8 research outputs found
Understanding the Impact of Field-Emitter Characteristics on Electron Beam Focusing in the VAPoR Time-of-Fight Mass Spectrometer
Simulations of field emission of electrons from an electron gun are used to determine the angular distribution of the emitted electron beam and the percentage of charge transmitted through the grid. The simulations are a first step towards understanding the spherical aberration present after focusing the electron beam. The effect of offset of the cathode with respect to the grid and the separation between cathode and grid on the angular distributions of emitted electrons and transmission of the grid are explored
Fabrication and Sub-Assembly of Electrostatically Actuated Silicon Nitride Microshutter Arrays
We have developed a new microshutter array (MSA) subassembly. The MSA and a silicon substrate are flip-bonded together. The MSA has a new back side fabrication process to actuate the microshutters electrostatically, and the new silicon substrate has light shields. The microshutters with a pixel size of 100 x 200 sq micrometers are fabricated on silicon with thin silicon nitride membranes. The microshutters rotate 90 deg on torsion bars. The selected microshutters are actuated, held, and addressed electrostatically by applying voltages on the electrodes the front and back sides of the microshutters. The substrate has the light shield to block lights around the microshutters. Also, electrical connections are made from the MSA to a controller board via the substrate
Developing a Novel Platform for Characterizing Thermoelectric Materials for Uncooled Detectors for Land Imaging Applications
Thermal land imaging (imaging at ~8-14 micron optical wavelength) is an essential tool for understanding and managing terrestrial freshwater resources. Current thermal imaging instruments employ low temperature detectors, which require cryocoolers. Consequently, cost-saving reductions in size, weight, and power can be achieved by employing uncooled detectors. One uncooled detector concept, which NASA is pursuing, is a thermopile detector with sub-micron thick doped-Si thermoelectric materials. In order to characterize the thermoelectric properties of the doped silicon, we designed and optimized a novel apparatus. This simple apparatus measures the Seebeck coefficient with thermally isolated stages and LABVIEW automation. We optimized thermal stability using PID tuning and optimized the thermal contact between the thin film samples and stages using electrically conductive springs. Utilizing our apparatus, we measured the Seebeck coefficient of 0.45 micron thick phosphorus-doped single crystal Si samples bonded to alumina substrates. Using these Seebeck coefficient measurements and four-wire electrical resistivity measurements, we determined the relationship between the thermoelectric figure of merit and dopant concentration. These characterization results for doped-Si will guide our thermopile detector design to provide an optimal and competitive detector alternative for future thermal imaging instruments
Trade and Exchange in Anglo-Saxon Wessex, AD 600-780
This paper assesses the provenance and general distribution of coins of the period c 600–c 780 found in the west of Anglo‐Saxon Wessex. It shows that the distribution of coin finds is not a function of the habits of metal detectorists, but a reflection of the real pattern of losses. In the second part of the paper, an analysis of the observed distributions is presented which reveals that the bulk of trade, of which the coins are a sign, was carried on through local ports and that foreign trade was not mediated through Hamwic, but came directly from the continent. The distribution of coin finds also suggests an important export trade, probably in wool and woollen goods, controlled from major local centres. There are also hints of a potentially older trade system in which hillforts and other open sites were important
Developing a New Generation of Integrated Micro-Spec Far Infrared Spectrometers for the EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM)
The current state of far-infrared astronomy drives the need to develop
compact, sensitive spectrometers for future space and ground-based instruments.
Here we present details of the -Spec spectrometers currently in
development for the far-infrared balloon mission EXCLAIM. The spectrometers are
designed to cover the m range with a resolution of $\rm R\
=\ \lambda / \Delta\lambda\ =\ 512\rm 638\ \mu\rm \mu\rm R = 64\ \muM{=}2{\sim}8\times10^{-19}\rm W/\sqrt{Hz}\rm \mu$-Spec
spectrometers for EXCLAIM.Comment: 9 pages, 5 figures, to appear in the Proceedings of the SPIE
Astronomical Telescopes + Instrumentation (2022
Characterization of Si-Membrane TES Bolometer Arrays for the HIRMES Instrument
The High Resolution Mid-Infrared Spectrometer (HIRMES) instrument will fly onboard NASA's airborne Stratospheric Observatory for Infrared Astronomy (SOFIA) in 2019. HIRMES will provide astronomers with a unique observing window (25 122 m) for exploring the evolution of protoplanetary disks into young solar systems, and the composition of our Solar System. There are two focal plane detector arrays for the instrument: a high-resolution (/ = 100,000) 8x16 detector array with a target noise-equivalent power, NEP 3x10-18 W/Hz; and a low-resolution (/ = 2,000 19,000) 16x64 detector array with a target NEP 2x10-17 W/Hz. The detectors for both of these arrays are superconducting Mo/Au bilayer transition edge sensor (TES) bolometers on thin suspended single-crystal silicon membranes. Here we present our characterization results for the detectors in both arrays, including measurements of thermal conductance with comparison to phonon transport models, saturation power, noise, and array uniformity