Implants are poised to revolutionize personalized healthcare by monitoring and actuating physiological functions. Such implants operate under challenging constraints of limited battery energy, heterogeneous tissue-dependent channel conditions and human-safety regulations. To address these issues, we propose a new cross-layer protocol for galvanic coupled implants wherein weak electrical currents are used in place of classical radio frequency (RF) links. As the first step, we devise a method that allows multiple implants to communicate individual sensed data to each other through CDMA code assignments, but delegates the computational burden of decoding only to the on-body surface relays. Then, we devise a distributed beamforming approach that allows coordinated transmissions from the implants to the relays by considering the specific tissue path chosen and tissue heating-related safety constraints. Our contributions are two fold: First, we devise a collision-free protocol that prevents undue interference at neighboring implants, especially for multiple deployments. Second, this is the first application of near-field distributed beamforming in human tissue. Results reveal significant improvement in the network lifetime for implants of up to 79% compared to the galvanic coupled links without beamforming.

Galvanic coupling is the enabler of closed-loop communication between implanted sensors and embedded actuating devices (such as drug injectors) by providing energy-efficient and reliable non-RF transmission through links formed within tissue. For safe deployment, it is critical to verify that the amount of heat generated within tissues during signal propagation stays within permissible bound. In this paper, we analyze the thermal distribution within tissues, for galvanic coupling-based communication for varying transmission power levels, number of collocated transmitters, and blood perfusion conditions using finite element based numerical simulation and skin-phantom based experiments. Our results confirm that tissue heating remains well below safe limit of 1 °C. Using the temperature dissipation profile, we derive the suitable transmission duty cycles, separation distances and number of concurrent sources that may co-exist without raising the tissue temperature. The proposed strategies provide upto four fold increase in bandwidth efficiency through concurrent transmissions, ensuring sufficient bandwidth for implant communications.

Implanted sensors and actuators in the human body promise in-situ health monitoring and rapid advancements in personalized medicine. We propose a new paradigm where such implants may communicate wirelessly through a technique called as galvanic coupling, which uses weak electrical signals and the conduction properties of body tissues. While galvanic coupling overcomes the problem of massive absorption of RF waves in the body, the unique intra-body channel raises several questions on the topology of the implants and the external (i.e., on skin) data collection nodes. This paper makes the first contributions towards (i) building an energy-efficient topology through optimal placement of data collection points/relays using measurement-driven tissue channel models, and (ii) balancing the energy consumption over the entire implant network so that the application needs are met. We achieve this via a two-phase iterative clustering algorithm for the implants and formulate an optimization problem that decides the position of external data-gathering points. Our theoretical results are validated via simulations and experimental studies on real tissues, with demonstrated increase in the network lifetime.

Implanted medical sensors and actuators within the human body will enable remote data gathering, diagnosis, and the ability to directly control drug delivery actuators. To establish the communication links through the body tissues, we adopt galvanic coupling that uses low frequency electrical signals of weak amplitude. In this paper, we propose a topology management strategy using Weiszfeld algorithm that attempts to minimize the transmission power of the body nodes by reducing the distance from the source nodes to pick-up points or relays that gather and forward the received information. It takes into account the unique propagation model of the electrical signals within the body at various tissue layers, which is completely different from over the air RF. Our algorithm considers separately the constraints of on-skin nodes and the implanted nodes, especially in terms of minimizing the energy for the latter, which cannot be easily retrieved and re-charged. It also considers the difference in specific bandwidth requirements for the applications running within the nodes, by moving relays closer towards the high data rate demanding regions. We show that by optimizing the position of the relay node, the energy consumption can be significantly improved to extend the lifetime of the intra-body network up to several years.