I have been trying to model a multi-layer simulation for analysing the vibro-acoustic propagation in multi-layered strutures.

The multiple layers are different in terms of their elasticity and density.

I define all the layers as different acoustic bodies with mass densities and speed of sound.

Additionally, I also define Impedance boundaries at the interfaces of two layers with an acoustic impedance for each interface.

The FSI are defined for all the layer interfaces and the outer layer face in contact with air (which is defined as a big spherical body with properties of air)

My question is: How do I define a harmonic source on the outermost layer to produce SPLs in the inner layers? My objective is to apply a vibration at the outermost surface and measure the SPL on some other region on that outermost surface as an indicative of the acoustic properties of all the layers.

I have been trying to do that by using Normal Surface velocity but it doesnt work. I need the results in terms of frequency response of total  deformation and Acoustic SPL distribution at the defined frequency sweep in the analysis settings.