  We propose a new approach to the generation of acoustic frequency combs (AFC)
-- signals with spectra containing equidistant coherent peaks. AFCs are
essential for a number of sensing and measurement applications, where the
established technology of optical frequency combs suffers from fundamental
physical limitations. Our proof-of-principle experiments demonstrate that
nonlinear oscillations of a gas bubble cluster in water insonated by a
low-pressure single-frequency ultrasound wave produce signals with spectra
consisting of equally spaced peaks originating from the interaction of the
driving ultrasound wave with the response of the bubble cluster at its natural
frequency. The so-generated AFC posses essential characteristics of optical
frequency combs and thus, similar to their optical counterparts, can be used to
measure various physical, chemical and biological quantities.
