Sheath wave trap for movable cable especially of NMR local antenna

摘要

The trap is based on a resonant circuit (7) coupled inductively to the cable (4) outside an enclosure in which the local antenna is attached to a patient within the field of a system of coils. A rectangular conductive loop (9) has a coupling length (10) laid parallel to the cable, with a gap in the opposite length (11) bridged by a capacitor (12). The inductance and capacitance determine the resonant frequency of the circuit which preferably is held stationary while the cable moves to and fro in the direction of its length. Alternatively the coupling length may take the form of a tube through which the cable is threaded.