A Study on Antenna Design for Wearable Information Terminals

随着电子技术的飞速发展，信息终端和计算机正在从移动的向可穿戴的方向发展。开发可穿戴信息终端的关键点之一是如何将其装备到人体中，同时天线性能的劣化较小，并且人体内的电磁能量吸收（SAR：Specific Absorption Rate）较低。在这项研究中，我们首先开发了一个新的模块的基础上，商业上可用的计算机人体模型软件创建一个任何姿势的人与移动的或可穿戴的无线终端。人类的体型是基于日本成年男性的平均水平。利用这个新模块，我们创建了一些数值人体模型与这些终端的典型用途，然后使用子网格时域有限差分（FDTD）算法计算的天线性能和SAR。对于位于头部一侧的天线，我们发现人体躯干对天线辐射方向图和峰值SAR的影响微不足道。一个孤立的头部模型是足够的设计这些类型的天线。另一方面，对于安装在诸如膝上型PC或PDA设备的无线终端的一侧中的天线，我们已经发现身体效应主要阻挡朝向身体侧的高达20 dB的辐射，并且设备上的操作手主要阻挡朝向与头部成角度的方向的高达10 dB的辐射。高SAR出现在手中，因此由于阻挡效应，头部的SAR显著降低。作为可穿戴终端的设计中的准则，从具有稳定的辐射性能的观点来看，在手附近装备天线不是好的选择。在大多数情况下，躯干应该是一个更好的候选人。本研究的主要结果已发表在IEEE和IEICE等参考期刊上。

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.