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.

Scattering of electromagnetic waves by a perfectly conducting cylinder with a thin lossy magnetic coating

Abstract: We study the scattering interaction of electromagnetic (EM) waves with an infinite cylinder coated with a lossy dielectric material with frequency-dependent material properties. These properties are hypothetical, yet representative of a wide class of available materials. The monostatic and bistatic scattered widths (SW) are evaluated for the TM or TE polarization cases. These calculations require the use of algorithms to evaluate Bessel-Hankel functions of complex arguments. These algorithms are based on a continued fraction approach, which ensures stability of the recursion relations. The bistatic plots of the TM and TE scattering widths for the coated body are displayed in a convenient color-graded scale. The reductions in the scattering widths produced by this type of coating are determined in selected frequency bands and angular sectors, in both polarization cases. It is quantitatively shown how curvature and polarization shift the effectiveness band of the coating. The determined regions in which the SW are minimally affected are the most suitable for target identification purposes.

Laser-Based Layer-by-Layer Polymer Stereolithography for High-Frequency Applications

Abstract: In this paper, a summary of works in creating truly three-dimensional structures for high-frequency applications will be presented using an additive manufacturing method, laser-based layer-by-layer polymer stereolithography. This polymer stereolithography is shown to have very good fabrication tolerances, which are necessary for making miniature RF components and narrow-band filters. The prototype components using this stereolithography include high-Q resonators, low-loss cavity filters and evanescent-mode filters, antennas, and miniature ion traps for mass spectrometry.

Are more models better?: the effect of the model transition matrix on the IMM filter

Abstract: The purpose of this investigation was to determine what approach is best to deal with the question of how to choose the model transition matrix for the interactive multiple model filter. The desire is to determine an approach to choosing the model transition matrix that is "best" in some sense. In the study, many target tracking simulations were run using the interacting multiple models algorithm (IMM) with two models: constant velocity and constant acceleration. During these simulations, the transition matrix used and the target tracks used were varied to allow viewing of behavior of the IMM under different conditions. It is difficult to decide whether changing the probabilities gives better performance, since performance is not measured by one number, but by a balance of competing interests. Using a three-model IMM inputs were used in order to test which values should be on the diagonal and what effect changing the off-diagonal elements would have on the filter's behavior. The results obtained imply that having three models is not necessary except in exceptional cases. This leads one to pose the question: Are more models better?.

Signal processing of the echo signatures returned by submerged shells insonified by dolphin "clicks:" Active classification

Abstract: A large set of dolphin-emitted acoustic pulses (“echolocation clicks”) have been examined, which were reflected from various elastic shells that were suspended, underwater, 4.5 m in front of the animal in a large test site in Kaneohe Bay, Hawaii. A carefully instrumented analog-to-digital system continuously captured the emitted clicks and also the returned, backscattered echoes (A/D conversion at 500 kHz). Using standard conditioning techniques and food reinforces, the dolphin is taught to push an underwater paddle when the “correct” target—the one he has been trained to identify—is presented to him. He communicates his consistently correct identifying choices in this manner. Many echoes returned by three types of cylindrical shells in both the time and frequency domains as well as in the joint time-frequency (t-f) domain, by means of Wigner-type distributions have been examined. It will be shown exactly how specific features observable in these displays are directly related to the physical characteristics of the shells. This processing takes advantage of certain fundamental resonance principles to show which echo features contain information about the size, shape, wall thickness, and material composition of both the shell and its filler substance. In the same fashion that these resonance features give the identifying characteristics of each shell, it is believed they may also give them to the dolphin. These echo features may allow him to extract the target properties by inspection without any need for computations. It is claimed that this may be the fundamental physical explanation of the dolphin’s amazing target ID feats, upon which they base their recognition choices. This claim may be substantiated by the detailed analysis of many typical echoes returned by various shells, when they are interrogated by several dolphins. Thus far, this analysis of many echoes from many shells has only been carried out for a single dolphin.

Bearing Condition Monitoring by Pattern Recognition Based on Bicoherence Analysis of Vibrations

Abstract: For automatic detection and diagnosis of localized defects in rolling element bearings, bicoherence spectra are used to derive features that signify the condition of a bearing. These features quantitatively describe the degree of phase correlation among any three harmonics of bearing characteristic defect frequencies. Employing these features, a linear discriminant classifier is implemented to detect localized defects on a roller and the outer race of a bearing. Experimental results show that the proposed scheme is effective in bearing defect detection and sensitive to incipient defects.