A sensor inductor (1) for magnetic fields, particularly of the saturating-core type, has at least one inductor coil (10) which is wound as a planar spiral about a core (20). More preferably a plurality of planar spirals (10a-10d) are stacked along the axis (50) of the core. A pair of adjacent coils (10a:10b) are wound as spirals of opposite sense with the inner ends (32a: 32b) connected together by bridges (44). Two or three such pairs may be used. The plural coils (10a-10d) and the central core (20) may be fabricated using planar selective deposition techniques known from the semiconductor industry. The magnetic core (50) may be a separate entity inserted into an axial hole formed through the stack of coils. A preferred core material is permalloy. Turns width (w), spacing (s) and thickness (t) of the spiral coils is discussed together with the axial spacing (d) between coils and core diameter ( PHI )
