Acoustic band gaps created by rotating square rods in a two-dimensional lattice.

Acoustic band gaps can be opened and tuned by rotating square rods in two-dimensional liquid sonic crystals. For the systems of mercury rods with square cross section in a water host, the width of lowest gaps increases as the rotation angle of the square rods increases. But opposite results are found for the inverse systems of water rods in mercury, where the lowest gaps narrow with an increase in the rotation angle. This gap-tuning effect becomes more evident with the filling fraction increase. Such an effect should open up a new way for designing acoustic band gaps in two-dimensional phononic crystals.