Introduction

This project proposes fNIRSBand, a textile-based fNIRS headband designed for academia to track focus, relaxation, and fatigue during study sessions and throughout the day.

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Design & Technology

fNIRSBand is a soft, stretchable textile headband lined with light-blocking silicone to minimize ambient interference. This product contains multiple layers. The outermost layer distributes mechanical tension to maintain optode contact pressure, as well as serves as structural housing for the wiring that runs within the headband. It also provides comfort and aesthetics for the consumer, through its use of technical fabric. The headband comes in a few colours, which allows consumers to choose what suits them best. Next is a 1-2mm light-blocking silicone layer. This liner is made with black carbon-loaded PDMS silicone, which is known for its strong light absorption and thermal properties, as well as durability (Hiremath et al., 2021). Encapsulated within the silicone layer are semi-rigid optode modules that contain NIR LEDs & photodiodes to detect hemodynamic changes. They are each located ~30mm apart. Each headband has 4 optical channels placed across the forehead, following the International 10-10 placement system. More specifically this device contains sensors located at F3, F4, AF3 & AF4, which are positioned over Brodmann area 9 & 46 (Homan et al., 1987; Scrivener & Reader, 2022). These areas are involved in many executive functions such as working memory, decision making, sustained attention, stress-detection, and cognitive control (Gupta & Tranel, 2012).

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Device Metrics

This device will report a variety of metrics to users such as focus/attention, cognitive load, stress, and mental fatigue. Focus/attention will be derived from the simultaneous increase in oxygenated hemoglobin (HbO) and decrease in deoxygenated hemoglobin (HbR) in the dorsolateral prefrontal cortex (DLPFC), located at channels F3 & F4. Research has found that higher activation in these areas is associated with higher engagement (Harrivel et al., 2013; Gu et al., 2022). Cognitive load will be derived from an increase in HbO at all 4 channels. Fatigue will be derived from either the gradual reduction in oxygenated hemoglobin response amplitude over time or a hemispheric asymmetry between channels F3 & F4 (Yan et al., 2025). This is because fatigue is associated with high activation of the prefrontal cortex and slower recovery (Li et al., 2020). Stress will be derived from elevated HbO in the right prefrontal (F4, AF4) during stress and the balanced signals during relaxation (Wutzl et al., 2024). In other words, it will compare F4 & F3 channels for signs of asymmetry.

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Challenges, Tradeoffs & Limitations

Although this device has some good qualities, every design comes with inherent limitations and challenges. A major downside to fNIRSBand is its limitation in what and how much it can measure. Firstly, it only contains 4 channels located over the prefrontal cortex of the brain (F3, F4, AF3, AF4). This means that signals from other relevant cortical regions are being missed. Similarly, fNIRS has a limited spatial resolution and can only measure hemodynamic changes 1-2 cm deep. This means that certain mental states can only be inferred from the data rather than directly observed, which significantly constrains the accuracy of collected metrics. The temporal resolution of this technique is also relatively low since it only measures slow hemodynamic responses seconds after neural activity occurs. However, due to the intended functions of the band, this doesn’t pose that large of an issue.

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User Experience & Software

fNIRSBand’s analytics can be viewed through an intuitive smartphone application. Users will initially be prompted to measure their baseline activity. At the top of the page, the user will be able to see both their focus and relaxation scores on a simple colour-coded scale based on incoming brain data. These scales will change colour depending on how calm (blue), focused (green), stressed (orange), or fatigued (red) the user is at a given moment. As an individual continues to use the product, the app will pick up on the user’s brain trends. These trends will then be translated into ready to use consumer information through graphs, flow duration charts, and mental fatigue timelines. It will also provide daily feedback on ideal focus times, break suggestions, and environmental correlations such as the time of day or type of event. This will allow users to learn how to optimize their circadian rhythms for success. They will also have the option to log when they are doing certain activities for better trend recognition.

