Characterization of Target Spheres for Broad-Band Calibration of Acoustic Systems
Sonars and echo sounders are frequently calibrated using echoes from spheres of copper or tungsten carbide at spot frequencies in narrow frequency bands. Modern transducers require methods for calibration of broader frequency bands. In this paper a method is presented and applied to two commercial transducers centred at 120 kHz and 200 kHz, respectively. A demand for accurately known parameters of the calibration spheres was recognized. A method for determining compressional and shear wave speeds in such spheres is demonstrated, using dominant dips in the echo spectra in combination with computed form functions, and an inversion scheme based on the Nelder-Mead simplex algorithm. The wave speeds of 4 tungsten carbide spheres and 9 copper spheres were determined. The copper spheres ageing from 30 years to recent were examined for possible evidence of age effects, and none were found. Suspending the spheres in mono filament nylon cages requires soaking in water for at least 5 hours to obtain stable echoes. This time is not affected by dipping the spheres in detergent solutions. Finally, an approximate method to find the magnitude of the transducer transfer functions is demonstrated.
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Document Type: Research Article
Publication date: May 1, 2013
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- Acta Acustica united with Acustica, published together with the European Acoustics Association (EAA), is an international, peer-reviewed journal on acoustics. It publishes original articles on all subjects in the field of acoustics, such as general linear acoustics, nonlinear acoustics, macrosonics, flow acoustics, atmospheric sound, underwater sound, ultrasonics, physical acoustics, structural acoustics, noise control, active control, environmental noise, building acoustics, room acoustics, acoustic materials, acoustic signal processing, computational and numerical acoustics, hearing, audiology and psychoacoustics, speech, musical acoustics, electroacoustics, auditory quality of systems. It reports on original scientific research in acoustics and on engineering applications. The journal considers scientific papers, technical and applied papers, book reviews, short communications, doctoral thesis abstracts, etc. In irregular intervals also special issues and review articles are published.
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