What is Harvesting Efficiency

In ambient energy harvesting applications, metamaterials and metasurfaces are useful in localizing and absorbing energy from the surroundings. This chapter reviews past achievements, recent developments and future trends in metamaterial-based radio-frequency (RF) energy harvesters. The chapter begins by introducing metamaterial energy harvesters from a general perspective, covering mechanical, acoustic, and electromagnetic metamaterial energy harvesters. The subsequent section focuses specifically on the working principle of electromagnetic metamaterial energy harvesters in the RF regime. To enhance understanding of the absorption mechanism and performance evaluation, a simulation of an Omega-ring-shaped metamaterial harvester operating at a frequency of 5.8 GHz is demonstrated. The absorption efficiency, harvesting efficiency, and conversion efficiency of the metamaterial harvester are determined and discussed. Furthermore, the state-of-the-art design of metamaterial RF harvesters and their respective performance are reviewed.