Microwave Modified For Disinfecting

We’re all hopefully a little more concerned about health these days, but with that concern comes a growing demand for products like hand sanitizer, disinfectant, and masks. Some masks are supposed to be single-use only, but with the shortage [Bob] thought it would be good if there were a way to sanitize things like masks without ruining them. He was able to modify a microwave oven to do just that.

His microwave doesn’t have a magnetron anymore, which is the part that actually produces the microwaves for cooking. In its place is an ultraviolet light which has been shown to be effective at neutralizing viruses. The mask is simply placed in the microwave and sterilized with the light. He did have to make some other modifications as well since the magnetron isn’t always powered up when cooking, so instead he wired the light into the circuit for the turntable so that it’s always powered on.

Since UV can be harmful, placing it in the microwave’s enclosure like this certainly limits risks. However, we’d like to point out that the mesh on the microwave door is specifically designed to block microwaves rather than light of any kind, and that you probably shouldn’t put your face up to the door while this thing is operating. Some other similar builds have addressed this issue. Still, it’s a great way to get some extra use out of your PPE.

29 thoughts on “Microwave Modified For Disinfecting

    1. This.
      Finding a UV transmissive plastic is actually pretty hard, and fairly expensive.
      Regular float glass almost completely blocks UVC as well.

      Reflectivity is also harder than you think. Teflon, for example, reflects 90% of UVC, whereas chrome and polished aluminum only score about 60%.

      1. That is when you need to use an exotic “dielectric multilayer mirror” AKA “distributed bragg reflector”, which is tuned to efficiently reflect over a narrow range of wavelengths. You can increase the reflectivity by having lots of layers. It is produced using any of the thin-film deposition methods.

    2. Even if plastic doesn’t transmit UV all that well I’d want to replace the plastic with glass that’s been treated with a UV blocking coating.

      Most plastics are susceptible to UV damage. I guess it makes sense then that they don’t transmit UV. They are absorbing it. I wouldn’t want to be looking at that door when it cracks all to pieces!

  1. A UV reflective shield on the back of the door would block UV getting out and increase performance.

    Also, the magnetron power is controlled by a relay so you could bridge the secondary contacts and use the existing wiring and leave the carousel as it was.

    1. Yes, we did something similar at work some time ago. We modified an old microwave oven to expose to UV the photosensitive resin coated over the copper side of PCBs, using a transparent mask with the circuit traces printed on it, for a small batch of circuits we were building. The timer and the rotating plate (to get a more uniform exposure) were a bonus.

      Best regards,

      A/P Daniel F. Larrosa
      Montevideo – Uruguay

    1. You’re right. We should judge everything before it ends up here with our personal thoughts and interests as the only metric. 100%. God forbid these ideas inspire others to take on and improve or modify methods. “Lovinit doesn’t like it, shut it down! “

  2. I have modified a UV device that for sure emits ionizing UV to desinfect masks and non-washable groceries, back in the first days of corona.

    Unfortunately we discovered very soon that the masks are clean hygenically but not mechanically. Meaning the dust particles that stick in the mask stay there even after UV exposure. This makes an irradiated mask harder and harder to breathe in. There is no way around to actually wash a mask to clean it.

    Second biggest problem is to actually know how much ionizing UVC light your lamp puts out. Without proper measurement devices for this yo have no idea how long you must place items under the light for them to become clean. Also most UV sources only produce UVA and maybe UVB light, both of which do not break down DNA chains. Finding something that actually produces UVC is quite difficult.

    Last problem is that UVC disinfection is not comparable to gamma radiation based disinfection. Gamma rays go through almost everything amd disinfect below the surface. With UVC only parts that are illuminated get disinfected. Anything in the shadow won’t disinfect. You might think, let’s just put a glass layer and a lamp from the underside, but as stated something transparent for visible light does not necessarily have to be transparent for UVC light. It is quite hard to find a material that is non-opaque to UVC and does not deteriorate after being exposed to UVC.

    1. UVC lamps and quarz glas are not hard to find they are just expensive! and possibly restricted to medical use depending on the regulations in your country. UVC lamps are very common in microbiology labs and applications.

  3. I have to say, I expected a lot more UV related disinfecting devices / hacks etc because of the pandemic, but there is a significant lack of attention towards UV. I really wonder why is that?

  4. I read somewhere that that the UV-C light does not travel very far into the fibers of, say a mask, so you could still have virus in it even after blasting it with UV-C. Not sure if its true, but its something to be avare of.

  5. the blue hue in the picture got me all excited for a second i thought he made a cold plasma device. i wonder why there is not more hack about plasma disinfection there was a lot of research going the last couple of years and it all looked pretty promising.

    1. Though you’d get pretty powerful UV if you just unhooked the magnetron and hooked it’s power supply up to a couple of carbon rods rigged in a spark gap, all the UV and plasma you want. :-D … hot plasma though.

  6. UVC is energetic enough to break down many plastics that do not have high reflectivity for that optic band—basically, the photon energy is enough to break the polymer bonds. I think he will find that the window will fog and crumble.

    In any case why are people complicating things so much? as they say, weeks of futzing about in the lab converting microwave ovens to UVC can save an hour of literature research that finds that the best recommended sanitization method is a warm toaster oven (30 min in 70 deg Celsius, which happens to be the WARM setting in my tabletop oven)



  7. UVC photons are energetic enough to break polymer bonds in most plastics, unless they are reflective enough to limit the photon ingress. I think they will find that the window will fog and crumble.

    In any case, why complicate things? As they say, weeks in the lab, converting microwaves to UVC, can save an hour of literature research (sorry for broken link—trying to avoid spam detectors that would otherwise eat it)

    https :// http://www.livescience.com/sanitizing-medical-masks-for-reuse-coronavirus.html
    https :// http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781738/

    they recommend dry oven heating. My tabletop toaster oven just happens to be 170F/70C on WARM setting, so I just bake my masks in a glass container on WARM for 30 minutes.

  8. Seems heating things to 92°C for 15 minutes works:

    So for things that don’t melt, 20 minutes in the oven at 100 should work rather well with a bit of margin.

    Having designed sterilisation kit, not keen on line of sight techniques. Everything has an inside or a fold for muck to hide in. Heat gets everywhere.

    Boiling caustic soda would also be good at killing stuff, and dissolving glassware.

  9. I made a UV exposure box for double sided photoresist PCBs from an old microwave back in 2007, 6x philips facial solarium UVA tubes in the bottom and top (no turntable any more), glass tray in the middle. Kind of worked but was a bit hit and miss to be honest, timer was a bonus though. Looked very like this picture when it was on!

  10. I think that cellphone manufacturers wallet makers and the manufacturers of chipped car keys and remote key fobs should band together and start making and selling home UV sterilizers at cost. They stand to make a fortune when people start replacing those objects far more often because they get in the habit of sticking them in the sterilizer every night despite what UV does to plastic.

    Also the treasury department had better get ready to start printing replacements for and disposal of UV faded bills at an unprecedented rate.

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