is used to power the sensor node. An experimental setup comprising a 1000 × 821 × 1.5 mm aluminium plate was designed to model an aircraft skin panel. Pairs of piezoelectric transducers were positioned along the longer edges of the plate. The electric impedance characteristics of three transducer types were measured. A circuit simulation MATLAB code was written. An input and output power measurement system was developed. The MFC M8528-P1 transducer type was identified as providing the best performance. The use of inductors to compensate for the capacitive characteristics of transducers was shown to provide up to 170-fold power throughput increase. The propagation of Lamb waves in the experimental plate was mapped using a scanning laser vibrometer and simulated using LISA finite difference method software. An optimised laboratory system transmitted 17 mW of power across a distance of 54 cm while being driven by a 20 V, 224 kHz signal. This figure can be easily increased by using a higher drive voltage. This shows that the system is capable of supplying sufficient power to wireless SHM sensor nodes, which currently have a maximum power requirement of approximately 200 mW.

The thermoelectric dimensionless figure-of-merit, ZT, which consists of the Seebeck coefficient, , electrical resistivity,  and thermal conductivity, , is an important parameter that characterizes the energy conversion performance of thermoelectric materials and devices. Larger ZT indicates higher performance of thermoelectric device. Current techniques for determining ZT involve measurements of ,  and  individually or ZT directly, but all techniques are carried out under a small temperature difference (T). In reality, a thermoelectric device generally operates under a much larger T and with an electrical current flowing through the thermoelectric materials. Clearly, ZT values are conventionally evaluated under a condition which differs significantly from the real operating conditions of thermoelectric devices. Recently, a novel principle for ZT measurement has been proposed, which has the capability of measuring ZT values under a large T and with an electrical current flowing through the samples. The main objective of the research embodied in this thesis is to investigate experimentally the feasibility of the proposed technique and subsequently to develop a laboratory measurement system for thermoelectric materials research. The feasibility of the proposed technique was investigated initially using thermoelectric modules. The results show a reasonable agreement with conventional techniques when it is used to measure ZT under a small T. Furthermore, the investigation reveals that ZT obtained under a large T differ significantly from those obtained under a small T. This confirms the unique capability of the proposed technique. The implementation of this technique for measuring the ZT of thermoelectric materials has proved to be very challenging due to the low electrical resistance (< 0.01 ) of the material samples. Following an in-depth experimental and theoretical investigation, a new design with a modified operating principle was proposed and carried out. The measurement system based on this new design was successfully developed, which has the capability of measuring single materials with different dimensions and under a larger T. The performance of this system was investigated using a standard Bi2Te3 sample as the reference for calibration. The results show that the system has a repeatability of <10% and an accuracy of 13-32%. Investigation on single materials and segmented structures showed that there were noticeable differences between a small and a large T, which can be attributed to the Thomson effect and changes in  values. This finding contributes to an improved understanding and new knowledge of thermoelectric behaviour under a large temperature difference. The measurement technique developed in this work will provide a useful tool for investigation and for the optimization of advanced thermoelectric structures.

The RF circuitry in the physical layer of any wireless communication node is arguably its most important part. The front-end radio is the hardware that enables communication by transmitting and receiving information. Without a robust and high performance front-end, all other higher layers of signal processing and data handling in a wireless network are irrelevant. This thesis investigates the radio circuitry of wireless-networked nodes, and introduces several proposals for improvement. As an emerging market, analysis starts by examining available and ratified network standards suitable for low power applications. After identifying the IEEE 802.15.4 standard (commercially known as ZigBee) as the one of choice, and analysing several front-end architectures on which its transceiver circuitry can be based, an application, the Tyre Pressure Monitoring System (TPMS) is selected to examine the capabilities of the standard and its most suitable architecture in satisfying the application’s requirements. From this compatibility analysis, the most significant shortcomings are identified as interference and power consumption. The work presented in this thesis focuses on the power consumption issues. A comparison of available high frequency transistor technologies concludes Silicon CMOS to be the most appropriate solution for the implementation of low cost and low power ZigBee transceivers. Since the output power requirement of ZigBee is relatively modest, it is possible to consider the design of a single amplifier block which can act as both a Low Noise Amplifier (LNA) in the receiver chain and a Power Amplifier (PA) on the transmitter side. This work shows that by employing a suitable design methodology, a single dual-function amplifier can be realised which meets the required performance specification. In this way, power consumption and chip area can both be reduced, leading to cost savings so vital to the widespread utilisation of the ZigBee standard. Given the importance of device nonlinearity in such a design, a new transistor model based on independent representation of each of the transistor’s nonlinear elements is developed with the aim of quantifying the individual contribution of each of the transistors nonlinear elements, to the total distortion. The methodology to the design of the dual functionality (LNA/PA) amplifier starts by considering various low noise amplifier architectures and comparing them in terms of the trade-off between noise (required for LNA operation) and linearity (important for PA operation), and then examining the behaviour of the selected architecture (the common-source common-gate cascode) at higher than usual input powers. Due to the need to meet the far apart performance requirements of both the LNA and PA, a unique amplifier design methodology is developed The design methodology is based on simultaneous graphical visualisation of the relationship between all relevant performance parameters and corresponding design parameters. A design example is then presented to demonstrate the effectiveness of the methodology and the quality of trade-offs it allows the designer to make. The simulated performance of the final amplifier satisfies both the requirements of ZigBee’s low noise and power amplification. At 2.4GHz, the amplifier is predicted to have 1.6dB Noise Figure (NF), 6dBm Input-referred 3rd-order Intercept Point (IIP3), and 1dB compression point of -3.5dBm. In low power operation, it is predicted to have 10dB gain, consuming only 8mW. At the higher input power of 0dBm, it is predicted to achieve 24% Power-Added Efficiency (PAE) with 8dB gain and 22mW power consumption. Finally, this thesis presents a set of future research proposals based on problems identified throughout its development.

