A sensor may include a core and a coil. The core may include a rectangular substrate, a layer of magnetically-permeable material disposed on the substrate, and an adhesive rigidly coupling two ends of the substrate so as to form a tube with the rectangular substrate. The coil may be wound on the tube. The core may further include a layer of radiopaque material. The core may further include a flex pad for electrically coupling the coil with an external system.
