Echoes from double elastic spherical shell in water

Acoustic scattering by double concentric elastic spherical shell in water is studied. The Rayleigh normal mode solution is derived using exact elastic theory and separation of variables. The backscattering form functions of single and double shell were calculated and compared. To analyze echo structure the echo pulse sequence of a narrow incident pulse were also presented. Calculation results show that echo characteristics of double shell constituted by a very thin outer shell and a thicker inner shell are dependent mainly on the inner shell. At low ka echoes from double shell can be approximated by a sum of two echoes one of which is from the outer shell with water filled and the other is from the inner shell with vacuum filled.