Add to ORKG"RF Energy Harvesting and Transport for Wireless Autonomous Sensor Network Applications: Principles and Requirements" - For wireless energy transfer over longer distances, the far-field transfer of RF energy may be used. We make a distinction between harvesting RF energy from signals present in the ambient and transferring RF energy by intentionally transmitting RF signals. After a discussion of the power densities, we will continue with (intentionally) RF energy transfer for powering sensors to be used in Smart Buildings. The blocks of a far field RF energy transfer system will be discussed: Transmit antenna (and maximum allowed transmit power), propagation channel and rectifying antenna or rectenna. The components of the rectenna: rectifi...