Surface Vibration Reconstruction Using Inverse Numerical Acoustics

This paper explores the use of inverse numerical acoustics to reconstruct the surface vibration of a noise source. Inverse numerical acoustics is mainly used for source identification. This approach uses the measured sound pressure at a set of field points and the Helmholtz integral equation to reconstruct the normal surface velocity. The number of sound pressure measurements is considerably less than the number of surface vibration nodes. An overview of inverse numerical acoustics is presented and compared with other holography techniques such as nearfield acoustical holography and the Helmholtz equation least squares method. In order to obtain an acceptable reproduction of the surface vibration, several critical factors such as the field point selection and the effect of experimental errors have to be handled properly. Other practical considerations such as the use of few measured velocities and regularization techniques will also be presented. Examples will include a diesel engine, a transmission housing and an engine cover

Computer and internet interventions to optimize listening and learning for people with hearing loss: accessibility, use, and adherence

Purpose: The aim of this research forum article was to examine accessibility, use, and adherence to computerized and online interventions for people with hearing loss. Method: Four intervention studies of people with hearing loss were examined: 2 auditory training studies, 1 working memory training study, and 1 study of multimedia educational support. Results: A small proportion (approximately 15%) of participants had never used a computer, which may be a barrier to the accessibility of computer and Internet based interventions. Computer competence was not a factor in intervention use or adherence. Computer skills and Internet access influenced participant preference for the delivery method of the multimedia educational support program. Conclusions: It is important to be aware of current barriers to computer and Internet-delivered interventions for people with hearing loss. However, there is a clear need to develop and future-proof hearing-related applications for online delivery

Acoustic cloak based on Bézier scatterers

[EN] Among the different approaches proposed to design acoustic cloaks, the one consisting on the use of an optimum distribution of discrete scatters surrounding the concealing object has been successfully tested. The feasibility of acoustic cloaks mainly depends on the number and shape of the scatterers surrounding the object to be cloaked. This work presents a method allowing the reduction of the number of discrete scatterers by optimizing their external shape, which is here defined by a combination of cubic Bézier curves. Based on scattering cancellation, a two-dimensional directional cloak consisting of just 20 Bézier scatters has been designed, fabricated and experimentally characterized. The method of fundamental solutions has been implemented to calculate the interaction of an incident plane wave with scatterers of arbitrary shape. The acoustic cloak here proposed shows a performance, in terms of averaged visibility, similar to that consisting of 120 scatterers with equal circular cross sections. The operational frequency of the proposed cloak is 5940 Hz with a bandwidth of about 110 Hz.J. Sanchez-Dehesa acknowledges the financial support by the Spanish Ministerio de Economia y Competitividad and the European Union Fondo Europeo para el Desarrollo Regional (FEDER) under Grant with Ref. TEC2014-53088-C3-1-R. Lu Zhimiao acknowledges the financial support from the program of China Scholarships Council (No. 201503170282), Wen Jihong, Cai Li and Lu Zhimiao acknowledge the support by National Natural Science Foundation of China (Grant Nos 51275519 and 11372346)Lu, Z.; Sanchis Martínez, L.; Wen, J.; Cai, L.; Bi, Y.; Sánchez-Dehesa Moreno-Cid, J. (2018). Acoustic cloak based on Bézier scatterers. Scientific Reports. 8. https://doi.org/10.1038/s41598-018-30888-7S8Cummer, S. A. & Schurig, D. One path to acoustic cloaking. New J. Phys. 9(3), 45 (2007).Cai, L.-W. & Sánchez-Dehesa Analysis of Cummer–Schurig acoustic cloaking. J. New J. Phys. 9(12), 450 (2007).Chen, H. & Chan, C. Acoustic cloaking in three dimensions using acoustic metamaterials. Appl. Phys. Lett. 91(18), 183518 (2007).Norris, A. N. Acoustic cloaking theory. Proc. R. Soc. A 464(2097), 2411–2434 (2008).Torrent, D. & Sánchez-Dehesa, J. Acoustic cloaking in two dimensions: a feasible approach. New J. Phys. 10(6), 063015 (2008).Zhang, S., Xia, C. & Fang, N. Broadband acoustic cloak for ultrasound waves. Phys. Rev. Lett. 106, 024301 Jan (2011).Popa, B.-I., Zigoneanu, L. & Cummer, S. A. Experimental acoustic ground cloak in air. Phys. Rev. Lett. 106, 253901 Jun (2011).Zigoneanu, L., Popa, B.-I. & Cummer, S. A. Design and measurements of a broadband two-dimensional acoustic lens. Nat. Mat 13, 352 (2014).Kan, W. et al. Broadband acoustic cloaking within an arbitrary hard cavity. Phys. Rev. Applied 3, 064019 Jun (2015).Scandrett, C. 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Univ. of Texas at Austin (2012).Guild, M. D., Haberman, M. R. & Alú, A. Plasmonic-type Acoustic cloak made of a bilaminate shell. Phys. Rev. B 86(10), 104302 (2012).Rohde, C. A. et al. Experimental demonstration of underwater acoustic scattering cancellation. Sci. Rep. 5, 13175 (2015).Popa, B.-I. & Cummer, S. A. Cloaking with optimized homogeneous anisotropic layers. Phys. Rev. A 79, 023806 Feb (2009).Urzhumov, Y., Landy, N., Driscoll, T., Basov, D. & Smith, D. R. Thin low-loss dielectric coatings for freespace cloaking. Opt. Lett. 38(10), 1606–1608 (2013).Andkjaer, J. & Sigmund, O. Topology optimized low-contrast all-dielectric optical cloak. Appl. Phys. Lett. 98(2), 021112 (2011).Climente, A., Torrent, D. & Sánchez-Dehesa, J. Sound focusing by gradient index sonic lenses. Applied Physics Letters 97(10), 104103 (2010).Håkansson, A., Sánchez-Dehesa, J. & Sanchis, L. Acoustic lens design by genetic algorithms Phys. Rev. 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Rise and demise of the global silver standard

