In human body communication (HBC) systems, radio-frequency signals are excited in the human body through a wearable antenna comprised of electrodes that are in contact with the surface of the body. The input impedance characteristics of these antennas are important design parameters for increasing transmission efficiency and reducing signal reflection, similar to other wireless circuits. In this study, we discuss variations of input impedance characteristics of a wearable antenna prototype caused by differences among real human subjects. A realistic human arm model is used for simulations, and the analytical results obtained are compared to measured data obtained from real human subjects, in a range from 1 to 100 MHz. The simulations of input impedance characteristics from antennas worn on the wrists of male and female models with dry and wet skin conditions show that the impedance variation between genders is small. The moisture condition of the skin has little influence on frequencies exceeding several MHz. Measurements with a proto-type wearable antenna and 22 real human subjects reveal that HBC is robust against the variations of individual users from the viewpoint of the voltage standing wave ratio. Moreover, a simplified rectangular prism model is proposed to analyze the thickness of body tissues. Comparisons of measured input impedances indicate that individual differences in impedance are mainly due to differences in the thickness of skin and fat layers. The model also enables us to design the antenna prototype without multiple subject experiments.

中文翻译：

---

穿戴式天线的输入阻抗分析和实际人体实验研究：各个用户之间的差异

在人体通信（HBC）系统中，射频信号是通过可穿戴天线在人体中激发的，该天线由与人体表面接触的电极组成。与其他无线电路类似，这些天线的输入阻抗特性是提高传输效率和减少信号反射的重要设计参数。在这项研究中，我们讨论了由真实人类受试者之间的差异引起的可穿戴天线原型输入阻抗特性的变化。使用逼真的人体手臂模型进行仿真，并将获得的分析结果与从真实人体对象获得的测量数据（范围为1至100 MHz）进行比较。在干燥和潮湿皮肤条件下，男性和女性模型的手腕上佩戴的天线的输入阻抗特性的仿真表明，性别之间的阻抗变化很小。皮肤的水分状况对超过几兆赫兹的频率影响很小。使用原型可穿戴天线和22位真实人体进行的测量表明，从电压驻波比的角度来看，HBC可以抵抗单个用户的变化。此外，提出了一种简化的矩形棱柱模型来分析人体组织的厚度。对测量的输入阻抗的比较表明，阻抗的个体差异主要是由于皮肤和脂肪层厚度的差异所致。该模型还使我们能够设计天线原型，而无需进行多个主题实验。