Abstract
The impedance characteristics of the electrode structures on wearable transmitters for body-centric networks were analyzed using a TLM (Transmission Line Matrix) method and were compared with experimental results. The input impedance between the two electrodes can be evaluated using a human arm model; it varies proportionally to the distance between the electrodes and inverse proportionally to the lengths and widths of the electrodes. Approximation formulas of these characteristics were derived and used to design a pair of electrodes to fit in the back of a wrist watch (approximately 30 mm by 30 mm). The optimum size and arrangement of electrodes to match a 50 Ω transmission line was a pair of 11.2 mm by 30 mm rectangular electrodes separated by a distance of 7.6 mm. Transformers or stubs were not necessary. This electrode size and arrangement enhances transmission efficiency by 2 dB to 12 dB compared to other electrode sizes and arrangements.
