Prolonging the Lifetime of Wireless Sensor Networks: A Review of Current Techniques

Table 2

Wireless power transfer technologies [8].

Wireless Power Transfer Technologies		Strengths	Weakness	Examples
Inductive Coupling		Simple, high power transfer efficiency in centimeters	Short Charging distance, requiring accurate alignment in charging direction.	Electric toothbrush, charging pad for cell phones and laptops.
Electromagnetic	Omnidirectional	Tiny receiver size	Rapid drop of power transfer efficiency over distances, ultra-low-power reception	Charging WSN for environmental monitoring (temperature, moisture, light)
	Unidirectional	Effective power transmission over long distances	Requiring LOS and complicated tracking mechanisms.	Sharp unmanned plane
Magnetic Resonant Coupling		High efficiency over several meters under omnidirection. Not requiring LOS and insensitive to weather conditions	High Efficiency only within several meters	Charging mobile devices, electric vehicles, implantable devices and WSNs.