Sonic　crystals　are　composite　materials　made　of　periodic　distributions　of　inclusions　embedded　in　a　matrix.　Due　to　the　periodicity,　these　materials　may　exhibit　complete　acoustic　band　gaps　within　which　sound　and　vibrations　are　forbidden.　In　this　paper,　the　band　gap　characteristics　of　a　2-D　square　array　of　hollow　cylinders　and　spit-ring　hollow　cylinders　embedded　in　air　are　investigated　by　COMSOL®　finite　element　method,　and　then　verified　by　plane　wave　expansion　method.　The　results　are　very　consistent,　proving　that　COMSOL®　can　be　employed　for　the　full　characterization　of　the　structures.　©　2011　IEEE.