A point charge is a hypothetical charge located at a single point in space.

summation (n.)
1760, "process of calculating a sum," from Modern Latin summationem (nominative summatio) "an adding up," noun of action from Late Latin summatus, past participle of summare "to sum up," from Latin summa (see sum (n.)). Meaning "a summing up" is from 1836.

summing-up; plural noun: summing-ups; plural noun: summings-up
a restatement of the main points of an argument, case, etc.
"he was obviously startled at her cynical summing-up of his offer"
LAW
a judge's review of evidence at the end of a case, with a direction to the jury regarding points of law.
"his summing-up left the jury in no doubt about his own views"

To give a brief and accurate summary, description, assessment, or representation of something; to summarize.

e quation; plural noun: equations

1.
MATHEMATICS
a statement that the values of two mathematical expressions are equal (indicated by the sign =).

Similar:
mathematical problem
sum

There does not appear to be a amplitude modulating signal in the brain. But, a brain wave frequency may change it's amplitude.

Clinicians have learned not just to measure but to also manipulate brainwaves in non-invasive ways. ... In Neuropsychology, therapists use methodologies like LENS, Transcranial Magnetic Stimulation, or learning-based neurofeedback, to alter undesirable brain states.

Semiconductor quantum dots are capable of emitting polarization entangled photon pairs with ultralow multipair emission probability even at maximum brightness. ... Our work demonstrates the viability of quantum dots as light sources for entanglement-based quantum key distribution and quantum networks.

Radio-frequency identification uses electromagnetic fields to automatically identify and track tags attached to objects. An RFID system consists of a tiny radio transponder, a radio receiver and transmitter.

Piezoelectric nanomaterials have shown to be a very promising tool for a wireless, non-invasive, and targeted electric stimulation of cells and tissues13. When these nanomaterials undergo mechanical deformations, they are able to generate electric potentials on their surface thanks to the direct piezoelectric effect.

One of the most creative approaches to reduce the active components of implanted probes is to do away with interconnects altogether. Micro- and nanoparticles can be considered the simplest implementation of an external “probe” used for specific or localized stimulation or recording and, with other modalities described below (see the “Optical stimulation,” “Magnetic stimulation,” and “Ultrasound stimulation” sections), require untethered “wireless” operation.

One example is the concept of “neural dust”: cellular-scale particles recently put forth by Seo and coworkers (76, 77) that rely on individual, freestanding sensing nodes ~10 to 100 μm in size and scattered through the brain target area. The neural signal is recorded as a differential signal between two electrodes on the node, which electromechanically modulates a piezoelectric crystal. The piezoelectric modulation varies the ultrasonic backscatter that is interrogated and recorded by a transceiver device implanted subdurally. This concept is still in its infancy. Although a large-scale demonstrator (800 μm) has been reported (77), challenges include downscaling node size while minimizing SNR losses, addressing power considerations of subcranial ultrasonic transceivers and implantation strategies.