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Validation & Scientific Credibility

In order to validate metrics, fNIRSBand will go through a variety of phases prior to being released to the general public. The first phase would be a controlled lab validation, where fNIRSBand’s metrics would be directly compared to clinical fNIRS caps during a variety of standardized cognitive tasks. These tasks would focus on both focus and relaxation. Examples might include the Stroop or breath-focused tasks. The correlation coefficient should be > 0.7 for HbO trends. If successful, it will move on to the behavioural validation phase, where tests will be done to validate the correlations between task performance and reported focus scores. This might be done through reaction time or memory recall tasks. Correlations should be between r= 0.4-0.7 to be considered valid. The next phase would be a field study, where fNIRSBand would be brought into daily life to examine its ecological validity. Devices would likely be sent out to 50+ users for 2-4 weeks to collect self-reported metrics such as concentration, productivity, and mood scores. These metrics would then be compared to actual incoming data. This phase would also help filter out additional motion artifacts. Finally, there would be a pre-market pilot where a small group of early adopters will test the band for usability and comfort. Feedback from this phase would be used to make any final refinements before official production and release. In total, this process would be expected to take approximately 12-18 months to complete.

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Business & Market Reality

The device will cost ~$130 to manufacture due to the variety of parts it requires such as optical sensors, detectors, electronics, battery + housing, headband materials, connectors, etc. In addition, it will likely require additional costs such as assembly, quality control, and packaging. In order to make the product viable, it would retail for ~$225-275. This positions the device as a relatively accessible consumer neurotech product. The primary target market includes students, productivity seekers, and mindfulness users. It also has the potential to be aimed for gamers or researchers.

References

  1. Gupta, R., & Tranel, D. (2012). Memory, Neural Substrates. Elsevier, 593–600. https://doi.org/10.1016/B978-0-12-375000-6.00230-5
  2. Gu, Y., Yang, L., Chen, H., Liu, W., & Liang, Z. (2022). Improving Attention through Individualized fNIRS Neurofeedback Training: A Pilot Study. Brain Sciences, 12 (7). https://doi.org/10.3390/brainsci12070862
  3. Harrivel, A., Weissman, D., Noll, D., & Peltier, S. (2013). Monitoring attentional state with fNIRS. Frontiers in Human Neuroscience. https://doi.org/10.3389/fnhum.2013.00861
  4. Hiremath, S., Shrishail, H., &Kulkarni, S. (2021). Progression and characterization of polydimethylsiloxane-carbon black nanocomposites for photothermal actuator applications, Elsevier, 319. https://doi.org/10.1016/j.sna.2020.112522
  5. Homan, R. W., Herman, J., & Purdy, P. (1987). Cerebral location of international 10–20 system electrode placement. Electroencephalography and Clinical Neurophysiology, 66 (4), 376–382. https://doi.org/10.1016/0013-4694(87)90206-9
  6. Leber, A., Cholst, B., Sandt, J., Vogel, N., & Kolle, M. (2018). Stretchable Thermoplastic Elastomer Optical Fibers for Sensing of Extreme Deformations. Institute of Particle Technology. 1-8. https://doi.org/10.1002/adfm.201802629
  7. Li, G., Huang, S., Xu, w., Jiao, W., Jiang, Y., Gao, Z., & Zhang, J. (2020) The impact of mental fatigue on brain activity: a comparative study both in resting state and task state using EEG. BMC Neuroscience. https://doi.org/10.1186/s12868-020-00569-1
  8. Scrivener, C., & Reader, A. (2022) Variability of EEG electrode positions and their underlying brain regions: visualizing gel artifacts from a simultaneous EEG ‐ fMRI dataset. 12(2). https://doi.org/10.1002/brb3.2476
  9. Wutzl, B., Leibnitz, K., Murata, M. (2024). An Analysis of the Correlation between the Asymmetry of Different EEG-Sensor Locations in Diverse Frequency Bands and Short-Term Subjective Well-Being Changes. Brain Sciences, 14 (3). https://doi.org/10.3390/brainsci14030267
  10. Yan, Y., Guo, Y., Zhou, D. (2025). Mental fatigue causes significant activation of the prefrontal cortex: A systematic review and meta-analysis of fNIRS studies. PubMed, 62 (1). https://doi.org/10.1111/psyp.14747