Abstract
Passing through the transformation of wood to coal then to oil and gas, we find ourselves fortunate to witness the next major transformation, which will lead us to the "New Energy Era." Due to advancements in the field of electronics, energy harvesting has attracted great attraction from researchers and scientists to enhance portability and reliability with reduction in battery wastes. Moreover, wearable electronic devices are also becoming quite popular these days because of their usage in a broad range of applications like sports, health sciences, emergency, and so forth. In order to make sure smooth operation and to increase the working time span of these devices, it has become really important to bring wearable devices and radio frequency (RF) energy harvesting to the same platform. RF energy harvesting is one of the best suitable technology for wearable devices. The abundance of RF energy in surroundings and the ability of RF signal to penetrate buildings play an important role to empower wearable devices. One of the major challenges is to improve power conversion efficiency of wearable rectenna for energy harvesting due to requirements of less efficient bio-compatible materials for such antennas with conformability issues. This article mainly aims to present different wearable rectenna design techniques, reported over the years. It also presents a tabular comparison of rectenna performance in terms of power conversion efficiency and gains for diverse frequency bands, substrate materials, and conducting materials. In addition, this article also includes the challenges and obstacles in designing an efficient RF energy harvesting rectenna for wearable devices.