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4. Microtransduction: actuation and sensing 213
Figure 4.32 Lorentz force acting on a linear wire carrying a current I in an external
magnetic field B
This general principle is implemented in MEMS devices by means of loops
that can be either circular or rectangular. Figure 4.33 sketches a rectangular
loop which can be placed on a mobile structure for instance. The loop carries
the current I and is placed in an external magnetic field B, which is parallel
to the plane of the loop, as indicated in the same figure.
Figure 4.33 Rectangular loop carrying a current in an external magnetic field
Because the field B is parallel to the current in the shorter arms of the loop
(of length there is no force acting on those sides. However, there will be
two forces acting on each of the longer arms, one entering the loop’s plane (it
is indicated by an x in a circle) and the other one exiting the same plane (it is
shown by a point in a circle). According to the Lorentz force definition of Eq.
4.57, these two forces are equal and opposite, and their value is:
