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Thousand Oaks, CA, United States

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Demkowicz L.,University of Texas at Austin | Gatto P.,University of Texas at Austin | Kurtz J.,University of Texas at Austin | Paszynski M.,AGH University of Science and Technology | And 6 more authors.
Computer Methods in Applied Mechanics and Engineering | Year: 2011

We focus on the development of a reliable numerical model for investigating the bone-conduction of sound in the human head. The main challenge of the problem is the lack of fundamental knowledge regarding the transmission of acoustic energy through non-airborne pathways to the cochlea. A fully coupled model based on the acoustic/elastic interaction problem with a detailed resolution of the cochlea region and its interface with the skull and the air pathways, should provide an insight into this fundamental, long standing research problem. To this aim we have developed a 3D hp-finite element code that supports elements of all shapes (tetrahedra, prisms and pyramids) to better capture the geometrical features of the head. We have tested the code on a multilayered sphere and employed it to solve an idealized model of head. In the future we hope to attack a model with a more realistic geometry. © 2011 Elsevier B.V.


Bleszynski E.,Monopole Research | Bleszynski M.,Monopole Research | Jaroszewicz T.,Monopole Research
Optics Letters | Year: 2014

Propagation of short infrared/optical pulses in dilute random media (e.g., atmospheric clouds, fog, dust, or aerosols) consisting of large, compared to the wavelength, scatterers is analyzed. A rigorous approach based on analytic complex-contour integration of numerically determined cut and pole singularities of the radiative transport equation solution in the Fourier space is presented. It is found that the intensity of a propagating pulse, in addition to the coherent ("ballistic") contribution and a long late-time diffusive tail, also exhibits a sharply rising early-time component that (i) can be attributed to the small-angle diffractive part of the scattering cross-section on medium particles, (ii) is attenuated proportionally to the nondiffractive rather than total cross-section, and (iii) can be extracted by high-pass filtering of the received pulse. © 2014 Optical Society of America


Bleszynski E.,Monopole Research | Bleszynski M.,Monopole Research | Jaroszewicz T.,Monopole Research
2016 IEEE/ACES International Conference on Wireless Information Technology, ICWITS 2016 and System and Applied Computational Electromagnetics, ACES 2016 - Proceedings | Year: 2016

A novel procedure Is presented for the evaluation of matrix elements of the tensor Green function with Rao-Wilton-Glisson basis functions appearing in surface integral equations in electromagnetics. The procedure, at this point applicable to planar geometries, reduces four-dimensional surface integrals with singular integrands to line integrals over triangle edges with regular integrands. The main advantage of the derived expressions is that they offer simplicity and easily controllable accuracy without the need of using numerical singularity extraction methods. © 2016 IEEE.


Bleszynski E.,Monopole Research | Bleszynski M.,Monopole Research | Jaroszewicz T.,Monopole Research
2015 9th European Conference on Antennas and Propagation, EuCAP 2015 | Year: 2015

We discuss here propagation of short electromagnetic pulses through dilute particulate random media consisting of scatterers in situations where the wave attenuation is dominated by scattering, rather than absorption. Examples of such phenomena include propagation of laser pulses through atmospheric clouds or through sprays in combustion processes. In such scenarios the coherent wave attenuation is controlled by the mean free path ℓt = 1/(n0 σt), where n0 is the medium number density and σt is the total cross-section for scattering of the wave on a single medium particle. The incoherent intensity is attenuated at a lower rate, but, typically, develops a long temporal tail due to multiple scattering in the medium and the ensuing diffusion. In both cases the medium effects cause serious deterioration of image quality in pulse-based imaging and bandwidth in communication; we propose here an approach for alleviating these difficulties. © 2015 EurAAP.


Bleszynski E.H.,Monopole Research | Bleszynski M.C.,Monopole Research | Jaroszewicz T.,Monopole Research
IEEE Transactions on Antennas and Propagation | Year: 2012

Evolution of an oscillatory wide-band pulse in a sparse medium composed of randomly distributed, uncorrelated, discrete scatterers (such as atmospheric clouds, dust, or other aerosols) is studied. The frequency-dependent (dispersive) losses are evaluated by taking into account energy absorption in the medium constituents as well as scattering itself. A reduced, algebraic attenuation of the pulse energy is observed, provided the pulse contains a significant frequency content in the region of strongly varying medium dispersive properties. These frequencies can be provided by pulse carrier frequency selection, short rise and fall times of the pulse, or pulse chirping. It is shown that different types of algebraic attenuation, over the range of penetration depth corresponding to several orders of mean-free path, can be present depending on the inter-relations between characteristic frequencies of the pulse spectrum and the medium dispersive properties. A simple analytical model is constructed that captures relevant features of the propagating pulse energy decay, as well as ranges of penetration depths, and hence may serve as a useful tool in designing and analyzing various scenarios of wide-band pulse propagation in dispersive media in the context of, e.g., signal transmission, imaging, or target detection. © 1963-2012 IEEE.


