Download or read book Time Reversal Acoustics written by Woon Siong Gan and published by Springer Nature. This book was released on 2021-08-06 with total page 111 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book highlights time reversal acoustics, techniques based on the symmetry properties of acoustic fields. It has the unique feature that the first eleven chapters of the book are on the indepth studies of the theories of time reversal acoustics. The remaining chapters are on the four major applications of time reversal acoustics, together with their experimental setups and case studies: underwater communication, seismic exploration,nondestructive evaluation, and medical ultrasound imaging.. The gauge invariance approach to acoustic fields, proposed by the author in 2007, is confirmed by the successful fabrication of acoustical metamaterials and the applications of time reversal acoustics to superresolution. The book also presents groundbreaking applications of time reversal acoustics to underwater communication technology and the application of metamaterials to time reversal acoustics.

Download or read book Time Reversal Acoustics for Small Targets Using Decomposition of the Time Reversal Operator written by Peter C. Simko and published by . This book was released on 2008 with total page 278 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electromagnetic Time Reversal written by Farhad Rachidi and published by John Wiley & Sons. This book was released on 2017-01-09 with total page 262 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this book is to familiarize the reader with the concept of electromagnetic time reversal, and introduce up-to-date applications of the concept found in the areas of electromagnetic compatibility and power systems. It is original in its approach to describing propagation and transient issues in power networks and power line communication, and is the result of the three main editors' pioneering research in the area.

Download or read book Principles of Phase Conjugation written by B.Y. Zel'Dovich and published by Springer. This book was released on 2013-06-29 with total page 263 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book has been prompted by our des ire to share with others our apprecia tion of the harmony and beauty in a particular sphere of modern optics known as "optical phase conjugation". Practical applications of the phase conjugated wave are likely to be far-reaching. Optical phase conjugation (OPC) combines in itself aesthetic and pragmatic attractiveness, a synthesis that has made OPC a subject of general attention. The figure presents the ap proximate rate of publications (number of articles per year) on OPC in the world literature for recent years, the lower curve denoting the work carried out in the USSR. The efforts of a large unofficial international collective have yielded an impressive result. 150 100 50 1975 1980 At present, the physical pro ces ses underlying various OPC methods are quite understandable, and it is the physics of OPC to which our book is devoted. Practical and scientific applications of phase-conjugated waves, which are of no less interest, have been touched upon in short, as major achievements in this sphere are a matter of the future. Today there are two main methods of OPC: i) by backward stimulated light scattering, ii) by four-wave mixing. Naturally, much attention is given to these methods in our book which, after the introductory Chap. 1, can be divided into two almost independent parts - Chaps. 2 - 5, and Chaps. 6 - 8.

Download or read book Ocean Time reversal Acoustics and Application to Reverberation Reduction written by Seongil Kim and published by . This book was released on 2002 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Wave Propagation and Time Reversal in Randomly Layered Media written by Jean-Pierre Fouque and published by Springer Science & Business Media. This book was released on 2007-06-30 with total page 623 pages. Available in PDF, EPUB and Kindle. Book excerpt: The content of this book is multidisciplinary by nature. It uses mathematical tools from the theories of probability and stochastic processes, partial differential equations, and asymptotic analysis, combined with the physics of wave propagation and modeling of time reversal experiments. It is addressed to a wide audience of graduate students and researchers interested in the intriguing phenomena related to waves propagating in random media. At the end of each chapter there is a section of notes where the authors give references and additional comments on the various results presented in the chapter.

Download or read book Theoretical Evaluation of Continuous wave Time Reversal Acoustics in a Half space Environment written by Blaine Harker and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Time reversal (TR) acoustics is a technique used to locate sources, using a set of transducers called a time reversal mirror (TRM) and is especially useful in reverberant environments. TR is commonly used to find acoustically small sources using a pulsed waveform. Here TR is applied to simple sources using steady-state waveforms using a straightforward, computational point source propagation theoretical model in a half-space environment. It is found that TR can effectively localize a simple source broadcasting a continuous wave, depending on the angular spacing. Furthermore, the aperture (angular coverage around the source) of the TRM is the most important parameter when creating a setup of receivers for imaging a source. This work quantifies how a TRM may be optimized when the source's location is known to be within a certain region of certainty.

