### ASA 127th Meeting M.I.T. 1994 June 6-10

## 3aPA12. Prediction of a radiation field of a spherical sound source with a
local responsive surface from measurements of diffraction field
characteristics.

**Ilja E. Tsukernikov
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*AO ``NIIpolygraphmash'' ul. Profsojusnaya, 57, Moscow, 117420, Russia
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A method is offered for the calculation of radiation field using
measurements of sound pressure and the vibration velocity normal component on a
spherical surface surrounding the sound source and setting it off from
extraneous sound sources. The total diffraction field is presented as a
superposition of the spead radiation field and the field to be scattered by the
source surface (a direct field) as well as standing waves describing a
reflected field and a field of extraneous sources. The scattering properties of
the emitting sphere are given with the help of modal impedances. The field
components are represented as an expansion in terms of the spherical harmonics.
The expansion coefficients for the scattered field pressure on the source
surface are calculated by solving of the integral equation of the second kind
which is derived from the discontinuity properties of the Helmholtz integral on
the boundary surface and from the impedance boundary condition. The radiation
field is found as the difference of the direct field and the scattered field
presented with the help of the Helmholtz integrals calculated over the measured
and emitted surfaces. The method is illustrated by calculating the radiation
field of a sphere pulsating with the prescribed velocity in the space bounded
by the perfect reflecting spherical surface.

All posters will be on display from 8:00 a.m. to 12:00 noon. To allow
contributors an opportunity to see other posters, contributors of odd-numbered
posters will be at their posters from 8:00 a.m. to 10:00 a.m. and contributors
of even-numbered posters will be at their posters from 10:00 a.m. to 12:00
noon.