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Open source UVGI respiratory mask

Kills bacteria, viruses and mould spores in the air before inhalation and after exhalation

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Wearing face masks in public has a long tradition in Asia, most notably in Japan, China and Korea. In the case of epidemics such as the coronavirus, in some regions of Asia it is even compulsory to wear a face mask in public. People usually wear simple surgical masks to prevent smear and droplet infections. However, these masks do not help sufficiently, the risk of infection is still very high, they have to be changed daily or even several times a day and breathing through these masks is difficult. Viruses are also transmitted via aerosols suspended in the air where even HEPA filters are ineffective.
When the corona virus outbreak occurred in China, I started thinking the first time about how these respiratory masks could be improved. At the beginning I thought of some chemical-soaked inserts in the mask, then my attention turned to ultraviolet germicidal irradiation, a disinfection method that uses short-wavelength ultraviolet (UVC) light to kill or inactivate microorganisms.

A few weeks ago I became aware of the mid-power UVC-LED VLMU35CM00-280-120 from Vishay, designed for disinfection and sterilization. It comes in a 3.5 x 3.5 x 1.2mm re-flow soldering compatible surface-ceramic mount package with a quartz window. Its radiant power is typically 15mW at 100mA, the wavelength is usually 278nm and it has a nominal forward voltage of 5V. A built-in Zener diode will limit voltage in case of surge or if wrong voltage is applied. Its lifetime is 25000 h, while mercury lamps have a lifetime of 10000 h. Furthermore, compared to mercury lamps, this new UVC LED  is not shock-intensive, environmentally friendly, has no heating phase, can be used in the low voltage range and consumes much less power. The price for one of these Vishay LEDs is currently almost 40 USD though! However, UVC LEDs with almost identical technical parameters are available in China at a fraction of the price, even though Vishay's LED is also manufactured in China.

I ordered three of them from Digikey for first experiments, already in the back of my mind to design a improved breathing mask by irradiating the respiratory flow with short-wave ultraviolet light. The idea of a UVC breathing mask is not new. There are dozens of patents. Here is an exemplary drawing from the US patent US8733356B1. You don't want to wear that kind of mask. It won't work. Except the UVC light will burn your face, lips, and throat as skin exposure to UVC light can produce rapid sunburn and skin cancer. Exposure of the eyes to this UV radiation can produce extremely painful inflammation of the cornea and temporary or permanent vision impairment, up to and including blindness in some cases.

I have applied for a patent as well. It is not difficult to have an idea and to get a patent for it. The difficulty is rather to develop a technically mature product and find a market for it. I think the market for this mask will be mainly in Asia, but a market could emerge anywhere in the world, as current developments show. In this context I am looking for an Asian supplier who can produce the mask. If you think you're suitable, drop me a message. Maybe I will run a Kickstarter or Indiegogo campaign.

The LED is powered via a USB micro B connector. Since the power consumption is relatively high and the mask is worn in public for a long period of time, a portable power supply is needed, preferably 5V, hence a power bank, connected to the mask via USB cable. As already mentioned, the forward voltage is according to the datasheet typically 5V but  it's not exactly 5V. After some measurements and taken the USB voltage range of 4.75 to 5.25V in account I decided to use a current limiting resistor of 5.6 Ohm.

It is only a very narrow range of wavelengths that our eye can detect. It ranges from red (750 nm) to violet (400 nm). As you can see the UVC LED from Vishay emits a small amount of bluish light. The ultraviolet light with the typical wavelength of 278 nm, which the LED also emits, is not visible to the human eye and camera. The data sheet states: Depending on the mode of operation, these devices emit highly concentrated non visible ultraviolet light which can be hazardous to the human eye and skin.

The UVC LED has a quartz window for a reason. Normal glass and many plastics block UVC radiation. This can be shown with a simple experiment. If a test tube with dissolved fluorescein is exposed to UVC light from outside, no fluorescence occurs. If the liquid is directly exposed to UVC light, it fluoresces. But one can see that the UVC-radiation does not penetrate far even in liquids.

As the breathing air is led through a circular chamber with a diameter of about 40 mm in which the disinfection takes place, the LED must kill bacteria and viruses in this range immediately by destroying nucleic acids and disrupting their DNA so that they are no longer able to perform vital cell functions. Whether it will do so in this configuration remains to be...

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smd6060-uvc-led-high-power.pdf

Datasheet of the high power UVC-LED S6060-W275-P100-MH

Adobe Portable Document Format - 768.51 kB - 04/07/2020 at 19:57

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fzz - 19.77 kB - 03/26/2020 at 09:01

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SSEYO Koan Play File - 17.60 MB - 03/26/2020 at 08:59

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10118192.pdf

Dimensional drawings and PCB layout of the USB Micro B connector

Adobe Portable Document Format - 99.68 kB - 02/29/2020 at 17:24

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pt0491-1903-uvled.pdf

Additional notes about ceramic-based UV LEDs from Vishay

Adobe Portable Document Format - 1.08 MB - 02/29/2020 at 17:22

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  • High Power UV-C LED

    M. Bindhammer04/07/2020 at 19:55 0 comments

    Finally I found a 6060 SMD UV-C LED with a radiant flux of 100mW @350mA and 6V,  275nm, named S6060-W275-P100-MH, datasheet can be found at the FILES section. Disadvantage is however the short life time, typically 1000 to 3000 h, depending on power output.

