330 research outputs found
High Spatial Resolution Fast-Neutron Imaging Detectors for Pulsed Fast-Neutron Transmission Spectroscopy
Two generations of a novel detector for high-resolution transmission imaging
and spectrometry of fast-neutrons are presented. These devices are based on a
hydrogenous fiber scintillator screen and single- or multiple-gated intensified
camera systems (ICCD). This detector is designed for energy-selective neutron
radiography with nanosecond-pulsed broad-energy (1 - 10 MeV) neutron beams.
Utilizing the Time-of-Flight (TOF) method, such a detector is capable of
simultaneously capturing several images, each at a different neutron energy
(TOF). In addition, a gamma-ray image can also be simultaneously registered,
allowing combined neutron/gamma inspection of objects. This permits combining
the sensitivity of the fast-neutron resonance method to low-Z elements with
that of gamma radiography to high-Z materials.Comment: Also published in JINST:
http://www.iop.org/EJ/abstract/1748-0221/4/05/P0501
A describing function for resonantly commutated H-bridge inverters
AbstractâThe paper presents the derivation of a describing function to model the dynamic behavior of a metal oxide semiconductor field effect transistor-based, capacitively commutated H-bridge, including a comprehensive explanation of the various stages in the switching cycle. Expressions to model the resulting input current, are also given. The derived model allows the inverter to be accurately modeled within a control system simulation over a number of utility input voltage cycles, without resorting to computationally
intensive switching-cycle level, time-domain SPICE simulations. Experimental measurements from a prototype H-bridge inverter employed in an induction heating application, are used to demonstrate a high degree of prediction accuracy over a large variation of load conditions is possible using the simplified model
Implementation of Design Changes Towards a More Reliable, Hands-off Magnetron Ion Source
As the main ion source for the accelerator complex, magnetron ion
sources have been used at Fermilab since the 1970s. At the offline test stand,
new R&D is carried out to develop and upgrade the present magnetron-type
sources of ions of up to 80 mA and 35 keV beam energy in the context of
the Proton Improvement Plan. The aim of this plan is to provide high-power
proton beams for the experiments at FNAL. In order to reduce the amount of
tuning and monitoring of these ion sources, a new electronic system consisting
of a current-regulated arc discharge modulator allow the ion source to run at a
constant arc current for improved beam output and operation. A solenoid-type
gas valve feeds gas into the source precisely and independently of
ambient temperature. This summary will cover several studies and design changes
that have been tested and will eventually be implemented on the operational
magnetron sources at Fermilab. Innovative results for this type of ion source
include cathode geometries, solenoid gas valves, current controlled arc pulser,
cesium boiler redesign, gas mixtures of hydrogen and nitrogen, and duty factor
reduction, with the aim to improve source lifetime, stability, and reducing the
amount of tuning needed. In this summary, I will highlight the advances made in
ion sources at Fermilab and will outline the directions of the continuing R&D
effort.Comment: 4 pp. arXiv admin note: substantial text overlap with
arXiv:1701.0175
Integrated Optimal Design of a Passive Wind Turbine System: An Experimental Validation
This work presents design and experimentation of a
full passive wind turbine system without active electronic part(power and control). The efficiency of such device can be obtained only if the system design parameters are mutually adapted through an Integrated Optimal Design (IOD) method. This approach based on multiobjective optimization, aims at concurrently optimizing the wind power extraction and the global system losses for a given wind speed profile while reducing the weight of the wind turbine generator. It allows us to obtain the main characteristics (geometric and energetic features) of the optimal Permanent Magnet Synchronous Generator (PMSG) for the passive wind turbine. Finally, experiments on the PMSG prototype built from this work show a good agreement with theoretical predictions. This validates the design approach and confirms the effectiveness of such passive device
A new single-stage current source inverter for photovoltaic and fuel cell applications using reverse blocking IGBTs
