Concentric ring and jerusalem cross arrays as frequency selective surfaces for a 45° incidence diplexer

Typical crosspolar levels of ?33 dB in the reflection band and slightly lower levels in transmission were recorded for the concentric ring array in the 45° planes of the feed/array combination. The Jerusalem cross array gave higher levels in transmission. The band centre frequency ratios were 1.4 and 1.6.     

An on-line microcomputing system for the acquisition and processing of data from a fourier spectrometer

A microcomputing system has been developed to provide on-line data acquisition and analysis for a Fourier transform spectrometer, and the interface between the spectrometer and the microcomputer is described in detail. The system has been equipped with software which includes a fast Fourier transform programme for use in either conventional or dispersive Fourier transform spectroscopy, and programmes for calculating the optical constants and dielectric functions of solids from complex spectra obtained by dispersive Fourier transform spectroscopy.     

Al2TiO5-ZrTiO4-ZrO2 Composites: A New Family of Low-Thermal-Expansion Ceramics

The characterization and properties of ceramic composites containing the phases Al₂TiO₅, ZrTiO₄, and ZrO₂ are described. The range of compositions investigated gives very low average thermal expansions (α_24–1000°C as low as −2.0 × 10⁻⁶°C⁻¹) and excellent high-temperature stability. The low thermal expansions are apparently due to a combination of microcracking by the titanate phases and a contractive phase transformation by the ZrO₂. The crystal chemistry and microstructure of the product are processing dependent. Although the composites represent a complex microcracking system, the low thermal expansions and high-temperature stability make them potential candidates for commercial applications requiring thermal shock resistance.     

Interconnect-based system-level energy and power prediction to guide architecture exploration

We present a novel technique to predict energy and power consumption in an electronic system, given its behavioral specification and library components. The early prediction gives circuit designers the freedom to make numerous high-level choices (such as die size, package type, and latency of the pipeline) with confidence that the final implementation will meet power and energy as well as cost and performance constraints. Our unique statistical estimation technique associates low-level, technology dependent physical and electrical parameters, with expected circuit resources and interconnect. Further correlations with switching activity yield accurate results consistent with implementations. All feasible designs are investigated using this technique and the designer may tradeoff between small size, high speed, low energy, and low power. The results for designs of two popular signal processing applications, predicted prior to synthesis, are within 10% accuracy of power estimates performed on synthesized layouts.     

Exploiting the Terahertz Band for Radionavigation

This paper demonstrates the feasibility of GPS-like ranging at terahertz (THz) frequencies. It is well established that GPS carrier signals are vulnerable to jamming via radio-frequency interference (RFI). As a result, there is a need for alternative radionavigation systems. THz signals offer a compelling option. Because of their high frequency (roughly ×100 higher than GPS), THz signals can be used to make highly precise range measurements. In addition, the large separation between the GPS and THz frequencies means that interference at GPS frequencies is very unlikely to impact the THz band. This paper lays the groundwork for a GPS-like ranging capability at THz frequencies. To this end, we identify key differences between THz hardware and GPS (radio frequency) hardware; we experimentally evaluate performance of a 0.30-THz system on a compact outdoor test range, and we introduce a measurement error model that highlights the distinctive role that multipath interference plays at THz frequencies.     

Neodymium-doped tantalum pentoxide waveguide lasers

The fabrication, spectroscopic properties, and laser performance of Nd/sup 3+/-doped Ta/sub 2/O/sub 5/ channel waveguide lasers are described. Lasing is obtained at both 1.066 and 1.375 /spl mu/m with threshold pump powers as low as 2.7 mW. The rib waveguides are reactive-ion-etched into Nd:Ta/sub 2/O/sub 5/ layers formed by reactive magnetron sputtering. These high-index low-loss rare-earth-doped waveguides are fabricated on silicon substrates and offer the potential for integration with photonic crystal structures for compact optical circuits.     

Determination of the far infrared optical constants of η-doped bulk CdxHg1−xTe (CMT) by dispersive fourier transform spectroscopy

Far infrared phase and amplitude reflectivity measurements have been made on two bulk Cd_xHg_1?xTe mixed crystals with composition x=0.29 and x=0.22 by dispersive Fourier transform spectroscopy (DFTS). The results have been used to calculate the real and imaginary parts of the dielectric function (?′, ?″) from the Fresnel relations. A plasma contribution is observed in the spectra in addition to the phonon response. For both samples a broad but weak reflection band around 95–105 cm^?1 is observed as well as the expected two-oscillator response from the HgTe-like and CdTe-like optical phonons. This feature is attributed to absorption due to phonon combination bands, but it is too broad to enable assignments to be made. There is no evidence of additional features in the CdTe region due to clustering.     

Multi-Fidelity High-Throughput Optimization of Electrical Conductivity in P3HT-CNT Composites

Combining high-throughput experiments with machine learning accelerates materials and process optimization toward user-specified target properties. In this study, a rapid machine learning-driven automated flow mixing setup with a high-throughput drop-casting system is introduced for thin film preparation, followed by fast characterization of proxy optical and target electrical properties that completes one cycle of learning with 160 unique samples in a single day, a > 10 ×  improvement relative to quantified, manual-controlled baseline. Regio-regular poly-3-hexylthiophene is combined with various types of carbon nanotubes, to identify the optimum composition and synthesis conditions to realize electrical conductivities as high as state-of-the-art 1000 S cm⁻¹. The results are subsequently verified and explained using offline high-fidelity experiments. Graph-based model selection strategies with classical regression that optimize among multi-fidelity noisy input-output measurements are introduced. These strategies present a robust machine-learning driven high-throughput experimental scheme that can be effectively applied to understand, optimize, and design new materials and composites.     

复杂RF环境下的RFID测试挑战

亚微米互补金属氧化物半导体（CMOS）的最新发展,可望进一步扩展RFID技术的应用。高精度供应链管理、无接触POS交易、防伪和资产追踪／监测技术所带来的各项优势,正推动着RFID技术的迅速普及。但是,这种新技术自身也面临着许多测试挑战。本文讨论复杂RFID工作环境中的测试挑战,包括多个阅读器、密集模式环境和预先存在的非RFID信号可能引起的吞吐量和通信问题。     

Bistability of theDX center in GaAs and AlxGa1-xAs,and experimental tests for negativeU of theDX level

We summarize a large body of experimental and theoretical work, especially in Si-doped GaAs and Al _x Ga_1-x As, regarding the bistability of theDX center. There is good evidence that theDX center is just the simple donor, and that each donor can exist in either of two distinct lattice configurations, each with its own spectrum of bound electronic states. Generally, the substitutional configuration binds electrons in shallow hydrogenic states, but many observations also indicate a deep (highly localized) state ofA ₁ symmetry. These states are to be distinguished from bound states of a lattice-distorted configuration, the lowest-lying of which is the deepDX level. The occupation of theDX level in thermal equilibrium with the states of the conduction band can be reasonably well modeled by assuming thatDX is either a one-electron or a two-electron state, and we discuss the reasons for this ambiguity. However, we then show that such thermal equilibrium results are consistent with thermal capture and emission kineticsonly if we assume thatDX is a two-electron state. Our results thus support the model of Chadi and Chang in which the distorted configuration is stabilized by capture of two electrons. In other words, the defect exhibits negative effective correlation energy (negativeU).