Technology for controlling non-uniformity in the B.sub.1 field includes selecting the phase, magnitude, frequency, time, or spatial relationship among various elements of a multi-channel excitation coil in order to control the radio frequency (RF) power emanating from the coil antenna elements. Non-uniformity can be used to steer a constructively interfering B.sub.1 field node to spatially correlate with an anatomic region of interest. A convex (quadratically constrained quadratic problem) formulation of the B.sub.1 localization problem can be used to select parameters for exciting the coil. Localization can be used in simulated Finite Difference Time Domain B.sub.1 field human head distributions and human head phantom measurement.