Renewable energy sources such as photovoltaics (PVs) or fuel cells (FCs) are not fitted for direct power grid connection because they deliver DC voltage and current. This is why a power electronic interface is needed, consisting usually of a current-mode operated step-up DC/DC converter with/without isolation that boosts the voltage at a level that can be processed by a DC/AC inverter. This paper presents the implementation of a three-phase power electronic interface for PV/FCs that uses a single conversion stage approach based on a current source inverter (CSI) topology that would need only six reverse blocking IGBTs. In order to overcome the poor switching behavior of this device, a new way of implementing the CSI is proposed, which is proved to be more efficient. A new cost-effective CSI topology for multiple DC sources independently controlled is also proposed.The performance is assessed both in simulation and experimental
Improvements on the Stability and Operation of a Magnetron H- Ion Source
The magnetron H- ion sources developed in the 1970s currently in operation at
Fermilab provide beam to the rest of the accelerator complex. A series of
modifications to these sources have been tested in a dedicated offline test
stand with the aim of improving different operational issues. The solenoid type
gas valve was tested as an alternative to the piezoelectric gas valve in order
to avoid its temperature dependence. A new cesium oven was designed and tested
in order to avoid glass pieces that were present with the previous oven,
improve thermal insulation and fine tune its temperature. A current-regulated
arc modulator was developed to run the ion source at a constant arc current,
providing very stable beam outputs during operations. In order to reduce beam
noise, the addition of small amounts of N2 gas was explored, as well as testing
different cathode shapes with increasing plasma volume. This paper summarizes
the studies and modifications done in the source over the last three years with
the aim of improving its stability, reliability and overall performance.Comment: 8 pages, 19 figure
American Semiconductor v. Sage Silicon Respondent\u27s Brief 2 Dckt. 43011
https://digitalcommons.law.uidaho.edu/idaho_supreme_court_record_briefs/7232/thumbnail.jp
Photovoltaic Energy Harvesting for Millimeter-Scale Systems
The Internet of Things (IoT) based on mm-scale sensors is a transformational technology that opens up new capabilities for biomedical devices, surveillance, micro-robots and industrial monitoring. Energy harvesting approaches to power IoT have traditionally included thermal, vibration and radio frequency. However, the achievement of efficient energy scavenging for IoT at the mm-scale or sub mm-scale has been elusive. In this work, I show that photovoltaic (PV) cells at the mm-scale can be an alternative means of wireless power transfer to mm-scale sensors for IoT, utilizing ambient indoor lighting or intentional irradiation of near-infrared (NIR) LED sources through biological tissue. Single silicon and GaAs photovoltaic cells at the mm-scale can achieve a power conversion efficiency of more than 17 % for silicon and 30 % for GaAs under low-flux NIR irradiation at 850 nm through the optimized device structure and sidewall/surface passivation studies, which guarantees perpetual operation of mm-scale sensors. Furthermore, monolithic single-junction GaAs photovoltaic modules offer a means for series-interconnected cells to provide sufficient voltage (> 5 V) for direct battery charging, and bypassing needs for voltage up-conversion circuitry. However, there is a continuing challenge to miniaturize such PV systems down to the sub mm-scale with minimal optical losses from device isolation and metal interconnects and efficient voltage up-conversion. Vertically stacked dual-junction PV cells and modules are demonstrated to increase the output voltage per cell and minimize area losses for direct powering of miniature devices for IoT and bio-implantable applications with low-irradiance narrowband spectral illumination. Dual-junction PV cells at small dimensions (150 ”m x 150 ”m) demonstrate power conversion efficiency greater than 22 % with more than 1.2 V output voltage under low-flux 850 nm NIR LED illumination, which is sufficient for batteryless operation of miniaturized CMOS IC chips. The output voltage of dual-junction PV modules with eight series-connected single cells is greater than 10 V while maintaining an efficiency of more than 18 %. Finally, I demonstrate monolithic PV/LED modules at the ”m-scale for brain-machine interfaces, enabling two-way optical power and data transfer in a through-tissue configuration. The wafer-level assembly plan for the 3D vertical integration of three different systems including GaAs LED/PV modules, CMOS silicon chips, and neural probes is proposed.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163261/1/esmoon_1.pd
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