A Wearable Prefrontal Headband Measuring Cerebral Hemoglobin Concentration for Brain-Computer Interfaces

Non-invasive brain-computer interfaces (BCIs) that monitor brain activity via hemodynamic signals enable motor and language rehabilitation for individuals with disabilities and provide multiple communication capabilities, such as sleep monitoring and fatigue alerts, for healthy individuals. Here, we propose a wearable prefrontal headband with an embedded array of 4 photodetectors and 4 micro-LEDs to form a fiberless functional near-infrared spectroscopy (fNIRS) system measuring the change in oxyhemoglobin and deoxyhemoglobin concentrations, thus indirectly reflecting the cognitive functions of the brain and constructing BCI. The utilization of dual short-channel measurements and long-short channel multiplexing in the fNIRS system enables all 10 optodes to contribute to both long- and short-channel acquisitions, achieving a long-short-channel optode proportion of 100% with improvement in removal of superficial physiological noise. The average signal-to-noise ratio of long channels reaches 64 dB, and the minimum dynamic optical range of short channels is 122 dB due to the time-division measurement scheme for two types of channels, demonstrating the feasibility of the proposed channel configuration. In simulated driving tasks, the headband captured discriminable physiological features to distinguish mental-fatigue states, indicating its potential for real-world BCI applications.