Predictions on absorption and scattering characteristics of acoustic scatterers modified with micro-perforated panels

Download
2012
Odabaş, Erinç
In this study, the basic absorption and scattering characteristics of acoustic scatterers, specifically Schroeder Diffusers, are investigated. Schroeder Diffusers are one of the most widely used acoustic scatterers in which the scattering phenomenon is predictable due to the geometry of the diffuser, based on a particular mathematical sequence. It is shown that it is possible to increase the amount of absorption by modifying the diffuser structure by means of adding perforated panels into the wells or narrowing diffuser wells. In room acoustics applications, diffusers are conventionally mounted to a wall or ceiling assumed to be rigid enough such that sound wave cannot penetrate through. This thesis proposes a new modification on these diffusers where the diffuser is not backed by a rigid surface; it is hung over a space instead. To construct such a configuration, diffuser wells are terminated with micro-perforated panels (MPP). Inclusion of MPP introduces additional losses; hence, higher absorption can be achieved. However, the most significant absorption in this configuration is achieved below the first resonance frequency of the panel-air space system due to the existence of non-rigid backing. This thesis aims to model the absorption and scattering mechanisms enabled with the non-rigid backing by improving a previously introduced mathematical model.

Suggestions

Near-field scanning in the time domain on a spherical surface - A formulation using the free-space Green's function
Koc, S; Aydın Çivi, Hatice Özlem; Buyukdura, OM (2001-10-01)
Two formulations for determining the characteristics of an unknown source of acoustic waves using the measurement of its field at its near zone are presented. The measurement in both cases is to be performed on a spherical scan surface which encapsulates the source. The first is for an ideal probe which measures the field at its location. The knowledge of the field is sufficient; its normal derivative is not required. In the second formulation a realistic probe is considered. This time it is required only t...
Design and implementation of an annular acoustic levitation system
Kandemir, Mehmet Hakan; Çalışkan, Mehmet; Department of Mechanical Engineering (2014)
In standing wave acoustic levitation technique, a standing wave is obtained between a source and a reflector. Particles can be attracted towards pressure nodes in standing waves owing to the spring action. Hence, particles can be suspended in air. This operation can be performed on continuous structures as well as in several numbers of axes. In this study an annular acoustic levitation set-up is designed and built. The set-up consists of two langevin type piezoelectric transducers, two waveguides, an annula...
Response of acoustic imaging systems using convergent leaky waves to cylindrical flaws
Günalp, Nilgün; Atalar, Abdullah (Institute of Electrical and Electronics Engineers (IEEE), 1989-9)
A theoretical study of imaging systems utilizing focused leaky surface acoustic waves (SAWs), and their response to certain kind of defects is presented. In particular, circular cylindrical inhomogeneities with axes perpendicular to the surface are considered. The scattering of the SAW from this cylinder is formulated with some approximations. The surface wave incident on the inhomogeneity is initially found as an angular spectrum of plane waves. However, to apply the boundary conditions at the cylindrical ...
Numerical and analytical investigation of aerosol acoustics through ducts
Arslan, Ersen; Çalışkan, Mehmet; Department of Mechanical Engineering (2017)
The aim of this thesis is to develop a numerical approach which can solve the sound propagation problem in air-filled circular duct containing water droplets (regarded as an aerosol) in order to obtain acoustic absorption and dispersion characteristics of the system. There exist several analytical approaches in literature for treatment of basic aerosol problems with certain limitations; however; in order to solve rather complex cases, these limitations must be handled and worked out. In this study, a couple...
Analysis of the peak position and linewidth as a function of temperature for the phase transitions in LiKSO4
Yurtseven, Hasan Hamit (World Scientific Pub Co Pte Lt, 2016-02-20)
Analysis of the peak position and the linewidths of various infrared modes is performed at high (300-850 K) and low (1.5-300 K) temperatures using the experimental data from the literature for LiKSO4 which exhibits a sequence of phase transitions. The temperature dependences of the frequency and the linewidth which are derived from the anharmonic self-energy are fitted to the observed peak positions and the linewidths of the S-O stretching modes (internal nu(3) modes at 1135 cm(-1) and at 1180 cm(-1)), peak...
Citation Formats
E. Odabaş, “Predictions on absorption and scattering characteristics of acoustic scatterers modified with micro-perforated panels,” M.S. - Master of Science, Middle East Technical University, 2012.