The effect of circuit parasitics on resonant switched capacitor converters

Switched Capacitor (SC) converters have been used for several years in low-power, power electronic energy conversion systems. However, because of their attractive features such as low-weight and high-density energy conversion and with the emergence of new circuit topologies and SiC switching devices, these circuits have recently been proposed for higher power applications. The resonant switched capacitor topology is a good candidate for high-power due to its very low-switching loss, but circuit parasitic inductance and resistance can have a significant effect on the resonant frequency of each cell. This paper discusses the influence of these parasitics on the performance of the converter and proposes a method by which these parasitics can be estimated. Simulation results and measurements from a hardware prototype are used to validate the technique.

Identification of oxidized phospholipids by electrospray ionization mass spectrometry and LC-MS using a QQLIT instrument

Phospholipids are complex and varied biomolecules that are susceptible to lipid peroxidation after attack by free radicals or electrophilic oxidants and can yield a large number of different oxidation products. There are many available methods for detecting phospholipid oxidation products, but also various limitations and problems. Electrospray ionization mass spectrometry allows the simultaneous but specific analysis of multiple species with good sensitivity and has a further advantage that it can be coupled to liquid chromatography for separation of oxidation products. Here, we explain the principles of oxidized phospholipid analysis by electrospray mass spectrometry and describe fragmentation routines for surveying the structural properties of the analytes, in particular precursor ion and neutral loss scanning. These allow targeted detection of phospholipid headgroups and identification of phospholipids containing hydroperoxides and chlorine, as well as the detection of some individual oxidation products by their specific fragmentation patterns. We describe instrument protocols for carrying out these survey routines on a QTrap5500 mass spectrometer and also for interfacing with reverse-phase liquid chromatography. The article highlights critical aspects of the analysis as well as some limitations of the methodology.

Resonant cavity Fibre Bragg grating sensor interrogation

This thesis presents a novel high-performance approach to time-division-multiplexing (TDM) fibre Bragg grating (FBG) optical sensors, known as the resonant cavity architecture. A background theory of FBG optical sensing includes several techniques for multiplexing sensors. The limitations of current wavelength-division-multiplexing (WDM) schemes are contrasted against the technological and commercial advantage of TDM. The author’s hypothesis that ‘it should be possible to achieve TDM FBG sensor interrogation using an electrically switched semiconductor optical amplifier (SOA)’ is then explained. Research and development of a commercially viable optical sensor interrogator based on the resonant cavity architecture forms the remainder of this thesis. A fully programmable SOA drive system allows interrogation of sensor arrays 10km long with a spatial resolution of 8cm and a variable gain system provides dynamic compensation for fluctuating system losses. Ratiometric filter- and diffractive-element spectrometer-based wavelength measurement systems are developed and analysed for different commercial applications. The ratiometric design provides a low-cost solution that has picometre resolution and low noise using 4% reflective sensors, but is less tolerant to variation in system loss. The spectrometer design is more expensive, but delivers exceptional performance with picometre resolution, low noise and tolerance to 13dB system loss variation. Finally, this thesis details the interrogator’s peripheral components, its compliance for operation in harsh industrial environments and several examples of commercial applications where it has been deployed. Applications include laboratory instruments, temperature monitoring systems for oil production, dynamic control for wind-energy and battery powered, self-contained sub-sea strain monitoring.

A study of the effect of harmonics in the system on the performance of residual current-operated circuit-breakers and electromechanical overcurrent relays

Residual current-operated circuit-breakers (RCCBs) have proved useful devices for the protection of both human beings against ventricular fibrillation and installations against fire. Although they work well with sinusoidal waveforms, there is little published information on their characteristics. Due to shunt connected non-linear devices, not the least of which is the use of power electronic equipment, the supply is distorted. Consequently, RCCBs as well as other protection relays are subject to non-sinusoidal current waveforms. Recent studies showed that RCCBs are greatly affected by harmonics, however the reasons for this are not clear. A literature search has also shown that there are inconsistencies in the analysis of the effect of harmonics on protection relays. In this work, the way RCCBs operate is examined, then a model is built with the aim of assessing the effect of non-sinusoidal current on RCCBs. Tests are then carried out on a number of RCCBs and these, when compared with the results from the model showed good correlation. In addition, the model also enables us to explain the RCCBs characteristics for pure sinusoidal current. In the model developed, various parameters are evaluated but special attention is paid to the instantaneous value of the current and the tripping mechanism movement. A similar assessment method is then used to assess the effect of harmonics on two types of protection relay, the electromechanical instantaneous relay and time overcurrent relay. A model is built for each of them which is then simulated on the computer. Tests results compare well with the simulation results, and thus the model developed can be used to explain the relays behaviour in a harmonics environment. The author's models, analysis and tests show that RCCBs and protection relays are affected by harmonics in a way determined by the waveform and the relay constants. The method developed provides a useful tool and the basic methodology to analyse the behaviour of RCCBs and protection relays in a harmonics environment. These results have many implications, especially the way RCCBs and relays should be tested if harmonics are taken into account.

