As shown in the previous chapters the general solution for the acoustic pressure can be written as

with

for the classical solution, and

for the Gaussian beam approximation. Either expression does not take into account the dissipation of energy due to material absorption, and due to the transfer of energy every time the acoustic wave bounces on a boundary. Such dissipation is frequency-dependent (and more relevant as frequency increases), and implies using a corrected amplitude , which corresponds to the original amplitude, multiplied by two decaying factors and :

where and stand, respectively, for the decay due to boundary reflections, and due to volume absorption. Both factors are described in the following sections.

Orlando Camargo Rodríguez 2012-06-21