A cavity-backed annular slot antenna designed for the use in smartwatches in the 2.4-GHz Wi-Fi band is proposed. The cavity is metallic and has a cylindrical shape with a volume of π ×21 2 × 10 mm 3 . An annular slot is cut along the edge of the top surface (as the smartwatch screen) of the cavity. The circumference of the annular slot is about 1λ, making the design small enough for the smartwatch applications. The resonant modes, current distribution, and transverse mode of the cavity-backed annular slot antenna are studied using simulations and the results are used to design a smartwatch antenna. The proposed smartwatch is studied in free space, on a computer hand model, and on a phantom hand using simulations and measurements. Measured results show that the antenna has an efficiency of 57%-66% on a phantom hand. To study the antenna in a more realistic environment, the electronic components inside the smartwatch are modeled as a metallic block. For health risk concerns related to exposure to an electromagnetic radiation, the specific absorption rate for the smartwatch in the wrist-worn and next-to-mouth conditions is also studied using simulations.
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Wu et al. (2017) studied this question.
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