Page 230 - Mechanics of Microelectromechanical Systems
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4. Microtransduction: actuation and sensing 217
where is the isolated magnetic charge or the pole strength – Sadiku [4].
As shown in Eq. (4.72), the vectors m and l are parallel.
Figure 4.36 Short magnet: (a) Magnetic field; (b) Interaction with an external magnetic
field
When this magnet is placed in an external magnetic field, as shown in Fig.
4.36 (b), a couple will act on the magnet about a direction perpendicular to
its plane, and will attempt to align the magnet with the external field. The
moment of this couple can be calculated by the generic Eq. (4.67), which
becomes:
The same moment of Eq. (4.73) can be conceived as being the effect of two
equal and opposite forces that act at the magnet’s poles and are defined as –
Sadiku [4]:
The two forces are opposite because the magnetic charge is positive at one
pole and negative at the other, as shown in Fig. 4.36, and, as a consequence,
no resultant force will act on the magnet, just the couple produced by the two
forces, which is equal to:
By combining Eqs. (4.74) and (4.75), the moment of Eq. (4.73) is retrieved.
