Harvest energy using a piezoelectric buzzer
From ElectronicsWeekly.com, here is an article on producing electricity from vibrations such as body movement:
Thanks to the decreasing size and low-power requirements of today’s wearable devices, it is feasible to replace batteries in some low-power systems with power generators that capture energy from the user’s environment, such as the vibration energy a user produces during walking or running. This Design Idea uses the piezoelectric effect of a standard and easy-to-find piezoelectric buzzer to turn mechanical vibrations into electrical energy.Tweet
