ABSTRACT
Radiofrequency (RF) and mechanical energy transducers generate an alternating (ac) voltage and current that is proportional to the available power in the environment. This chapter describes two important ac energies (RF and mechanical) and the most used energy harvesting circuits. An RF transducer (antenna) can be modeled as a voltage ac source in series with an output impedance. Antenna shapes and dimensions vary widely, and several distinct antenna designs have been employed in RF and radiofrequency identification (RFID) harvesting applications. The chapter discusses different extraction circuits for piezoelectric energy harvesters. There are two main types of circuits that inject charge to the piezoelectric element: synchronous, switched harvesting with inductor, and prebias circuits. The trend in energy harvesters is to integrate several energy conditioning circuits into the same chip in order to extract energy from multiple energy sources.
