Circumferential Gap in a TE/sub 01/-Mode-Transmitting Multimode Circular Waveguide

Higher-order modes produced in a guide and fields radiated out of a guide by a circumferential gap in a multimode circular waveguide that is used for millimeter wave transmission, were investigated by means of fictitious equivalent magnetic current for the gap. These results were compared with the analysis obtained by Bethe's method, which was used for the problem of diffraction of fields by a small hole in a plane conducting sheet. The two results agreed well for narrow gap.     

A comparison of quantizers optimized for corrupted and uncorrupted input signals

It is known from literature how to design optimal quantizers for input signals with a given probability density function. In this paper, optimal quantizers for input signals corrupted by noise are designed. In addition to that it is shown by a separation theorem that the optimal quantizer can be replaced by an estimator for the corrupted input signal followed by an optimal quantizer for the estimate. Furthermore, some numerical results for processes with a Gaussian probability density function are given.     

Digital computer solutions of the rigorous equations for scattering problems

A survey of recently developed techniques for solving the rigorous equations that arise in scattering problems is presented. These methods generate a system of linear equations for the unknown current density by enforcing the boundary conditions at discrete points in the scattering body or on its surface. This approach shows promise of leading to a systematic solution for a dielectric or conducting body of arbitrary size and shape. The relative merits of the linear-equation solution and the variational solutions are discussed and numerical results, obtained by these two methods, are presented for straight wires of finite length. The computation effort required with the linear-equation solution can be reduced by expanding the current distribution in a series of modes of the proper type, by making a change of variables for integration, and by employing interpolation formulas. Solutions are readily obtained for a scattering body placed in an incident plane-wave field or in the near-zone of a source. Examples are included for both cases, using a straight wire of finite length as the scattering body. The application of these techniques to scattering by a dielectric body is illustrated with dielectric rods of finite length.     

Graded-index-type crystalline fibre for IR light transmission

A new method for making a graded-index-type crystalline fibre is proposed. A fibre for IR light transmission with crystalline claddings was desired for improving the reliability of the crystallinc fibre and for avoiding any excess loss at the core surface. A fibre with the core-cladding structure was made by complex extrusion with KRS-5 as the core and KRS-6 as the cladding. Obtaining a smooth core-cladding interface was very difficult. This problem was overcome by a diffusion of composite ions by annealing after the extrusion. The fibre has a concentration distribution that can be accounted for by a GI fibre. The transmission loss of the CO2 laser is 0.2 dB/m with a launching NA of 0.05.     

Early-time currents induced on a cylinder by a cylindricalelectromagnetic wave

An analytical study of the early-time current response of a perfectly conducting circular cylinder to a cylindrical electromagnetic wave, produced by a parallel filament carrying a unit-step current, is presented. Surface current density expressions for both the shadow and illuminated regions are obtained by applying the Watson transformation to the frequency-domain solution and then evaluating the corresponding integrals separately, in the shadow region by a residue series and in the illuminated region by using the saddle point technique. Analytical results obtained by using a double Laplace transform approach for the shadow region and the Luneberg-Kline expansion approach for the illuminated region are given. Numerical results illustrate the variation of the distribution of current density with time for different locations of the line current with respect to the cylinder, and also allows a comparison of the alternate methods applied by the authors, showing their corresponding range of validity. The response to an impulsive plane wave is derived as a special case     

Holographic data storage systems

In this paper, we discuss fundamental issues underlying holographic data storage: grating formation, recording and readout of thick and thin holograms, multiplexing techniques, signal-to-noise ratio considerations, and readout techniques suitable for conventional, phase conjugate, and associative search data retrieval. Next, we consider holographic materials characteristics for digital data storage, followed by a discussion on photorefractive media, fixing techniques, and noise in photovoltaic and other media with a local response. Subsequently, we discuss photopolymer materials, followed by a discussion on system tradeoffs and a section on signal processing and en/decoding techniques, succeeded by a discussion on electronic implementations for control, signal encoding, and recovery. We proceed further by presenting significant demonstrations of digital holographic systems. We close by discussing the outlook for future holographic data storage systems and potential applications for which holographic data storage systems would be particularly suited.     

Phase-Noise-Compensated Optical Frequency-Domain Reflectometry

The theory of phase-noise-compensated optical frequency-domain reflectometry (PNC-OFDR), a novel type of optical frequency-domain reflectometry (OFDR) with a measurement range much longer than the laser coherence length, is described, and the signal and noise spectral densities are deduced for a discussion of signal-to-noise ratio (SNR). The analysis of PNC-OFDR shows the possibility of obtaining a high SNR by using many reference signals for phase-noise compensation. By using a “concatenately generated phase” (CGP), only a single auxiliary interferometer is needed for phase-noise compensation, and other reference signals can be easily generated by performing a calculation based on signal use obtained from the single auxiliary interferometer. An experimental investigation shows the feasibility of using CGPs for PNC-OFDR by dividing the fiber under test into several sections for phase-noise compensation. Moreover, the influence of strong reflection events on Rayleigh backscattering is discussed by considering the dead zone caused by a fiber/air Fresnel reflection. It is shown theoretically that a dead zone that has no influence on the neighboring section can be achieved by using suitable parameters in an actual system.      

