Geometric resonance in intermediate state of type I superconductors

The attenuation of ultrasound (the geometric resonance) in an intermediate state of the type I superconductors at kaN >> 1 is researched. The oscillating dependence of ultrasound attenuation, which has an amplitude modulation as a result of presence of the Andreev reflec-tions by the electronic excitations on the boundaries between the normal metal layer and the superconducting layer in an intermediate state of the type I superconductor, is obtained. The derived theoretical equation explains the nature of experimental results in [1, 2].