Naval Surface Warfare Center

About: Naval Surface Warfare Center is a facility organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Sonar & Radar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.

Magnetic dipole localization using the gradient rate tensor measured by a five-axis magnetic gradiometer with known velocity

Abstract: The use of the magnetic gradient tensor in the point-by-point localization of a magentic dipole was first demonstrated by Wynn in 1971, with a more explicit solution derived by Frahm in 1972. This algorithm maps the five independent components of the magnetic gradient tensor at a point into the dipole bearing vector and the dipole moment vector scaled by the inverse fourth power of the range to the dipole. This inversion produces four solutions, two of which are reflections through the origin of the bearing and scaled moment vectors of the other two. In the present paper, we describe an algorithm for mapping the time rate of change of the gradient tensor measured by a sensor of known velocity into the dipole bearing vector and the dipole moment vecot scaled by the inverse fifth power of the range. An extensive computer exercise with random position and moment vector geometries consistently produces at least one and at most four distinct solutions, with an equal number of additional solutions related to these by reflection of the bearing vector through the origin, for a total of at least two and at most eight solutions. In the same exercise, the solution common to this algorithm and the gradient equation iversion algorithm is consistently unique, and the two different moment vector scalings allow the range to be determined, resulting in a unique solution for dipole position and moment vectors. A general proof of uniqueness is not yet available.

On Measuring Shielding Effectiveness of Sparsely Moded Enclosures in a Reverberation Chamber

Abstract: Recently, there has been great interest in evaluating the shielding effectiveness of physically small enclosures (all linear dimensions between 0.1 and 2 m) using a reverberation chamber. In cases where the enclosure is also electrically small (linear dimensions on the order of a free-space wavelength or less), the enclosure supports only discrete resonant modes whose lineshapes have little or no overlap in frequency. This sparsely moded or “undermoded” cavity poses a number of complex challenges to defining and measuring shielding effectiveness. This study contributes to the development of a measurement process for evaluating shielding effectiveness in electrically small enclosures. Specifically, we demonstrate the performance advantages of a traveling-wave antenna (long-wire probe) as a means of fully sampling the field throughout the volume of the enclosure without the need for multiple, wall-mounted probes. Furthermore, the good impedance match of the long-wire antenna permits a large dynamic range in the shielding effectiveness measurements. A simple and fast test method is presented that is accurate and repeatable, and embodies the desired “dovetailing” of shielding effectiveness values obtained as frequency increases and the enclosure transitions from undermoded to overmoded operation. Finally, a rudimentary statistical analysis is provided to assess typical uncertainties inherent in the shielding effectiveness evaluation.

Ignition and Combustion Enhancement of Boron with Polytetrafluoroethylene

Abstract: The ignition and combustion properties of fuel-rich mixtures of boron and polytetrafluorethylene in air and argon were studied as a function of pressure at a heating rate of approximately 1×105 K/s to simulate heating rates that individual ingredients may be subjected to in propellant burning. Mixtures ranging from 20 to 100 wt% boron (balance polytetrafluorethylene) and pressures up to 7 MPa were considered in this study. Ignition of the samples was achieved by joule heating of a platinum filament within a pressure vessel of selected atmospheres. Ignition of the mixture was characterized by monitoring broadband light emission, whereas boron ignition specifically was verified by identification of the BO2 molecule using emission spectroscopy. At atmospheric pressure, none of the mixtures ignited within the duration of the experiment. Mixtures containing more than 80% boron did not consistently ignite under any conditions within the duration of the experiment. It was found that the ignition temperature for...

Technical Note: The Effect of Heat Treatment on the Pitting Behavior of SiCw/AA2124

Abstract: A study was initiated at this laboratory to better understand the role of heat treatment on the pitting behavior of SiC/AA2124

Observation of higher order parametric x-ray spectra in mosaic graphite and single silicon crystals.

Abstract: We have observed up to 8 orders ([ital n]) in the spectra of parametric x-radiation (PXR) in the range 5--40 keV, produced by the interaction of a 90 MeV electron beam with mosaic graphite and single silicon crystals. The measured yields and intensity ratios, [ital I]([ital n][ge]2)/[ital I]([ital n]=1), in graphite are not in agreement with the theory of PXR for mosaic crystals. In comparison, the ratios of intensities in silicon are close to the predictions of PXR theory for perfect crystals. The bandwidths of spectral lines measured in both silicon and graphite are in good agreement with theoretical predictions.