Piezoelectric resonator with clamped edges

Dear all,

I try to solve the next problem in COMSOL 5.2:

1. Brass beam with thin AlN film - flexural mode resonator
2. Electrical BC Ground and Terminal applied to electrodes area on top surface (no electrodes in model, only area)
3. Mechanical BC Fixed constrained applied to beam short opposite edges.

A first solution is eigenfrequency, its OK. I find the second harmonica at about 7 kHz.
Second solution is frequency domain. I want to excite the beam electricaly at second harmonics.
During the solution, close to resonance frequency, the error is appeared: the solution is not convergent. I suppose this error due to the fixed BC. I tried reduce the relative tolerance, but I had very weak resonance response which suppressed by edge fixing. I tried to apply moving mesh, but no result.

Help me please, what the mistake in my model?? I attached the model here.


Best,

Vladimir