Magnetic Quantities, Units, Materials, and Measurements

Abstract

It should hardly need to be pointed out that in an interdisciplinary endeavor such as biomagnetism it is necessary to use consistent, unambiguous terminology. Thus we will use the term “magnetic field” as a generic term relating to a particular class of phenomena that exists or is evidenced throughout some region of space. Hence the use of the word “field.” Two of the most-used quantitative attributes of the magnetic field, to be dealt with later in this chapter, are the “field strength” (an alternative term is “field intensity”), usually symbolized by H, and the “flux density” (alternatively, the “magnetic induction”), symbolized by B. The two fields are proportional in an evacuated space but have a more complicated relationship within a material such as a magnet. This terminology for H and B is consistent with that of nearly all modern English-language textbooks on electricity and magnetism and with the 1971 recommendation of the International Bureau of Weights and Measures. On the other hand, in the technical literature the term “magnetic field” is generally used for all three purposes; not only as a generic term but also to mean field strength or flux density, and sometimes for other purposes as well. This practice is convenient, but students and non-specialists should be forewarned that the meaning of the term must be inferred from the context.