Design of a wideband power-efficient inductive wireless link for implantable biomedical devices using multiple carriers

This paper presents a novel design for wireless transmission of power and bidirectional data to biomedical implantable microelectronic devices using multiple carrier frequencies. Two separate pairs of coils have been utilized for inductive power and forward data transmission. A back telemetry link is established with a pair of patch antennas in the Industrial-Scientific-Medical (ISM) band. Achieving high power transmission efficiency and high data transmission bandwidth with minimum Bit Error Rate (BER) are the main goals in this application. One of the major challenges is to minimize the interference among carriers especially on the implantable side, where size and power are highly limited. The planar power coils are spiral shaped, and optimized in size to provide maximum coupling coefficient. The data coils are designed rectangular across the power coils diameter and oriented at right angles to the power coils planes to maximize their direct coupling, while minimize their cross-coupling with the power coils. The power, forward data, and back telemetry carriers, which are orders of magnitude different in amplitude, are widely separated in frequency at 125 kHz, 50 MHz, and 2.45 GHz range to further reduce the interference and facilitate filtering. Robust modulation and encoding techniques are currently under development to minimize the effects of interference even further.