Damping of the piezoelectric material

Hi,

In my numerical model involving piezoelectric transducers vibrating under the influence of fluid flow, I want to include piezoelectric damping effect. Based on the related literature, I could understand the piezoelectric damping to be of three types- mechanical damping (Rayleigh damping), Dielectric loss and Coupling loss. I can see two different options in COMSOL- 

1) Under material properties of piezoelectric material, I can add loss factor of coupling matrix, loss factor of elasticity matrix and loss factor of electrical permittivity matrix.

2) Under solid mechanics tab, I can add mechanical damping, coupling loss and dielectric loss. 

Could someone explain me the difference in between these two options if there is any, and what is the right way of adding the damping effect to the system? What is the method of calculating alpha and beta coefficients of Rayleigh damping using numerical approach?  I appreciate your help. 

Thanks,

-Sajiree