The example of a mechanical system which behaves like a double negative medium within a certain frequency band is suggested. The analytical expressions for the frequency dependence of its effective density and compressibility are derived. The results of numerical simulations in the two–dimensional case of an impulse propagating through the layer made of the considered medium are presented. The presence of negative refraction is shown while the causality principle is satisfied.
43.35.+d Ultrasonics, quantum acoustics, and physical effects of sound
43.60.+d Acoustic signal processing
Department of acoustics, Faculty of Physics, Lomonosov Moscow State University, Moscow 119991, Russia