Echo statistics associated with discrete scatterers: A tutorial on physics-based methods

Author Posting. © Acoustical Society of America, 2018. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America, 144(6), (2018): 3124-3171. doi: 10.1121/1.5052255.When a beam emitted from an active monostatic sensor system sweeps across a volume, the echoes from scatterers present will fluctuate from ping to ping due to various interference phenomena and statistical processes. Observations of these fluctuations can be used, in combination with models, to infer properties of the scatterers such as numerical density. Modeling the fluctuations can also help predict system performance and associated uncertainties in expected echoes. This tutorial focuses on “physics-based statistics,” which is a predictive form of modeling the fluctuations. The modeling is based principally on the physics of the scattering by individual scatterers, addition of echoes from randomized multiple scatterers, system effects involving the beampattern and signal type, and signal theory including matched filter processing. Some consideration is also given to environment-specific effects such as the presence of boundaries and heterogeneities in the medium. Although the modeling was inspired by applications of sonar in the field of underwater acoustics, the material is presented in a general form, and involving only scalar fields. Therefore, it is broadly applicable to other areas such as medical ultrasound, non-destructive acoustic testing, in-air acoustics, as well as radar and lasers.The content of this work is based on research conducted in the past from years of support from the U.S. Office of Naval Research and the Woods Hole Oceanographic Institution, Woods Hole, MA. Writing of the manuscript by W.-J.L. was also supported by the Science and Engineering Enrichment and Development Postdoctoral Fellowship from the Applied Physics Laboratory, University of Washington, WA. The authors are grateful to Dr. Benjamin A. Jones of the Naval Postgraduate School, Monterey, CA for his thoughtful suggestions on an early draft of the manuscript. The authors are also grateful to the reviewer for the in-depth and constructive recommendations. W.-J.L. and K.B. contributed equally to this work.2019-06-0

Investigation of a method for real time quantification of gas bubbles in pipelines

The need to measure the dynamic void fraction (the proportion of flowing bubbly liquid that is gas) is common across many power, processing and manufacturing industries. Many such pipelines and liquids are optically opaque, and work on margins that require a low cost solution that is not commensurate with the size of the challenge. Such a solution will therefore be a compromise, and in this paper costs are reduced by using a narrowband acoustic solution that cannot, on its own, contain enough information to characterise the void fraction in real time unambiguously. The ambiguity is reduced using likely estimates of the general shape of the bubble size distribution so that, with a single source-receiver pair attached to the outside of the pipe, the absolute gas content can be estimated. Whilst the data that are required a priori (the general shape of the bubble size distribution) are not identical to the output of the inversion (the absolute void fraction of gas entrained as bubbles in the flow), the requirement for such a priori information could limit the usefulness of the technique in industry

Demonstration comparing sound wave attenuation inside pipes containing bubbly water and water droplet fog

This paper describes a demonstration and explanation of sound absorption in water due to bubbles,and in air due to a fog of water droplets. It is suitable for 10–12 year olds, but the paper indicates where further exploration of the simplifications in the explanations provided for that age range would allow the demonstration to be used for undergraduate and Masters-level teaching. Applications to submarines, the space shuttle, and neutron generators are described. The demonstration is designed for transportation in a family-sized car

Acoustic attenuation, phase and group velocities in liquid-filled pipes: theory, experiment, and examples of water and mercury

Del Grosso’s [Acustica 24, 299–311 (1971)] formulation, which predicts the phase speed of propagating axisymmetric modes inside a liquid-filled tube, is here extended to the complex domain in order to predict the attenuation, as well as the sound speed, of the modes as a function of frequency. Measurements of the sound speeds and the attenuations of the modes were performed in a water-filled Poly (methyl methacrylate) (PMMA) tube of internal radius, b=4.445 cm, in the range of the wavenumber-radius product, k1b, from 2 to 10. Parts of three or four modes were investigated and the measured sound speeds and the damping of the modes were compared with the theoretical predictions. The theory was then used to estimate the modal sound speeds and attenuations in a stainless-steel pipe filled with mercury having the same dimensions as are used in the Spallation Neutron Source at Oak Ridge National Laboratory, Tennessee

Acoustic attenuation, phase and group velocities in liquid-filled pipes III: nonaxisymmetric propagation and circumferential modes in lossless conditions

Equations for the nonaxisymmetric modes that are axially and circumferentially propagating in a liquid-filled tube with elastic walls surrounded by air/vacuum are presented using exact elasticity theory. Dispersion curves for the axially propagating modes are obtained and verified through comparison with measurements. The resulting theory is applied to the circumferential modes, and the pressures and the stresses in the liquid-filled pipe are calculated under external forced oscillation by an acoustic source. This provides the theoretical foundation for the narrow band acoustic bubble detector that was subsequently deployed at the Target Test Facility (TTF) of the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL), TN.<br/

Controlled Regulation of the Nitrile Activation of a Peroxocobalt(III) Complex with Redox-Inactive Lewis Acidic Metals

