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Proceedings Paper

New approach to active sound absorption for tube reciprocity calibration of transducers
Author(s): D. D. Ebenezer; Ralph Sebastian
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Paper Abstract

A new simple approach to active sound absorption is presented for the tube reciprocity calibration of electro- acoustic transducers. In the tube reciprocity method, a region is created inside the tube in which plane waves travelling in only one direction are present, by using an active absorption system at the end of the tube. In the approach widely used, the magnitude and phase of the voltage applied to the system are manually adjusted until the desired condition has been achieved. In the present approach, a model of the active termination is used to determine the voltage to be applied. The termination consists of a thin piezoelectric disk with a thin water- proof coating. First, a disk is used as a sensor and the steady-state open circuit voltage generated by it when it is excited by a harmonic acoustic wave is measured. When the same acoustic wave is incident upon it the second time, a voltage is applied to the disk such that there is no reflected wave. The voltage to be applied is determined by using a three port distributed parameter plane-strain model of the disk. The model is used to express the magnitude and phase of the voltage to be applied as a function of the generated voltage. It is shown, theoretically, that almost all the incident acoustic power is electrically absorbed when the wave is incident from water and the disk is backed by air. It is also shown that the reflected coefficient will be less than -20 dB even if the voltage actually applied differs from the exact voltage to be applied by 10% in magnitude or 5 degrees in phase. Experimental results are also presented showing that the reflection coefficient is less than -20 dB when the active absorber is used.

Paper Details

Date Published: 16 April 1998
PDF: 11 pages
Proc. SPIE 3321, 1996 Symposium on Smart Materials, Structures, and MEMS, (16 April 1998); doi: 10.1117/12.305599
Show Author Affiliations
D. D. Ebenezer, Naval Physical and Oceanographic Lab. (India)
Ralph Sebastian, Naval Physical and Oceanographic Lab. (India)

Published in SPIE Proceedings Vol. 3321:
1996 Symposium on Smart Materials, Structures, and MEMS
Vasu K. Aatre; Vijay K. Varadan; Vasundara V. Varadan, Editor(s)

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