EINDHOVEN, Netherlands — A new
polymer material has been developed that
can undulate and propel itself forward
when exposed to light.
Scientists at Eindhoven University of
Technology and Kent State University
clamped a strip of the polymer material
in a rectangular frame and illuminated
it with one fixed light source; then they
watched as it “walked” on its own.
The maximum speed is about half a
centimeter per second — equivalent to
that of a caterpillar. The researchers think
the material can be used to transport
small items in hard-to-reach places or
to keep the surface of solar cells clean.
They placed grains of sand on the strip
and these were removed by the undulating
movement. The strip can even transport
uphill an object that is much bigger and
heavier than the device itself.
The motion of the new material is due
to the fact that one side contracts in reaction to light, and the other one expands,
causing it to bulge when illuminated.
That deformation disappears instantaneously once the light is gone. The material
looks transparent to the human eye, but it
fully absorbs the violet light the researchers used, creating a shadow behind it.
The research team was able to create
a continual undulating movement using
this self-shadowing effect. They attached
a strip of the material in a frame shorter
than the strip itself, causing it to bulge.
Then they shone a concentrated LED
light on it, from in front. The part of the
strip that was in the light started to bulge
downward, creating a dent in the strip. As
a consequence, the next part of the strip
that was in the light started to deform.
The dent moved backward, creating the
TECH pulse • • • • • • • •
rolling movement. This set the device
in motion, walking away from the light.
When the device was placed upside down,
the wave traveled in the opposite direc-
tion, causing it to walk toward the light.
The research has been published in
the journal Nature (doi: 10.1038/nature
New polymer material goes for a walk when illuminated
Eindhoven University of Technology scientist Anne Hélène Gélébart is showing the walking device.
A timelapse image of the walking device.
PASADENA, Calif. — A novel camera
uses an ultrathin optical phased array
(OPA) in place of lenses to enable a thin,
light, flexible design. The OPA manipulates light through a large array of
receivers. Each receiver can add a tightly
controlled phase shift to the light it receives, enabling the camera to selectively
look in different directions and focus on
The 2D lensless camera has an array
composed of 64 light receivers in an 8 ×
8 grid. The 8 × 8 OPA receiver operates
using a heterodyne architecture on a thin
silicon-photonics integrated silicon-on-in-sulator (SOI) substrate. It has a receiving
beam width of 0.75° and beam steering
range of 8°.
The camera, which is capable of creating a full image, was built by a team from
the California Institute of Technology
(Caltech). The resulting images have low
resolution, but according to the team,
the system represents a proof of concept
for a fundamental rethinking of camera
“The ability to control all the optical
properties of a camera electronically
using a paper-thin layer of low-cost
silicon photonics without any mechanical movement, lenses or mirrors opens
a new world of imagers that could look
like wallpaper, blinds or even wearable
fabric,” said professor Ali Hajimiri.
Last year, the team introduced a one-
dimensional version of the camera that
was capable of detecting images in a line,
similar to a lensless barcode reader but
with no mechanically moving parts.
“With our new system, you can selectively look in a desired direction and at a
very small part of the picture in front of
you at any given time, by controlling the
timing with femtosecond — quadrillionth
of a second — precision,” said Hajimiri.
Light waves that are received by each
element of the camera across the array
cancel each other from all directions
except one. In that one direction, the
waves amplify each other to create a
focused “gaze” that can be electronically
“What the camera does is similar to
looking through a thin straw and scan-
Ultrathin camera creates images without lenses