So, many people use lifts, and fingers are dirty. UV LEDs are now inexpensive and available in a variety of bug- killing wavelengths. The problem is that you can't just irradiate the inside of a lift with UV... So, I propose making the lift buttons like the objective-oil-coverslip interface on a TIRF microscope (now would be an excellent time to go and have a look at wikipedia...). The idea being that a lift button could be constructed so that it totally internally reflects the light from the UV LED mounted behind it. This would produce a short range evanescent wave at the button's surface. This would extend a few hundred nano metres and be more than enough to finish off any nasty bugs there lurking. The range is so short however that it will not penetrate through more than a couple of layers of dead outer skin cells, keeping it all nice and safe.
The beauty lies in the fact that the more a button is used the more it is UV'd, so use and sterilization are coupled. The button could have a small amount of a fluophore mixed into the plastic, or whatever so some of the UV would go to make a pleasing visible glow, making a 2nd visible light LED redundant.
This idea could of course be extended to all buttons and rails in all slightly grubby places.
Or make them out of copper, that would work but be nowhere near as cool...-- bs0u0155, Dec 10 2011 TIRF microsopy http://en.wikipedia...rescence_microscope [bs0u0155, Dec 10 2011] Increase Safety When Doffing PPE with UV Light — Frustrated Total Internal Reflection and Ultraviolet Evanescent Wave Penetration for Targeted, Continuous Decontamination of Personal Protective Equipment https://challenges....-equipment-ftir-ppeMentioned in my anno. Idea for a hospital gown that works the same way [notexactly, Apr 25 2019] Are lift buttons really a significant source of infection? Compared, say, to the person next to you coughing in an small enclosed space?
Furthermore this would put decent, hard-working telephone sanitizers out of work.
But very elegant, assuming the physics is correct.-- mouseposture, Dec 10 2011 I have an aunt who's a telephone sanitiser, but she's not decent. She upsets people at funerals.-- nineteenthly, Dec 10 2011 If you can make them cheaply and easily why not. If they end up being a bit pricey, perhaps hospitals are a better deployment.... Actually this would be great for all medical machinery.... drip pumps and the like...-- bs0u0155, Dec 10 2011 Definitely a better deployment. Would be a commercial success regardless of whether it actually worked.-- mouseposture, Dec 10 2011 [+] for using TIRF. Bear in mind that the average bacterium is maybe a micron or two across, so this might not work for bugs stacked two-deep.-- MaxwellBuchanan, Dec 11 2011 Pretty sure this only works if the optical surfaces remain clean, since if the evanescent wave hits anything, it scatters the energy, so the moment the buttons got dirty, you'd have UV energy in the cab.-- MechE, Dec 11 2011 I think not. TIRF is used mainly because it only illuminates things very close to the surface. So, you can put a cell on the coverslip, illuminate it with TIRF, and you only see a thin proximal slice of the cell - the light doesn't scatter out into the body of the cell.-- MaxwellBuchanan, Dec 11 2011 Double checked, it may only be true if the contacting material is transparent and has a higher index of refraction than the air.
You know, like finger oils.-- MechE, Dec 11 2011 //Double checked,// Source?-- MaxwellBuchanan, Dec 11 2011 Clearly, if the angle of incidence is shallow enough, then total internal reflection will be maintained for contacting materials having a refractive index greater than air but less than the lift buttons.
Macgyver: Quick! Give me the diamond. Now, point the vial of plague bacilli towards the lift button, and shield your eyes...-- spidermother, Dec 11 2011 Wikipedia, one article from the link. But I'd read up on the effect before, just couldn't remember the details.
And [spider], it doesn't actually have to be in contact.-- MechE, Dec 11 2011 This might also work in elevators.-- swimswim, Dec 11 2011 //it doesn't actually have to be in contact// Quite so, but anything that remains within a few wavelengths of the surface of a lift button for a significant time is likely, for all in tents and porpoises, to be in contact.
Of course, there are many common materials with refractive indices similar to glass or plastic - sand, for instance. Perhaps the lift buttons should be made of diamond.-- spidermother, Dec 11 2011 Hang on. I'm not sure everything's right, especially as regards MechE's comments and suchlike.
As far as I'm aware, the evanescent wave which is created at the glass/sample interface (or in this case, the lift-button/grot interface) is not a photon as such, and hence cannot be scattered or radiated away from the few-hundred-nanometre- thick layer where it originates.
