Professor Antonio Tadeu from the University of Coimbra in Portugal recently visited the Wessex Institute and gave a lecture on "The Acoustic Insulation Provided by Single and Double Panels". The presentation concentrated on developing an analytical model. The study of the sound transmission mechanism has proved to be increasingly important in modern life and is related to the comfort of every day working and living environments.

Antonio is an Associate Professor at his University. He received a PhD at MIT and is well known in the field of Computational Modelling in Engineering and Sciences. He has participated in many WIT conferences, including being Co-Chairman of the World Conferences on BEM 23 which took place in Sintra.

He is author of a book published by WIT Press and co-authored by Eduardo Kausel of MIT, another of WIT's collaborators. Both researchers are renowned for their work on earthquake engineering and dynamics. Antonio is a member of the Editorial Board of the International Journal of Engineering Analysis with Boundary Elements (EABE).

The presentation focused on developing a way of solving the Helmholtz equation using sources. The solution is complicated by the presence of lawyer media assumed to extend to infinity. The effect of the lawyers is represented by modifications to the classical fundamental solution.

In practice, the procedure to represent the transmission of pressure waves requires the consideration of the fluid medium and the solid layers which are assumed to extend to infinity. Internal losses are modelled by using a complex Young's module. Once the computations are performed in the frequency domain, the response in the time domain can be found by applying an inverse Fourier transform.

Antonio presented some interesting examples for single and double wall configurations, which were displayed using advanced visualisation techniques. The cases discussed showed the interaction of the incident field with reflected waves.

The case of double walls, ie those with a cavity in between two solid walls is particularly interesting. In this application, there are a series of resonance frequencies corresponding to the solid walls on their own, the cavity and the whole assembly. Antonio's results also show how the solution is affected when introducing some insulation material between the two solid walls.

Comparison of the reduction of the sound pressure level obtained by double walls with that generated by a single wall with the same global mass demonstrated the substantial improvement that can be obtained using double walls.

Antonio also compared his analytical solutions with laboratory experiments. They consisted of tests for single and double glass specimens. Reasonable agreement was found in spite of some localised excitations due to the limitations of the model and the difficulty of modelling low frequencies.

The models presented by Antonio can be used to study different types of structures in fluids as well, but for more complex geometries, the solution needs to be generalised, using boundary elements.