The automation of resonant thermometer probe measurements

An ultrasonic thermometer has been developed for high temperature measurement over a wide temperature range. It is particularly suitable for use in measuring nuclear fuel rod centerline temperatures in advanced liquid metal and high flux nuclear reactors. The thermometer which was designed to determine fuel temperature up to the fuel melting point, utilizes the temperature dependence of the ultrasonic propagation velocity (related to the elastic modulus} in a thin rod sensor as the temperature transducing mechanism. A pulse excitation technique has been used, where the mechanical resonator at the remote end of the acoustic·line is madto vibrate. Its natural frequency is proportional to the ultrasonic velocity in the material. This is measured by the electronic instrumentation and enables a frequency­ temperature or period-temperature calibration to be obtained. A completely digital automatic instrument has been designed, constructed and tested to track the resonance frequency of the temperature sensors. It operates smoothly over a frequency range of about 30%, more than the maximum working range of most probe materials. The control uses the basic property of a resonator that the stored energy decays exponentially at the natural frequency of the resonator.The operation of the electronic system is based on a digital multichannel transmitter that is capable of operating with a predefined number of cycles in the burst. this overcomes a basic defect in the previous deslgn where the analogue time-delayed circuits failed to hold synchronization and hence automatic control could be lost. Development of a particular type of temperature probe, that is small enough to fit into a standard 2 mm reactor tube has made the ultrasonic thermometer a practicable device for measuring fuel temperature. The bulkiness of previous probes has been overcome, the new design consists of a tuning fork, integral with a 1mm line, while maintaining a frequency of no more than 100 kHz. A magnetostrictive rod, acoustically matched to the probe is used to launch and receive the acoustic oscillations. This requires a magnetic bias and the previously used bulky magnets have been replaced by a direct current coil. The probe is supported by terminating the launcher with a short heavy isolating rod which can be secured to the reactor structure. This support, the bias and launching coil and the launcher are made up into a single compact unit. On the material side an extensive study of a wide range of refractory materials identified molybdenum, iridium, rhenium and tungsten as satisfactory for a number of applications but mostly exhibiting to some degree a calibration drift with thermal cycling. When attention was directed to ceramic materials, Sapphire (single crystal alumina) was found to have numerous advantages, particularly in respect of stability of calibration which remained with ±2°C after many cycles to 1800oC. Tungsten and thoriated tungsten (W - 2% Tho2) were also found to be quite satisfactory to 1600oC, the specification for a Euratom application.

Chemical studies of plasma etchants used in integrated circuit manufacture

Plasma or "dry" etching is an essential process for the production of modern microelectronic circuits. However, despite intensive research, many aspects of the etch process are not fully understood. The results of studies of the plasma etching of Si and Si02 in fluorine-containing discharges, and the complementary technique of plasma polymerisation are presented in this thesis. Optical emission spectroscopy with argon actinometry was used as the principle plasma diagnostic. Statistical experimental design was used to model and compare Si and Si02 etch rates in CF4 and SF6 discharges as a function of flow, pressure and power. Etch mechanisms m both systems, including the potential reduction of Si etch rates in CF4 due to fluorocarbon polymer formation, are discussed. Si etch rates in CF4 /SF6 mixtures were successfully accounted for by the models produced. Si etch rates in CF4/C2F6 and CHF3 as a function of the addition of oxygen-containing additives (02, N20 and CO2) are shown to be consistent with a simple competition between F, 0 and CFx species for Si surface sites. For the range of conditions studied, Si02 etch rates were not dependent on F-atom concentration, but the presence of fluorine was essential in order to achieve significant etch rates. The influence of a wide range of electrode materials on the etch rate of Si and Si02 in CF4 and CF4 /02 plasmas was studied. It was found that the Si etch rate in a CF4 plasma was considerably enhanced, relative to an anodised aluminium electrode, in the presence of soda glass or sodium or potassium "doped" quartz. The effect was even more pronounced in a CF4 /02 discharge. In the latter system lead and copper electrodes also enhanced the Si etch rate. These results could not be accounted for by a corresponding rise in atomic fluorine concentration. Three possible etch enhancement mechanisms are discussed. Fluorocarbon polymer deposition was studied, both because of its relevance to etch mechanisms and its intrinsic interest, as a function of fluorocarbon source gas (CF4, C2F6, C3F8 and CHF3), process time, RF power and percentage hydrogen addition. Gas phase concentrations of F, H and CF2 were measured by optical emission spectroscopy, and the resultant polymer structure determined by X-ray photoelectron spectroscopy and infrared spectroscopy. Thermal and electrical properties were measured also. Hydrogen additions are shown to have a dominant role in determining deposition rate and polymer composition. A qualitative description of the polymer growth mechanism is presented which accounts for both changes in growth rate and structure, and leads to an empirical deposition rate model.

