In Situ Near-Field Path Loss and Data Communication Link for Brain Implantable Medical Devices Using Software-Defined Radio

Abstract

The rapid evolution in brain implantable medical devices (BIMDs) promises a new paradigm of medical diagnosis, monitoring, and therapeutics. The MedRadio frequency band (401–406 MHz) offers an acceptable penetration of electromagnetic (EM) fields in biological tissues and thus is well suited for wireless medical telemetry (WMT). Unlike other parts of the body, head tissues exhibit a high level of EM fields absorption, which provides a significant challenge for devices implanted in this part of the body. Therefore, it is important to appraise data communication and path loss over this difficult channel. In this article, a brain implantable antenna and an exterior antenna are developed to operate at 406 MHz MedRadio band. The exterior antenna is a miniaturized composite loop-patch antenna with tuning slots, whilst the implantable antenna is a capacitively loaded loop with parasitic patches. A near-field communication link is tested via a software-defined radio (SDR) module in a cerebrospinal fluid (CSF) phantom and pig primate. The link budget of the in situ communication link demonstrates a reliable data transfer of 200 kb/s with a low level of input power (−17.55 dBm) and high signal-to-noise ratio (SNR) for near-field transmission. Since, the EM fields decay rapidly in head tissues, a path loss model is thus essential for BIMDs. The developed path loss model in CSF phantom and pig primate yield an attenuation between 43 and 56 dB for a distance ranging from 20 to 60 mm at 406 MHz. Overall, the results show that near-field data communication link for BIMDs can be utilized over the conventional far-field link for a better signal-to-noise ratio (SNR) with a low power requirement.