Parameters influencing the performance of an IGBT gate drive

This paper presents an improvement of an IGBT gate drive implementing Active Voltage Control (AVC), and investigates the impact of various parameters affecting its performance. The effects of the bandwidths of various elements and the gains of AVC are shown in simulation and experimentally. Also, the paper proposes connecting a small Active Snubber between the IGBT collector and its gate integrated within the AVC. The effect of this snubber on enhancing the stability of the gate drive is demonstrated. It will be shown that using a wide bandwidth operational amplifier and integrating the Active Snubber within the gate drive reduces the minimum gate resistor required to achieve stability of the controller. Consequently, the response time of the IGBT to control signals is significantly reduced, the switching losses then can be minimised and, hence, the performance of gate drive as whole is improved. This reflects positively on turn-off and turn-on transitions achieving voltage sharing between the IGBTs connected in series to construct a higher voltage switch, making series IGBTs a feasible practice. ©2008 IEEE.

Electrically switchable random to photonic band-edge laser emission in chiral nematic liquid crystals

Using a chiral nematic liquid crystal with a negative dielectric anisotropy, it is possible to switch between band-edge laser emission and random laser emission with an electric field. At low frequencies (1 kHz), random laser emission is observed as a result of scattering due to electro-hydrodynamic instabilities. However, band-edge laser emission is found to occur at higher frequencies (5 kHz), where the helix is stabilized due to dielectric coupling. These results demonstrate a method by which the linewidth of the laser source can be readily controlled externally (from 4 nm to 0.5 nm) using electric fields. © 2012 American Institute of Physics.

Application of the fractional Fourier transform to the design of LCOS based optical interconnects and fiber switches

It is shown that reflective liquid crystal on silicon (LCOS) spatial light modulator (SLM) based interconnects or fiber switches that use defocus to reduce crosstalk can be evaluated and optimized using a fractional Fourier transform if certain optical symmetry conditions are met. Theoretically the maximum allowable linear hologram phase error compared to a Fourier switch is increased by a factor of six before the target crosstalk for telecom applications of -40 dB is exceeded. A Gerchberg-Saxton algorithm incorporating a fractional Fourier transform modified for use with a reflective LCOS SLM is used to optimize multi-casting holograms in a prototype telecom switch. Experiments are in close agreement to predicted performance. © 2012 Optical Society of America.

Free-space optoelectronic switching cores with MPLS for SANs over WDM ring networks

With increasing demands on storage devices in the modern communication environment, the storage area network (SAN) has evolved to provide a direct connection allowing these storage devices to be accessed efficiently. To optimize the performance of a SAN, a three-stage hybrid electronic/optical switching node architecture based on the concept of a MPLS label switching mechanism, aimed at serving as a multi-protocol label switching (MPLS) ingress label edge router (LER) for a SAN-enabled application, has been designed. New shutter-based free-space multi-channel optical switching cores are employed as the core switch fabric to solve the packet contention and switching path conflict problems. The system-level node architecture design constraints are evaluated through self-similar traffic sourced from real gigabit Ethernet network traces and storage systems. The extension performance of a SAN over a proposed WDM ring network, aimed at serving as an MPLS-enabled transport network, is also presented and demonstrated. © 2012 OSA.

Ferroelectric liquid crystal mixture integrated into optical waveguides

We report an on-chip integrated ferroelectric liquid crystal (FLC) waveguide structure suitable for telecommunication applications. Single gaps with different widths of 5, 10, and 20 μ m inside individual silica waveguides were filled with an FLC mixture. The waveguide devices operate as a binary switch or an attenuator in a temperature range from 30 °C to 60 °C. The FLC mixture exhibited a good alignment quality in these gaps without alignment layers. A good extinction ratio of up to 33.9 dB and a low insertion loss of <4.3 dB at λ = 1550 nm were observed. Switching times of <100 μs were obtained for the low electric fields applied in this experiment. © 2012 IEEE.

Comparisons between 28 Gb/s NRZ, PAM, CAP and optical OFDM systems for datacommunication applications

Theoretical investigations have been performed to analyze and compare the link power budget and power dissipation of a 28 Gb/s datacommunication system for data center switch scenarios using NRZ, PAM-4, CAP-16 and 16-QAM-OFDM modulation schemes. © 2012 IEEE.