Redox-inactive metal ions play vital roles in biological O-2 activation and oxidation reactions of various substrates. Recently, we showed a distinct reactivity of a peroxocobalt(III) complex bearing a tetradentate macrocyclic ligand, [Co-III(TBDAP)(O-2)](+) (1) (TBDAP = N,N&apos;-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane), toward nitriles that afforded a series of hydroximatocobalt(III) complexes, [Co-III(TBDAP)(R-C(=NO)O)](+) (R = Me (3), Et, and Ph). In this study, we report the effects of redox-inactive metal ions on nitrile activation of 1. In the presence of redox-inactive metal ions such as Zn2+, La3+, Lu3+, and Y3+, the reaction does not form the hydroximatocobalt(III) complex but instead gives peroxyimidatocobalt(III) complexes, [Co-III(TBDAP)(R-C(=NH)O-2)](2+) (R = Me (2) and Ph (2(Ph))). These new intermediates were characterized by various physicochemical methods including X-ray diffraction analysis. The rates of the formation of 2 are found to correlate with the Lewis acidity of the additive metal ions. Moreover, complex 2 was readily converted to 3 by the addition of a base. In the presence of Al3+, Sc3+, or H+, 1 is converted to [Co-III(TBDAP)(O2H)(MeCN)](2+) (4), and further reaction with nitriles did not occur. These results reveal that the reactivity of the peroxocobalt(III) complex 1 in nitrile activation can be regulated by the redox-inactive metal ions and their Lewis acidity. DFT calculations show that the redox-inactive metal ions stabilize the peroxo character of end-on Co-eta(1)-O-2 intermediate through the charge reorganization from a Co-II-superoxo to a Co-III-peroxo intermediate. A complete mechanistic model explaining the role of the Lewis acid is presented

Three dimensional a-Si:H thin-film solar cells with silver nano-rod back electrodes

We present three dimensional (3-D) amorphous silicon (a-Si:H) thin-film solar cells with silver nano-rods as back electrodes, which are fabricated by low cost nano imprint lithography (NIL). After conformal deposition of thin metal and semiconductor layers, we can achieve a dome-shaped geometry, which is shown to be effective in reducing the reflectance at the front surface due to the graded refractive index effect. In addition, the enhancement of the diffused reflectance over a broad wavelength in this dome-shaped geometry provides light trapping due to the increase in the effective light propagation length. Using this 3-D solar cell, we achieved 54% increase in short circuit current density and 45% increase in the conversion efficiency compared to the control cells with flat Ag surfaces. This 3-D structure can be also used for improving light harvesting in various photovoltaic devices regardless of materials and structures.close

Simple and fast fabrication of a-Si:H/c-Si hetero-junction solar cells by dual-chamber hot wire chemical vapor deposition

One of the fabrication issues in hetero-junction crystalline Si solar cells is the overhead time between the deposition steps of the top and bottom surfaces, because flipping of the progressing wafer is necessary to process the both sides of the wafer. To reduce the overall processing time by reducing the overhead time, we propose a dual-chamber deposition system, where thin films on the top and bottom surfaces of the Si wafer are simultaneously deposited. We have evaluated the proposed deposition system by demonstrating fabricated hetero-junction crystalline Si solar cells, which were compared with solar cells fabricated by a conventional plasma-enhanced chemical deposition system. We have obtained the power conversion efficiency of 15.5% from solar cells fabricated by our dual-chamber system; and additional analyses confirmed that the proposed dual-chamber system is, in principle, competitive with conventional systems in terms of the fabricated solar cell performance. This novel concept for the fabrication of a hetero-junction crystalline Si solar cell is expected to lay an important foundation in the future thin film crystalline Si based photovoltaic industry.close

Thermal Ablation and High-Resolution Imaging Using a Back-to-Back (BTB) Dual-Mode Ultrasonic Transducer: In Vivo Results

We present a back-to-back (BTB) structured, dual-mode ultrasonic device that incorporates a single-element 5.3 MHz transducer for high-intensity focused ultrasound (HIFU) treatment and a single-element 20.0 MHz transducer for high-resolution ultrasound imaging. Ultrasound image-guided surgical systems have been developed for lesion monitoring to ensure that ultrasonic treatment is correctly administered at the right locations. In this study, we developed a dual-element transducer composed of two elements that share the same housing but work independently with a BTB structure, enabling a mode change between therapy and imaging via 180-degree mechanical rotation. The optic fibers were embedded in the HIFU focal region of ex vivo chicken breasts and the temperature change was measured. Images were obtained in vivo mice before and after treatment and compared to identify the treated region. We successfully acquired B-mode and C-scan images that display the hyperechoic region indicating coagulation necrosis in the HIFU-treated volume up to a depth of 10 mm. The compact BTB dual-mode ultrasonic transducer may be used for subcutaneous thermal ablation and monitoring, minimally invasive surgery, and other clinical applications, all with ultrasound only.11Nsciescopu