Author(s): Herrero-Durá Iván, Picó Rubén, Sánchez-Morcillo Víctor José, Garcia-Raffi Lluís Miquel, Romero-García Vicente
Flexural waves are the main type of waves propagating in thin plates and play a relevant role in the field of noise and vibration. In this work, the study of the conditions for the absorption of sound due to flexural resonances is reported. Two systems composed of thin clamped aluminum square plates with an absorptive layer in contact are studied: (i) a plate backed by an air cavity ended by a rigid wall, and (ii) a plate in contact with an absorptive layer. Absorption in both systems is studied analytically and numerically by using the transfer matrix method and considering viscoelastic and viscothermal losses in the waveguide and in the plate, respectively. The Ross-Kerwin-Ungar (RKU) model is used to model the absorptive layer. For the case of the reflection problem (rigidly backed system), the analysis of the reflection coefficient in the complex frequency plane is used to identify the zeros and poles of this coefficient and to tune the overall losses of the system in order to establish the conditions for achieving critical coupling and, thus, perfect sound absorption. For the case of the transmission problem, the system is not rigidly backed, and losses are increased by adding an absorptive layer in contact with the plate, creating a composite that is analyzed as a single layer with effective properties.
Name: Mr Iván Herrero-Durá