24.04.2012. :: Seminar - Hui Zhang
U utorak 24.04.2012. godine u sali biblioteke Instituta za fiziku, sa pocetkom u 11.00 odrzace se seminar:
Acoustic Concentrators Designed by Acoustic Metamaterials
Dr. Hui Zhang
Institute of Acoustics
"The acoustic metamaterials with negative elastic modulus and /or negative mass density, which has been recognized to play key roles to reach acoustic subwavelength imaging and enhanced transmission. Particularly, some acoustic devices, such as the acoustic contractors and the acoustic birefringence materials, become the popular research fields. In this presentation, a two-dimensional cylindrical acoustic concentrator is designed with multilayered alternative homogeneous materials, which can focus acoustic field and enhance acoustic energy in a given area. The frequency response analysis of the acoustic concentrator demonstrates that the acoustic energy can be concentrated within the device over a wide frequency band. Meanwhile, there are contradictory relations between the acoustic concentrating performances in the inner region and the scattering properties in the outer region of these concentrators. When the contradictory relations satisfy compromise balance, the concentration ratio can reach at least 70%. In addition, Dual-negative refraction (DNR) phenomenon was theoretically implemented in the two-dimensional triangular phononic crystals. The DNR effect is caused by that the frequency of the incident wave is overlapping 2nd and 3rd Bloch bands. The potential working areas of DNR are calculated by band structure theory for scatterers with different shapes and symmetries. Specifically, two types of lattices (triangular and honeycomb) and four different shapes of scatterers (circle, hexagon, square and triangle) are considered. The optimum operating frequencies of DNR with different crystal structures are discussed."
Dr. Zhang received his PhD degree in Nanjing University (NJU) in 2006. From then, he has worked as a teacher in Nanjing University. From 2006 to 2007, he worked as a Visiting Scholar in Katholieke Universiteit Leuven, Belgium. Now he is an Associate Professor in Institute of Acoustics NJU. His research interests are in acoustic actuators and acoustic sensors, and nonlinear vibrations of the micro-beam in the atomic force acoustic microscope. As the author and co-author he has published more than 30 papers in SCI journals including APL, ,JAP, JASA, IEEE TUFFC, CPL and Ultrasonics.