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Proceedings of Meetings on Acoustics

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POMA - 162nd Meeting Acoustical Society of America
Conference Location: San Diego, California Conference Date: 31 October - 4 November 2011
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A direction-selective filter with a rational beam pattern

Dean J. Schmidlin

POMA Volume 14, pp. 055001 (October 2011); (9 pages)

Online Publication Date: October 25, 2011

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Presented in this paper is a direction-selective filter whose beam pattern is a rational function of a direction cosine. First, a plane-wave sinusoidal pressure function is converted from a four-dimensional function to a two-dimensional one by restricting the spatial points to lie on a radial line extending out from the origin in a prescribed look direction. The two-dimensional pressure function is then input into a linear filter characterized by a second-order partial differential equation with constant coefficients. The natural and forced responses are determined from which expressions for the beam pattern of the filter and the time constant of the natural response are found. The beam pattern is the reciprocal of a second-degree polynomial function of the plane wave's direction cosine. It is shown that the frequency range over which the integrity of the beam pattern is maintained is a function of the filter's natural response. An example is presented which illustrates the directivity index that is achievable in contrast to that of a vector or dyadic sensor, both of which have beam patterns that are polynomial functions of a direction cosine.
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43.60.Fg Acoustic array systems and processing, beam-forming
43.60.Gk Space-time signal processing, other than matched field processing
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Applications of rhythm algorithm for periodic broadband signals

Alexander Ekimov

POMA Volume 14, pp. 055002 (April 2012); (11 pages)

Online Publication Date: April 03, 2012

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A rhythm algorithm, recently published in JASA 129(3), 2011, was developed to analyze periodic broadband signals. This algorithm was applied in human and animal footsteps studies for signals from a node of orthogonal sensors and for underwater studies of sperm whale clicks measured using hydrophones. Some new applications of this rhythm algorithm are presented and discussed. The rhythm algorithm was applied to signals from breaking waves on a lake shore. The signals were recorded by a node of two orthogonal sensors on the lake shore consisting of a narrow-band ultrasonic microphone and a Doppler sonar unit. The narrow-band ultrasonic microphone showed detectable levels of ultrasonic signals for breaking waves while the Doppler sonar showed the maximum velocity of the waves. Signals from this node were recorded and processed simultaneously using the rhythm algorithm. The rhythm algorithm was applied to musical periodic sound, enabling detection of the music rhythms and temporal variations of these rhythms using the Short Term Fourier Transform.
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43.60.Hj Time-frequency signal processing, wavelets
43.75.Zz Analysis, synthesis, and processing of musical sounds
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