[MechE] can you clarify which bit of the Wikipedia article supports your contention? (NB - the first figure on the Wikipedia page shows emitted light from the sample being transmitted back through the coverslip and into the lens. But this emitted light is fluorescence from the sample in response to the evanescent wave - not the UV light.)-- MaxwellBuchanan, Dec 11 2011 A simple demonstration of what [MechE] is talking about: Look through an aquarium such that one wall appears to be a mirror (demonstrating total internal reflection). Nothing is visible outside the aquarium, through that wall. Then touch that wall from the outside. Your finger print is then clearly visible, where it is sufficiently close to (loosely speaking, touches) the glass. The evanescent wave has become real photons, which are then absorbed or reflected by the finger.
If you repeat this, but substitute transparent plastic with a refractive index less than water (but greater than air) for the finger, it should be possible to find a new, shallower angle at which total internal reflection is restored.
Seriously, it's not all that complicated. Total internal reflection is possible if, and only if, two transparent media are in contact, and the medium on the inside has the greater refractive index. The greater the ratio of refractive indices, the closer to normal the angle at which total internal reflection begins.-- spidermother, Dec 11 2011 [spidermother] I think we're talking at cross porpoises. [MechE] was saying that the evanescent wave can be scattered away from the button surface, and I'm saying that, as long as the refractive index of the button is higher than that of what's on it (and as long as the UV light hits the interior of the button at a shallow enough angle), that can't happen.
In the aquarium situation, you're looking from the inside (ie, you can see the fingerprint from "inside the button" in the context of the lift button).-- MaxwellBuchanan, Dec 11 2011 It's in the TIR (not the TIRF) article, under the evanescent wave section.-- MechE, Dec 11 2011 I think [MechE] has missed the point that if the contacting object has a refractive index greater than air but less than the button, then all that is needed is a shallower angle of incidence for TIR to occur.
I think [MaxwellBuchanan] has missed the point that an object that absorbs light (such as dirt, a finger, or a fluorescent molecule) disrupts TIR, whatever the angle of incidence.-- spidermother, Dec 11 2011 [Spider] There is no angle at which the evanescent wave doesn't occur. If that wave encounters an object with a higher index of refraction, energy is lost to the outside, no matter what.-- MechE, Dec 12 2011 As long as we're clear that the touching object needs to have a //higher index of refraction// than the *button*, not simply than the *air*, then we agree.-- spidermother, Dec 12 2011 //However, if a third medium with a higher refractive index than the low-index second medium is placed within less than several wavelengths distance from the interface between the first medium and the second medium, the evanescent wave will be different from the one under "ordinary conditions" and it will pass energy across the second into the third medium.//
Quote from the Wikipedia article on total internal refraction. Note that the third material is only required to have a higher index than the second (low index) medium, in this case, air.-- MechE, Dec 12 2011 I think that statement is oversimplified; I would suggest that it *may* pass energy across the second into the third medium, but whether it does depends on the particular refractive indices and arrangement of the materials. However, it's given me something to think about some more...-- spidermother, Dec 12 2011 I press them with my knuckle. But Im for anything that increases sanitation.-- bob, Dec 13 2011 I'm reasonably certain I've never become sick from a contaminated elevator button, and I've been in some pretty nasty elevators. I stayed in a hotel in Rome that proudly upheld a 400-year tradition of not cleaning their elevator.-- Alterother, Dec 13 2011 I think people probably get infected by mucus on lift buttons quite a lot, and maybe by people not washing their hands after consulting the oracle. Copper buttons would sort it but UV would be cooler. How about the whole lift is flooded with UV radiation all the time it's empty? And in swimming pools and public toilets?-- nineteenthly, Dec 13 2011 also you can't use copper on everything, the steampunks would get all overexcited....-- bs0u0155, Dec 13 2011 This could also be applied to faucet handles. I thought of it in the bathroom earlier, and was going to post it as its own idea, but Google led me here when I looked for prior art, and it's not really enough of a different thing to warrant posting on its own. And the concern about FTIR leading to unwanted free-space release of UV is something I didn't think of.
N/A [2019-04-25]
I also found some prior art (for my having of the idea today)/posterior art (for this idea posted back in 2011) about a self-sterilizing hospital gown that works the same way: [link]-- notexactly, Apr 25 2019 That gown thing isn't very well thought through. It's not at all clear how the whole surface will be exposed to light. That's mainly because it can't be. It's relatively easy to TIRF the surface of a button but a big light flexible disposable coat? You're having a laugh mate.-- bs0u0155, Apr 26 2019 //you can't just irradiate the inside of a lift with UV.// Well not with people currently inside. A locked out self cleaning mode sounds prototype-able with, of course, an appropriate radioactive isotope for that sizzling clean.-- wjt, Apr 27 2019 random, halfbakery