A magnetic field sensor for a medical device, the magnetic sensor assembly comprising a substrate having a plurality of planar sections, wherein adjacent planar sections are joined by a transition section, and wherein the planar sections are arranged in a substantially C-shaped arrangement such that an inner surface of the magnetic field sensor is concave, and wherein the plurality of planar sections includes a first planar section oriented in a first plane and a second planar section oriented in a second plane orthogonal to the first plane. A first magneto-resistive (MR) sensor is mounted to the first planar section and defining a first axis of sensitivity, and a second MR sensor is mounted to the second planar section and defining a second axis of sensitivity that is orthogonal to the first axis of sensitivity.