Magnetic properties of nickel filament polymer-matrix composites

The magnetic properties of polyethersulfone-matrix composites with 3-19 vol.% polycrystalline nickel filaments (0.4 (im diam) were investigated. These filaments were found to exhibit hysteresis energy loss 10800 J/m³ of nickel and coercive force 16.9 kA/m, compared to corresponding values of 4930 J/m³ and 4.7 kA/m for 2 μ.m diam polycrystalline nickel fibers, 1020 J/m³ and 0.5 kA/m for 20 μm diam polycrystalline nickel fibers, and 1280 J/m³ and 2.3 kA/m for solid polycrystalline nickel.     

Reduction of EMI emission from power converter using soft-switchingtechniques

Measured, conducted, and radiated electromagnetic interference (EMI) from a hard-switched flyback converter and a soft-switched converter of the same power are presented. Results indicate that the EMI emission can be substantially reduced by using the soft-switching technique in power converters     

A systematic design method to obtain broadband characteristics for singly-fed electromagnetically coupled patch antennas for circular polarization

We present a systematic, empirical design technique to obtain optimum broadband impedance, axial-ratio (AR) and gain bandwidths for a singly-fed electromagnetically coupled patch antenna for circular polarization. Our investigation has also revealed tradeoffs amongst obtainable AR, impedance bandwidth and AR bandwidth. Using two design examples at different frequency bands and for different senses of circular polarization, we have demonstrated the effectiveness of the proposed knowledge-based tuning method. We have obtained at C-band measured values of impedance bandwidth (VSWR/spl les/2) equal to 43%, 3-dB AR bandwidth of 8%, AR of less than 0.3 dB and a mean gain level of 7 dB. For the Ku-band element, a 40% impedance bandwidth and a 17.3% of 3-dB AR bandwidth have been obtained with a peak gain of 7.2 dBic.     

Rheological Behavior of Thermal Interface Pastes

Polyol-ester-based thermal pastes containing carbon black, fumed alumina or nanoclay exhibit Bingham plastic behavior with shear thinning. Carbon black gives double yielding, but fumed alumina and nanoclay give single yielding. The plastic viscosity increases with the solid content. Antioxidants increase the plastic viscosity and yield stresses. Nanoclay (1.0 vol.%) gives low shear moduli, high critical shear strain, and high loss tangent, thus resulting in low bond-line thickness and high thermal contact conductance for smooth (0.009 μm) proximate surfaces. Carbon black (Tokai, 8.0 vol.%) gives high moduli, low critical strain, and low loss tangent, thus resulting in high bond-line thickness, though the high thermal conductivity due to the high solid content results in high thermal contact conductance for rough (15 μm) proximate surfaces. Antioxidants enhance the solid-like character, increase the yield stress, plastic viscosity, and bond-line thickness, and decrease the thermal contact conductance.     

Optimal shape design of microwave device using FDTD and designsensitivity analysis

In this paper, a novel optimal shape design method is proposed using the finite-difference time-domain (FDTD) method and the design sensitivity analysis to obtain broad-band characteristics of microwave devices. In shape design problem, the nodes that describe the shape of geometry to be optimized are taken as design variables. The design sensitivity is evaluated using the adjoint variable equation that is obtained from a terminal-value problem. The adjoint equation can be solved by the FDTD technique with the backward time scheme. With this method, a Ka-band unilateral fin line is tested to show validity     

Ultra fast symmetry and SIMD-based projection-backprojection (SSP) algorithm for 3-D PET image reconstruction

Remarkable progress in positron emission tomography (PET) development has occurred in recent years, in hardware, software, and computer implementation of image reconstruction. Recent development in PET scanners such as the high-resolution research tomograph (HRRT) developed by CTI (now Siemens) represents such a case and is capable of greatly enhanced resolution as well as sensitivity. In these PET scanners, the amount of coincidence line data collected contains more than 4.5 x 10(9) coincidence lines of response generated by as many nuclear detectors as 120 000. This formidable amount of data and the reconstruction of this data set pose a real problem in HRRT and have also been of the major bottle neck in further developments of high resolution PET scanners as well as their applications. In these classes of PET scanners, therefore, obtaining one set of reconstructed images often requires many hours of image reconstruction. For example, in HRRT with full data collection in a normal brain scan (using SPAN 3), the image reconstruction time is close to 80 min, making it practically impossible to attempt any list-mode-based dynamic imaging since the image reconstruction time would take many days (as much as 43 h or more for 32-frame dynamic image reconstruction). To remedy this data-handling problem in image reconstruction, we developed a new algorithm based on the symmetry properties of the projection and backprojection processes, especially in the 3-D OSEM algorithm where multiples of projection and back-projection are required. In addition, the single-instruction multiple-data (SIMD) technique also allowed us to successfully incorporate the symmetry properties mentioned above, thereby effectively reducing the total image reconstruction time to a few minutes. We refer to this technique as the symmetry and SIMD-based projection-backprojection (SSP) technique or algorithm and the details of the technique will be discussed and an example of the application of the technique to the HRRT's OSEM algorithm will be presented as a demonstration.     

On the Robustness of Scheduling Against Channel Variations

In this paper, we study the robustness of scheduling against channel variations. Specifically, we consider a class of generalized proportional fairness (PF) schedulers that achieve optimal throughput-fairness trade-off and study their robustness in terms of maintaining a certain fairness criterion when the channel statistics change from the additive white Gaussian noise (AWGN) to Rayleigh fading for all users. We conclude that the scheduler is robust only when it is configured to achieve the proportional fairness. For the other scheduler configurations, which are not robust, we show how fairness deviates from the ideal one when the channel statistics change and show how scheduler parameters need to be adjusted to restore the desired fairness. We also show simulation results.     

Wavelength and repetition rate tunable optical pulse source using a chirped fiber Bragg grating and a nonlinear optical loop mirror

We experimentally demonstrate a simple and novel scheme for tunable real-repetition-rate multiplication, based on the combined use of fractional Talbot effect in a linearly tunable chirped fiber Bragg grating (FBG) and cross-phase modulation (XPM) effect in a nonlinear optical loop mirror (NOLM). By tuning the group-velocity dispersion of the chirped FBG fabricated with the S-bending method using a uniform FBG, we obtain high quality pulses at pseudorepetition rates of 20/spl sim/50 GHz from an original 8.5-ps 10-GHz soliton pulse train. We subsequently convert this pseudorate multiplication into a real-rate multiplication using XPM effect in an NOLM. A wavelength tuning is also achieved over a /spl sim/15-nm range.     

Structural Fault Based Specification Reduction for Testing Analog Circuits

Specification reduction can reduce test time, consequently, test cost. In this paper, a methodology to reduce specifications during specification testing for analog circuit is proposed and demonstrated. It starts with first deriving relationships between specifications and parameter variations of the circuit-under-test (CUT) and then reduces specifications by considering bounds of parameter variations. A statistical approach by taking into account of circuit fabrication process fluctuation is also employed and the result shows that the specification reduction depends on the testing confidence. A continuous-time state-variable benchmark filter circuit is applied with this methodology to demonstrate the effectiveness of the approach.