Observation Of Band Gaps In The Gigahertz Range And Deaf Bands In A Hypersonic Aluminum Nitride Phononic Crystal Slab

We report on the observation of elastic waves propagating in a two-dimensional phononic crystal composed of air holes drilled in an aluminum nitride membrane. The theoretical band structure indicates the existence of an acoustic band gap centered around 800 MHz with a relative bandwidth of 6.5% that is confirmed by gigahertz optical images of the surface displacement. Further electrical measurements and computation of the transmission reveal a much wider attenuation band that is explained by the deaf character of certain bands resulting from the orthogonality of their polarization with that of the source. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3598425]