Theoretical investigation of the response of gas-filled micropores and cavitation nuclei to ultrasound

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Abstract
Theory was discussed for the transverse oscillation of a small circular interface set into a rigid baffle between gas and liquid. The angular resonance frequency is given by (15.pi.T/4 .rho.a3)1/2, in which a is the radius of the interface, T is the interfacial surface tension and .rho. is the density of the liquid. Damping parameters are obtained for the radiation, viscous and boundary-layer mechanisms of dissipation. This model system is extended for discussion of the pulsation of gas trapped in a pit or cavity in a solid, which may simulate one type of cavitation nucleus, and straight-through cylindrical holes or pores in a solid sheet, which is applicable to the hydrophobic membranes with gas-trapping micropores used in studies of biological effects produced by ultrasound. Fixed and free conditions at the three-phase line at the periphery of an interface are considered. The partially gas-filled cavity was treated, and also the partially gas-filled pore with 2 interfaces which have different mass, stiffness and damping parameters. The results of these theoretical considerations are expected to be of value for quantitatively evaluating that specific form of stable cavitation which involves the direct activation of pre-existing, stable bodies of gas into ultrasonic pulsation, as experimentally observed, for example, by Miller.
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