    I spent two days to design a new high power UV-C LED driver, based on the LT1618. The width of the PCB is exactly the same as of the TO220, so I can use TO220-heat sinks. I added two mounting holes to attach two 25mm long TO220-heat sinks. The left cutout is for a push button, so the UV-C LED module will only turn on if it is correctly inserted in the disinfection chamber. The right cutout is for a status LED.

    My favorite PCB fab Aisler will support me on my COVID-19 projects and provide PCBs and stencils free of charge. Thanks again, Felix!

    Three of the 100mW UV-C LEDs, 30€ each:

    Suitable heatsink samples:

  • Other UVC-LED-based respiratory mask projects

    M. Bindhammer03/31/2020 at 21:11 0 comments
  • Design

    M. Bindhammer03/31/2020 at 20:58 0 comments

    Respiratory masks will be part of the street scene in the near future. In Asia they are already, in the rest of the world they will be. These masks will become items of clothing like caps, scarves or gloves. Therefore, in addition to the basic requirements of respirators, they must be stylish and comfortable to wear. That is why I have been working on the design over the last few days. What bothered me most of all was the mask's widely protruding filter, top-heavy and easy to get stuck somewhere and pull the mask off your head. When I looked at my cat, I got the idea of a L-shaped filter. I explain this most easily with a picture:

    Btw, this is not my cat...

    And here is a first artistic view. I wanted to know how the mask looks like on a Chinese girl, with the skyline of Shanghai in the background. My GIMP skills are not the best, but I am improving...

  • UV dose

    M. Bindhammer03/08/2020 at 12:04 0 comments

    The UV dose d is a measurement of the energy Φe per unit area A that is incident on a surface. The UV dose is the product of the average intensity acting on a microoranism from all directions and the exposure time t:

    The UV dose required for inactivation of virtually all pathogens is 40mJ/cm2.

    Calculating the velocity of the air flow through the disinfection chamber is difficult because we are dealing with turbulent flow, mainly caused by the ventilation slots and ribs at the entrance and exit of the chamber. Therefore we have to make some assumptions.

    The volume of gas inhaled or exhaled from a person's lungs is around 0.5L. Let us assume that we need 2 seconds per breath, then this results in a volume flow Q of 0.25L/s or 0.00025m3/s. If we also assume that it is only laminar flow through a round tube with flow cross-section A○ and inner diamter di, the speed v of the breathing gas flowing through the disinfection chamber is given by:

    With the inner diameter of the disinfection chamber of 40 mm this results in a speed of 0.20m/s. The disinfection chamber of the prototype has a length of 20mm. If we assume that the microoranism takes the straight path through the chamber, it needs 0.1s. Together with a surface area of 2x4cm this results in a UV dose of only 0.19mJ/cm2. This means the UVC LED must have a radiant power of 3.2W to reliably kill all pathogens in the chamber.

    UVC LEDs with a radiant flux of up to 100mW are currently available on the market. But these high-power LEDs generate a considerable amount of heat and can only be operated with an appropriate heat sink.

    The t/A ratio cannot be improved significantly. The volume flow Q is to be regarded as constant. The exposure time t depends on the area A, since the area has an effect on the flow velocity. On the other hand this paper states "Literature supports UVGI exposures of 1 J/cm2 are capable of decontaminating influenza virus on N95 FFRs and exposures as low as of 2-5 mJ/cm2 are capable inactivating coronaviruses on surface". Using a LED with a radiant flux of 100mW we would get a dose of 1,266 mJ/cm2 in the respiratory airflow at assumed flow velocity. So we would have to halve or even better divide the flow velocity by three, which I think is feasible, to deactivate at least corona viruses. And a surface is different to an air stream, as viruses can "hide" in the pores and microscopic irregularities due to their small size. In the air stream, however, they are also enveloped in aerosols, but this is an advantage because these tiny droplets act like microscopic lenses.

    Another concern was the formation of ozone but I can rule this out now. Only UV radiation below 200 nm splits oxygen molecules into atomic oxygen. The recombination of the atomic oxygen would then lead to the formation of ozone.

  • UVC-LED driver board

    M. Bindhammer02/29/2020 at 17:02 0 comments

    I ordered a stainless steel stencil with the PCBs because some components (USB connector and UVC LED) require reflow process. I used low melting solder paste and a hot air gun. The distances between the individual pins of the USB Micro B connector are so close that solder bridges can form during the re-flow process, but this can be remedied with a soldering iron with a very fine tip. I used the "without flange style" connector, because the front side of the USB connector must be led through a corresponding opening in the upper plastic part of the UVC LED module.

