title: Ultrasonic band gaps and negative refraction.
abstract: The first experimentally observed ultrasonic band gaps in periodic bidimensional composited are reviewed here. The studied basic structure consists of an aluminum alloy plate with a periodic arrangement of cylindrical holes filled with mercury. Localization phenomena in linear and point defects have been observed and an ultrasonic waveguide capable to bend the ultrasonic radiation by 90 degrees has been achieved. We also revisit twinned-square periodic structures for ultrasonic wave bending and splitting. Such devices allow 45 degrees bending of waves, whereas an extreme anomalous refraction law at the grain boundaries has also been experimentally observed. Finally, a preliminary study about the possibility of "left-handed" behaviour in ultrasonic crystals is presented in this work. The device consists of a slab of the above mentioned metallic composite attached to an epoxy wedge. In this system, clues to negative refraction are theoretically shown.
authors.affiliation: Instituto de Física Aplicada, Consejo Superior de Investigaciones Científicas (CSIC), Serrano 144, 28006 Madrid, Spain. manolo@iec.csic.es
authors.forename: M
authors.initials: M
authors.lastname: Torres
authors.forename: F R
authors.initials: FR
authors.lastname: Montero de Espinosa