Casimir energy for a scalar field with a frequency dependent boundary condition

ζ-function. The use of the Debye asymptotic expansion forBessel functions allows to determine the dominant (volume,area, ...) terms in the Casimir energy. The possible interestof this kind of models for dielectric media (and its applicationto sonoluminescence) is also discussed.12.20.Ds, 03.70.+k, 78.60.MqI. INTRODUCTION