As pharmaceutical companies around the globe tirelessly work towards a vaccine for COVID-19, it is imperative that we provide hospital staff serving on the frontlines with necessary personal protective equipment (PPE). Unfortunately, as cases of the virus surge around the world, PPE supplies are running short. The ability to properly sterilize masks for re-use will be critical in the coming months, and optics play an important role in this process. Specifically, UV-C lighting can be used inside of appropriately configured decontamination chambers to provide the necessary sterilization.

A study has recently been conducted between the E.L. Ginzton Laboratory and the Stanford Photonics Research Center to analyze the performance of two different decontamination chamber geometries for mask sterilization. This study compared the results of measurements obtained from prototype chambers against simulations conducted using Zemax OpticStudio. Dr. Jeff Wilde led the modeling efforts, leveraging many of the capabilities within the non-sequential mode of OpticStudio to achieve an accurate simulation. This included creating realistic models of the UV-C light sources, the decontamination chamber (for both a rectangular cabinet and cylindrical trash can geometry), and the N95 mask. These models involved using built-in functionality as well as importing CAD geometries. For the mask, it was also important to provide realistic surface properties, including the effects of surface scattering.

Dr. Wilde was able to validate that the irradiance distribution on the masks would achieve appropriate levels needed for sterilization using custom-make detector geometries within OpticStudio. The results for both the rectangular cabinet and cylindrical trash can geometry showed excellent agreement with measurement, as shown below for cases in which the mask geometry was not included in the simulation.

Rectangular cabinet:

Cylindrical trash can:

As expected, the peak irradiance is significantly higher for the cylindrical trash can geometry, reducing the exposure time needed to sterilize masks in this chamber configuration. However, this higher irradiance is offset by the fact that the cylindrical geometry supports the placement of fewer masks in the chamber at any time.

The excellent agreement between simulation and measurements found in this design study validates the chamber design, and these results are now being used to drive the production of UV-C decontamination chambers throughout the world. As the global community continues the fight against COVID-19, this work will play a key role in our success.

Read the full paper Modeling UV-C Irradiation Chambers for Mask Decontamination using Zemax OpticStudio which has been published by the Optical Society of America (OSA).

Sanjay Gangadhara
CTO, Zemax