Wearable Bioimpedance Sensor Characterization for Blood Flow Monitoring.

Bioimpedance is a powerful wearable sensing modality for continuous and non-invasive human deep tissue monitoring. When bioimpedance sensors are placed on the human body aligned with the underlying arteries – such as radial, ulnar, and digital – the impedance measurements show variations based on the changes in the artery dimensions due to the presence of blood pressure pulse waves. These variations can be leveraged to extract complex cardiovascular information, such as blood pressure. However, the level of impedance variations due to volumetric changes in the arteries is minimal (in the order of tens of mOhms) compared to the overall tissue impedances (in the order of hundreds of Ohms) requiring careful bioimpedance circuit and system design. In this paper, we provide comprehensive analyses of the bioimpedance sensor design requirements for arterial blood flow monitoring through numerical calculations, spice simulations, and experimental measurements. We provide analyses on signal-to-noise ratio (SNR) and effective number of bits (ENOB) requirements, indicating an 86dB SNR and 14-bit ENOB for high-resolution sensing. We believe this paper will further motivate the adoption of the promising wearable bioimpedance technology for applications of precision medicine.