Piezoelectric transducer

I am going to model langevin piezoelectric transducer in comsol 4.3b.I have following questions in my mind:

1.How to calculate resonance frequency of the whole transducer and resonance frequency of individual components like piezoelectric rings,front and back sections ?

2.Which study should be used to calculate resonance frequency?

3.Which displacement should be meant correct the one which is obtained from eigen frequency study or frequency domain?

4.How to calculate impedance?

5.Which physics should be used in modeling of pzd transducer?

Thanks