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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...
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-ppe
Mentioned in my anno. Idea for a hospital gown that works the same way [notexactly, Apr 25 2019]
[link]
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Are lift buttons really a significant source of
infection? Compared, say, to the person next to you
coughing in an small enclosed space? |
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Furthermore this would put decent, hard-working
telephone sanitizers out of work. |
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But very elegant, assuming the physics is correct. |
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I have an aunt who's a telephone sanitiser, but she's
not decent. She upsets people at funerals. |
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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... |
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Definitely a better deployment. Would be a
commercial success regardless of whether it actually
worked. |
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[+] 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. |
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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. |
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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. |
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Double checked, it may only be true if the
contacting material is transparent and has a higher
index of refraction than the air. |
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You know, like finger oils. |
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//Double checked,// Source? |
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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. |
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Macgyver: Quick! Give me the diamond. Now, point the vial of plague bacilli towards the lift button, and shield your eyes... |
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Wikipedia, one article from the link. But I'd read up
on the effect before, just couldn't remember the
details. |
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And [spider], it doesn't actually have to be in
contact. |
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This might also work in elevators. |
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//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. |
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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. |
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Hang on. I'm not sure everything's right,
especially as regards MechE's comments and
suchlike. |
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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. |
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[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.) |
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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. |
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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. |
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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. |
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[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. |
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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). |
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It's in the TIR (not the TIRF) article, under the
evanescent wave section. |
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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. |
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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. |
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[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. |
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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. |
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//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.// |
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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. |
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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... |
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I press them with my knuckle. But Im for anything
that increases sanitation. |
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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. |
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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? |
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also you can't use copper on everything, the
steampunks would get all overexcited.... |
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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. |
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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] |
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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. |
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//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. |
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