Characterization of in- and near-body radio frequency transmission loss for biomedical implants

The experimental methodologies for characterizing in- and near-body radio frequency (RF) transmission loss are studied in this paper. Traditionally, the RF transmission loss was investigated using numerical model with a specific implanted antenna. The results obtained are antenna dependent and therefore not suitable for universal link budget calculation for biomedical implant systems. It will be desirable if the transmission loss within/outside the body can be decoupled from the antenna. In this paper, the methods and measurement set-ups for characterizing the in- and near-body RF transmission loss with decoupled antenna effect are presented. Dipole and loop antennas are used in the measurement; by embedding the antennas in high dielectric constant tissue, the size of the testing antennas is much reduced and therefore only a small piece of the tissue sample will be adequate for the measurement. Furthermore, the fields of the antennas are confined within the tissue, the characteristics of the embedded antennas are little affected by the presence of the tested tissue samples, which is vital for achieve accurate and reliable results. The studies are carried out at the Medical Implanted Communication Service (MICS) band of 402-405 MHz and the unlicensed Industrial, Scientific and Medical (ISM) band of 902-928 MHz.