Smartwatch low-SAR approach based on antenna integrated with metamaterial protection layer

The design of smartwatch antennas confronts two challenges. The forward problem is related to how to reduce the performance degradation caused by the arm effect, while the inverse problem involves how to diminish the electromagnetic exposure of the antenna to the human body, especially for children who are sensitive to radiation. This paper presents a smartwatch antenna featuring a metamaterial protection layer, which satisfies the requirements of 4 G communication and Wi-Fi. The smartwatch antenna loaded with the metamaterial layer is fabricated. The electromagnetic exposure dose is simulated, and the reflection coefficient of the antenna is measured when it is worn on the arms of adults and children, respectively. Simulation and measurement results demonstrate that the addition of the metamaterial layer can alleviate the frequency shift; the bandwidth is improved by 8.8%, and the gain is enhanced by 7.8% at most. Furthermore, the peak specific absorption rate (SAR) values in the arms of children and adults decrease by up to 6% and 14%, respectively, conforming to the safety limits stipulated by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. The findings indicate that the proposed metamaterial layer with reflective performance can mitigate the reduction in radiation performance caused by the arm and concurrently minimize the radiation dose absorbed by the arm. This presents a viable strategy for electromagnetic radiation protection.