Читать книгу Essentials of MRI Safety - Donald W. McRobbie - Страница 54

Maxwell’s second equation states that the “divergence of B is zero.” This means that there is no magnetic equivalent of electrical charge – no “magnetic monopoles”. Magnetic sources are not like electrostatic ones, but exist as dipoles with a north and south pole (just like the Earth). Magnetic field lines have no beginning or end, but form complete loops from north pole to south (Figures 2.2, 1.23). The nature of the B₀ fringe field depends upon this.

Figure 2.2 Magnetic field lines from a permanent bar magnet.