Electrode impedance characterisation for implantable neural interfaces
File(s)
Author(s)
Manatchinapisit, Vichaya
Type
Thesis
Abstract
Neurological disorders such as Parkinson’s disease and epilepsy affect millions in the UK. In drug-resistant cases, deep brain stimulation (DBS) is often required; however, traditional DBS delivers continuous stimulation, which may lead to adverse effects. Closed-loop DBS, which adapts stimulation based on real-time biosignals, improves efficacy and reduces side effects. Maintaining long-term effectiveness requires stable implanted electrodes, which can degrade over time due to tissue encapsulation, inflammation, and stimulation-induced changes. Monitoring electrode impedance is therefore essential for assessing performance, ensuring device reliability, and maintaining patient safety.
This thesis presents a system for characterising electrode impedance in implantable neural interfaces. The project was conducted in three phases: (1) establishing an accelerated degradation testing protocol; (2) developing a benchtop impedance measurement platform; and (3) designing an integrated circuit (IC)-based impedance measurement system. The accelerated testing protocol, incorporating continuous impedance monitoring, was validated using electrochemical impedance spectroscopy (EIS) under simulated degradation induced by thermal and electrical stimulation. A custom PCB platform was designed to perform EIS from 48 Hz to 100 kHz, demonstrating impedance measurements of DBS electrodes in phosphate-buffered saline (PBS) and tungsten wire under accelerated degradation.
Furthermore, a NeuroZ chip, fabricated in 180 nm CMOS technology, enabled EIS from 1 Hz to 100 kHz and resistance values between 100 Ω and 1 MΩ. The chip was validated with DBS, stereoelectroencephalography (SEEG), electrocorticography (ECoG), and cuff electrodes. A multi-sine impedance measurement approach was also explored to reduce measurement time and minimise interference with neuromodulation treatments.
Overall, this work presents the development of an integrated circuit capable of performing impedance characterisation. Accelerated testing, benchtop validation, and IC-based measurements were conducted, providing a systematic framework to evaluate electrode performance. The outcomes of this research support the future design of more reliable and efficient neural interface technologies.
This thesis presents a system for characterising electrode impedance in implantable neural interfaces. The project was conducted in three phases: (1) establishing an accelerated degradation testing protocol; (2) developing a benchtop impedance measurement platform; and (3) designing an integrated circuit (IC)-based impedance measurement system. The accelerated testing protocol, incorporating continuous impedance monitoring, was validated using electrochemical impedance spectroscopy (EIS) under simulated degradation induced by thermal and electrical stimulation. A custom PCB platform was designed to perform EIS from 48 Hz to 100 kHz, demonstrating impedance measurements of DBS electrodes in phosphate-buffered saline (PBS) and tungsten wire under accelerated degradation.
Furthermore, a NeuroZ chip, fabricated in 180 nm CMOS technology, enabled EIS from 1 Hz to 100 kHz and resistance values between 100 Ω and 1 MΩ. The chip was validated with DBS, stereoelectroencephalography (SEEG), electrocorticography (ECoG), and cuff electrodes. A multi-sine impedance measurement approach was also explored to reduce measurement time and minimise interference with neuromodulation treatments.
Overall, this work presents the development of an integrated circuit capable of performing impedance characterisation. Accelerated testing, benchtop validation, and IC-based measurements were conducted, providing a systematic framework to evaluate electrode performance. The outcomes of this research support the future design of more reliable and efficient neural interface technologies.
Version
Open Access
Date Issued
2025-03-12
Date Awarded
01/11/2025
License URL
Advisor
Constandinou, Timothy
Sponsor
Thailand
Publisher Department
Department of Electrical and Electronic Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)