Capacitive-Coupling-Based Information Transmission System for Implantable Devices: Investigation of Transmission Mechanism

Many medical electronic devices that can be implanted deep inside the body have been developed recently. These devices are designed to transmit the information that is collected inside the body to receiving antennas outside the body. In this work, we examine a method that uses a high-frequency current in the transmitting electrodes of the implanted device for the transmission of information to receiving electrodes attached to the body surface. To investigate the transmission mechanism and the factors that determines the optimum frequency, the output voltage V₂ and the input and output impedance (Z_in and Z_out) were analyzed by conducting a finite-difference time-domain electromagnetic simulation. The results clearly show that the receiving part (electrodes and wire), including biological tissue, acts as a loop antenna. The maximum V₂ value was obtained at the first parallel resonance frequency of Z_out at 370 MHz under a load resistance of 1 MΩ. In contrast, the output current of the source increased at the series resonance frequency of Z_in. The series resonance frequency could be adjusted to move a target frequency by adding an inductance between the source and the transmitting electrodes.