    In general the LED can be operated via a series resistor or PMW. Here you can see a driver board, where the LED is controlled by PWM. A TLC555I provides a square wave signal of about 220Hz, 50% duty cycle. Since the output of the timer cannot switch the LED directly, an n-channel MOSFET takes care of this. The LED is operated without series resistor. The LED warms up noticeably. The circuit draws approx. 80mA.

    Completed UVC-LED module:

    Schematic:

    The upper and lower housing of the UVC LED module were glued together and to the PCB. As usual, 2-component epoxy resin was used.

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Discussions

mart.hohensee wrote 05/11/2020 at 07:24 point

220nm is no good as it generates Ozone O3.
There is a thing called UV-photolysis: - ozone is generated @ wavelength 100<242nm (peak 185nm)- ozone is destroyed @ wavelength 242<315nm (peak 254nm) So the design should be based on 242<315 nm, whereas range in 250<280nm is absorbed well by nucleotides of DNA according to studies. I would suggest to use 275nm diodes.

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Manuel Báez wrote 04/30/2020 at 14:49 point

Hi, This one is good, but I think that you must think about somethings. First: Please,  Use LEDs with 222nm, thas are better and more safety. SEcond: Use a interchage wit alot area, reduce the speed for use a lite power and kill a lot virus. 

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Alejandro Brindis wrote 04/20/2020 at 04:06 point

What about using something like aerogel to make the air stream path long, so you get enough time to kill viruses

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M. Bindhammer wrote 04/20/2020 at 07:31 point

Good idea, thought about this as a filter material layer.

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Andrey Shubin wrote 04/17/2020 at 07:57 point

Hi! Guys everything is cool, but it doesn't work! For effective air disinfection, 385 j/m3 is required. We made a similar project and also put it in the public domain.
https://bit.ly/34JhnMs
My team has worked on this issue in detail. And we've given up on LEDs. From now on, we will only work with UV lamps. The design is cool. I suggest creating a joint product.

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M. Bindhammer wrote 04/19/2020 at 21:21 point

Do you have a datasheets of the LEDs you're using in your kickstarter video? I doubt those LEDs are in the UVC range. Mid- or high-power-UVC-LEDs are expensive and not easy to operate. You need a deticated driver and cooling for it. Also, I don't want to disinfect 1000 liters of air, just 500ml in a relatively short time, which is feasible according to my calculations.

Good luck with your campaign!

  Are you sure? yes | no

Andrey Shubin wrote 04/20/2020 at 11:19 point

Yes, the price of LEDs with a wavelength of 254 nm is about $ 120 and higher. For 265 nm of about$40. We were helped with the delivery of LEDs by good people. Unfortunately, there is no specification for them. An adult (with a respiratory volume of 0.5 liters and a frequency of 14 respiratory movements per minute) passes 7 liters of air through the lungs per minute. In a state of physical exertion, the minute volume of breath can reach 120 liters per minute. People are different and since we make a product that should keep a person healthy, we build calculations with stock. As I said, we have moved away from LEDs, since they need a lot and they have a small angle. In addition. The LEDs will need to be serviced, as they will get dusty. This will further reduce their effectiveness. I will be happy if your calculations are correct and you will succeed.

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mattgarrison wrote 04/07/2020 at 04:04 point

Had some ideas to contribute that. 

Since these LEDs are not able to instantaneously kill a virus when exposed to the LED, minimum size of the air being exposed to the UV will need to be at least the size of a tidal breathe, which on average is 500ml. That is pretty large to be attached to a face mask. A more realistic solution in my opinion would be a belt attachment with a hose feeding the mask. It could then be large enough to disinfect a significantly larger volume of air, while simultaneously keeping the LED farther from your face, which just seems safer. Being mostly a battery, some LEDs and empty space, it would be light. 

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M. Bindhammer wrote 04/07/2020 at 21:21 point

You do not inhale 500ml of air at once. It takes a few seconds for the lungs to fill up.  Same with exhalation. With your solution you would need a two-way valve to separate the inhaled air from the exhaled air. And most likely the hose would be too long to breathe directly through it, a ventilator or similar would be needed additionally. And what about the exhaled air? It would not be sterilized.

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M. Bindhammer wrote 03/26/2020 at 12:11 point

Please stop to use multiple accounts to try teaming up. You waste my time. And I don't have time.

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Andrew Smith wrote 03/25/2020 at 16:49 point

Interesting concept :)
Very nice!
But if you can! plz attach the schematic file.

Best!

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M. Bindhammer wrote 03/25/2020 at 18:43 point

I added the schematic in the "UVC-LED driver board" log

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M. Bindhammer wrote 03/07/2020 at 15:25 point

Second law of photochemistry

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Dan Maloney wrote 03/06/2020 at 18:47 point

Interesting concept. If I'm not mistaken, UV disinfection is directly proportional to the dose the target bug gets, which in turn is dependent on time of exposure. You might have to figure out a way to increase the "dwell time" of the air stream over the LEDs, to make sure the bugs get enough light to kill them.

Good luck!

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