1 University School of Automation and Robotics, Guru Gobind Singh Indraprastha University, East Delhi Campus, Delhi, India.
2 Department of Electronics and Communication Engineering, National Institute of Technology Silchar, Silchar, India.
3 Department of Electronics and Communication Engineering, Galgotias College of Engineering and Technology, Greater Noida, Uttar Pradesh, India. gupta.sachin0708@gmail.com.
4 Department of Electronics and Communication Engineering, Dr. B. R. Ambedkar National Institute of Technology Jalandhar, Jalandhar, India.
5 School of Electronic and Electrical Engineering, Kyungpook National University, Daegu, Republic of Korea.
6 School of Electronic and Electrical Engineering, Kyungpook National University, Daegu, Republic of Korea. kang_kim@ee.knu.ac.kr.
7 Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Canada.
8 Department of Electrical and Computer Engineering, California State University, Northridge, CA, USA.
9 Department of Electrical and Computer Engineering, Concordia University, Montreal, Canada.

This paper proposes a circularly polarized ultra-thin flexible antenna with a flexible rectifier and power management unit (PMU) for smartwatch/wristband applications. The flexible antenna is compact (0.17?₀ × 0.20?₀ × 0.0004?₀) and has a stepped ground plane. A parasitic element is used at the substrate bottom to reduce the specific absorption rate (SAR) and enhance the gain up to 3.2 dBi, at the resonating frequency of WLAN/Wi-Fi (2.45 GHz). The SAR of the proposed design is also analysed at the resonating frequency, and it satisfies the guidelines of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and IEEE C95.1-2019 human safety standards. An impedance matching circuit is used between the antenna and the RF energy harvester to improve conversion efficiency. Polarization mismatch is avoided with the help of circular polarization, achieved by tuning stubs of size 0.02?₀ × 0.044?₀. The integration of the antenna and rectenna results in a good conversion efficiency of 78.2% at - 5 dBm of input power with a load resistance of 2 KO. The availability of RF signals allows the user to charge the smartwatch/wristband by connecting the PMU circuit with the RF energy harvester.