An elongate medical device includes a sensor configured to detect one or more characteristics of an electromagnetic field in which the device is disposed. The sensor includes an electrically-insulative substrate, rectangular in shape, and a patterned, conductive trace disposed on the substrate. The patterned trace includes a plurality of diagonal sections parallel to one another, arranged with a relatively low pitch. The substrate is wrapped into a cylindrical shape thereby forming a three-dimensional spiral capable of functioning as a micro-electromagnetic sensor. A medical positioning system is responsive to the signal from the sensor to determine a position and/or orientation of the sensor.
