Enhanced absorption in structural acoustic silencers using piezo-shunting

Structural acoustic silencers (sas) consist of a thin flexible plate that is introduced into a wall of an otherwise rigid-walled duct in which acoustic noise is propagating. Transmission loss (TL) in sas arises from reflection due to impedance mismatch, as well as partial absorption due to material damping in the plate. Reflection-based TL is less preferable than absorption-based TL, especially where back-pressure is undesirable. In this study, the TL arising out of absorption is increased by increasing the effective plate damping using the piezo-shunting method. Experiments are conducted on a custom-made sas with copper sheets of two different thicknesses. Piezo-shunting to increase the damping of the copper plate is done by connecting an electrical resistor to the external circuit of a thin piezoelectric bimorph attached to the copper plate. The effect of piezo-shunting on the sas TL is analyzed using a model. Piezo-shunt increases the fraction of power absorbed and decreases the reflected power fraction. The dependency of these fractions on the value of the electrical resistor and the impedance of the plate are discussed. This study demonstrates that piezo-shunting can be used to improve absorption-based TL in sas.