Orientation-Insensitive Multi-Antenna Reader for Wireless Biomedical Applications.

This paper presents a multi-antenna external reader system that enables orientation insensitive communication with implantable medical devices (IMDs) for wireless biomedical applications. The proposed system consists of a circular array with six loop antennas. The antenna placement and orientations are determined by analyzing the near-field magnetic field variations of the loop antenna. The proposed system is first simulated using HFSS electromagnetic simulation software. Our simulations show that the received power at the proposed external reader with six antennas only varies about 5 dB for any given orientation of the implanted antenna, which is highly significant compared to the 20-35 dB variation with a single external antenna. Here, we select the antenna which provides the largest coupling between the IMD to receive/transmit signals. A prototype of the proposed multi-antenna external reader is then implemented using custom-designed PCBs that interconnect loop antennas, transceiver ICs, and commercially-available circuit components. A custom PCB with a miniaturized loop antenna is used to emulate an implantable device. Based on measurement results, the received power in the external reader only varies about 3 dB when the miniaturized antenna rotates with respect to the x-axis. These measurements show good agreement with the simulated reader.