ADI-FDTD Method With Fourth Order Accuracy in Time

This letter presents an unconditionally stable alternating direction implicit finite-difference time-domain (ADI-FDTD) method with fourth order accuracy in time. Analytical proof of unconditional stability and detailed analysis of numerical dispersion are presented. Compared to second order ADI-FDTD and six-steps SS-FDTD, the fourth order ADI-FDTD generally achieves lower phase velocity error for sufficiently fine mesh. Using finer mesh gridding also reduces the phase velocity error floor, which dictates the accuracy limit due to spatial discretization errors when the time step size is reduced further.     

Pi-coefficient analysis of update algorithms for adaptive systems

This paper finds the appropriate pi-coefficients for a parameter estimation adaptive system and uses them to analyze the stability of two estimation algorithms. The estimation error dynamics of the system are modeled by a linear time-invariant subsystem and a nonlinear time-varying update law in a feedback loop. Then the so-called max-p problems are formulated and solved to obtain the pi-coefficients for the linear subsystem and nonlinear update low. For the investigated system, the quantitative results show that the least-squares update algorithm has larger stability range than that of the gradient algorithm, and the σ-modification scheme gives larger stability ranges for both algorithms.     

Novel Folded Waveguide Resonator Filter Using Slot Technique

This letter presents a primary investigation into developing a compact and low-loss bandpass filter using novel folded-waveguide resonators with a footprint reduction. A slot coupling between adjacent resonators is introduced, which is characterized using full-wave electromagnetic simulations and verified experimentally. Two two-pole folded-waveguide resonator filters of this type have been designed, fabricated and tested. Simulation and measurement results are presented to validate the design and to show the advantages of this type of filter.     

Effect of Heat Treatment on Microstructure and Stress Rupture Properties of a Ni-Mo-Cr-Fe Base Corrosion-Resistant Superalloy

The influences of heat treatment and test condition on the microstructure and stress rupture properties of a Ni-Mo-Cr-Fe base corrosion-resistant superalloy have been investigated in this paper. Optical microscope and scanning electron microscope were employed for the microstructure observation, and X-ray diffraction, electron probe micro-analyzer, and transmission electron microscope were used for phase determination. It was found that the grain size increased and the volume fractions of initial M₆C carbides decreased along with the increase in solution treatment temperature. When tested at 650 °C/320 MPa, the stress rupture lives decreased with the increase in solution treatment temperature, but the stress rupture lives increased slightly at first and then decreased for the samples solution heat treated at 1220 °C when tested at 700 °C/240 MPa. The elongations showed the descendent trends under these two conditions. The stress rupture life and elongation for the aged samples all showed a noticeable improvement at 650 °C/320 MPa, but there was no noticeable improvement at 700 °C/240 MPa. The reasons can be attributed to the grain size, test conditions, and the initial and secondary carbides.     

Analysis of a closed-boundary axilens with long focal depth and high transverse resolution based on rigorous electromagnetic theory

We find that a microcylindrical axilens with a closed boundary and with an f-number less than 1 still can achieve the properties of long focal depth and high transverse resolution, unlike a microcylindrical axilens with an open boundary, which fails to maintain those properties for low f-numbers. The focusing characteristics of the closed-boundary axilens and the open-boundary axilens are numerically investigated based on the boundary integral method. The numerical results show that the ratio of the extended focal depth of the closed-boundary axilens to the focal depth of the conventional microlens can reach up to 1.26 and 2.12 for the preset focal depths 3 and 5 microm, respectively, even though the f-number is reduced to 1/3.     

