[institut] Potsetnik i predavanje u utorak

[Dr. Dragan D. Markushev]

Postovane koleginice i kolege,

potsecam vas da ce u ponedeljak 23.04.2012. godine u sali biblioteke 
Instituta za
fiziku, sa pocetkom u 12.00 biti odrzano predavanje

“Acoustic nonlinearities in thermoacoustic refrigerators driven by 
loudspeakers”

koji ce odrzati Dr. Li Fan.

Takodje vas pozivam da u utorak 24.04.2012. godine u sali biblioteke 
Instituta za
fiziku, sa pocetkom u 11.00 prisustvujete seminaru

“Acoustic Concentrators Designed by Acoustic Metamaterials”

koji ce odrzati

Dr. Hui Zhang
Associate Professor
Institute of Acoustics
Nanjing University
Nanjing, China

ABSTRACT

"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."

BIOSKETCH

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.

Srdacan pozdrav

Dragan D. Markushev

-- 
Dr. Dragan D. MARKUSHEV
Senior Research Associate
Laboratory for Atomic, Molecular
and Laser Spectroscopy
Institute of Physics Belgrade
Pregrevica 118,
11080 Belgrade, SERBIA
phone: +381113713158
fax: +381113162190
http://www.ipb.ac.rs/