Abstract: The device comprises an electrically insulating substrate comprising a principal section (3). First and second principal surfaces (1a, 1b) of the principal section (3) support first and second pairs of conductor tracks, respectively. Each pattern comprises a series of coil elements (7), opposite each coil element of the first pattern there being situated a coil element of the second pattern. Each coil element (7) comprises a spiral-shaped conductor track, having an inner end (9) and an outer end (11), and some coil elements are electrically interconnected in a two-by-two fashion by means of a connection track (13) which extends between their outer ends, the connection tracks on each of the two principal surfaces extending opposite parts of the other principal surface which are free from connection tracks. The principal section (3) is folded, so that the coil elements are situated in mutually parallel planes.

Abstract: A piezoelectric device, comprising a number of polarizable ceramic plates 1 which are stacked with intermediate metal plates which serve as electrodes. The stack is subjected to a large amount of preload by a preloading element having a relatively flat spring-force characteristic over the piezoelectric operating range of the device which is formed by a cylindrical housing having two sets of parallel pairs of slots 7, 10, rotationally displaced by 90 degrees, the preloading force being applied to the stack by threaded end plugs 4 and 5. The ceramic plates are polarized only after assembly and preloading.