Detecting air pockets for architectural concrete quality assessment using visual sensing

Air pockets, one kind of concrete surface defects, are often created on formed concrete surfaces during concrete construction. Their existence undermines the desired appearance and visual uniformity of architectural concrete. Therefore, measuring the impact of air pockets on the concrete surface in the form of air pockets is vital in assessing the quality of architectural concrete. Traditionally, such measurements are mainly based on in-situ manual inspections, the results of which are subjective and heavily dependent on the inspectors’ own criteria and experience. Often, inspectors may make different assessments even when inspecting the same concrete surface. In addition, the need for experienced inspectors costs owners or general contractors more in inspection fees. To alleviate these problems, this paper presents a methodology that can measure air pockets quantitatively and automatically. In order to achieve this goal, a high contrast, scaled image of a concrete surface is acquired from a fixed distance range and then a spot filter is used to accurately detect air pockets with the help of an image pyramid. The properties of air pockets (the number, the size, and the occupation area of air pockets) are subsequently calculated. These properties are used to quantify the impact of air pockets on the architectural concrete surface. The methodology is implemented in a C++ based prototype and tested on a database of concrete surface images. Comparisons with manual tests validated its measuring accuracy. As a result, the methodology presented in this paper can increase the reliability of concrete surface quality assessment

Nucleation, growth, and control of ferroelectric-ferroelastic domains in thin polycrystalline films

The unique response of ferroic materials to external excitations facilitates them for diverse technologies, such as nonvolatile memory devices. The primary driving force behind this response is encoded in domain switching. In bulk ferroics, domains switch in a two-step process: nucleation and growth. For ferroelectrics, this can be explained by the Kolmogorov-Avrami-Ishibashi (KAI) model. Nevertheless, it is unclear whether domains remain correlated in finite geometries, as required by the KAI model. Moreover, although ferroelastic domains exist in many ferroelectrics, experimental limitations have hindered the study of their switching mechanisms. This uncertainty limits our understanding of domain switching and controllability, preventing thin-film and polycrystalline ferroelectrics from reaching their full technological potential. Here we used piezoresponse force microscopy to study the switching mechanisms of ferroelectric-ferroelastic domains in thin polycrystalline Pb 0.7Zr0.3TiO3 films at the nanometer scale. We have found that switched biferroic domains can nucleate at multiple sites with a coherence length that may span several grains, and that nucleators merge to form mesoscale domains, in a manner consistent with that expected from the KAI model. © 2012 American Physical Society.

RFID Tag Location Systems

We describe a methods of locating an RFID tag. One method comprises: transmitting tag location signals from a plurality of different transmit antennas, wherein said antennas are spaced apart by more than a near field limit distance at a frequency of a said signal; receiving a corresponding plurality of receiving return signals from said tag; and processing said tag return signals to determine a range to said tag; wherein said transmitting comprises transmitting at a plurality of different frequencies; wherein said processing comprises determining a phase difference at said plurality of different frequencies to determine said range, and wherein said determining of said phase difference determines a phase difference between either i) two or more of said transmit signals resulting in a maxima in the returned signal RSSI or ii) a first transmit signal and its corresponding return signal; and wherein said determining of said range to said tag uses said return signals weighted responsive to a respective received signal strength of the return signal. Further data which may be used for averaging may be generated by using the above techniques along with changes in the polarisation state of the transmit and receive antennas and/or physical reconfiguration of the antennas (e.g. switch the transmit and receive elements).

A finite element model of magnetization of superconducting bulks using a solid-state flux pump

Superconductors have a bright future; they are able to carry very high current densities, switch rapidly in electronic circuits, detect extremely small perturbations in magnetic fields, and sustain very high magnetic fields. Of most interest to large-scale electrical engineering applications are the ability to carry large currents and to provide large magnetic fields. There are many projects that use the first property, and these have concentrated on power generation, transmission, and utilization; however, there are relatively few, which are currently exploiting the ability to sustain high magnetic fields. The main reason for this is that high field wound magnets can and have been made from both BSCCO and YBCO, but currently, their cost is much higher than the alternative provided by low-Tc materials such as Nb3Sn and NbTi. An alternative form of the material is the bulk form, which can be magnetized to high fields. This paper explains the mechanism, which allows superconductors to be magnetized without the need for high field magnets to perform magnetization. A finite-element model is presented, which is based on the E-J current law. Results from this model show how magnetization of the superconductor builds up cycle upon cycle when a traveling magnetic wave is induced above the superconductor. © 2011 IEEE.

