The pandemic has led to N95 masks quickly becoming one of the world’s most in demand resources, as key workers burned through billions of them. New research could lead to an N95 that you can recharge instead of throwing away – or even one that continually fills itself for maximum efficiency.
The proposed system, from researchers at the Technion-IIT in Israel and the Tata Institute of Fundamental Research in India, is not a decontamination as one might expect. Instead, it focuses on another aspect of N95 masks that makes them less effective over time.
N95s use both mechanical filtration, where particles are trapped in a matrix of microscopic fibers, and electrostatic filtration, where particles are attracted by surfaces carrying a static charge. It̵
The combination of these two methods makes N95 masks very effective, but the electrostatic charge, like any charge, disappears as air and moisture pass over it. While decontamination via UV or high temperature can help prevent the mechanical filter from becoming a small petri dish, they do nothing to restore the electrostatic charge that acted as another barrier to entry.
In a paper published in the journal Physics of Fluids, Dov Levine and Shankar Ghosh (from Technion and Tata, respectively) show that it is possible to recharge an N95 filter to the point where it was close to shelf level for efficiency. All that is needed is to place the filter between two plate electrodes and apply a strong electric field.
“We find that the total charge deposited on the masks depends strongly on the charging time … with the pristine value almost restored after a 60 minute charge at 1000 V,” the researchers write in their paper.
However, it is unlikely that healthcare professionals will disassemble their masks after each shift. While a service and a special mask type could (and if it is effective, should) be established to do this, the team also explored the possibility of a mask with a built-in battery that constantly recharges:
A solution that can help rebuild the lost charge on the masks in real time would be desirable. In this section, we provide a proof-of-concept method of keeping the masks charged, which comes as a logical extension of our recharging method.
We tested a technique where the filter material maintains its charge and thus its filtration efficiency … As the required currents are extremely small, a large battery is not required and it is possible that a small compact and practical solution may be possible.
The image above shows a prototype that the team found to work quite well.
Of course, it is not quite ready for implementation; The IEEE Spectrum asked Peter Tsai, the creator of the N95 mask, for his opinion on it. He suggested that the team’s method of testing filtration efficiency is “probably questionable”, but did not take issue with the rest of the study.
Although it will not be in hospitals tomorrow or next week, the team notes that “crucially, our method can be performed using readily available equipment and materials and can therefore be used in both urban and rural areas.” So once it is thoroughly tested, it is possible that these rechargeable masks may start to appear everywhere. Lets hope so.