Photographic film affected by RF? - Page 1
Forum section: electronics / general

author: Circlotron
author_rank: Super Contributor
timestamp: April 18, 2019, 02:31:27 am
content: We all know that photographic film is sensitive to X-rays, presumably UV, visible light, and some films to infra red. What about ordinary RF? At least microwave. They are all electromagnetic, just different places on the wavelength / frequency scale.

author: Ampera
author_rank: Super Contributor
timestamp: April 18, 2019, 03:57:56 am
content: Probably at some level, direction, and intensity. The same RF that is used to deliver a signal to your laptop can probably completely melt the film so long as there's a bit of water around (like in the air).The key difference with the sorts of EMR you're talking about (X-Rays, visible and just outside visible light like UV and IR) is that they are /considerably/ higher in frequency on a considerable order of magnitude, and as the frequency goes up, the damaging effects EMR can have usually intensify. Once you start getting to UV and onwards, EMR becomes ionizing.There's a lot of, if, but, and or's here. What sort of RF? How intense? Directional/Focused?

author: hamster_nz
author_rank: Super Contributor
timestamp: April 18, 2019, 04:36:29 am
content: My guess would be that below a certain frequency the photons wouldn't have enough energy to initiate the chemical reaction in the film. It seems that about 1mm (300GHz) is that cutoff point.(seehttps://www.thomasnet.com/articles/instruments-controls/Infrared-Filmfor talk of IR films)On the other hand, given enough RF you heat almost anything enough to make it change colour

author: Berni
author_rank: Super Contributor
timestamp: April 18, 2019, 04:45:15 am
content: Technically very powerful RF could heat up the film enough trough dielectric losses to leave a mark on it.The actual way film works is that a photon hits a molecule with enough energy to break a chemical bond. The material used on photographic film contains a bond that takes particularly little energy to break and once broken the molecule breaks apart in a different compound. This other compound is then turned into a strong dark color during the chemistry of the film development process.Because these photons deliver energy in quantized packets means that a single photon needs to carry enough energy to overpower that particular chemical bond. If the energy is too low then energy the photon applied to the bond will just result in a bit more vibration of the molecule, increasing its temperature slightly. This energy is directly proportional to the photons wavelength. This is why UV light is more harmful than visible light, the short wavelengths of UV give the photons enough energy to break all sorts of chemical bonds, going higher to Xrays there is enough energy to not only break particularly weak bonds but even knock entire atoms out, creating ions (hence ionizing radiation).So basically film that could image RF would need to be made out of a compound that has a particularly weak bond so that the tiny energy of RF photons can break it. Problem however is that long wave infrared photons have more energy than even 100GHz RF. So such a film would be so unstable it would need to be kept at just above absolute zero (-273°C) to avoid the film generating its own IR photon and breaking apart on its own. Also the box you keep the film in needs to be at near absolute zero or the box walls could also emit photon powerful enough to ruin your ultra sensitive film.Long story short, its easier to use antennas to detect RF.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 18, 2019, 12:05:58 pm
content: Right, by the same quantum mechanism, it won't. So that leaves more classical mechanisms. Dielectric heating could cause chemical changes in the film, leading to poor performance when it is finally used, or effectively exposing it in situ. Extreme fields can cause breakdown, creating light and exposing things in the usual way. Note that the fields don't need to be all that extreme -- partial (dielectric) discharge can be triggered by mere static electricity.Going back to the quantum model, these sorts of processes are allowed by alternate pathways (chemical equilibrium), and effective up-conversion (many photons act together in a medium, producing fewer higher energy photons). Sparks have zillions of photons involved in the creation of the phenomena, so again, it's not useful to try and work in the quantum domain here, it's adequate merely to note that, yes, it is a possible mechanism.Tim