I am not an expert but the first think I would try is a serial connection of the pizoeletric generators

Article Determination of the appropriate piezoelectric materials for...

https://www.sciencedirect.com/search?qs=voltage%20and%20current%20rate%20efficiency%20for%20piezoelectric%20crystal&show=25&sortBy=relevance

The selection of the appropriate piezoelectric material is of fundamental importance. PZT and KNN are probably the best, but many other materials can also be used. With the piezo material chosen, the piezo layer thickness, the shape of the capacitors and the method of stress generation in the piezo layer should be chosen accordingly. Serial connection of piezo capacitors allows to multiply the maximum voltage generated by the harvester. Increasing the current is possible by using piezo capacitors with a larger surface area.

Jerzy Zajac Thanks for your kind suggestion sir. could you suggest me any simulation software for piezoelectric materials please?

Dear Sayed,

I am very interested to the topic. A partial answer is given in

Article Propagation and filtering of elastic and electromagnetic wav...

where the authors show that a layered bi-material structure made of piezoelectric components may have a very high elastic-to-electromagnetic energy conversion ratio (see Fig. 8). I hope that this is of your interest.

Best wishes,

Domenico

Thanks Sir Domenico Tallarico for your attachment and suggestion, I wish that will help me to figure this out. let me study and will give you feedback,

Best regards,

Sayed Bin Osman