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12688 APPLICATION OF THE T-MATRIX METHOD TO THE NUMERICAL MODELING OF A LINEAR ACTIVE SONAR ARRAY - Presented by LTJG Erhan Ozer, TKAbstract: Classically, the T-matrix method is a procedure to exactly compute the multiple scattering of an incident wave from a “cloud” of objects given knowledge of the free-field scattering properties of a single object from an arbitrary incident wave. For acoustic waves, Profs. Baker and Scan- drett have extended the T-matrix method to the case in which the radiation sources are also the scatterers, that is, to the case of an array of active transducers. This thesis is the first successful practical demonstration of the T-matrix method applied to an active sonar array for which a finite-element model was employed to compute the scattering properties of a single transducer. For validation, a T-matrix model of a linear array of piezoelectric spherical thin-shell transduc- ers was modeled, for which analytical approximate values of the T-matrix element values are known. Subsequently, a T-matrix model of a linear array of piezoelectric class V flextensional “ring-shell” transducers, for which no analytic approximate values of the T-matrix element val- ues are available was modeled. Beam patterns of the linear array models computed with the T-matrix method are compared with a non-interacting array, demonstrating that the T-matrix method produces more realistic beam patterns, especially for end fire arrays.
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Wed, 19 Jun 2013 10:29:55 GMT AN EFFICIENT METHOD TO OBTAIN THE OPTICAL PROPERTIES OF MULTILAYERED MEDIA IN THE TERAHERTZ RANGE - Presented by MAJ Michael Martin, USMCAbstract: Structures optimized for high absorption characteristics are desired when designing a device for use in a terahertz (THz) detector. Such structures can have layers of thin metal films, which are known to be highly absorptive, and metamaterials, which are artificially made materials that are capable of near 100 percent absorption at specific frequencies. Accurately predicting the optical properties of these structures is crucial to designing a THz detector for use in real time imaging or spectroscopic applications. As part of an effort supporting the development of a THz detector, this thesis accomplishes two goals: (1) it develops an analytical method based on the Transfer Matrix Method to compute the optical characteristics of multilayered structures that are composed of various materials in the THz region of the electromagnetic spectrum, and (2) it provides an implementation of this method in the form of computer program.
The developed method can be generalized for any number of layers composed of homogenous materials or homogenized materials enabling accurate analysis of positive and negative index materials indistinctly. The method is derived and explained, and then validated by comparison with experimental data for thin metal films, and metamaterial data reported in the literature. Preliminary results show good agreement for a wide range of structures, materials and frequencies and indicate that the method has a great potential for design and optimization of sophisticated multilayered structures, for various applications.
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Wed, 19 Jun 2013 10:25:44 GMT