James E. Green

Repurposing of ATX computer power supplies for PV applications in developing countries

To date, the recycling process for most Waste Electrical and Electronic Equipment (WEEE) simply involves recovering materials using pyrometallurgy and similar techniques due to the difficultly of removal of their constituent components. Thus most components are incinerated with all other non-recyclable materials. However, for specific types of WEEE an alternative approach has evolved namely the reuse or repurposing of particular parts of the equipment suitable for second life. This paper presents a novel photovoltaic system suitable for disparate population centers in the developing world utilising the ubiquitous ATX computer power supply.

Quantifying and Correcting Ionospheric Effects on P-Band SAR Images

Faraday rotation and scintillation will seriously affect P-band SAR images if methods are not used to deal with them. There are published methods for correcting Faraday rotation when polarimetric data are available, but less is known about scintillation. Scintillation is unlikely to present a problem if data acquisitions at low and mid latitudes avoid the post-sunset equatorial region, but correction procedures are likely to be needed in the auroral zones. Such correction is possible using autofocus methods; this is demonstrated using the Phase Gradient Algorithm applied to SAR imagery seriously affected by simulated scintillation.

Investigation of Nonoverlapping Stator Wound-Field Synchronous Machines

Three-phase nonoverlapping stator wound-field synchronous (NSWFS) machines having salient pole rotors are investigated systematically in this paper. The influence of the rotor pole number on the NSWFS machines is investigated via optimized designs. Using two-dimensional (2-D) finite-element analysis (FEA), the NSWFS machines are found to exhibit higher torque than the nonoverlapping segmented rotor NSWFS (SNSWFS) machines. The FEA-predicted back-electromotive force (EMF), cogging torque, and static torque of the NSWFS machines are validated by experiments on prototype machines.

Second life of computer power supplies in PV battery charging applications

This paper proposes and investigates the second life application of computer power supplies for PV applications. The emphasis is on reclamation and reuse of operational power supply components and circuits. Results shown verify operational limits of the power supply validating its suitability for PV-MPPT systems.

Avalanche Photodiodes in High-Speed Receiver Systems

The avalanche photodiode (APD) is widely used in optical fibre communications (Campbell, 2007) due to its ability to achieve high internal gain at relatively high speeds and low excess noise (Wei et al., 2002), thus improving the system signal-to-noise ratio. Its internal mechanism of gain or avalanche multiplication is a result of successive impact ionisation events. In an optical receiver system, the advantage of internal gain, in the APD, is experienced when the amplifier noise dominates that of a unity-gain photodiode. This increases the signal-to-noise ratio (SNR) and ultimately improves the receiver sensitivity as the gain increases until the APD noise rises to become dominant. Indium Phosphide (InP) is widely used as the multiplication layer material in commercially available APDs for applications in the 0.9–1.7μm wavelength region with In0.53Ga0.47As grown lattice-matched to it as the absorption layer. It has been predicted that Indium Alluminium Arsenide (In0.52Al0.48As) will replace InP, as a more favourable multiplication layer material due to its lower excess noise characteristics (Kinsey et al., 2000). In comparison to InP, tunnelling currents remain lower in InAlAs due to its larger bandgap. While holes ionise more readily than electrons in InP, the opposite holds true for InAlAs and InGaAs, as electrons ionise more readily than holes; thus making the InGaAs/InAlAs combination superior to InGaAs/InP in a SAM APD, in terms of lower excess noise, higher gain-bandwidth product, and improved sensitivity. Studies have also shown that the breakdown voltage of InAlAs APDs is less temperature dependent compared to InP (Tan et al., 2010), which would be useful in temperature sensitive applications, thus making temperature control less critical. The sensitivity performance criterion for digital receivers is its bit-error rate (BER), which is the probability of an error in the bit-identification by the receiver. The receiver sensitivity is defined as the minimum average optical power to operate at a certain BER; 10-12 being a common standard for digital optical receivers. The sensitivity of APD-based high speed optical receivers is governed by three main competing factors, namely the excess noise, avalanche-buildup time and dark current of the APD. Generally, the excess noise and avalanche-buildup time increases with APD gain. Thus, for a fixed multiplication layer thickness, there is a sensitivity-optimised gain that offers a balance between SNR while keeping the degrading contributions from the excess noise factor and intersymbolinterference (ISI) at a minimum. More importantly, changing the thickness of the multiplication layer strongly affects the receiver sensitivity, as the aforementioned three

Avalanche Noise in Al 0.52 In 0.48 P Diodes

Multiplication and avalanche excess noise measurements have been undertaken on a series of AlInP homojunction p-i-n and n-i-p diodes with i region widths ranging from 0.04 to 0.89 μm, using 442 and 460 nm wavelength light. Low dark currents of <;170 nA cm-2 at 95% of breakdown voltage were obtained in all the devices because of its wide bandgap and there was no tunneling dark current present even at high fields >1000 kV/cm. For a given multiplication factor, the excess noise decreased as the avalanche width decreased due to the dead-space effect. Using 460 nm wavelength light, measurements showed that a separate absorption multiplication avalanche photodiode with a nominal multiplication region width of 0.2 μm had an effective k (hole to electron ionization coefficient ratio) of ~0.3.

Impact Ionization Coefficients in 4H-SiC by Ultralow Excess Noise Measurement

Photomultiplication and excess noise measurements have been undertaken on two 4H-SiC avalanche photodiodes (APDs) using 244-nm light and 325-nm light. The structures are APDs with separate absorption and multiplication regions having multiplication regions of 2.74 and 0.58 μm , respectively. Pure injection conditions in the thicker device permit the measurement of pure-hole-initiated photomultiplication and an excess noise factor. Ionization coefficients for both carrier types have been extracted from these data using a local model. The use of the excess noise factor to infer the value of the less readily ionizing coefficient α from pure hole injection measurements is more robust than direct extraction from mixed injection measurements. This is because mixed injection introduces uncertainty in the generation profile. We report a significant reduction of the electron ionization coefficient α at low fields. The more readily ionizing hole coefficient β remains very similar to prior work.

Experimental evaluation of impact ionization in dilute nitride GaInNAs diodes

The anomalous behavior of impact ionization in dilute-nitride GaInNAs photodiodes with a range of nitrogen content below 4% is investigated. The ratio of hole- and electron-initiated ionization coefficients, k = β/α, is enhanced by a factor up to ∼4 with increasing nitrogen content. The absolute ionization coefficients are suppressed by up to two orders of magnitude at low electric fields in samples with 3% N. The narrow band gap, suppressed impact ionization, and increased breakdown voltage characteristics of GaInNAs make it a suitable material for use as part of a composite collector in GaAs-based heterojunction bipolar transistors.

A transimpedance amplifier for excess noise measurements of high junction capacitance avalanche photodiodes

This paper reports a novel and versatile system for measuring excess noise and multiplication in avalanche photodiodes (APDs), using a bipolar junction transistor based transimpedance amplifier front-end and based on phase-sensitive detection, which permits accurate measurement in the presence of a high dark current. The system can reliably measure the excess noise factor of devices with capacitance up to 5 nF. This system has been used to measure thin, large area Si pin APDs and the resulting data are in good agreement with measurements of the same devices obtained from a different noise measurement system which will be reported separately.

Internal Model Control of a Domestic Microwave for Carbon Composite Curing

This paper outlines the conversion of a domestic microwave oven for use in composite curing applications. It compares several strategies for temperature control. The converted oven has vacuum ports, connectors, and fiber optic thermocouple sensors. Experimental data are provided for each control strategy based on a