Teshome, Assefa (2017) Implant Communication Using Intrabody Communication (IBC) Mechanisms. PhD thesis, Victoria University.

Abstract

The current trend in healthcare is the move towards proactive health monitoring and making health one’s responsibility. This has seen a proliferation of wearable devices that monitor physical and physiological parameters in real time. However, there is an increasing need to monitor internal body parameters, detect risks and act on them in a timely manner. Implanted medical devices (IMDs) are gaining recent attention due to their capability to provide diagnostic, therapeutic and assistive functionalities. With a projected annual growth of 7.1 % (2016- 2022) the global market share of IMDs is expected to reach 116.3 billion USD by year 2022. In Australia alone, the clinical use of remotely monitored IMDs has risen sharply from 987 (2013-14) to 2269 in just two fiscal years. The increasing demand for ubiquitous and minimally invasive implants is due to the prevalence of chronic disease and growing aging population. While bio-sensing and implant drug delivery techniques have improved tremendously, implant communication technology has advanced at a slower rate. This poses problems for the new generation of implants such as brain computer interfaces (BCI), controllers for artificial prostheses and bionics which will require higher data rates. Existing IMD communications are mainly enabled through antenna based radio frequency links that rely on electromagnetic (EM) wave propagation at ultra high frequencies (UHF). The Medical Device Radio Communication Services (MedRadio) band (401-406 MHz) and Industrial Scientific and Medical radio (ISM) band (2.4 GHz) are most commonly used. However, the human body has a high attenuation to signals at these high radio frequencies; as a result, transceivers tend to consume high power and require complex circuitry to mitigate channel attenuation effects. Lower RF frequencies (lower attenuation through the body) require larger antenna sizes resulting in larger implant sizes. On the other hand, while inductively coupled techniques use lower frequencies (lower path loss), they generally have a narrow transmission band and lower data rates. Thus, the race is on to develop new implant data transmission techniques that consume less power yet provide high (acceptably high) data rates. The thesis addresses this challenge by investigating an alternative implant communication technique using intrabody communication (IBC) mechanisms, specifically galvanically coupled IBC (gc-IBC). This communication method utilises the human tissue as a volume conductor for data communications. In this thesis we began by critically reviewing existing and emerging implant communications technologies. We then proposed and investigated gc-IBC as a new alternative implant communication technology. A novel analytical framework that modeled the human body as a communication channel was proposed. Simulation results were experimentally confirmed by measurements on phantom body solutions. The framework was then extended to analyse a hybrid communication scheme for cortical implants that utilised gc-IBC and the popular inductively coupled data transfer (ic-DT). It was found that for the same frequency range, gc-IBC offers a wider bandwidth for data transmission compared to ic-DT while ic-DT was better for wireless power transfer due to its narrow band characteristic and lower path loss at the resonant frequency. It was also shown that gc-IBC provided 20 dB lower path loss than antenna based RF schemes for the same transmit power. Then, an integrated sensor gc-IBC implant transceiver prototype was designed and developed to characterise and demonstrate the feasibility of implant communication using gc-IBC mechanism. The integration of the sensor into the transmitter was made in a way that minimises transmitter complexity which was crucial to achieve high degree of miniaturisation and low power consumption. Transceiver characterisation experiments were conducted using an automated mechatronic rig that is specifically designed and built for this work. The rig moves the receiver inside the phantom solution in the three axes with respect to the transmitter and is capable of computing the bit error rate (BER) of the reception. The transceiver demonstrated the feasibility of gc-IBC scheme for implants with a BER of 1.1 ×10−4 at signal to noise ratio (SNR) of 8 dB which is better compared to existing uncoded schemes. The gc-IBC channel noise was characterised for the first time as a function of transmission distance and was found to be -118 dB/Watt on average. Future work will focus on extending the framework to model more complex parts e.g., organs, channel capacity estimation under different setting, testing different coding schemes to improve transceiver performance and miniaturisation.

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