Apparatus, including a flexible insulatingsubstrate, having a first side and a second side, rolledabout an axis parallel to the substrate. The apparatusalso includes a first conducting spiral that isright-handed relative to a normal to the substrate, and asecond conducting spiral that is left-handed relative tothe normal, formed on the first side of the substrate.The first conducting spiral has a first initialtermination and a first final termination, the secondconducting spiral has a second initial termination and asecond final termination, the spirals have a displacementtherebetween, with a preset magnitude so that when thesubstrate is rolled about the axis the first initialtermination aligns with the second initial termination.The apparatus also has a via penetrating the substratefrom the first side to the second side so as tointerconnect the first initial termination and the secondinitial termination.
