Wearable antennas for body-centric wireless communications

Abstract

In recent years, a study on body-centric wireless communications has become an active and attractive area of research because of their various applications such as e-healthcare, support systems for specialized occupations, personal communications, and so on. Whereas UHF bands are subjects of interest especially in Europe and USA, relatively low frequency bands below several megahertz are of great interest especially in Japan. Hence, all of the prospective frequencies are in an extremely wide range, and an objective idea on how to select a right frequency band for individual applications is required. Currently in our laboratory, we have been studying on frequency dependence of basic characteristics of wearable antennas as well as body-centric wireless communication channels in the range of HF to UHF (3 MHz-3 GHz). There are experimental, analytical, and numerical ways to clarify the basic characteristics of the antennas and communication channels. In experiments, we have to ensure impedance matching at certain frequency points because of sensitivity limitations; therefore, it is hard to obtain such broadband characteristics. Theoretical analysis is useful to understand physical mechanism; however, complex geometry and motion of the human body cannot be modeled. By contrast to them, numerical simulation can solve complex problems with relative ease. For example, Hall et al. have shown that the dynamics of the human body can be modeled by dividing the motion into several frames, and the simulated results agree with the measured results. Also in our study, observations of channel characteristics are conducted by employing numerical simulations. In this paper, firstly, electric field distributions around the human body wearing a small top-loaded monopole antenna are numerically calculated and compared in a wide range of HF to UHF bands. Then, received open voltages at receiving antennas which are equipped at several different points on the human body are numerically investigated. The received open voltages are also numerically calculated and compared with several different postures of the human body. Statistic characterization and experimental validation will be necessary in further studies.