The Internet of Things (IoT) has a great number of sensor nodes distributed in different environments, and the traditional approach uses batteries to power these nodes: however, the resultant huge cost of battery replacement means that the battery-powered approach is not the optimal solution. Micro energy harvesting offers the possibility of self-powered sensor nodes. This paper provides an overview of energy harvesting technology, and describes the methods for extracting energy from various sources, including photovoltaic, thermoelectric, piezoelectric, and RF; in addition, the characteristics of the four types of energy sources and the applicable circuit structures are summarized. This paper gives the pros and cons of the circuits, and future directions. The design challenges are the efficiency and size of the circuit. MPPT, as an important method of improving the system efficiency, is also highlighted and compared.

A low-power dual-mode receiver is presented for ultra-high-frequency (UHF) radio frequency identification (RFID) systems. The reconfigurable architecture of the tag is proposed to be compatible with low-power and high-sensitivity operating modes. The read range of RFID system and the lifetime of the tag are increased by photovoltaic, thermoelectric and RF energy-harvesting topology. The receiver is implemented in a 0.18-μm standard CMOS process and occupies an active area of 0.65 mm × 0.7 mm. For low-power mode, the tag is powered by the rectifier and the sensitivity is −18 dBm. For high-sensitivity mode, the maximum PCE of the fully on-chip energy harvester is 46.5% with over 1-μW output power and the sensitivity is −40 dBm with 880 nW power consumption under the supply voltage of 0.8 V.

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