Effects of interaction between two bubble scatterers

The backscattering of sound from two regularly arranged bubbles is studied theoretically and experimentally. In well-controlled laboratory experiments a bistatic acoustic system is used to interrogate the scatterers, which ar e placed on a very fine thread at the same distance d From the combined bea m axis of the set of transmitting and receiving transducers. The radius of each bubble is 585 mu m. The frequency range is 80-140 kHz, and d is varied so that the variable kd spans the range 0.2-21, where k is the acoustic wa ve number. Scattering calculations are carried out using an exact, closed-f orm solution derived from the multiple scattering series. Several experimen ts are performed, and the results are in close agreement with the calculati ons. It is verified that multiple scattering induces an oscillatory behavio r about the exact coherent scattering level, with decreasing amplitude for increasing kd. For interbubble distance 2d approximate to lambda/2 the back scattered radiation is maximized, while for 2d<lambda/2 the radiation is re duced considerably. These and other effects are discussed. (C) 2000 Acousti cal Society of America. [S0001-4966(00)02106-8].