Band structure and sound transmission loss of infinite periodic partitions: Numerical studies with COMSOL

Since the implementation of Bloch boundary conditions the COMSOL software can be used for studying the dynamics of infinite periodic media, in particular Bloch waves and their dispersion (band structure). COMSOL can be applied also for the calculation of the transmission loss of infinite partitions which are periodic in one or two dimensions. It is shown how this can be accomplished in principle. Two partition examples illustrate the approach: (i) a sinusoidally corrugated plate (""Wellblech"") and (ii) a metamaterial-like double-leaf partition. Understanding the transmission loss curves is - at least for light adjacent fluids - facilitated by entering the trace wave (""Spurwelle"") of an incident plane wave in the band structure of the Bloch waves of the partition in vacuum. Like with homogeneous partitions, coincidence effects may occur. Which Bloch waves are excited most by an incident wave at a particular frequency can be inferred from a comparison of the shape of the ""transmission wave"" with the shapes of Bloch waves with appropriate wave vector.