The elastic deformation of the molecular structure of ferromagnetic materials like iron, nickel, cobalt and their alloys is called magnetostriction. The micromechanical deformation takes place during a change in the magnetisation. The magnetic structure of ferromagnetic materials consists of the sum of countless small elementary magnets. The elementary magnets with the same magnetic orientation are grouped in limited areas called Weiss domains. The magnetic orientation of the Weiss
domains is arbitrary in the non-magnetised state. When exposed to an external magnetic field, a certain number of domains spontaneously
orient themselves in the direction of the magnetism. The number of domains that orient themselves in the direction of magnetisation is dependent both on the magnetic field strength of the external field and on the mechanical properties of the ferromagnetic material. The change in magnetisation of the domains produces a spontaneous change in the mechanical form, whereby a mechanical wave results. The mechanical wave is a torsion wave which results at the location of the excitation by the external magnetic field. The torsion wave is propagated in the ferromagnetic material at a speed of 2,800 m/s. This physical property is the basis for magnetostrictive position transducers.
A ferromagnetic material with a marked magnetostrictive property (waveguide) is positioned along the measuring path in a rugged housing. An external magnetic field (position transducer) marks the measuring position. The spontaneous change in magnetisation is triggered by the interaction of the external magnetic field and a very short current pulse, which flows through the waveguide. The torsion wave is propagated in the waveguide. The time between excitation and the reception of the torsion wave in a wave converter is converted to the corresponding position value in the electronics.