Beta 1


Title Inverse problems in acoustic reflectometry
Author Vinther, Michael
Supervisor Hansen, Per Christian (Institut for Informatik og Matematisk Modellering, Danmarks Tekniske Universitet, DTU, DK-2800 Kgs. Lyngby, Denmark)
Institution Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
Thesis level Master's thesis
Year 2004
Abstract We examine acoustic reflectometry as a method for determining the inner cross section of a cavity. The cavity is modeled as a cylindrical tube with varying cross section area. A method for making practical measurements using a speaker, a microphone and sampling hardware is described, and algorithms for computing the cross section area from the measurements are derived. Both a lossless and a lossy model is derived, and issues in creating and using the models are studied. The cross section area is computed using an inverse scattering algorithm working on the impulse response of the cavity. Estimating the impulse response from our experi­men­tal data proves to be an ill-posed problem, i.e. with a solution that is very sensitive to per­tu­r­bations in the input. The performance of different regularization methods applied to this problem is investigated with respect to quality of the result and computational complexity. Determining the cross section area is also a potentially ill-posed problem, and stability of the suggested methods is examined. In Danish: Akustisk reflektometri bliver undersøgt som metode til at bestemme det indre tværsnit af en rørformet kavitet. I den forbindelse beskrives en mulig metode til at foretage de faktiske målinger v.h.a. lydgiver, mikrofon og samplinghardware, og algoritmer til at beregne tvær­snitsareal ud fra måledata udledes. Kaviteten modelleres både som et tabsfrit og et tabsgivende rør, og problematikker omkring modellering af tab studeres. Tværsnitsarealet viser sig at kunne beregnes simplest ud fra kavitetens impulssvar, og at bestemme impulssvaret kræver løsning af et regulariseringsproblem. Derfor bliver for­skel­lige regu­lariserings­metoder undersøgt med hensyn til beregningseffektivitet og deres evne til at frembringe tilfresstillinde resultater. Både bestemmelse af tværsnitsareal og impulssvar er såkaldte inverse problemer, hvortil løsningen potentielt er meget følsom overfor forstyrrelser i måledata.
Note The project has been completed in collaboration with Oticon. The project can be acquired by contacting Per Christian Hansen, pch@imm.dtu.dk
Imprint Department of Informatics and Mathematical Modeling, Technical University of Denmark, DTU : DK-2800 Kgs. Lyngby, Denmark
Keywords Acoustic reflectometry; inverse problems; regularization; devonvolution; inverse scattering; loss modeling
Admin Creation date: 2006-06-22    Update date: 2012-12-21    Source: dtu    ID: 154809    Original MXD