Patent ID: 8116167

Claim:
A system for determining information about a rock formation penetrated by a borehole, the system comprising: a first plurality of transducers configured to generate a first acoustic beam signal at a first frequency and a second plurality of transducers configured to generate a second acoustic beam signal at a second frequency different from the first frequency, the first plurality of transducers and the second plurality of transducers being intermingled so that the first acoustic beam signal and the second acoustic beam signal are substantially collinear, the first acoustic beam signal and the second acoustic beam signal are arranged for collinear mixing in a volume of rock outside the borehole in order to generate a collimated third acoustic beam in the rock formation propagating in a same direction as a direction of the first and second acoustic beams beyond the mixing volume at a frequency substantially equal to a difference between the first frequency and the second frequency, wherein the frequency of the collimated third acoustic beam is between about 500 Hz and about 10 kHz; a controller configured to control a direction of the first acoustic beam signal, the second acoustic beam signal or both by controlling a relative phase between the first plurality of transducers and a relative phase between the second plurality of transducers; one or more receivers disposed in the borehole configured to detect a resultant signal that results from the interaction of the collimated third acoustic beam with inhomogeneities in the rock formation as the collimated third acoustic beam propagates through the rock formation; and a processor programmable with machine executable instructions for analyzing the resultant signal to determine information about the rock formation.