Resonant two-wave mixing in photorefractive materials with the aid of dc and ac fields

A recently predicted resonant effect for the enhancement of two-wave mixing in photorefractive materials is investigated. The resonance occurs when the frequency of the applied ac field agrees with the eigenfrequency of the excited space-charge wave. Experimentally a clear resonance is found, as predicted by the theory, for high dc electric fields, but the resonance is smeared out for lower fields. A modified theory, taking into account the second temporal harmonic of the space-charge wave, shows good agreement with the experimental results.

Resonant gradient force on atom interacting with laser field

The gradient force, as a function of position and velocity, is derived for a two-level atom interacting with a standing-wave laser field. Basing on optical Bloch equations, the numerical solutions for the gradient force f_(|_;n) (n = 0, 1, 2, 3, 4, ...) pointing in the direction of the transverse of the laser beam are given. It is shown the higher order gradient force plays important role at strong intensity (G = 64), the contribution of them can not be neglected.

Vibration analysis of a printed circuit board

The reliability of the printed circuit board assembly under dynamic environments, such as those found onboard airplanes, ships and land vehicles is receiving more attention. This research analyses the dynamic characteristics of the printed circuit board (PCB) supported by edge retainers and plug-in connectors. By modelling the wedge retainer and connector as providing simply supported boundary condition with appropriate rotational spring stiffnesses along their respective edges with the aid of finite element codes, accurate natural frequencies for the board against experimental natural frequencies are obtained. For a PCB supported by two opposite wedge retainers and a plug-in connector and with its remaining edge free of any restraint, it is found that these real supports behave somewhere between the simply supported and clamped boundary conditions and provide a percentage fixity of 39.5% more than the classical simply supported case. By using an eigensensitivity method, the rotational stiffnesses representing the boundary supports of the PCB can be updated effectively and is capable of representing the dynamics of the PCB accurately. The result shows that the percentage error in the fundamental frequency of the PCB finite element model is substantially reduced from 22.3% to 1.3%. The procedure demonstrated the effectiveness of using only the vibration test frequencies as reference data when the mode shapes of the original untuned model are almost identical to the referenced modes/experimental data. When using only modal frequencies in model improvement, the analysis is very much simplified. Furthermore, the time taken to obtain the experimental data will be substantially reduced as the experimental mode shapes are not required.In addition, this thesis advocates a relatively simple method in determining the support locations for maximising the fundamental frequency of vibrating structures. The technique is simple and does not require any optimisation or sequential search algorithm in the analysis. The key to the procedure is to position the necessary supports at positions so as to eliminate the lower modes from the original configuration. This is accomplished by introducing point supports along the nodal lines of the highest possible mode from the original configuration, so that all the other lower modes are eliminated by the introduction of the new or extra supports to the structure. It also proposes inspecting the average driving point residues along the nodal lines of vibrating plates to find the optimal locations of the supports. Numerical examples are provided to demonstrate its validity. By applying to the PCB supported on its three sides by two wedge retainers and a connector, it is found that a single point constraint that would yield maximum fundamental frequency is located at the mid-point of the nodal line, namely, node 39. This point support has the effect of increasing the structure's fundamental frequency from 68.4 Hz to 146.9 Hz, or 115% higher.

Effect of electron-phonon coupling on transmission through Luttinger liquid hybridized with resonant level

We show that electron-phonon coupling strongly affects transport properties of the Luttinger liquid hybridized with a resonant level. Namely, this coupling significantly modifies the effective energy-dependent width of the resonant level in two different geometries, corresponding to the resonant or antiresonant transmission in the Fermi gas. This leads to a rich phase diagram for a metal-insulator transition induced by the hybridization with the resonant level.

