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Acoustic Signal Processing
Published in Richard C. Dorf, Circuits, Signals, and Speech and Image Processing, 2018
Juergen Schroeter, Gary W. Elko, M. Mohan Sondhi, Vyacheslav Tuzlukov, Won-Sik Yoon, Yong Deak Kim
Underwater acoustics entails the development and employment of acoustical methods to image underwater features, to communicate information via the oceanic wave-guide, or to measure oceanic properties. Underwater acoustics is the active or passive use of sound to study physical parameters and processes, as well as biological species and targets (for example, ships, submarines, mines, fishes, phyto- and zooplankton, etc.) at sea. In some cases, a specifically designed sound source is used to learn about the ocean and its boundaries or targets (active underwater acoustics). In other research, a natural sound or a sound generated by targets in the sea is analyzed to reveal the physical or biological characteristics of the sound source (passive underwater acoustics). Light, radar, microwaves, and other electromagnetic waves attenuate very rapidly and do not propagate any significant distance through salt water. Because sound suffers very much less attenuation than electromagnetics, it has become the preeminent tool for sensing, detection, identifying, and communicating under the ocean surface. And yet, for decades, inadequate oceanographic information about the extraordinary spatial and temporal variability of this medium has hindered underwater acousticians in their desire to predict sound propagation. It was necessary to learn more about those ocean characteristics that the traditional oceanographic instruments measure rather crudely, with great difficulty, and at great expense.
The design of one-dimensional elastic diffusers
Published in Waves in Random and Complex Media, 2022
Finn John Paul Allison, Stewart Gavin Haslinger, Özgür Selsil, Fan Shi
There are many practical applications in which the ability to design surfaces with specific scattering properties is highly desirable. For example, in the field of NDE, ultrasonic testing methods are used to characterize the location, size and roughness of cracks [3, 33–35]. For instance, the scattering intensities from databases of known defect classes may be used to predict the characteristics of an undetermined crack or defect [36, 37]. There has been a recent focus on the study of inverse problems for ultrasonic NDE, particularly with deep learning and Bayesian inference methods [38–40]. There are also applications in underwater acoustics for high-resolution ultrasonic sonars [41] and even in medical sciences [42, 43]. For the stochastic method employed here, there may also be applications to digital communication and cryptography. For example, the input MDRC may incorporate sensitive information to be sent securely. This information may be encoded as a PDF and through a stochastic process, the scattering taken from thousands of surfaces may be averaged to reconstruct the original message. Therefore, each surface will contain a component of the message, which by itself is meaningless and therefore secure, with the requirement for all surfaces to successfully reproduce the sensitive message.
Micromechanical technique based prediction of effective properties for hybrid smart nanocomposites
Published in Mechanics of Advanced Materials and Structures, 2022
Piezocomposites have been used as smart materials in various fields such as biomedical, underwater acoustics, sensors, transducers, and actuators. The technological and scientific solicitation of these piezo composites has undoubtedly expanded the scope for the research in the field of micromechanics of such materials in the last couple of years [4,5]. The use of various types of fibers in a single matrix has prompted improvements in the effective properties of the hybrid NC. The inadequacy in the properties due to the use of a unique fiber can be supplemented by using a hybrid composite that comprises at least two types of fibers [6]. The properties of nanoparticle composites were determined and observed that they can also be used as thermal insulating materials [7]. The NC was also studied for its use in biocompatibility [8]. A micromechanics model was given by Benveniste [9] for the estimation of the fibrous piezo composite’s effective properties. Unidirectional composites also have weak mechanical properties in the transverse directions [10]. Multiple attempts have been made to examine the multiphase composite properties based on the micromechanics method [11–13]. Efforts were made to enhance the effective properties of CNT-reinforced composites in the orthogonal direction [14]. A multiscale micromechanics method was proposed to predict elastic coefficients for hybrid composites [15]. Various micromechanics models were proposed for the scrutiny of the effective properties of composites [16–18].
Stealth path planning for a high speed torpedo-shaped autonomous underwater vehicle to approach a target ship
Published in Cyber-Physical Systems, 2018
Jonghoek Kim, Sanghoek Kim, Youngmin Choo
Ray and normal-mode models have been classically used in underwater acoustics due to their analytic expressions for the acoustic fields [22]. The ray model uses ray series based on high-frequency approximation, which enables graphical description of the acoustic field. However, the acoustic field from the ray model becomes inaccurate near shadow and convergence zones that are usually observed in a refractive water medium with sound channel axis as in the numerical environment in this work.