A Study on Antenna Design for Wearable Information Terminals

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With the rapid progress of electronics, information terminals and computers are being unified and changed from mobile ones to wearable ones. One of the key points in developing a wearable information terminal is how to equip it into human body with less degradation of antenna performance and low electromagnetic energy absorption (SAR:Specific Absorption Rate) inside the human body. In this study, we first developed a new module based on a commercially available computer mannequin software for creating an any posture of a human with a mobile or wearable wireless terminal. The human's bodily shape was based on averaged Japanese adult males. With this new module we created some numerical human models with typical usage of these terminals, and then calculated the antenna performance and SAR using a sub-grid finite difference time domain (FDTD) algorithm. For an antenna at one side of the human head, we have found an insignificant effect of the human torso on both the antenna radiation pattern and the peak SAR. An isolated head model is sufficient for the design of these typed antennas. On the other hand, for an antenna mounted in one side of a wireless terminal such as a laptop PC or PDA device, we have found that the body effect is mainly blocking the radiation up to 20 dB towards the body side, and the operating hands on the device are mainly blocking the radiation up to 10 dB towards the direction at an angle to the head. High SARs appear in the hands and therefore yield a significant SAR reduction in the head due to the blocking effect. As a guideline in the design of wearable terminals, equipping an antenna near the hand is not a good choice from the point of view of having a steady radiation performance. The torso should be a better candidate in most cases. The main results of this study have been published on referred journals such as IEEE and IEICE.