Piezoelectric generator 

For  n = 1  , Frequency  = 1.42  MHz
For  n = 2  , Frequency  = 2.84  MHz
For  n = 3  , Frequency  = 4.26  MHz
Magnetostriction generator

For  n = 1  , Frequency  = 48.9  kHz
For  n = 2  , Frequency  = 97.7  kHz
For  n = 3  , Frequency  = 146.6  kHz