Smart sensor fitted into N95 face mask detects wearer’s physiological data

Dubbed FaceBit, the lightweight sensor uses a tiny magnet to attach to any N95 cloth or surgical face mask.

It is capable of sensing the user’s real-time respiration rate, heart rate and mask wear time, and may also be able to measure the fit of the mask.

All this information is then wirelessly transmitted to a smartphone app, which contains a dashboard for real-time health monitoring. The app can alert the user when issues such as an elevated heart rate or a leak in the mask unexpectedly arise.

The physiological data could also be used to predict fatigue, physical health status and emotional state.

Although a tiny battery powers the device, FaceBit is designed to harvest energy from any variety of ambient sources – including the force of the user’s breathing, motion and heat from a user’s breath as well as from the sun. This extends the sensor’s battery life, lengthening time between charges.

“We wanted to design an intelligent face mask for healthcare professionals that does not need to be inconveniently plugged in during the middle of a shift,” said Northwestern’s Josiah Hester, who led development of the device.

“We augmented the battery’s energy with energy harvesting from various sources, which means that you can wear the mask for a week or two without having to charge or replace the battery.”

FaceBit’s accuracy was found to be similar to clinical-grade devices, and the battery lasted longer than 11 days between charges.

To ensure their N95 masks are properly sealed to their faces, health care workers periodically undergo a 20-minute “fit test.”

During this process, health care workers first put on an N95 respirator followed by a clear hood over their entire head. Another worker then pumps either sweet or bitter aerosol mists into the hood. The concentration of the aerosol is gradually increased inside the hood until it can be detected by the person wearing the respirator. If the wearer tastes bitter or sweet before a certain number of aerosol pumps, then the mask is not properly sealed.

Although Hester’s FaceBit cannot yet replace this cumbersome process – which is a long-standing challenge in the medical industry – it can ensure the mask retains proper fit between testing events. If the mask becomes loose throughout the day or if the user bumps the mask during an activity, for example, FaceBit can alert the wearer.

“If you wear a mask for 12 hours or longer, sometimes your face can become numb,” Hester said.

“You might not even realise that your mask is loose because you cannot feel it or you are too burnt out to notice. We can approximate the fit-testing process by measuring mask resistance. If we see a sudden dip in resistance, that indicates a leak has formed, and we can alert the wearer.”

By gathering various physiological signals such as heart and respiratory rates, FaceBit can help wearers better understand their own bodies in order to make beneficial health decisions.

Hester said that every time a person’s heart beats, their head moves an imperceptibly tiny amount. FaceBit can sense that subtle motion and differentiate it from other motions in order to calculate heart rate.

“Your heart is pushing a lot of blood through the body, and the ballistic force is quite strong,” he said. “We were able to sense that force as the blood travels up a major artery to the face.”

Because stressful events can elicit physiological responses, including rapid breathing, FaceBit can use that information to alert the user to take a break, go for a walk or take some deep breaths to calm down.

Hospital systems also could use this data to optimise shift and break schedules for its workers, the researchers said.