In this paper, we present a new microfabricated fluxgate sensor structure using cascaded planar rings as the ferromagnetic core. The planar ring structures provide closed magnetic excitation loops enabling uniform core saturation with relatively small excitation magnetic field. The magnetic excitation is provided with a rod passing through the ring cores. Planar coils placed under the edges of the core are used as sensing elements. By using this structure, fluxgate sensors having a closed core configuration are realized with a developed microfabrication process in a very small area (<0.1 mm(2)) with reduced number of via connections. The ferromagnetic rings are realized with a standard FeNi (iron nickel) electroplating process. The main advantage of this structure is the possibility to arrange the linear operation range of the sensor by only changing the number of ring cores, without affecting the excitation mechanism. This is demonstrated by simulations and microfabricated prototypes having 18 and 12 ring cores with +/- 300 mu T and +/- 550 mu T linear operation ranges, respectively. A maximum linear operation range of +/- 2 mT is achieved with a larger size, 4-ring core. This is the widest linear operation range achieved with the microfabricated fluxgate type sensors, without using a feedback loop, to the best of our knowledge. (C) 2010 Elsevier B.V. All rights reserved.