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D. George and M. J. Madou
liquid bead at the fold region enhances the driving force (Maxwells pressure). Moreover, an application of a high electric field is possible in this technique since the breakdown electric field increases considerably with the introduction of the liquid. Therefore, a high actuation force can be attained here, as compared to a system without
any such liquid. This liquid bead prefers to be at the folds due to the electrophoretic
forces generated by the high electric field there.
The integration of capillary origami to other existing MEMS components can be
realized by patterning conductive materials on top of them. Gold is considered as one
of the best options for this application due to its high conductivity and low elastic
modulus. The electrical connection between the faces is achieved through the gold
connections that are running through the hinges [88]. The low modulus of the gold
makes sure that the effect of gold on the folding is minimal. A hand-free bending of
the faces is achieved by building conducting loops on them using gold, followed by
the application of Lorentz force [129].
As far as the magnetically driven folding is concerned, a sheet where the particle
orientation on adjacent faces of the origami is such that they are facing each gives
rise to folding in the presence of a uniform magnetic field, as shown in Fig. 15.
Aligned magnetic materials are achieved in a polymer matrix through a direct writing
technique by sending unaligned magnetizable NdFeB particles through a printer head
equipped with aligning magnetic field. In this technique, the aligning magnetic field
reorients the particles, and the rheology of the printed material keeps the aligned
particle in place. The orientation of the magnetic particles with respect to the printing
platform is adjusted by controlling the magnetic field direction and the printing
direction.
4 Permanent Folding
A strategy to make a permanently folded structure is to alter the required bending
energy temporarily by softening and stiffening the material at relevant instants. A
soft material folded with elastocapillary effects if converted into stiff material after
the folding can retain the bent shape. This retention is due to the energy-expensive
route that it must take to go back to the original flat configuration. One of the ways to
achieve this is by exploiting the softening of the polymers. At a lower temperature, the
mobility of the molecular chains is low, and this low mobility causes a high stiffness.
Polymers, when heated, undergo softening because of the increased mobility of the
polymer chains inside the material. The reduced stiffness enables easy folding at an
elevated temperature. Subsequent cooling ensures retention of the folded structure.
Although such a technique lets the folded structure to keep its shape, it is still not a
completely permanent folding method since it can go back to the original shape at an
elevated temperature. Chemically altering the polymer could help in overcoming this
shortcoming. One way to achieve this change is by controlling the crosslinking of the
polymer. The higher the level of crosslinking of a polymer, the higher the stiffness
of the material. One of the most explored techniques where crosslinking can be
D. George and M. J. Madou
liquid bead at the fold region enhances the driving force (Maxwells pressure). Moreover, an application of a high electric field is possible in this technique since the breakdown electric field increases considerably with the introduction of the liquid. Therefore, a high actuation force can be attained here, as compared to a system without
any such liquid. This liquid bead prefers to be at the folds due to the electrophoretic
forces generated by the high electric field there.
The integration of capillary origami to other existing MEMS components can be
realized by patterning conductive materials on top of them. Gold is considered as one
of the best options for this application due to its high conductivity and low elastic
modulus. The electrical connection between the faces is achieved through the gold
connections that are running through the hinges [88]. The low modulus of the gold
makes sure that the effect of gold on the folding is minimal. A hand-free bending of
the faces is achieved by building conducting loops on them using gold, followed by
the application of Lorentz force [129].
As far as the magnetically driven folding is concerned, a sheet where the particle
orientation on adjacent faces of the origami is such that they are facing each gives
rise to folding in the presence of a uniform magnetic field, as shown in Fig. 15.
Aligned magnetic materials are achieved in a polymer matrix through a direct writing
technique by sending unaligned magnetizable NdFeB particles through a printer head
equipped with aligning magnetic field. In this technique, the aligning magnetic field
reorients the particles, and the rheology of the printed material keeps the aligned
particle in place. The orientation of the magnetic particles with respect to the printing
platform is adjusted by controlling the magnetic field direction and the printing
direction.
4 Permanent Folding
A strategy to make a permanently folded structure is to alter the required bending
energy temporarily by softening and stiffening the material at relevant instants. A
soft material folded with elastocapillary effects if converted into stiff material after
the folding can retain the bent shape. This retention is due to the energy-expensive
route that it must take to go back to the original flat configuration. One of the ways to
achieve this is by exploiting the softening of the polymers. At a lower temperature, the
mobility of the molecular chains is low, and this low mobility causes a high stiffness.
Polymers, when heated, undergo softening because of the increased mobility of the
polymer chains inside the material. The reduced stiffness enables easy folding at an
elevated temperature. Subsequent cooling ensures retention of the folded structure.
Although such a technique lets the folded structure to keep its shape, it is still not a
completely permanent folding method since it can go back to the original shape at an
elevated temperature. Chemically altering the polymer could help in overcoming this
shortcoming. One way to achieve this change is by controlling the crosslinking of the
polymer. The higher the level of crosslinking of a polymer, the higher the stiffness
of the material. One of the most explored techniques where crosslinking can be