In the early modern period, the world economy gravitated around the expansion of long-distance commerce. Together with navigation improvements, silver was the prime commodity which moved the sails of such trade. The disparate availability and the particular demand for silver across the globe determined the participation of producers, consumers, and intermediaries in a growing global economy. American endowments of silver are a known feature of this process; however, the fact that the supply of silver was in the form of specie is a less known aspect of the integration of the global economy. This chapter surveys the production and export of silver specie out of Spanish America, its intermediation by Europeans, and the reexport to Asia. It describes how the sheer volume produced and the quality and consistency of the coin provided familiarity with, and reliability to, the Spanish American peso which made it current in most world markets. By the eighteenth century, it has become a currency standard for the international economy which grew together with the production and coinage of silver. Implications varied according to the institutional settings to deal with specie and foreign exchange in each intervening economy of that trade. Generalized warfare in late eighteenth-century Europe brought down governance in Spanish America and coinage fragmented along with the political fragmentation of the empire. The emergence of new sovereign republics and the end of minting as known meant the cessation of the silver standard that had contributed to the early modern globalization

Surface Vibration Reconstruction using Inverse Numerical Acoustics

This paper explores the use of inverse numerical acoustics to reconstruct the surface vibration of a noise source. Inverse numerical acoustics is mainly used for source identification. This approach uses the measured sound pressure at a set of field points and the Helmholtz integral equation to reconstruct the normal surface velocity. The number of sound pressure measurements is considerably less than the number of surface vibration nodes. An overview of inverse numerical acoustics is presented and compared with other holography techniques such as nearfield acoustical holography and the Helmholtz equation least squares method. In order to obtain an acceptable reproduction of the surface vibration, several critical factors such as the field point selection and the effect of experimental errors have to be handled properly. Other practical considerations such as the use of few measured velocities and regularization techniques will also be presented. Examples will include a diesel engine, a transmission housing and an engine cover

Statistical errors in the estimation of time-averaged acoustic energy density using the two-microphone method

Copyright © 2004 Acoustical Society of AmericaTime-averaged acoustic energy density can be estimated using the auto- and cross-spectral densities between two closely spaced microphones. In this paper, an analysis of the random errors that arise using two microphone measurements is undertaken. An expression for the normalized random error of the time-averaged acoustic energy density spectral density estimate is derived. This expression is verified numerically. The lower and upper bounds of the normalized random error are derived. It is shown that the normalized random error of the estimate is not a strong function of the sound field properties, and is chiefly dependent on the number of records averaged. © 2004 Acoustical Society of America.Justin Ghan, Ben Cazzolato, and Scott Snyde