Zijlstra designed his instrument in order to study the hysteresis curves of microscopic (a few µm across) single domain particles. Using a fine (38 µm x 20 mm) gold wire as a resonant element, a resolution of 10-11 JT-1 was reported. Zijlstra’s experimental set-up was configured so that the alternating gradient field was oriented vertically, in the same direction as the
applied DC field.