  In order to improve low-frequency characteristics of micro-perforated panel
absorbers, sound absorption structures composed of micro-perforated panels and
expansion chambers are design, and an optimization design method is constructed
based on the transfer function model and the simulated annealing algorithm.
First, a single-chamber structure composed of a micro-perforated panel and an
expansion chamber is build, and the sound absorption curve is simulated by the
finite element method. Second, for the sake of enlarging the continuous
absorption bandwidth with absorption coefficients not less than 0.8, a
three-chamber structure is designed, which has a sound absorption bandwidth of
1277Hz (27-1304Hz) covering 5.6 octave bands. Then, the transfer function model
of the structure is established, and a series of theoretical formulae are
derived to calculate the absorption coefficients. Subsequently, the sound
absorption bandwidths calculated by the theoretical formulae and the finite
element method are compared, and the relative error is 3.68%. Finally, an
optimization design method is constructed by combining the transfer function
model and the simulated annealing algorithm, where the optimization objective
is to maximize the absorption bandwidth and the optimization variables are
structural parameters of the three-chamber structure. The results show, after
optimization, the three-chamber structure exhibits an excellent sound
absorption performance, with a continuous bandwidth of 1591Hz (4-1595Hz),
realizing 8.6 octave bands.
