Examiners:
Associate Professor Jonas Brunskog, DTU Elektro
Professor Martin Berggren, Umeå University (Sweden),
Professor Jean-Philippe Groby, Le Mans Université (France)

Associate Professor Cheol-Ho Jeong, DTU Elektro

Computer-based simulation and optimization tools can provide engineers with valuable
insight into the behaviour of acoustic devices. These tools can also reduce the need for
expensive prototypes, which are often rebuilt in multiple iterations of manufacturing and
experimental validation.
Microphones and loudspeakers are acoustic transducers. The general trend is to reduce
their size as much as possible so they can fit inside, for example, smartphones and hearing
aids. As the size is reduced, sound waves inside such devices are modified in their
propagation by acoustic losses, which are explained by the viscosity of air and the heat
exchange with the device material. Including these effects into simulations with traditional
methods comes at a significant computational cost, which in turn makes simulation and
optimization of these small devices very challenging.
The Boundary Element Method (BEM) and the more extended Finite Element Method (FEM) are numerical tools that allow the study of physical setups through computer models.
Both methods have the possibility of including acoustic losses, at the cost of a higher
computational load. The BEM with acoustic losses can be advantageous in some
particularly demanding cases, but it has some potential shortcomings that can lead to
undesirable inaccuracies.
This PhD project investigates and improves on the existing BEM with acoustic losses by
using two new mathematical coupling strategies that circumvent the mentioned weakness
of the method. The new coupling strategies are evaluated and tested through several test
cases, showing increased stability and reduced errors.
Based on this improved BEM, a shape optimization technique is developed. In shape
optimization, the computer calculates and progressively modifies an acoustic setup,
following a set of criteria previously defined by the user. The new shape optimization
technique using BEM with acoustic losses is among the first to include acoustic viscous and
thermal effects in the optimization process. It has a potential for the efficient design and
improvement small acoustic devices, which is demonstrated in this PhD project using
several examples.