Low-profile antennas for implantable medical devices: optimized designs for antennas/human interactions

Based on the FDTD simulations and the return loss measurement setup, a spiral-type microstrip antenna and planar inverted F antenna (PIFA) are optimized to operate in a human body at the biomedical frequency band and their electric characteristics are compared in terms of physical dimension and radiation characteristics. Although the radiation patterns are similar to each other, the PIFA has advantages over a microstrip antenna, specifically smaller dimensions and higher radiation efficiency. The SAR calculation of two low profile antennas indicates that the dielectric layer used for the superstrate are useful to protect the skin tissue in front of the antenna and make it possible for the implanted antenna to deliver more than 25 μW for short-range biomedical devices.