Phononic structures or crystals made of rows of steel pipes privilege the existence of band gaps and pass bands. The first ones are frequency domains where the incident wave cannot pass through the structure. By introducing small changes about the positioning of the pipes, it is possible to expand greatly the width of the band gaps. By varying the thickness of the pipes in a phononic crystal with a square symmetry, the effect of an incident plane wave which propagates in the direction of the variation is to create thin pass bands in the band gap obtained initially when the pipes have the same thickness. If the incidente wave propagates perpendicularly to the direction of the thickness variation of the pipes, convergent or divergent acoustic lenses which could deviate acoustic beams are created. Finally, when a crystal constituted by the steel pipes is inserted in an array of polyethylene pipes, numerical simulations show that a sound wave can be guided at frequencies corresponding to the pass bands of a steel phononic crystal.
