On-Body Antennas and Propagation: Recent Development

There have been growing interests in body-centric wireless communications [1] due to their abundance applications, for example, in personal healthcare, smart home, personal entertainment and identification systems, space exploration and military etc. A generic concept of body-centric wireless communications may include scenarios which RF sensor nodes are placed in/on body. Antennas and propagation is the central part of body-centric wireless systems and plays an important role in the implementation of miniaturised, spectrum and power efficient RF sensor nodes and the integrity of in/on/off body communications. Of the aforementioned aspects, on-body antennas and propagation has its distinct properties due to the presence of human body. It has been found [2] that wearable antennas can suffer from reduced efficiency, radiation pattern fragmentation and variations in impedance at the feed. For on-body radio channels, main features such as shadowing effects, dynamic variation in path loss and time delay components make it different to characterise the channel behaviour. Previous studies [3, 4] demonstrated preliminary measurement results based on classic antennas such as microstrip patch, monopole, wideband bowtie etc. It is noted that the on-body radio propagation is predominantly based on space waves, creeping waves and a combination of both. In this paper, we shall present recent development in on-body antennas and propagation research, specifically, the analysis of antenna diversity for on-body communication systems; the investigation of interference between two body-centric wireless networks at 2.45GHz and 5.8GHz; the design of small antennas within ISM frequency bands for wireless wearable sensors and their on-body performance evaluation. Numerical and system modelling are essential for understanding and optimising on-body communications. Further to [4, 5], a dynamic on-body channel modelling tool has been developed to enable the description of dynamic events and ultimately characterised the on-body channel statistically.