ABSTRACT
The search coil technique uses three magnetic fields oscillating at different frequencies and directed along three orthogonal axes x, y and z. The fields are generated by six large coils arranged in a cubelike fashion. Coil pairs lying on parallel surfaces of the cube are driven with currents of the same frequency. Measurement errors of the search coil method are generally caused by instabilities of the magnetic fields’ amplitudes, by temperature dependences of the electronic circuits in the processing unit, by use of different types of coils with different shapes and sensivities, and by other environmental factors. For example, metallic parts around the field generating coils will distort the magnetic fields. A Skalar annulus consists of a silicone rubber ring in which two search coils are embedded, one lying concentrically around the pupil and the other as an elongated figure eight wrapped such that it is effectively orthogonal to the first coil.