Download or read book Modeling and Computations in Electromagnetics written by Habib Ammari and published by Springer Science & Business Media. This book was released on 2008-01-12 with total page 239 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is nothing less than an essential text in what is a new and growing discipline. Electromagnetic modeling and computations is expanding as a result of the steadily increasing demand for designing electrical devices, modeling electromagnetic materials, and simulating electromagnetic fields in nanoscale structures. The aim of this volume is to bring together prominent worldwide experts to review state-of-the-art developments and future trends of modeling and computations in electromagnetics.

Download or read book The Topology of 4 Manifolds written by Robion C. Kirby and published by Springer. This book was released on 2006-11-14 with total page 114 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the classical theorems about simply connected smooth 4-manifolds: intersection forms and homotopy type, oriented and spin bordism, the index theorem, Wall's diffeomorphisms and h-cobordism, and Rohlin's theorem. Most of the proofs are new or are returbishings of post proofs; all are geometric and make us of handlebody theory. There is a new proof of Rohlin's theorem using spin structures. There is an introduction to Casson handles and Freedman's work including a chapter of unpublished proofs on exotic R4's. The reader needs an understanding of smooth manifolds and characteristic classes in low dimensions. The book should be useful to beginning researchers in 4-manifolds.

Download or read book Time Reversal for Waves in Random Media written by Ramón Verástegui and published by . This book was released on 2006 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Experimental Studies of Applications of Time Reversal Acoustics to Non Coherent Underwater Communications written by Michael G. Heinemann and published by . This book was released on 2000-03 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt: The most difficult problem in shallow underwater acoustic communications is considered to be the time-varying multipath propagation because it impacts negatively on data rates. Computationally intensive and complex signal processing algorithms are required to compensate for symbol overlapping. This thesis presents results of a tank scale experiment to test Time-Reversal Acoustics (TRA) approach for high data rate binary transmissions. TRA can environmentally adapt the acoustic propagation effects of a complex medium. Our results show the suitability of the TRA approach in underwater acoustic communications. The results also show good focusing properties at an intended target location. The focal region extends over a few wavelengths, outside of which scrambling of the message occurs, offering natural encryption. Range shifts of the focal region could be achieved by frequency shifting. We found that the time focusing is aperture-size independent, but the spatial focusing is aperture-size dependent. Overall, we showed that our algorithm can accomplish a fast, secure, and stable communication scheme with low computational complexity.

Download or read book Automotive Acoustics Conference 2015 written by Wolfgang Siebenpfeiffer and published by Springer Vieweg. This book was released on 2019-08-29 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt: Elektrofahrzeuge sind für Entwickler der Fahrzeugakustik ebenso eine Herausforderung wie eine höhere NVH-Performance durch Leichtbaustrukturen und kleinere Motoren mit Turbolader. Die Automobilforschung muss das Akustikmanagement im Fahrzeug neu denken. Die internationale Automotive Acoustics Conference bietet dazu als Fachtagung das notwendige Expertenwissen, um die künftigen Anforderungen an Antriebsstrang, Antriebssysteme und Fahrzeugarchitekturen zu erfüllen. Simulationsprozesse und Verfahren der Multiphysik sind dabei essenziell, um Ruhe in die Passagierkabine zu bringen. Die Konferenz zur car acoustics bietet dazu neustes Expertenwissen.