Advances in transistors with cut-off frequencies >400GHz have fuelled interest in security, imaging and telecommunications applications operating well above 100GHz. However, further development of passive networks has become vital in developing such systems, as traditional coplanar waveguide (CPW) transmission lines, the most fundamental passive component, exhibit high losses in the millimetre and sub-millimetre wave regime. This work investigates novel, practical, low loss, transmission lines for frequencies above 100GHz and high-Q passive components composed of these lines. At these frequencies, transmission line losses are primarily due to the influence of the waveguide substrate. We therefore focus on structures which elevate transmission line traces above the substrate using air-bridge technology. Thorough analysis is performed on a range of elevated structures, and analytic / semi-analytic formulae for component figures of merit obtained. These, along with comprehensive 2 and 3D simulations are used to design discrete lines and distributed passive networks, with a focus on the 140-320 GHz frequency range. Innovative fabrication and detailed characterisation of the components are also carried out. The key result is the development of a novel MMIC compatible transmission line structure, Elevated-Grounded CPW, with a relatively simple fabrication process. EGCPW provides high substrate isolation, resulting in a low losses and high-quality passive networks. 50Ω EGCPW transmission line shows an insertion loss of 2.5dB/mm at 320GHz, 2.5dB/mm less than CPW. EGCPW passive networks, including resonators and filters, show higher performance than both conventional CPW and other forms of elevated CPW. 30-80% improvements in quality factor are shown, and an EGCPW band-pass filter with the centre frequency of 220GHz shows a 12% reduction in bandwidth and 4.5dB reduced in-band loss compared with its CPW counterpart. Due to the superior performance of MMIC-compatible EGCPW, as well as its ability to support a wide range of characteristic impedances, this structure is suggested as a candidate for widespread use in sub-millimetre wave circuits in order to increase efficiency and reduce losses.

Early signs of intestinal cancer may be detected through variations in tissue autofluorescence (AF), however current endoscope-based AF systems are unable to inspect the small intestine. This thesis describes the design, fabrication, implantation, testing and packaging of a wireless pill capable of detecting the autofluorescence from cancerous cells, and able to reach parts of the gastrointestinal tract that are inaccessible to endoscopes. The pill exploits the fact that there is a significant difference in the intensity of autofluorescence emitted by normal and cancerous tissues when excited by a blue or ultra violet light source. The intensity differences are detected using very sensitive light detectors. The pill has been developed in two stages. The first stage starts with using an off-chip multi-pixel photon counter (MPPC) device as a light detector. In the second stage, the light detector is integrated into an application specific integrated circuit (ASIC). The pill comprises of an ASIC, optical filters, an information processing unit and a radio transmission unit, to transmit acquired data to an external base station. Two ASICs have been fabricated, the first stage of this work involved implementing an ASIC that contains two main blocks; the first block is capable of providing a variable DC voltage more than 72 V from a 3 V input to bias the MPPC device. The second main block is a front-end consisting of a high speed transimpedance amplifier (TIA) and voltage amplifiers to capture the very small current pulses produced by the MPPC. The second ASIC contains a high voltage charge pump up to (37.9 V) integrated with a single photon avalanche detector (SPAD). The charge pump is used to bias the SPAD above its breakdown voltage and therefore operate the device in Geiger mode. The SPAD was designed to operate in the visible region where its photon detection efficiency (PDE) peaks at 465 nm, which is near to human tissues autofluorescence peaking region (520±10 nm). The use of the ultra low light detector to detect the autofluorescence permits a lower excitation light intensity and therefore lower overall power consumption. The two ASICs were fabricated using a commercial triple-well high-voltage CMOS process. The complete device operates at 3V and draws an average of 7.1mA, enabling up to 23 hours of continuous operation from two 165mAh SR44 batteries.