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G. K. Ananthasuresh
Fig. 8 An unusual requirement of an electrostatically actuated beam: How should the beam at the
top be anchored to the substrate at the two points so that it moves down without bending, under the
influence of the electrostatic force from the drive electrode?
application, the beam should not deform at all. But then, as in any microfabrication
using photolithography, the beam has to be anchored to the substrate. The driving
electrode ought to be underneath to pull the beam down. This situation is shown in
Fig. 8. Those who know about elastic deformation of beams know that when a beam
is anchored at the ends, it will deform. But here, we want the beam to not deform but
still move down in the transverse direction. Much creative thinking is necessary to
solve this unusual design problem. A reader is urged to spend at least 15 min before
looking at the solution.
An ingenious solution to the problem posed in Fig. 8 was reported in [8]. As
shown in Fig. 9, it uses a two-layered structure sandwiching a sacrificial layer. This
design uses the well-known fact that a fixed–fixed beam under symmetric transverse
load deforms with zero slope at the midpoint. Therefore, by attaching a short segment
at the midpoint to the top beam, we get its downward motion without any bending
whatsoever. This basic idea is further extended by concatenating two beams so that
any tilting or vibration is also avoided. This is shown in Fig. 10, which shows a twosegment design in undeformed and deformed configurations. Figure 11 illustrates
how an array of such designs can be realized to form a grating element, wherein each
beam can be set at a different height, as desired by the intended wavelength of light.
The simple and elegant design of a polychromator serves its function really well.
It maintains bending-free transverse motion of a long beam. It is the kind of a design
that might occur quickly to a creative person in a flash or perhaps might occur (or
not) to anyone after much thought. In any case, when we see it, we get the “wow”
feeling. If it does not appear as an amazing design to a particular reader, he/she
Fig. 9 An ingenious design that makes a long beam move down without bending when actuated
from underneath and anchored at either end with an intermediate beam
G. K. Ananthasuresh
Fig. 8 An unusual requirement of an electrostatically actuated beam: How should the beam at the
top be anchored to the substrate at the two points so that it moves down without bending, under the
influence of the electrostatic force from the drive electrode?
application, the beam should not deform at all. But then, as in any microfabrication
using photolithography, the beam has to be anchored to the substrate. The driving
electrode ought to be underneath to pull the beam down. This situation is shown in
Fig. 8. Those who know about elastic deformation of beams know that when a beam
is anchored at the ends, it will deform. But here, we want the beam to not deform but
still move down in the transverse direction. Much creative thinking is necessary to
solve this unusual design problem. A reader is urged to spend at least 15 min before
looking at the solution.
An ingenious solution to the problem posed in Fig. 8 was reported in [8]. As
shown in Fig. 9, it uses a two-layered structure sandwiching a sacrificial layer. This
design uses the well-known fact that a fixed–fixed beam under symmetric transverse
load deforms with zero slope at the midpoint. Therefore, by attaching a short segment
at the midpoint to the top beam, we get its downward motion without any bending
whatsoever. This basic idea is further extended by concatenating two beams so that
any tilting or vibration is also avoided. This is shown in Fig. 10, which shows a twosegment design in undeformed and deformed configurations. Figure 11 illustrates
how an array of such designs can be realized to form a grating element, wherein each
beam can be set at a different height, as desired by the intended wavelength of light.
The simple and elegant design of a polychromator serves its function really well.
It maintains bending-free transverse motion of a long beam. It is the kind of a design
that might occur quickly to a creative person in a flash or perhaps might occur (or
not) to anyone after much thought. In any case, when we see it, we get the “wow”
feeling. If it does not appear as an amazing design to a particular reader, he/she
Fig. 9 An ingenious design that makes a long beam move down without bending when actuated
from underneath and anchored at either end with an intermediate beam