Integrated Wireless Power, Data Communication, and Thermal Sensing System for Autonomous Multisite Brain Implants

Implanted medical devices (IMDs) have been widely developed to support the monitoring and recording of biological data inside the body or brain. Wirelessly powered IMDs, a subset of implantable electronics, have been proposed to eliminate the limitations related to the physical size constraints, battery replacement issues, and the complexity of wired powering. Wireless power transmission (WPT) methods have been employed to transfer wireless power and data between the implanted units and an external medical unit. Ultrasonic, capacitive, optical, radio frequency, and inductive links are the most commonly used WPT methods, according to the literature. Implantable neural interfaces are an example of wirelessly powered IMDs to monitor and detect neurological disorders. To achieve this, an autonomous wirelessly powered system is required that has the capacity of recording neural signals, transferring them to the base station wirelessly, detecting seizure in real-time, and taking a responsive action or carrying out electrical stimulation to suppress the seizure from its initial onset. Consequently, an efficient and low-power wireless system is essential with the capability of multisite remote powering, bi-directional data communication, power management and control, and thermal sensing. This thesis presents a novel system-level concept by employing inductive links and CMOS electronics: a fully-implantable wirelessly powered closed-loop multisite implant.The proposed system has a three-layer architecture to support autonomous and closed-loop operations. An external base unit, embedded into a headstage, includes a system controller, battery, telemetry and inductive link for power and bi-directional data transmission to the implant. The central implanted unit (CIU) housed in a burr hole receives the wireless power, to recharge the battery, and downlink data from the headstage. The CIU further supplies wireless power and configuration data to autonomous smart patches (ASPs). The third layer of the proposed architecture consists of two ASPs that are implanted on the cortex surface. This thesis includes the analysis of the system-level modeling of the entire system using MATLAB Simulink, wireless power and data communication circuits in a CMOS technology, on-chip power control and thermal sensing, and system-on-chip measurement results to verify the proposed system. A hybrid powering solution is considered for the CIU, consisting of inductive wireless power transmission and a rechargeable battery. The required power of the ASPs is only supplied from the CIU using inductive links. A dual-band inductive link is employed at the CIU to provide multisite WPT to the two ASPs at two different frequencies. Hence, a power conversion chain (PCC) is designed in the CIU and ASPs to provide a stable DC voltage supply from the received magnetic waves. Bi-directional data communication between the external unit and the CIU and between the CIU and ASPs is required. Consequently, low-power wireless data communication units are proposed, using different modulation schemes. Furthermore, an on-chip CMOS temperature sensor is presented to provide on-chip thermal sensing and monitor temperature elevation inside the brain implants. The entire system including both CIU and ASPs is integrated and fabricated using 180 nm standard CMOS technology and the performance of the full system is measured and verified.