Nanophysics and nanotechnology applied to sensors, part 1

Sensors are usually electronic devices used to measure quantities such as magnetic field intensity, height from a surface, or perhaps the local density of magnetic moments. Of particular interest in this paper are arrays of sensors or scanning sensors that create images from the measured quantities. We categorize sensors by sensitivity and, in the case of imaging sensors, by spatial resolution in one, two or even three directions. In some cases, the sensitivity is limited by nanophysical laws. Examples include a fundamental limit φo = 2.07 X 10^-15 Wb, the quantum of magnetic flux, the Bohr radius ao = 0.0523 nm as a fundamental atomic size scale, or the Bohr magneton μB = 9.27 x 10^-24 J/T, the fundamental electronic magnetic moment. Sensing technology generally benefits from the miniaturization of electronic devices, and in the process something entirely new may appear. Moore's Law has described the evolution of billion-transistor silicon chips, doubling the device count about every 18 months, and the area of hard drives has developed even faster. Improvements have been made in two areas: more devices per unit area usually working faster and discovery of new operating principles.