High power flexible leads for das nmr

Abstract

A flexible, low-loss, low-capacitance, high-voltage, high-current, moderate-impedance, unshielded, balanced, rf-pulse transmission twinline is produced by etching parallel copper traces on opposite sides of a flexible substrate, spaced apart such that the distance between the conductors is greater than four times the substrate thickness and at least one of the conductors has a width greater than half of the separation between the conductors. A second, similar twinline may be etched on the same substrate beside the first twinline and paralleled at both ends with the first twinline to form a lower-impedance quadline such that alternate conductors in the quadline are on alternate sides of the substrate and have opposite current phases. Both surfaces may be coated with a thin, flexible dielectric to increase the voltage rating for a given conductor separation with minimal affect on propagation factor, attenuation constant, or flexibility. A second, similar quadline on a separate laminate displaced along the normal from the first may be paralleled with the first quadline forming a lower-impedance dual-quadline such that the two laminates have mean spacing comparable to or greater than the spacing between conductors within a twinline. The two quadlines are paralleled such that the phases in the conductors in one quadline are the same as the phases in the adjacent conductors in the adjacent quadline. The concepts may be extended in like manner for further reduction in characteristic impedance without sacrifice in propagation factor, attenuation constant, or flexibility.