Near-field scanning in the time domain on a spherical surface - A formulation using the free-space Green's function

Two formulations for determining the characteristics of an unknown source o f acoustic waves using the measurement of its field at its near zone are pr esented. The measurement in both cases is to be performed on a spherical sc an surface which encapsulates the source. The first is for an ideal probe w hich measures the field at its location. The knowledge of the field is suff icient; its normal derivative is not required. In the second formulation a realistic probe is considered. This time it is required only that the probe has an axially symmetric receiving characteristic. With this formulation, the time functions which characterize the source are found using only the s ignal at the output of the probe. Both formulations are such that they are not specific to the scan surface radius. Furthermore, they are entirely in the time domain, requiring no inverse Fourier transformations left to be pe rformed. (C) 2001 Acoustical Society of America.