Feasibility study of using the housing cases of implantable devices as antennas

Abstract

A novel antenna design for implantable pacemakers is proposed. The housing of a pacemaker is utilized as an antenna to cover both the 402-405 MHz Medical Implant Communication Service band and the 433-MHz Industrial, Scientific and Medical band. This is achieved by exploiting radiating characteristic current modes of the housing case. These modes are excited using a capacitive coupling element with the help of a matching circuit. The radiation pattern of this antenna is optimized to be in a desirable direction away from the body (off-body direction). The ability of the proposed antenna for communications is demonstrated using a transceiver and a base station at 433 MHz. A communication range of 1 m is established when a transmitter with the proposed antenna is implanted in a rabbit and the power fed by the transceiver to the antenna is 25 μ W. A longer range of up to 19 m can be established with the maximum allowable transmit power within the safety limits. Furthermore, the far field wireless power transfer through the proposed antenna is investigated by experiment. A received power of up to 22.38 μ W by the proposed antenna is demonstrated when an equivalent isotropically radiated power of 140 mW is transmitted 1 m away from a transmitting antenna. From the same transmitting antenna in the same distance, a power of 4 mW can be received when the transmit power is within safety limits. This power can be used to recharge a small battery or a capacitor, which can potentially cover the communication power consumption of the pacemaker and hence extend the life span of the primary battery.