Build-in electronics to control lens aperture.
The lens aperture is set by the controls on the MFT camera/camcorder body e.g. GH4.
Powered by camera body. no external power source required. (also accept 3rd party external power supply via MicroUSB socket)

Do refer to this site for compatibility specifications:

http://www.metabones.com/products/details/MB_EF-m43-BM1