EVAL AD5933 EBZ

Dear Sirs,

I am using the EVAL AD5933 EBZ evaluation board with resonance PZT sensors.  I am having a problem with the resonance part in the graph as it is flattening.  Please find the graph as an example.

Can you kindly tell me why and how can eliminate this problem?

I thank you in advance.

Best regards,

Niki