Читать книгу Essentials of MRI Safety - Donald W. McRobbie - Страница 79

What is the maximum force on a ferromagnetic steel cylinder of length 2 cm, diameter 2 mm in the fringe field of a MRI magnet with B = 50 mT and dB/dz = 0.25 Tm⁻¹? The material saturates at 1 T.

The maximum force occurs when the object’s long axis is aligned with B0. Firstly determine if the object is saturated. From Figure 2.14 or Equations A1.31 and 2.9a

This exceeds Bsat so use Equation 2.13

By contrast the gravitational force is

The magnetic force is 2.5 times the force due to gravity at this point.