Bleszynski E.H.,Monopole Research | Bleszynski M.K.,Monopole Research | Jaroszewicz T.,Monopole Research
Proceedings of the 2015 International Conference on Electromagnetics in Advanced Applications, ICEAA 2015 | Year: 2015

A procedure allowing conversion of integrals with singular integrands over tetrahedral (volume) and triangular (surface) supports which are present in matrix elements of tensor and vector Green functions with linear basis function to non-singular integrals over tetrahedra surfaces and triangles edges is presented. An advantage of the derived expressions is that they offer simplicity and easily controllable accuracy without the need of using conventional numerical singularity extraction methods. © 2015 IEEE.


Bleszynski E.H.,Monopole Research | Bleszynski M.K.,Monopole Research | Jaroszewicz T.,Monopole Research
IEEE Transactions on Antennas and Propagation | Year: 2013

A procedure for the evaluation of matrix elements of tensor and vector Green functions with linear basis functions appearing in volumetric integral equations in electromagnetics is presented. The procedure reduces six-dimensional volumetric integrals with singular integrands to four-dimensional surface integrals with nonsingular integrands - hence, it offers simplicity and accuracy achieved at low computational cost. © 1963-2012 IEEE.


Bleszynski E.H.,Monopole Research | Bleszynski M.C.,Monopole Research | Jaroszewicz T.,Monopole Research | Albanese R.,ADED Co
IEEE Transactions on Antennas and Propagation | Year: 2013

We describe an approach to construct a pulsed signal which, when propagating in an obscuring, discrete-scatterer medium (such as clouds, fog, dust or other aerosols) experiences reduced attenuation. The approach can thus find possible applications in communication or high resolution target detection. In the proposed scheme, the transmitted signal consists of a coherent train of short wide-band pulses emitted at chirped (linearly varying) time intervals. As the energy of a single pulse which has traveled a large distance in the medium is almost entirely concentrated in the precursor-type structures associated with its leading and trailing edges, the increase of the signal total energy is achieved by using trains with a large number of pulses. The (down-)range resolution is controlled by the chirp bandwidth characterizing the distribution of individual pulses in the train (that bandwidth may be sufficiently large to achieve a resolution typical of millimeter-wave radar), while the high cross-range resolution can be attained in analogy to the usual synthetic-aperture imaging. Processing of the received signal involves filtering associated with the chirp characteristics, analogous to that in the conventional matched-filter techniques. It is also shown that the proposed approach provides flexibility in choosing the chirped-train center frequency, e.g., to maximize the amount of energy passing through a selected atmospheric absorption window or to maximize the signal energy carried to a desired penetration depth. © 1963-2012 IEEE.


Bleszynski E.,Monopole Research | Bleszynski M.,Monopole Research | Jaroszewicz T.,Monopole Research
Inverse Problems | Year: 2013

An approach to autofocusing for large curved synthetic aperture radar (SAR) apertures is presented. Its essential feature is that phase corrections are being extracted not directly from SAR images, but rather from reconstructed SAR phase-history data representing windowed patches of the scene, of sizes sufficiently small to allow the linearization of the forward- and back-projection formulae. The algorithm processes data associated with each patch independently and in two steps. The first step employs a phase-gradient-type method in which phase correction compensating (possibly rapid) trajectory perturbations are estimated from the reconstructed phase history for the dominant scattering point on the patch. The second step uses phase-gradient-corrected data and extracts the absolute phase value, removing in this way phase ambiguities and reducing possible imperfections of the first stage, and providing the distances between the sensor and the scattering point with accuracy comparable to the wavelength. The features of the proposed autofocusing method are illustrated in its applications to intentionally corrupted small-scene 2006 Gotcha data. The examples include the extraction of absolute phases (ranges) for selected prominent point targets. They are then used to focus the scene and determine relative target-target distances. © 2013 IOP Publishing Ltd.


Grant
Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase II | Award Amount: 744.77K | Year: 2010

We propose to develop a new autofocus method applicable to large-scene surveillance with circular SAR. Our work constitutes a continuation, full implementation, and extensions of the new autofocus algorithm we developed and successfully tested during Phase I. The proposed method is applicable to large apertures and corrects effects of fine-scale (sub-wavelength) deviations in the platform motion along arbitrary curved trajectories. The proposed method will be accelerated with suitable fast imaging techniques. It will be also extended to multi-pass circular SAR measurements and augmented with autofocus methods for moving targets. BENEFIT: The proposed method will significantly enhance the capabilities of DoD SAR imaging technology. It will be applicable in a number of commercial and national security surveillance programs, e.g., in border monitoring.

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