Ultra-Wideband (UWB) Bandpass Filter With Embedded Band Notch Structures

A compact ultra-wideband (UWB) bandpass filter (BPF) with narrow notched (rejection) band in the UWB passband realized on a microstrip line is implemented and presented in this letter for use in wireless communication applications within the unlicensed UWB range set by the Federal Communications Commission (FCC). The filter consists of five short-circuited stubs separated by nonredundant connecting lines in order to exhibit a high selectivity filtering characteristic. The narrow notched (rejection) band was introduced by using a new technique which involves embedding open stubs in the first and last connecting lines in order to reject any undesired existing radio signal which may interfere with the determined UWB passband. The bandwidth of the notched filter can be controlled by adjusting the width of the stubs or the gaps or both. The length of the stubs can be tuned to select a specific frequency for the notched band. The embedded stubs can be used to excite single or double band-reject response. Two UWB BPFs with narrow notched band having a fractional bandwidth (FBW) of about 4.6% and 6.5% were realized theoretically and verified by full-wave EM simulation and the experiment. Excellent agreement between the predicted and measured results was obtained and is demonstrated     

Human-Body-Model Electrostatic-Discharge and Electrical-Overstress Studies of Buried-Heterostructure Semiconductor Lasers

Optoelectronic components such as laser diodes, light-emitting diodes, and photodiodes are susceptible to electrostatic discharge (ESD) and electrical overstress (EOS). Human-body model (HBM) is the most widely adopted method for the characterization of the ESD performance. In this paper, we report a comprehensive study of the ESD and EOS characteristics of buried-heterostructure (BH) semiconductor lasers using the HBM. Threshold current, optical power, optical spectrum, and reverse-bias current are characterized during the ESD study. We show that the ESD-failure thresholds depend upon the polarity. The chip can sustain the highest ESD stress under forward bias and the lowest one under forward/reverse bias. We also show that the BH lasers exhibit two types of ESD-degradation behavior. The soft degradation is characterized by a gradual increase in the threshold current, whereas the hard degradation is identified by a sudden jump in the threshold current during the ESD voltage ramp. The ESD-degradation behavior seems to be influenced by the cavity length. The failure-analysis results show that about 27% of the ESD failure is related to facet damage. The damage regions occur at the upper laser mesa structure and form preferentially on the bond-pad side. The preferential formation of the facet damage is suggestive of current-crowding effect. We have also found that the ESD-degradation behavior is a function of the facet damage. The soft-degradation failure shows a stronger correlation with the facet damage than the hard-degradation one. Finally, we demonstrate that the ESD performance of the laser can be improved by adding a protection diode.     

Temperature and current dependences of reliability degradation of buried heterostructure semiconductor lasers

Failure times of semiconductor lasers are usually lengthy under normal aging conditions. Determination of failure times typically involves extrapolation using a sublinear or linear model. It becomes increasingly difficult to experimentally determine activation energy and current exponent since data based on lower temperatures and lower stress currents are required. In this paper, the temperature and current dependences of 1310-nm buried heterostructure (BH) InP lasers were studied. We show that the activation energy of 1310-nm BH lasers based on life test data at 70/spl deg/C-100/spl deg/C is higher than the value of 0.4 eV suggested by Telcordia. The activation energies estimated by sublinear and linear models were 0.87 and 0.55 eV, respectively. We also show that the current exponents are 1.4 and 1.0, respectively, for sublinear and linear models. We discuss the implications of the reliability results in field reliability predictions.     

Fast alternating direction implicit method for efficient transient thermal simulation of integrated circuits

This paper presents fast alternating direction implicit (FADI) method for efficient transient thermal simulation of integrated circuits. The FADI method is formulated from Peaceman–Rachford's ADI and Douglas–Gunn's ADI methods. The update procedure of the proposed method has basic implicit form that features derivative‐free right‐hand side and hence, better efficiency and conciseness. Subsequently, through the basic implicit form of FADI method, the relationship between classical Peaceman–Rachford's and Douglas–Gunn's ADI methods can be clarified and elucidated in detail. A unified boundary condition that can cater to common kinds of boundary conditions in thermal simulation is also introduced. To further accelerate FADI method, the graphics processing unit is also utilized through Compute Unified Device Architecture implementation. It is shown that high efficiency gain can be achieved using the proposed FADI method through large time step size and data parallelism, while maintaining stability and good accuracy. As numerical illustration, an integrated circuit structure with microchannel cooling is demonstrated. Numerical results further ascertain the cooling effect of the microchannels. Copyright © 2015 John Wiley & Sons, Ltd.