Investigation of the radio frequency magnetic field inside a hollow cylinder used for nuclear magnetic resonance imaging

The homogeneity of the radio frequency (rf) axial magnetic field inside a solenoid composed of a set of current-carrying coils can be improved by imposing appropriate current densities in the various loops that constitute the structure. In the case of a hollow cylinder made from a single sheet of copper foil, the rf field so generated can also attain a similar degree of homogeneity without current compensation provided the copper foil is five to six times thicker than the skin depth and the cylinder’s form factor (diameter/length) is of the order or less than 0.5. Numerical calculations based on some basic equations allow us to predict the rf field pattern of a cylinder of given dimensions. Experimental results obtained from a 32 MHz transmission line resonator show good agreement between theory and practice. The filling factor of this type of cylinder can also be evaluated from these calculations.