An elongate medical device 26 includes a sensor 241 configured to detect one or more characteristics of an electromagnetic field in which the device 26 is disposed. The sensor 241 includes an electrically-insulative substrate 48, rectangular in shape, and a patterned, conductive trace 50a disposed on the substrate 48. The patterned trace 50a includes a plurality of diagonal sections parallel to one another, arranged with a relatively low pitch. The substrate 48 is wrapped into a cylindrical shape thereby forming a three-dimensional spiral capable of functioning as a micro-electromagnetic sensor 52a. A medical positioning system 110 is responsive to the signal from the sensor 52a to determine a position and/or orientation of the sensor 52a.
