RF Magnetic Field Mapping

Abstract

Abstract Radio‐frequency (RF) magnetic field mapping is the imaging of oscillating magnetic fields in space. The title of this article implies RF mapping, however, the technique is applicable to both higher frequency microwaves and lower audio frequency electromagnetic waves. Five mapping techniques are presented in this article. They were developed for mapping the oscillating magnetic fields (standing waves) associated with inductive–capacitive–resistive (LCR) circuits, such as cavity resonators and resonant coils used in magnetic resonance spectroscopy and imaging. LCR circuits store energy alternately in the capacitive element as electrical fields and in the inductive element as magnetic fields. The oscillating magnetic fields form a standing wave within the volume of the inductor. The electrical fields are either zero or separated in space from the magnetic fields, and hence generally are not detected in these circuits. This point is worth noting because some of the techniques presented in this article cannot distinguish oscillating magnetic and electrical fields. Because of the magnetic resonance application of these techniques, much of the magnetic resonance symbolism has been adopted, and some basic magnetic resonance theory will be presented. The mapping techniques are divided into two general categories: probe and imaging techniques. Probe techniques produce field values at discrete points in space that can be used to generate a B 1 map. Imaging techniques produce an image directly. The method depends on the proportionality of the intensity of a pixel in this image to the magnetic field at the corresponding point in space.