Thanks for the link Sabastien
dump the full bridge rectifier for two half bridges.
1) efficiency may double at these low voltages!
2) the common mode noise voltage created by a full bridge currupts the analog front end, getting worse with miniturization due to proximity of the power conversion
Piezo and electrostatic principles are applied for energy harvesting. Piezo will be able to generate more power at least 10 times more than the electrostatic device.Also piezo will have more life time than the other one.