Application of the reciprocity theorem to volume conduction based data communication systems between implantable devices and computers

There have been increasing needs for a wireless two-way information channel between computers and microdevices implanted within the human body. It has been demonstrated that this channel can be established based on the volume conduction property of the biological tissue. This paper presents a fundamental property of the volume conduction channel. By applying the reciprocity theorem to this channel, we show that it is a symmetric channel, i.e., the sensitivity of signal transmission is independent of the direction of information flow. We discuss several important factors in actual data communication systems that produce discrepancies from the assumptions of the reciprocity theorem. We also present experimental results based on a physically constructed volume conduction model. The reciprocity property demonstrated in this paper provides theoretical guidelines for the design of volume conduction based, energy-efficient data communication modules for various implantable devices.