Eye Mask Prototype With Bimodal Sensors and Hydrogel Electrodes Measures Biometrics

September 21, 2020 by Luke James

The researchers met the challenges of fabric-based sensors, combining the signal quality benefits of wet electrodes and the comfort benefits of dry electrodes.

Researchers at the University of Massachusetts (UMass) Amherst have created a sensing eye mask that could provide an unobtrusive and valuable insight into sleeping patterns. The lightweight wearable eye mask, known as Chesma, comes from the same team that previously developed physiology-sensing pajamas.

According to the researchers, in addition to improving the accuracy of existing technologies such as virtual reality (VR) headsets and applications in advertisement performance analysis, the mask’s ability to track pulse and eye movements may open future studies into sleep and psychology.


Electrooculography vs. Hydrogel Electrodes

Existing technology that’s used to track eye movements relies on electrooculography (EOG). And although it’s very good at measuring the eye’s electrical potential changes, the technique is over 50 years old and it requires the use of adhesive electrodes stuck to the user’s face, which is uncomfortable and intrusive. 


The “Chesma” eye mask is said to track eye movement and record cardiac signals

The “Chesma” eye mask is said to track eye movement and record cardiac signals. Image used courtesy of S. Zohreh Homayounfar, University of Massachusetts Amherst


In contrast, the UMass Amherst team’s mask, which is made from hydrogel electrodes with a pulse sensor, is said to provide accurate measurements without compromising user comfort. It can be placed over the user’s eyes to track movement as images are shown and then removed again very easily. It’s also washable, just like a regular eye mask, up to 15 times.


Overcoming Design Challenges

One of the design challenges of smart wearables is miniaturizing components that are both accurate and comfortable. This is why the UMass researchers decided to use the novel hydrogel electrode in their eye mask, which was developed in-house. 


Schematics of the bimodal sensing platform designed to capture physiological signals from the face

Schematics of the bimodal sensing platform designed to capture physiological signals from the face. Image used courtesy of Matter

The hydrogel electrode was created by growing polymers on fabrics, which filled the various nooks and crevices present in the fiber pattern. This enabled the hydrogen polymer to bond to and cover the fabric’s topology, creating a mechanically stable coating nearly invisible to the naked eye and imperceptible to touch.

These hydrogel electrodes were then combined with a pulse sensor to create an eye mask that can track eye movements and collect pulse signals from the artery at the brow bone. "Our team was able to really address that core problem to create a garment that you would be willing to wear and give you clinically accurate results when you use it," said senior author Trisha L. Andrew of UMass Amherst. 

Six fabric sensors along with two microcontrollers are interconnected via hydrophobic silver threads encased within cotton piping. The researchers say the resulting eye mask features high signal-to-noise ratio (30 dB). 


A Durable Eyemask

According to the research paper published in Matter, the electrodes perform just as well, if not better than, existing adhesive electrodes currently in use. They’re also extremely durable and can withstand long-term build-up from environmental pollutants, skin waste, and makeup products, which could fault other electrodes.

The researchers also found that the mask’s signal did not degrade even after six hours of continuous use where the hydrogen wasn’t rehydrated. It retains water so well that it takes almost 40 hours to dry out fully, say the researchers. 

The researchers will now look at reducing the device’s power demand with a view to make improvements that will enable the mask to be recharged once every three days instead of every eight hours.