Patent ID: 7477056

Claim:
A birdcage resonator for a magnetic resonance apparatus, said birdcage resonator comprising: a first ferrule and a second ferrule respectively disposed in ferrule planes that are parallel to and spaced from one another, each of said first and second ferrules having a ferrule center and a line connecting the respective ferrule centers defining an antenna axis that orthogonally intersects the respective ferrule planes; a plurality of antenna rods regularly distributed around said antenna axis, each antenna rod extending from said first ferrule to said second ferrule, said antenna rods exhibiting multiple resonant frequencies; a first coupling ring and a second coupling ring, in addition to said first and second ferrules; said first coupling ring surrounding said antenna axis in a first coupling plane orthogonal to the antenna axis and being spaced from, but coupling with, said first ferrule; said second coupling ring surrounding said antenna axis in a second coupling ring plane orthogonal to the antenna axis, and being spaced from, but coupling with, said second ferrule; said first and second coupling rings being tuned to cause the respective first and second ferrules coupled therewith to be resonant at frequencies other than without the respective first and second coupling rings; said ferrules coupling with each other in common eigenmodes including a common mode at a common mode frequency and a push-pull mode at a push-pull frequency differing from the common mode frequency; said first and second coupling rings being tuned to cause the frequency of one of the eigenmodes to correspond to no resonant frequency of the antenna rods; and a feed device that feeds electrical energy into the ferrules at the frequency of the eigenmode that corresponds with no resonant frequency of the antenna rods.