8 research outputs found
POINTING, ACQUISITION, AND TRACKING FOR DIRECTIONAL WIRELESS COMMUNICATIONS NETWORKS
Directional wireless communications networks (DWNs) are expected to
become a workhorse of the military, as they provide great network capacity in hostile
areas where omnidirectional RF systems can put their users in harm's way. These
networks will also be able to adapt to new missions, change topologies, use different
communications technologies, yet still reliably serve all their terminal users. DWNs
also have the potential to greatly expand the capacity of civilian and commercial
wireless communication. The inherently narrow beams present in these types of
systems require a means of steering them, acquiring the links, and tracking to
maintain connectivity. This area of technological challenges encompasses all the
issues of pointing, acquisition, and tracking (PAT).
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The two main technologies for DWNs are Free-Space Optical (FSO) and
millimeter wave RF (mmW). FSO offers tremendous bandwidths, long ranges, and
uses existing fiber-based technologies. However, it suffers from severe turbulence
effects when passing through long (>kms) atmospheric paths, and can be severely
affected by obscuration. MmW systems do not suffer from atmospheric effects
nearly as much, use much more sensitive coherent receivers, and have wider beam
divergences allowing for easier pointing. They do, however, suffer from a lack of
available small-sized power amplifiers, complicated RF infrastructure that must be
steered with a platform, and the requirement that all acquisition and tracking be done
with the data beam, as opposed to FSO which uses a beacon laser for acquisition and
a fast steering mirror for tracking.
This thesis analyzes the many considerations required for designing and
implementing a FSO PAT system, and extends this work to the rapidly expanding
area of mmW DWN systems. Different types of beam acquisition methods are
simulated and tested, and the tradeoffs between various design specifications are
analyzed and simulated to give insight into how to best implement a transceiver
platform.
An experimental test-bed of six FSO platforms is also designed and constructed
to test some of these concepts, along with the implementation of a three-node biconnected
network. Finally, experiments have been conducted to assess the
performance of fixed infrastructure routing hardware when operating with a
physically reconfigurable RF network
Optical Gas Sensing: Media, Mechanisms and Applications
Optical gas sensing is one of the fastest developing research areas in laser spectroscopy. Continuous development of new coherent light sources operating especially in the Mid-IR spectral band (QCL—Quantum Cascade Lasers, ICL—Interband Cascade Lasers, OPO—Optical Parametric Oscillator, DFG—Difference Frequency Generation, optical frequency combs, etc.) stimulates new, sophisticated methods and technological solutions in this area. The development of clever techniques in gas detection based on new mechanisms of sensing (photoacoustic, photothermal, dispersion, etc.) supported by advanced applied electronics and huge progress in signal processing allows us to introduce more sensitive, broader-band and miniaturized optical sensors. Additionally, the substantial development of fast and sensitive photodetectors in MIR and FIR is of great support to progress in gas sensing. Recent material and technological progress in the development of hollow-core optical fibers allowing low-loss transmission of light in both Near- and Mid-IR has opened a new route for obtaining the low-volume, long optical paths that are so strongly required in laser-based gas sensors, leading to the development of a novel branch of laser-based gas detectors. This Special Issue summarizes the most recent progress in the development of optical sensors utilizing novel materials and laser-based gas sensing techniques
Proceedings of the NASA Conference on Space Telerobotics, volume 1
The theme of the Conference was man-machine collaboration in space. Topics addressed include: redundant manipulators; man-machine systems; telerobot architecture; remote sensing and planning; navigation; neural networks; fundamental AI research; and reasoning under uncertainty
Servo-Assisted Position-Feedback MEMS Inclinometer with Tunable Sensitivity
In this paper a Micro Electro-Mechanical System (MEMS) inclinometer based on a double-actuator electrical servo-assisted position-feedback mechanism is presented. The mechanical position of the moveable part of the system is kept fixed thanks to a position-feedback loop that exploits a capacitive position sensor and two electrostatic force actuators. By adjusting specific loop parameters, the angle sensitivity can be finely tuned electrically. Experimental results show that the proposed system allows to tune the sensitivity up to 33.1 mV/deg, and to obtain a maximum angle resolution of 40 mdeg
Manufacturing Metrology
Metrology is the science of measurement, which can be divided into three overlapping activities: (1) the definition of units of measurement, (2) the realization of units of measurement, and (3) the traceability of measurement units. Manufacturing metrology originally implicates the measurement of components and inputs for a manufacturing process to assure they are within specification requirements. It can also be extended to indicate the performance measurement of manufacturing equipment. This Special Issue covers papers revealing novel measurement methodologies and instrumentations for manufacturing metrology from the conventional industry to the frontier of the advanced hi-tech industry. Twenty-five papers are included in this Special Issue. These published papers can be categorized into four main groups, as follows: Length measurement: covering new designs, from micro/nanogap measurement with laser triangulation sensors and laser interferometers to very-long-distance, newly developed mode-locked femtosecond lasers. Surface profile and form measurements: covering technologies with new confocal sensors and imagine sensors: in situ and on-machine measurements. Angle measurements: these include a new 2D precision level design, a review of angle measurement with mode-locked femtosecond lasers, and multi-axis machine tool squareness measurement. Other laboratory systems: these include a water cooling temperature control system and a computer-aided inspection framework for CMM performance evaluation
Tracing back the source of contamination
From the time a contaminant is detected in an observation well, the question of where and when the contaminant was introduced in the aquifer needs an answer. Many techniques have been proposed to answer this question, but virtually all of them assume that the aquifer and its dynamics are perfectly known. This work discusses a new approach for the simultaneous identification of the contaminant source location and the spatial variability of hydraulic conductivity in an aquifer which has been validated on synthetic and laboratory experiments and which is in the process of being validated on a real aquifer