Magnetization of bulk superconductors using thermally actuated magnetic waves

A novel technique is proposed to magnetize bulk superconductors, which has the potential to build up strong superconducting magnets. Instead of conventionally using strong magnetic pulses, periodical magnetic waves with strength as low as that of rare-earth magnets are applied. These magnetic waves travel from the periphery to the center of a bulk superconductor and become trapped little by little. In this way, bulk superconductors can gradually be magnetized. To generate these magnetic waves, a thermally actuated magnet was developed, which is constructed by a heating/cooling switch system, a rare-earth bulk magnet, and a Gadolinium (Gd) bulk. The heating/cooling switch system controls the temperature of the Gd bulk, which, along with the rare-earth magnet underneath, can transform thermal signals into magnetic waves. The modeling results of the thermally actuated magnet show that periodical magnetic waves can effectively be generated by applying heating and cooling pulses in turn. A YBCO bulk was tested in liquid nitrogen under the magnetic waves, and a notable accumulation of magnetic flux density was observed. © 2006 IEEE.

Design of a compact reconfigurable optical interconnection using nematic liquid crystal spatial light modulator

The wavelength-division multiplexing (WDM) has been proposed as a promising technology to efficiently use the available bandwidth of a single optical fibre. This can be achieved by transmitting different channels on the optical fibre with each channel modulating a different wavelength. The aim of this paper is to propose a compact design (35 mm×65 mm) of a reconfigurable holographic optical switch in order to access and manipulate 4 channels at a node of a fibre-optic communication network. A vital component of such a switch is a nematic liquid crystal spatial light modulator offering control and flexibility at the channel manipulation stage and providing the ability to redirect light into the desired output fibre. This is achieved by the use of a 2-D analogue phase computer generated hologram (CGH) based on liquid crystal on silicon (LCOS) technology. © 2012 SPIE.

Series-connected IGBTs using active voltage control technique

With series insulated-gate bipolar transistor (IGBT) operation, well-matched gate drives will not ensure balanced dynamic voltage sharing between the switching devices. Rather, it is IGBT parasitic capacitances, mainly gate-to-collector capacitance Cgc, that dominate transient voltage sharing. As Cgc is collector voltage dependant and is significantly larger during the initial turn-off transition, it dominates IGBT dynamic voltage sharing. This paper presents an active control technique for series-connected IGBTs that allows their dynamic voltage transition dV\ce/dt to adaptively vary. Both switch ON and OFF transitions are controlled to follow a predefined dVce/dt. Switching losses associated with this technique are minimized by the adaptive dv /dt control technique incorporated into the design. A detailed description of the control circuits is presented in this paper. Experimental results with up to three series devices in a single-ended dc chopper circuit, operating at various low voltage and current levels, are used to illustrate the performance of the proposed technique. © 2012 IEEE.

Programmable ZnO nanowire transistors using switchable polarization of ferroelectric liquid crystal

We demonstrate modulations of electrical conductance and hysteresis behavior in ZnO nanowire transistors via electrically polarized switching of ferroelectric liquid crystal (FLC). After coating a nanowire channel in the transistors with FLCs, we observed large increases in channel conductance and hysteresis width, and a strong dependence of hysteresis loops on the polarization states associated with the orientation of electric dipole moments along the direction of the gate electric field. Furthermore, the reversible switching and retention characteristics provide the feasibility of creating a hybrid system with switch and memory functions. © 2013 American Institute of Physics.

Insula and striatum mediate the default bias.

Humans are creatures of routine and habit. When faced with situations in which a default option is available, people show a consistent tendency to stick with the default. Why this occurs is unclear. To elucidate its neural basis, we used a novel gambling task in conjunction with functional magnetic resonance imaging. Behavioral results revealed that participants were more likely to choose the default card and felt enhanced emotional responses to outcomes after making the decision to switch. We show that increased tendency to switch away from the default during the decision phase was associated with decreased activity in the anterior insula; activation in this same area in reaction to "switching away from the default and losing" was positively related with experienced frustration. In contrast, decisions to choose the default engaged the ventral striatum, the same reward area as seen in winning. Our findings highlight aversive processes in the insula as underlying the default bias and suggest that choosing the default may be rewarding in itself.