The role of source boundary condition in spreading resistance calculations

Solutions are presented for the current density distribution at an equipotential disc electrode in contact with a slab backed by a perfect conductor. These exact solutions provide a basis for testing the validity of the two forms of source current density distribution assumed in approximate calculations of spreading resistance correction factors, viz. a uniform distribution and the distribution given by the classical solution for the infinitely thick slab. By using the latter distribution and the power loss definition for spreading resistance, a new correction factor integral has been obtained. Correction factors have been calculated by using this integral and those given by Schumann and Gardner, by Lee and by assuming a uniform current distribution. Except for Schumann and Gardner's method, all the methods yield results consistent with those obtained for the current density distributions. In the case of Schumann and Gardner's method, the correction factors obtained for thin slabs agree closely with those given by the exact method, despite the fact that the assumed source current distribution is in gross disagreement with the exact distribution. The close agreement in correction factors is fortuitous and is a consequence of the definition that Schumann and Gardner used for the spreading resistance. For a slab with a perfectly insulating substrate, exact solutions are not available. A comparative study has therefore been made in this case between the correction factors obtained by the four approximate methods themselves. The overall conclusion is that of the approximate methods, the uniform current density method is the most satisfactory from the point of view of self-consistency and overall accuracy.     

Method for the design of diffractive optical elements through low-dimensional optimization

A method for the simulation and design of diffractive optical structures is presented. In this paper, we present a design of a finite diffractive-optic structure that has been generated by solving for the electromagnetic fields inside an optimization loop. The scalar electromagnetic fields are computed in the region of a two-dimensional diffractive-optic structure by solving the scalar Helmholtz equation, using the finite-difference method. This analysis process is inserted into a simulated annealing algorithm that designs the optimal structure by maximizing a predetermined figure of merit. Computationally efficient methods that allow for reasonable computational requirements are described, including the defining of structure parameters as relatively simple polynomial functions. This allows for changes in the structure to be made by the program while maintaining a small number of dimensions for the search by the simulated annealing algorithm.     

Two-dimensional beam diffraction by a half-plane and wide slit

The far field of a two-dimensional beam resulting from an electric line source at a complex position is described, its half-power beamwidth determined, and its validity as an antenna beam indicated. Farfield diffraction by a half-plane is then determined from an exact uniform solution for an isotropic line source by making the source position complex. The same basic solution and technique are used for beam diffraction by a wide slit, with first-order interaction between the slit edges included. Numerical results for normal incidence illustrate the evolution of the diffraction patterns from those for an omnidirectional source to those for a highly directive beam. Results for plane wave incidence by a slit also come out of this solution. The remarkable simplicity and convenience of this method relative to alternative asymptotic procedures is discussed.     

A Stair-Building Strategy for Tailoring Mechanical Behavior of Re-Customizable Metamaterials

Re-customizable mechanical behavior is critical for versatile materials with tunable functions and applications, but inverse design for varying targets is often hindered by complex coupling between structural topologies and mechanics. In this work, a novel “stair-building” strategy for customizing as well as re-customizing target mechanical behavior for mechanical metamaterials is proposed. Similar to building a stair with bricks, customizing or re-customizing a target stress–strain (force–displacement) curve for the material can be realized by stacking the brick-like loading curves of bistable units visually. The mechanical feasibility of the “stair-building” strategy is firstly physically realized in a type of array-structured multistable mechanical metamaterial and then carefully verified by theoretical mechanics analysis. Accordingly, three specific simple design schemes are further proposed for implementation. The “stair-building” strategy is proved to be rapid, effective, and accurate for mechanical behavior customization by both experiments and finite element simulations. Moreover, re-customization for diverse mechanical behaviors in a wide range can be realized by the same piece of metamaterial. This design strategy provides a novel approach for tailoring metamaterials with re-customizable target mechanical behaviors and applies to a variety of bistable units.     

Multiresolution 3-D reconstruction from side-scan sonar images.

In this paper, a new method for the estimation of seabed elevation maps from side-scan sonar images is presented. The side-scan image formation process is represented by a Lambertian diffuse model, which is then inverted by a multiresolution optimization procedure inspired by expectation-maximization to account for the characteristics of the imaged seafloor region. On convergence of the model, approximations for seabed reflectivity, side-scan beam pattern, and seabed altitude are obtained. The performance of the system is evaluated against a real structure of known dimensions. Reconstruction results for images acquired by different sonar sensors are presented. Applications to augmented reality for the simulation of targets in sonar imagery are also discussed.     

