Surface nuclear magnetic resonance imaging of large systems

The general theory of surface NMR imaging of large electromagnetically acti ve systems is considered, motivated by geophysical applications. A general imaging equation is derived for the NMR voltage response, valid for arbitra ry transmitter and receiver loop geometry and arbitrary conductivity struct ure of the sample. When the conductivity grows to the point where the elect romagnetic skin depth becomes comparable to the sample size, significant di ffusive retardation effects occur that strongly affect the signal. Accounti ng for these now allows mon accurate imaging than previously possible. It i s shown that the time constant T-1 may in principle be inferred directly fr om the diffusive tail of the signal.