The sensors work by detecting extremely low-frequency electrical activity over a distance of 5 microns (one micron being equal to one millionth of a metre).
They categorised facial dimensions such as the distance between the eyes, then recorded the electrical activity of one brain cell at a time while they showed cartoons to the macaques.
Optical technologies have revolutionized long-distance communications, replacing low-capacity copper wiring that carries electrical signals with combinations of lasers and fiber-optic cabling that send information over many high-speed channels.
My initial interest was due to my electrical engineering background, I always thought that millimeter wave band was not suitable for long distance transmissions.