Three-dimensional inverse scattering of a dielectric target embedded in a lossy half-space

A modified iterative Born method is applied for three-dimensional inversion of a lossless dielectric target embedded in a lossy half-space. The forward solver employs a modified form of the extended Born method, and the half-space Green's function is computed efficiently via the complex-image technique. Example results are shown, with all scattering data based on a computational model, utilizing a rigorous forward solver distinct from that employed in the inversion. In addition, distinct gridding schemes are used in the forward and inverse solvers. Simple Tikhonov regularization is found to yield adequate results for inversion of noisy data.     

Efficient computation of high-frequency two-dimensional effects inmulticonductor printed interconnects

The spectral domain technique with a Galerkin moment method solution is used to study high-frequency, two-dimensional effects such as dispersion and leakage in multiconductor printed interconnects. A simple asymptotic procedure is used to significantly improve the convergence of oscillatory spectral integrals involving distant expansion and testing functions. Examples are given for leaky waves on two multiconductor printed transmission line geometries     

Porphyrin-based nanoporous network polymers

Network polymers exhibiting large surfaces areas (900-1000 m2g-1) are prepared by the highly efficient dibenzodioxane forming reaction between meso-tetrakis(pentafluorophenyl)porphyrin and a rigid bis(catechol) monomer.     

Low-Frequency Noise Assessment of Silicon Passivated Ge pMOSFETs With TiN/TaN/ HfO2 Gate Stack

The low-frequency noise of pMOSFETs fabricated in epitaxial germanium-on-silicon substrates is studied. The gate stack consists of a TiN/TaN metal gate on top of a 1.3-nm equivalent oxide thickness HfO₂/SiO₂ gate dielectric bilayer. The latter is grown by chemical oxidation of a thin epitaxial silicon film deposited to passivate the germanium surface. It is shown that the spectrum is of the 1/f^gamma type, which obeys number fluctuations for intermediate gate voltage overdrives. A correlation between the low-field mobility and the oxide trap density derived from the 1/f noise magnitude and the interface trap density obtained from charge pumping is reported and explained by considering remote Coulomb scattering     

Wave-oriented signal processing of dispersive time-domainscattering data

Phase-space data processing is receiving increased attention because or its potential for furnishing new discriminants relating to classification and identification of targets and other scattering environments. Primary emphasis has been on time-frequency processing because of its impact on transient, especially wideband, short-pulse excitations. Here, we investigate the windowed Fourier transform, the wavelet transform, and model based superresolution algorithms within the context of a fully quantified and calibrated test problem investigated by us previously: two-dimensional (2-D) short-pulse plane wave scattering by a finite periodic array of perfectly conducting coplanar flat strips. Because the forward problem has been fully calibrated and parametrized, some quantitative measures can be assigned with respect to the tradeoffs of these time-frequency algorithms, yielding tentative performance assessments of the tested processing algorithms     

Multi-aspect detection of surface and shallow-buried unexplodedordnance via ultra-wideband synthetic aperture radar

An ultra-wideband (UWB) synthetic aperture radar (SAR) system is investigated for the detection of former bombing ranges, littered by unexploded ordnance (UXO). The objective is detection of a high enough percentage of surface and shallow-buried UXO, with a low enough false-alarm rate, such that a former range can be detected. The physics of UWB SAR scattering is exploited in the context of a hidden Markov model (HMM), which explicitly accounts for the multiple aspects at which a SAR system views a given target. The HMM is trained on computed data, using SAR imagery synthesized via a validated physical-optics solution. The performance of the HMM is demonstrated by performing testing on measured UWB SAR data for many surface and shallow UXO buried in soil in the vicinity of naturally occurring clutter     

Hidden Markov models for multiaspect target classification

This article presents a new approach for target identification, in which we fuse scattering data from multiple target-sensor orientations. The multiaspect data is processed via hidden Markov model (HMM) classifiers, buttressed by physics-based feature extraction. This approach explicitly accounts for the fact that the target-sensor orientation is generally unknown or “hidden”. Discrimination results are presented for measured scattering data     

A study of slotline leaky-wave antennas

The results of an experimental investigation of several millimeter-wave slotline leaky-wave antennas at 94 GHz are given. The experimental results show how variations in the transverse slot geometry affect the radiation pattern. Additionally, slot geometry variations also change the polarization performance of the antenna. The narrow transverse slot array was more sensitive to a perpendicularly (E_y-E_z) polarized electric field than the wide slot case. Also, the change in the effective phase constant along the antenna with changing slot dimensions caused a noticeable shift in the angle of the main beams. However, the beamwidths for all cases remained about the same. A simple model is presented to explain this. For designing an antenna of this form, the effective phase constant, β, can be approximately determined using a numerical analysis of the uniform slot problem. Given β and the operating frequency and the scanning ranges, the element spacing can be determined. The attenuation constant does not change much when the transverse slot widths are varied. If greater sensitivity to an E _y-E_z polarized wave is desired, the transverse slots should be narrow     

Size effects on the DC characteristics and low frequency noise of double polysilicon NPN bipolar transistors

DC and low frequency noise measurements have been carried out for double polysilicon NPN bipolar transistors. Our experiments have highlighted unexpected geometrical dependencies for the base saturation current density and low frequency noise. A model, taking into account a variation of the interfacial oxide thickness at the periphery of the emitter has been proposed and it has been successfully applied to the experimental results.