The voltage output from a piezo disk using the radial axis, that is one allowed to flex, is about 3 times the output from one where pressure is applied to the surface, in the thickness axis. The very high sensitivity of piezoelectric discs is the single greatest advantage, outputs of several volts in response to a light nozzle contact are typical while repeatability may be in the region of a few µm. There are other directions of sensitivity, particularly that between the two surfaces of the ceramic disc: This is known as the thickness axis or sometimes as the axial axis. Expansion or contraction of the ceramic in this direction will cause the brass disk to which the PZT is bonded to dome outward or inward. The direction of this is determined by something called 'polling' which is done in manufacture and in piezoelectric disks this is radial, pointing from the centre of the diameter outwards. The piezoactive material in most piezo disks is a ceramic known as PZT which expands or contracts when a voltage is applied to it it also generates a voltage when it is put under pressure or strain.

The first known use of piezoelectric discs in this manner was by Njål Brekke who fitted piezo discs to respond to the bed pressure transmitted through bed leveling springs.

There have also been several postings in 3D printing forums speculating that they may be usable as nozzle touch sensors for FFF (FDM) 3D printers. Inexpensive piezoelectric discs have been used for touch sensing in the past on projects like maze running robots.

Piezo disc voltage output