32,759 research outputs found
Investigation of the preparation of materials in space. Task 4 - Field management for weightless containerless processing Quarterly progress report, 22 Aug. - 31 Oct. 1969
Weightless containerless processing for space, electromagnetic position control, force measurements and techniques, and hydrodynamic
Microwave Remote Sensing of Soil Moisture
Because of the large contrast between the dielectric constant of liquid water and that of dry soil at microwave wavelength, there is a strong dependence of the thermal emission and radar backscatter from the soil on its moisture content. This dependence provides a means for the remote sensing of the moisture content in a surface layer approximately 5 cm thick. The feasibility of these techniques is demonstrated from field, aircraft and spacecraft platforms. The soil texture, surface roughness, and vegetative cover affect the sensitivity of the microwave response to moisture variations with vegetation being the most important. It serves as an attenuating layer which can totally obscure the surface. Research indicates that it is possible to obtain five or more levels of moisture discrimination and that a mature corn crop is the limiting vegetation situation
Electronic test instrumentation and techniques: A compilation
The uses of test equipment and techniques used in space research and development programs are discussed. Modifications and adaptations to enlarge the scope of usefulness or divert the basic uses to alternate applications are analyzed. The items of equipment which have been of benefit to professional personnel in the enlargement and improvement of quality control capabilities are identified. Items which have been simplified or made more accurate in conducting measurements are described
Survey of methods for soil moisture determination
Existing and proposed methods for soil moisture determination are discussed. These include: (1) in situ investigations including gravimetric, nuclear, and electromagnetic techniques; (2) remote sensing approaches that use the reflected solar, thermal infrared, and microwave portions of the electromagnetic spectrum; and (3) soil physics models that track the behavior of water in the soil in response to meteorological inputs (precipitation) and demands (evapotranspiration). The capacities of these approaches to satisfy various user needs for soil moisture information vary from application to application, but a conceptual scheme for merging these approaches into integrated systems to provide soil moisture information is proposed that has the potential for meeting various application requirements
Antenna-coupled silicon-organic hybrid integrated photonic crystal modulator for broadband electromagnetic wave detection
In this work, we design, fabricate and characterize a compact, broadband and
highly sensitive integrated photonic electromagnetic field sensor based on a
silicon-organic hybrid modulator driven by a bowtie antenna. The large
electro-optic (EO) coefficient of organic polymer, the slow-light effects in
the silicon slot photonic crystal waveguide (PCW), and the broadband field
enhancement provided by the bowtie antenna, are all combined to enhance the
interaction of microwaves and optical waves, enabling a high EO modulation
efficiency and thus a high sensitivity. The modulator is experimentally
demonstrated with a record-high effective in-device EO modulation efficiency of
r33=1230pm/V. Modulation response up to 40GHz is measured, with a 3-dB
bandwidth of 11GHz. The slot PCW has an interaction length of 300um, and the
bowtie antenna has an area smaller than 1cm2. The bowtie antenna in the device
is experimentally demonstrated to have a broadband characteristics with a
central resonance frequency of 10GHz, as well as a large beam width which
enables the detection of electromagnetic waves from a large range of incident
angles. The sensor is experimentally demonstrated with a minimum detectable
electromagnetic power density of 8.4mW/m2 at 8.4GHz, corresponding to a minimum
detectable electric field of 2.5V/m and an ultra-high sensitivity of
0.000027V/m Hz^-1/2 ever demonstrated. To the best of our knowledge, this is
the first silicon-organic hybrid device and also the first PCW device used for
the photonic detection of electromagnetic waves. Finally, we propose some
future work, including a Teraherz wave sensor based on antenna-coupled
electro-optic polymer filled plasmonic slot waveguide, as well as a fully
packaged and tailgated device.Comment: 20 pages, 16 figure
NASA Tech Briefs Index, 1977, volume 2, numbers 1-4
Announcements of new technology derived from the research and development activities of NASA are presented. Abstracts, and indexes for subject, personal author, originating center, and Tech Brief number are presented for 1977
Transducer applications, a compilation
The characteristics and applications of transducers are discussed. Subjects presented are: (1) thermal measurements, (2) liquid level and fluid flow measurements, (3) pressure transducers, (4) stress-strain measurements, (5) acceleration and velocity measurements, (6) displacement and angular rotation, and (7) transducer test and calibration methods
Micro-Electro-Mechanical-Systems (MEMS) and Fluid Flows
The micromachining technology that emerged in the late 1980s can provide micron-sized sensors and actuators. These micro transducers are able to be integrated with signal conditioning and processing circuitry to form micro-electro-mechanical-systems (MEMS) that can perform real-time distributed control. This capability opens up a new territory for flow control research. On the other hand, surface effects dominate the fluid flowing through these miniature mechanical devices because of the large surface-to-volume ratio in micron-scale configurations. We need to reexamine the surface forces in the momentum equation. Owing to their smallness, gas flows experience large Knudsen numbers, and therefore boundary conditions need to be modified. Besides being an enabling technology, MEMS also provide many challenges for fundamental flow-science research
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