Wireless power transfer (WPT) is thetransmission of electrical power from a power source to a consuming devicewithout using manmade conductors. For long distance transmission without using wiresresearchers have developed several techniques for moving electricity. There aresome exists only as theories or prototypes but others are already in use. Thispaper provides the techniques used for wireless power transmission.
It is ageneric term that refers to a number of different power transmissiontechnologies that use time varying electromagnetic fields. Wireless transmission is useful topower electrical devices in case where interconnecting wires are inconvenient,hazardous, or are not possible. For example the life of WSN is its node whichconsist of several device controllers, memory, sensors, actuators, transceiversand battery and battery. The transceiver can operate in four states, i.e 1)Transmit 2) Receive 3) Idle and 4) Sleep. The major energy problem of atransmitter of a node is its receiving in idle state, as in this state it isalways being ready to receive, consuming great amount of power.
However, the batter has a very short lifetimeand moreover in some developments owing to both practically and economicallyinfeasible or may involve significant resists to human life. That is why energyharvesting for WSN in replacement of battery is the only and unique solution.In wireless power transfer, a transmitter device source, such as the mainspower line, transmits power by electromagnetic fields across an interveningspace to one or more receiver devices, where it is converted to electric power and then utilized.The goalof the communication is the transmissionof information, so the amount of power reaching the receiving antenna isunimportant till signal to noise ratiois high enough so that the information can be received intelligibly. In wirelesscommunication technologies, generally, only little amounts of power reach thereceiver.
By contrast the amount of power received is the important thing, sothe efficiency (fraction of transmitted power that is received) is the moresignificant parameter.