  Energy harvesting for wireless communication networks is a new paradigm that
allows terminals to recharge their batteries from external energy sources in
the surrounding environment. A promising energy harvesting technology is
wireless power transfer where terminals harvest energy from electromagnetic
radiation. Thereby, the energy may be harvested opportunistically from ambient
electromagnetic sources or from sources that intentionally transmit
electromagnetic energy for energy harvesting purposes. A particularly
interesting and challenging scenario arises when sources perform simultaneous
wireless information and power transfer (SWIPT), as strong signals not only
increase power transfer but also interference. This paper provides an overview
of SWIPT systems with a particular focus on the hardware realization of
rectenna circuits and practical techniques that achieve SWIPT in the domains of
time, power, antennas, and space. The paper also discusses the benefits of a
potential integration of SWIPT technologies in modern communication networks in
the context of resource allocation and cooperative cognitive radio networks.