Wire-junction matrix model for the TLM method

The additional capacitance and inductance introduced by a conducting wire can be modelled in the transmission line modelling (TLM) method by a special node. A symmetrical transmission-line structure is proposed for the modelling of wire junctions in a coarse mesh. The model is tested by calculating the response of a wire-cross scatterer and the RCS of a perfectly conducting plate simulated by means of a square wire mesh. Although, initially, TLM was not developed for solving wire structures, the results are in good agreement with the theoretical and moment-method solutions traditionally used for this type of structure     

Transient IR imaging of light and flexible microelectronic devices

An advanced method for the quality assessment of microelectronic assemblies has been developed by combining IR thermography and several techniques for stimulation by transient temperature fields. The method exploits singularities in materials and interconnections by the observation of perturbations in transient heat flow phenomena. For very light microelectronic systems like chip-on-flex assemblies a method was developed taking advantage of short stimulations by photoflash. Such a method provided possibilities for detecting defects on the level of a single interconnection with a pitch of 80 μm. In addition, a programmable array of thermo-electric converters, prepared for the testing of a large variety of microelectronic assemblies, was also used to perform transient IR imaging for chip-on-flex assemblies.     

On the barrier height of a metal-semiconductor contact with a thin interfacial layer

The free surface potential of a semiconductor has been studied by using a generalised definition of “neutral level.” Following this definition, an expression for the barrier height of an MIS structure has been derived, from which the expression for barrier height as derived by Cowley and Sze follows as a special case. Lastly, the formula used by previous workers for the determination of neutral level, has been modified for a more accurate calculation of the said parameter.     

Scaffolds Based on Biopolymeric Foams

A new approach for the preparation of hydrophilic and biocompatible porous scaffolds is described. The procedure involves the derivatization of a biopolymer by the introduction of vinylic moieties, formation of a high‐internal‐phase oil‐in‐water emulsion, and its subsequent polymerization. The ensuing materials are characterized by a highly porous morphology represented by pores completely interconnected by a plurality of holes. The hydrophilic and biocompatible nature of these materials make them good candidates for application as scaffolds for tissue engineering.     

A one-dimensional analytical model for the dual-gate-controlledthin-film SOI MOSFET

A one-dimensional analytical model for dual-gate-controlled SOI MOSFETs is presented and applied to a stacked p-channel MOSFET fabricated by epitaxial lateral overgrowth (ELO). The authors found and modeled a nonlinear dependence of front-gate threshold voltage on back-gate voltage if threshold is defined by a constant current instead of a constant silicon-surface potential. It is demonstrated by comparison of subthreshold slopes that surface potentials are not pinned to the onset of strong inversion or accumulation. Accurate one-dimensional modeling is a necessity for device characterization and a precondition for general SOI models for circuit simulation     

The Application of Planar Anistropy to Millimeter-Wave Ferrite Phase Shifters

The torque produced by the planar anistropy that occurs in some hexagonal ferrites is included in the equation of motion of the magnetization. The elements of the permeability tensor, derived here for a lossless approximation, are affected by the planar anistropy in much the same way as by an increase in saturation magnetization. This modified permeability has been incorporated into a model for a planar ferrite loaded rectangular waveguide, and the calculated values for differential nonreciprocal phase shift are found to increase substantially over those for a conventional isotropic ferrite.     

Fault Trees, Prime Implicants, and Noncoherence

The K&H algorithm for finding the p.i.'s of a noncoherent fault tree is too long and complicated for the purpose. The example that was used by K&H to illustrate the algorithm is reworked with known methods to show that alternatives are available that require less work. This correspondence is a series of four letters published as a sequel to a paper by Kumamoto & Henley (K&H) that presented an ``algorithm based on top-down analysis particularly designed for noncoherent fault trees'. The first of these letters is by Locks, claiming that the article is too complicated and that a shorter procedure is available. This is followed by Reply #1 by Ogunbiyi and Reply #2 by K&H. The note is concluded with a rebuttal by Locks to both replies.     

Low Complexity Decoder Architecture for Low-Density Parity-Check Codes

In this paper, we propose a low complexity decoder architecture for low-density parity-check (LDPC) codes using a variable quantization scheme as well as an efficient highly-parallel decoding scheme. In the sum-product algorithm for decoding LDPC codes, the finite precision implementations have an important tradeoff between decoding performance and hardware complexity caused by two dominant area-consuming factors: one is the memory for updated messages storage and the other is the look-up table (LUT) for implementation of the nonlinear function Ψ(x). The proposed variable quantization schemes offer a large reduction in the hardware complexities for LUT and memory. Also, an efficient highly-parallel decoder architecture for quasi-cyclic (QC) LDPC codes can be implemented with the reduced hardware complexity by using the partially block overlapped decoding scheme and the minimized power consumption by reducing the total number of memory accesses for updated messages. For (3, 6) QC LDPC codes, our proposed schemes in implementing the highly-parallel decoder architecture offer a great reduction of implementation area by 33% for memory area and approximately by 28% for the check node unit and variable node unit computation units without significant performance degradation. Also, the memory accesses are reduced by 20%.