Short-circuit and ground fault analyses and location in VSC-based DC network cables

The application of high-power voltage-source converters (VSCs) to multiterminal dc networks is attracting research interest. The development of VSC-based dc networks is constrained by the lack of operational experience, the immaturity of appropriate protective devices, and the lack of appropriate fault analysis techniques. VSCs are vulnerable to dc-cable short-circuit and ground faults due to the high discharge current from the dc-link capacitance. However, faults occurring along the interconnecting dc cables are most likely to threaten system operation. In this paper, cable faults in VSC-based dc networks are analyzed in detail with the identification and definition of the most serious stages of the fault that need to be avoided. A fault location method is proposed because this is a prerequisite for an effective design of a fault protection scheme. It is demonstrated that it is relatively easy to evaluate the distance to a short-circuit fault using voltage reference comparison. For the more difficult challenge of locating ground faults, a method of estimating both the ground resistance and the distance to the fault is proposed by analyzing the initial stage of the fault transient. Analysis of the proposed method is provided and is based on simulation results, with a range of fault resistances, distances, and operational conditions considered.

Investigation of EDFA power transients in circuit-switched and packet-switched optical networks

Erbium-doped fibre amplifiers (EDFA’s) are a key technology for the design of all optical communication systems and networks. The superiority of EDFAs lies in their negligible intermodulation distortion across high speed multichannel signals, low intrinsic losses, slow gain dynamics, and gain in a wide range of optical wavelengths. Due to long lifetime in excited states, EDFAs do not oppose the effect of cross-gain saturation. The time characteristics of the gain saturation and recovery effects are between a few hundred microseconds and 10 milliseconds. However, in wavelength division multiplexed (WDM) optical networks with EDFAs, the number of channels traversing an EDFA can change due to the faulty link of the network or the system reconfiguration. It has been found that, due to the variation in channel number in the EDFAs chain, the output system powers of surviving channels can change in a very short time. Thus, the power transient is one of the problems deteriorating system performance. In this thesis, the transient phenomenon in wavelength routed WDM optical networks with EDFA chains was investigated. The task was performed using different input signal powers for circuit switched networks. A simulator for the EDFA gain dynamicmodel was developed to compute the magnitude and speed of the power transients in the non-self-saturated EDFA both single and chained. The dynamic model of the self-saturated EDFAs chain and its simulator were also developed to compute the magnitude and speed of the power transients and the Optical signal-to-noise ratio (OSNR). We found that the OSNR transient magnitude and speed are a function of both the output power transient and the number of EDFAs in the chain. The OSNR value predicts the level of the quality of service in the related network. It was found that the power transients for both self-saturated and non-self-saturated EDFAs are close in magnitude in the case of gain saturated EDFAs networks. Moreover, the cross-gain saturation also degrades the performance of the packet switching networks due to varying traffic characteristics. The magnitude and the speed of output power transients increase along the EDFAs chain. An investigation was done on the asynchronous transfer mode (ATM) or the WDM Internet protocol (WDM-IP) traffic networks using different traffic patterns based on the Pareto and Poisson distribution. The simulator is used to examine the amount and speed of the power transients in Pareto and Poisson distributed traffic at different bit rates, with specific focus on 2.5 Gb/s. It was found from numerical and statistical analysis that the power swing increases if the time interval of theburst-ON/burst-OFF is long in the packet bursts. This is because the gain dynamics is fast during strong signal pulse or with long duration pulses, which is due to the stimulatedemission avalanche depletion of the excited ions. Thus, an increase in output power levelcould lead to error burst which affects the system performance.

Hybrid squeezing of solitonic resonant radiation in photonic crystal fibers

We report the existence of a kind of squeezing in photonic crystal fibers which is conceptually intermediate between four-wave-mixing-induced squeezing in which all the participant waves are monochromatic waves, and self-phase-modulation-induced squeezing for a single pulse in a coherent state. This hybrid squeezing occurs when an arbitrary short soliton emits quasimonochromatic resonant radiation near a zero-group-velocity-dispersion point of the fiber. Photons around the resonant frequency become strongly correlated due to the presence of the classical soliton, and a reduction of the quantum noise below the shot-noise level is predicted. © 2011 American Physical Society.

Design and optimisation of the resonant mirror, an optical biosensor, for the analysis of microalbuminuria in trauma patients

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