Download or read book Image Source Modeling of Time Reversal for Room Acoustics Applications written by Michael Hunter Denison and published by . This book was released on 2018 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt: Time Reversal (TR) is a technique that may be used to focus on acoustic signal at a particular point in space. While many variable contribute to the quality of TR focusing of sound in a particular room, the most important have been shown to be the number of sound sources, signal bandwidth and absorption properties of the medium [Ribay et al., J. Acoust. Soc. Am. 117(5), 2866-2872 (2005)]. However, the effect of room size on TR focusing has not been explored. Usint the image source method algorithm proposed by Allen and Berkley [J. Allen and D. A. Berkley, J. Acoust. Soc. Am. 65(4), 943-950 (1979)], TR focusing was simulated in a variety of rooms with different absorption and volume properties. Experiments are also conducted in a couple rooms to verify the simulations. The maximum focal and amplitude, the temporal focus quality, and the spatial focus clarity are defined and calculated for each simulation. The results are used to determine the effects of absorption and room volume on TR. Less absorption increases the amplitude of the focusing and spatial clarity while decreasing temporal quality. Dissimilarly, larger volumes decrease focal amplitude and spatial clarity while increasing temporal quality. This thesis also explores the placement of individual transducers within a room. It also compares the layout of several source transducers used for a reciprocal time reversal process. Maximum focal amplitude and spatial clarity are found to increase when the focus location is dual coplanar to the source location wile temporal quality is found to decrease in comparison to the case when source and focal location share only one plane. Maximum focal amplitude is found to be at a minimum source, while temporal quality steadily decreases and spatial clarity steadily increases farther from the source. The maximum focal amplitude and the temporal quality are not greatly affected by the type of array layout, but a circular array is ideal for maximizing spatial clarity.

Download or read book Pressure Sensitivity Kernels Applied to Time reversal Acoustics written by Kaustubha Raghukumar and published by . This book was released on 2009 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt: Time-reversal is a method of focusing sound in the ocean that has found a variety of applications in recent years, ranging from underwater communications to biological stone destruction. In order to produce a focal spot, the time-reversal process first needs to acquire the Green's function between source and receiver. This Green's function is time-reversed and retransmitted in order to produce a spatio-temporal focal spot at the original source location. If the medium properties in between the source and receiver change between the acquisition of the Green's function and the subsequent retransmission, the quality of the focal spot can degrade or even disappear. However, the time-reversal focal spot has been found to be surprisingly robust to changes in medium properties, which are chiefly sound speed fluctuations in underwater acoustics. At 445 Hz, the focal spot was seen to persist for a week, while at 3.5 kHz, the focal spot persists for about an hour. Sensitivity kernels have the ability to linearly map sound speed perturbations to a perturbation of an acoustic parameter such as travel-time or pressure. Sensitivity kernels have a Fresnel-like interference pattern with regions of positive and negative sensitivities in the medium. Time-reversal, which causes different arrival paths to arrive at the same time, results in overlapping sensitivity kernels that leads to a net reduction in pressure sensitivity at the focal spot. Upon expressing the pressure at the focal spot in terms of sensitivity kernels, source transmissions are derived that are even more robust than time-reversal. The theory developed using pressure sensitivity kernels is tested on experimental data, along with an internal wave model, using various metrics. The linear limitations of the kernels are explored in the context of time-evolving Green's functions. The optimized source functions are then tested using experimental Green's functions and their behavior is seen to be in the right sense. Finally, thermistor chain data gathered during a similar experiment allowed for the testing of a 'synthetic aperture thermistor chain'. Temperature observations, presumably caused by displacements of a reference temperature profile, are inverted to provide an estimate of the background temperature profile.

Download or read book Acoustic Room De reverberation Using Time Reversal Acoustics written by David W. Liddy and published by . This book was released on 1999-09-01 with total page 63 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis probes the performance of one-channel time-reversal acoustics in a chamber in terms of the geometry of the cavity. In particular, a rectangular chamber is compared to an enclosure that has a stadium shape. The mode structure in the rectangular cavity is highly symmetric, while it is highly irregular in the stadium-shaped cavity. Time- reversal acoustic techniques produce an improved focus in the latter. The focusing quality is determined as a function of frequency, time-reversal window size, and spatial extent. A scheme for encrypted acoustic communication, both in air and underwater, that uses multiple broadband signals with identical bandwidth, Hanning window source spectra, and center frequencies separated by half the bandwidth, allowing for null detection between adjacent signals, is successfully investigated.

Download or read book Time reversal for Temporal Compression and Spatial Focusing of Acoustic Waves in Enclosures written by Deborah Berebichez and published by . This book was released on 2004 with total page 257 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Acoustic Time Reversal in the Shallow Ocean written by and published by . This book was released on 2005 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: Acoustic time reversal is of interest to the United States Navy because it is an effective means for focusing sound in unknown underwater environments. For the last nine years, the Office of Naval Research has supported theoretical and numerical investigations at the University of Michigan into the performance of time reversing arrays in the ocean. This report summarizes the research accomplishments of these investigations.