Recent simulation techniques of viscous and thermal losses of sound waves in fluids and their applications in the micro-scale

In classical acoustics small devices in the scale of micrometers such as transducers, couplers or hearing aids are designed by adjusting lumped parameter models through experience and experimentation. In the last 15 years or so, new numerical tools based on the Finite Element Method (FEM) and the Boundary Element Method (BEM) have been developed that can describe sound fields with viscous and thermal losses. Creating numerical models of the acoustics of small devices is now possible, including not only losses, but also mechanical interaction and other effects. This new insight allows a better understanding of the acoustic phenomena in small structures and can lead to new designs that would have been difficult or impossible otherwise. This paper gives an overview of numerical tools applied to acoustic viscous and thermal losses, their advantages and shortcomings. Examples are included showing the performance of these tools. These issues, along with comments about possible future developments are brought up for discussion.