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In the Air Design Challenge - Pollen & Allergen Sensing – Post 1 (Pollen Sensor)

tomaja

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In the Air Design Challenge - Pollen & Allergen Sensing

 

image

Figure 1. Bad guy (Ambrosia pollen grain)

 

As I’m still waiting for my challenge kit I’m using the time to consider pollen sensing since that might be the weakest point of my project.

 

Possibilities

At this moment I have two alternatives for pollen sensor: Homemade and commercial one.

Using commercial one would make my project much easier and the focus would be on making some nice apps for desktop and mobile but with homemade sensor most efforts would be on making the sensor do its thing...

 

1) Homemade pollen sensor

As my plan is to detect pollen, I did some research and discovered a paper on pollen sensing that proposes an idea which seems feasible (Shigeto Kawashima et al. - An algorithm and a device for counting airborne pollen automatically using laser optics).

This task would require very much hard work and could easily turn out to be a failure but I can still try. Some optics would be required - hopefully I will be able to obtain all the necessary parts to build the prototype.

image

Figure 2. Pollen sensor

 

Authors propose that red laser should be used but I think that maybe green or yellow laser would be more appropriate because pollen colour is usually the same (i.e. it reflects green or yellow). I bought the green (532nm) one locally to be used for this purpose.

In order to observe the photodiode sensor signals an oscilloscope is required so I decided to order one that fits in the budget (PicoScope 2204A). It arrived in just two days(!) and as I last used the oscilloscope ~15 years ago (at university) I spend some time testing it – It turned out it’s like riding a bike image

 

2) Commercial sensor

Now some bad news regarding the commercial pollen sensor… The one that I found (http://www.shinyei.co.jp/stc/optical/poln/main_poln_e.html) is not suitable for my location.

It only detects Japanese Cedar and Cypress but these pollen particles are bigger than those of Ragweed (which is the most common allergen in this part of Europe). This is not completely bad news as someone in Japan might find this project useful even with this sensor but for me that's probably not good enough.

Ragweed pollen presence in Europe:

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Figure 3. Ragweed pollen presence in Europe (August 2014)

 

Conclusion

In short, I will most probably focus my work on homemade pollen detection. image

 

 

I will update as soon as my challenge kit arrives (at this moment it’s being held at the local customs)

Comments and suggestions are always welcome.

 

Dragan

Parents Comment
  • in reply to michaelwylie

    Thanks for your valuable input, Mike.

    I was thinking about using white LED ring (maybe even some additional IR LEDs) because different kinds of pollen might be affected by different wavelengths.

    Also, I don't know what is the wavelength of pollen radiated light (I read that it can vary for different plant species and even with different ozone levels in the air). So, filtering doesn't seem like a choice for me.

     

    Please note that my goal is not particle counting, just a rough measure of pollen presence is good enough to see if level is getting higher or not. Some pollen grains will certainly be trapped by my "light trap" but if I make the tube wide and short enough not too many I hope.

     

    Can you advise on photo diode selection? I will be needing a very sensitive one (with very low threshold). Maybe something other than PD?

     

    Dragan

Children
  • in reply to tomaja

    Hey Dragan,

     

    Very impressive that you're creating such a sensor!!

     

    I think Michael is the expert here, I don't really know much about the semiconductor sensors, but worst case for a proof-of-concept (not suitable for a real product) you could try using a photomultiplier tube (they are reasonable cost from ebay, probably because semiconductor sensors are now used more) although they do require a high voltage supply : (

     

    If it comes to that send me a message, I can send you some bits that I got for experimenting but have not used (including a supply). The PM tube I have has quantum efficiency >16% for 200-400nm, and >4% up to 550nm.

     

    But hopefully some semiconductor sensor can be found, since it would probably be more suitable.

  • in reply to tomaja

    The pollen particles are huge ( over 20 microns), so your PD selection will depend on the expected wavelength you want to measure and the bandwidth (flow rate of the air). You need to define those two parameters to select a PD. I don't have a recommendation based on the white light excitation. More importantly, how are you going to machine/print the sensor body?

  • in reply to shabaz

    Thank you for your kind offer shabaz!

    Yes, Mike is certainly an expert, he helps a lot with his comments and suggestions.

  • in reply to michaelwylie

    Thanks again Mike!

    I was thinking that I should use white LEDs so that I don't have to check what wavelength causes most luminance (because I don't know how could I manage that without proper resources).

     

    As an alternative to white LEDs, I guess I could try with a couple of different monochromatic light sources like laser diodes (one by one) and try to repeat same conditions and measure the light intensity radiated by the pollen grains for each tested source (or try to find some research results on that topic).

    Then I could use the one that caused most luminance and try different PDs to find the peak luminance wavelength. What do you say?

    EDIT: Your link from yesterday provides results I can use for PD selection.

     

    As for the sensor body, I was thinking about using some 3D printing service (I don't have access to 3D printer or CNC machine locally). But I'm still far from having any real design ready, still just thinking about possibilities. One thing I know is that I will somehow have to make the inner surface smooth if I want to use 3D printed body.

     

    I really appreciate your comments, I will have to give special credits to you if this project ends up successful image

     

    Thanks,

    Dragan

  • in reply to tomaja

    I think you should give it a shot, experiment a little like you are planning. Part of the process is learning, so learn and then let us know how it goes. I think if you can get the body done and the optics sorted you'll end up with a response. It might not be a great response, but you'll get something. Unless you've got some friends, machining is usually EXPENSIVE, especially for a single piece. I think you are correct to explore the 3D printing option. The price will depend on the size and tolerance of your sensor body.

     

    Have any friends at the local university or any friends who work with CNC?