Sensopad is based on the theory of resonant inductive-circuit sensing. The pucks that are employed consist of a simple capacitor on a piece of circuit board. The capacitor and tracks of the circuit board form a simple resonant LC circuit that will resonate in the presence of a suitable electromagnetic field. This resonance can be detected and measured using suitably arranged sensing coils. Linear positions can be resolved down to a few microns and angular rotations down to minutes.
Position sensing on a single linear axis is straightforward.
Rotational position sensing may also be achieved by simply wrapping the linear coils around a center of rotation. With slightly more sophisticated arrangements, both x-y position and rotational angle can be measured in a 2D or curved plane. The theory of inductive resonant circuit sensing sounds tricky, but in reality the technology is based on some very straightforward, low-cost parts. The passive resonant circuit in the puck is typically made as a small printed circuit board connected to a surface-mount capacitor. The sensing coils are also most practically embodied as tracks on a printed circuit board.