Energy Harvesting for Active RF Sensors and ID Tags

This chapter highlights the importance and significance of energy harvesting in applications involving use of active RF sensors and ID tags. The chapter begins by providing a basic overview on radio frequency identification (RFID) operation, various types of RFID tags, and the need for energy harvesting, especially for active RFID tags. Unlike passive tags, active tags utilize a battery to emit rather than reflect or backscatter RF energy. Advantages of active tags include improved range and read rate in electromagnetically unfriendly environments and improved link quality. Typical applications include monitoring enterprise/supply chain assets (e.g. laptops, computers, peripherals, electronic equipment, pallets, inventory items, etc.), personnel, patients, vehicles, and containers. Although a battery can substantially improve performance, it limits maintenance-free operational life. Therefore, harvesting energy from sources such as vibration or light has been shown to address this shortcoming but these sources must be adequate, available throughout the life of the application, and highly efficient. These available energy harvesting technologies are described, and basic design procedures and components for such systems are identified. This includes three key components namely, the energy harvesting transducer, power management circuit, and energy storage device. Each component of the energy harvesting system is described and important design criteria are highlighted. Specific emphasis is placed on the design of the power management component and the available energy storage device technologies. Disadvantages of using off-the-shelf DC-DC converters and rectifiers are emphasized and possible power management solutions for solar and vibrational energy harvesting are explained. Finally, the chapter concludes by describing the future directions and scope including development of integrated multiple source energy harvesting systems on thin-film substrates.