Abstract: A linear displacement transducer has an elongated current conducting, tubular coil which is mounted to an end cap in a hydraulic or pneumatic cylinder and extends into a hole bored in the piston/piston rod unit within the cylinder. An electrically conducting, nonferromagnetic tube lines the wall of the bore and reciprocates axially with the piston/piston rod unit varying its overlap of the coil and thereby varying the inductance of the coil at an applied frequency. An AC electrical energy source is connected to apply an AC signal to the coil, the frequency of this signal being at least high enough that the skin depth in the tubular wall is less than the physical depth of the tubular wall. A detector circuit means is connected to the coil for detecting a signal which is proportional to the coil inductance and therefore is proportional to the displacement of the piston/piston rod unit within the cylinder.

Abstract: An electromechanical transducer particularly useful as a linear alternator driven by a free-piston Stirling engine is disclosed. A relatively high permeability material is formed into a flux loop having at least two pairs of spaced gaps formed transversely through the loop. Each pair of gaps is aligned along a reciprocation path for a magnet which is mechanically mounted for reciprocation between alternate positions within the gaps of each pair. The magnets have a magnetization vector transverse to the reciprocation path and are drivingly linked to a mechanical energy input or output for operation respectively as an alternator or motor. The armature coil is wound around a portion of the flux loop.