Fully Integrated Bioimpedance Spectroscopy Interface for Wearable Electrical Impedance Myography
Time: Fri 2024-09-27 13.00
Location: Ka-Sal C (Sven-Olof Öhrvik), Kistagången 16, Kista
Video link: https://kth-se.zoom.us/j/2593490856
Language: English
Subject area: Information and Communication Technology
Doctoral student: Alejandro David Fernández Schrunder , Elektronik och inbyggda system, Mixed-Signals ICs and Systems
Opponent: Professor Andreas Demosthenous, University College London, Department of Electronic & Electrical Engineering
Supervisor: Professor Ana Rusu, Elektronik och inbyggda system; Associate Professor Saul Rodriguez, Elektronik och inbyggda system
QC 20240829
Abstract
Multi-Frequency surface Electrical Impedance Myography (MF-sEIM) is a technique that provides valuable electrophysiological information of muscles. This technique measures bio-Z spectroscopy of muscles, and applies Ohm's law by injecting a small-amplitude and high-frequency current into tissues and measuring the voltage response. As biological tissues are electrolytic conductors, this technique provides information on fundamental dielectric properties of tissues, which are an objective biomarker of neuromuscular disorders and have practical value in several muscle healthcare applications. Due to its versatility, simplicity, and ease of integration, this technique is a great candidate to complement stand-alone surface electromyography (sEMG) in wearable devices for continuous monitoring of muscle health. Nonetheless, wearable MF-sEIM imposes challenging requirements on the bio-Z spectroscopy interface. Previously reported solutions fall short of meeting these requirements, or do so with low power efficiency.
This thesis focuses on the research and development of a fully integrated bio-Z spectroscopy interface, which complies with the challenging requirements of wearable MF-sEIM in a power-efficient way. The electrophysiological mechanisms of MF-sEIM and the system-level requirements for clinical relevance were investigated, as MF-sEIM is a relatively novel technique, which requires standarization. From this established set of requirements, the main building blocks of the \mbox{bio-Z} spectroscopy interface, i.e., the current signal generator (CSG), and voltage readout, were developed. The CSG generates pseudo-sine waves through direct digital synthesis (DDS) to obtain the required linearity with high power efficiency. A high-linearity full current-mode CSG was also proposed to comply with the stricter bio-Z accuracy requirements of clinical diagnostics. The voltage readout is based on a low-IF quadrature (I/Q) demodulation architecture and features a pseudo 2-path bandpass (BP) Delta-Sigma ADC to achieve high precision and power-to-noise efficiency. A mixer-first analog front-end (AFE) was also proposed to enable bio-Z spectroscopy measurements employing dry electrodes. The bio-Z interface was integrated with a 16-Channel sEMG AFE and a 4-Channel neuromuscular stimulator (NMES) in an application-specific integrated circuit (ASIC). Experimental results show that the implemented bio-Z spectroscopy interface achieves a comparable performance with the state of the art, while being capable of detecting the large baseline and the time-varying impedances of muscle. A proof-of-concept system, based on the multi-modal ASIC, was developed. This system demonstrates the potential of combining real-time monitoring of MF-sEIM and sEMG for detecting muscle fatigue, enabling efficient closed-loop NMES.