The first experimentally observed ultrasonic full band gap in periodic bidimensional composites for the longitudinal wave mode is described in this Letter. The structure consists of an aluminum alloy plate with a square periodic arrangement of cylindrical holes filled with mercury. No propagation wave exists at the frequency range between 1000–1120 kHz irrespective of the measurement direction. The experiment was performed by means of an ultrasonic transmission technique, and a measurement of the position dependence of the acoustic amplitude was also performed.

• Received 29 May 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.1208