The Art and Signs of a Few Good Mechanical Designs in MEMS
37
The design of a comb drive actuator is simple, and it is easy to microfabricate.
There is another feature in it that makes it general. Myosin motor, which is the
fundamental building block for skeletal muscles, has the same interdigitated design
[22]. The thick and thin myosin filaments have an arrangement similar to the comb
drive design. It is hard to say, however, that myosin filaments inspired the comb drive.
Nevertheless, the comb drive actuator is a general feature of many MEMS devices.
It is the most widely used actuator in MEMS. This design is here to stay.
5 The “Wow” Factor of a Polychromator-Beam Mechanism
Sometimes a brilliant idea calls for a new design, and another brilliant idea is needed
for practical realization of that design. An example of this is a polychromator [23], a
MEMS device that is a miniaturized version of a correlation absorption spectrometer
to identify a substance from a distance. The brilliant idea was to use diffraction of
light to generate light of any wavelength from broadband white light, for the reference
spectrum, using an array of long beams suspended above the substrate. The idea is
illustrated in Fig. 7. Imagine a grating cell composed of an array of beams separated
from one another in the top view and set at different heights above the substrate. If the
gap between the beams and the substrate is of the same dimension as the wavelength
of light, the gaps can be adjusted by applying electrostatic force using individually
addressable drive electrodes. Then, the light rays reflecting from the top surfaces
of the beams and the substrate underneath diffract to give out light of a particular
wavelength. Different patterns of gaps give out diffracted light of desired spectral
content.
The design question then is: How do we make the beams move up and down
continuously for achieving any gap without distorting the beam? Since it is an optical
Fig. 7 An array of diffracting beams that can generate diffracted light of desired spectral content
by adjusting the vertical gaps between beams and the substrate
37
The design of a comb drive actuator is simple, and it is easy to microfabricate.
There is another feature in it that makes it general. Myosin motor, which is the
fundamental building block for skeletal muscles, has the same interdigitated design
[22]. The thick and thin myosin filaments have an arrangement similar to the comb
drive design. It is hard to say, however, that myosin filaments inspired the comb drive.
Nevertheless, the comb drive actuator is a general feature of many MEMS devices.
It is the most widely used actuator in MEMS. This design is here to stay.
5 The “Wow” Factor of a Polychromator-Beam Mechanism
Sometimes a brilliant idea calls for a new design, and another brilliant idea is needed
for practical realization of that design. An example of this is a polychromator [23], a
MEMS device that is a miniaturized version of a correlation absorption spectrometer
to identify a substance from a distance. The brilliant idea was to use diffraction of
light to generate light of any wavelength from broadband white light, for the reference
spectrum, using an array of long beams suspended above the substrate. The idea is
illustrated in Fig. 7. Imagine a grating cell composed of an array of beams separated
from one another in the top view and set at different heights above the substrate. If the
gap between the beams and the substrate is of the same dimension as the wavelength
of light, the gaps can be adjusted by applying electrostatic force using individually
addressable drive electrodes. Then, the light rays reflecting from the top surfaces
of the beams and the substrate underneath diffract to give out light of a particular
wavelength. Different patterns of gaps give out diffracted light of desired spectral
content.
The design question then is: How do we make the beams move up and down
continuously for achieving any gap without distorting the beam? Since it is an optical
Fig. 7 An array of diffracting beams that can generate diffracted light of desired spectral content
by adjusting the vertical gaps between beams and the substrate