AIM Diffusion Field Resonance is a phenomena which occurs when two or more espers with the same type of ability (and therefore similar AIM Diffusion Fields) gather together within a localized area. As the name suggests, the espers' AIM Diffusion Fields resonate with one another, which causes the effects of the fields to become greater and more prominent.
Normally, this phenomena is relative harmless for all parties involved. In Misaka Mikoto's case, this can allow for her to detect certain other espers with the same ability as her own; with the strength of this detection seemingly being dependent on how similar another esper's ability is to her own (such as how she was able to better sense the esper powers of her sisters than other Electromasters in close enough proximity).
However, when an overloaded esper, quite possibly in an unstable state of mind, comes into close proximity with other espers, it can lead to an occurrence of RSPK Syndrome. This can cause the relatively harmless AIM Diffusion Field Resonance to become harmful and potentially catastrophic to both those involved and the environment affected by it.
Toaru Kagaku no Railgun
- Main article: Poltergeist Arc
The possibility of an AIM Diffusion Field Resonance being the cause of the Poltergeist incidents happening across Academy City was initially referred to by Konori Mii. Sometime after this, Shirai Kuroko explained to Mikoto the relevance of the phenomena to the current poltergeist events happening all over the city.
It is later revealed by Therestina, that exposing Haruue Erii (since she can exhibit power beyond her level class when exposed to a specific wavelength) to the Crystallized Esper Essence would cause a resonance with Kiyama Harumi's Child Error students, allowing her to achieve that specific wavelength, causing her to achieve Level 6 at the cost of destroying the city.
- Main article: Sisters Arc
On August 15th, Mikoto was introduced to a child who had a similar power to her. The children asked if one day they could form a 'radio' together (i.e. if they could talk to each other with their powers). Mikoto told them that it was impossible, but if they were in an open space with no obstruction, then they would be able to detect each other. Mikoto then commented to herself that they could make a network if they had similar brainwaves, just like the Level Upper, then they could in theory make something similar to a radio.