Link Budget of Magnetic Antennas for Ingestible Capsule at 40 MHz

Magnetic antennas are suitable in short range medical in-body applications because they are less perturbed in the presence of the human tissues comparing to electrical antennas. After a preliminary study on magnetic antennas designed separately at 40 MHz with a matching system, a link budget between a spiral coil ingestible capsule transmitter antenna and a square coil onbody receiver antenna has been established in the presence of the human body. The efficiency (ratio of received power to transmitted power) of the magnetic induction link through a homogeneous human body (muscle) is equal to 0.6 % when the TX (transmitter) capsule is in front of the RX (receiver) antenna. If the transmission channel is a three-layered human body (muscle / fat / skin) the performances of the inductive link can be enhanced and the efficiency reaches 0.8 %. These performances can be improved (up to 1 %) when the dimensions of the receiver antenna increase. Consequently, the power consumption can be reduced and hence the battery life of the wireless capsule increases. Additionally, when the TX antenna is located randomly at an arbitrary orientation and position, the efficiency of the magnetic induction link can be improved by orienting the RX antenna parallel and perpendicularly to the human body surface.