NOVEL MATERIALS
growth in heat pumps is hesitant. The reason for this is insufficient
economic efficiency.
Electrocaloric heat pumps promise a significantly higher degree
of efficiency, which will promote the spread of heat pumps
for air conditioning in buildings. In refrigeration technology, the
research team focuses primarily on industrial cooling technology,
vehicle air conditioning, server and control cabinet cooling
and laboratory refrigerators. In principle, the technology is also
suitable for household cooling technology. Most manufacturers
are now switching to natural refrigerants such as isobutane or
propane. Although the latter are not environmentally harmful,
they are highly explosive, which is why they are out of question
for safety-critical applications – such as in industry or the
automotive sector.
The scientists will work on material and system design
to demonstrate the disruptive potential of the technology.
Fraunhofer IKTS has extensive experience with ceramic electrocaloric
materials and coatings. Fraunhofer IAP and LBF contribute
know-how for the development of polymer materials that
are enhanced for use in electrocaloric heat pumps. Fraunhofer
FEP develops special coatings for the insulation and functionalization
of components. In addition to functional polymers,
Fraunhofer LBF will also investigate the service life and reliability
of materials and systems. Fraunhofer IAF will develop the
electrical control for the heat pumps. Materials and components
must be stable over the long term, sufficiently available, costeffective
and, last but not least, harmless. All these competencies
are brought together to implement a completely new
system approach patented by Fraunhofer IPM. This approach
provides for heat transfer through a combination of evaporation
and condensation of a harmless fluid in so-called heat pipes
with a thermal diode.
Heat dissipation has so far proved to be a bottleneck in the
efficiency of electrocaloric systems: the faster it takes place, the
more powerful the pump is. Preliminary studies have shown that
this can be achieved much more quickly with the new concept.
The systems operate without active pumping and thus achieve
a much higher cycle frequency than previous systems. The
team’s goal is to have a demonstrator with an output of 100
watts and a temperature range of 30 K in four years’ time.
Laser-based ultrasound medical imaging could be cheap and remote
By Julien Happich
In a paper titled “Full noncontact laser ultrasound: first human
data” published in the Light Science & Applications journal,
researchers from MIT describe how they were able to not
only use an eye-safe laser to remotely generate ultrasound
within human tissue, but also to remotely read-out the subsequent
ultrasound echos in
order to analyse tissues up do
6cm deep.
Because the new technique
does not rely on the
use of an ultrasound probe,
the read-out technique is not
subject to image variability
(upon probe pressure and orientation),
a major challenge in
modern ultrasound imaging.
Here the ultrasound waves
are generated remotely by a
pulsed laser light tuned at a
particular wavelength to penetrates
the skin and to be absorbed
by blood vessels. The
blood vessels rapidly expand
and relax, instantly heated
by a laser pulse then rapidly
cooled by the body back to
their original size, only to be
struck again by another light
pulse. The resulting mechanical
vibrations generate sound
A new ultrasound technique uses lasers to produce images beneath
the skin, without making contact with the skin as conventional
ultrasound probes do. The new laser ultrasound technique was
used to produce an image (left) of a human forearm (above), which
was also imaged using conventional ultrasound (right). Image
courtesy of the researchers.
waves that travel through the skin, bouncing off muscle, fat, and
other soft tissues before reflecting back to the skin.
The researchers used a second laser to remotely detect the
reflected waves (through the Doppler effect) and translate them
into an image similar to conventional ultrasound. This contactless
ultrasound imaging technique may help remotely image
and assess health of infants, burn victims, and accident survivors
in hard-to-reach places.
Scanning the forearms of several volunteers, the authors of
the paper report the observation of common tissue features
such as muscle, fat, and bone, down to about 6 centimetres
below the skin, all done from half a meter away.
Although at this point, the laser ultrasound (LUS) images are
only comparable to images
achieved at the early stages
of medical ultrasound imaging
decades ago, the researchers
are confident those could
be drastically improved by
leveraging known beam forming
and image processing
techniques already used for
ultrasound imaging.
Beyond the use of a fast
amplitude-modulated optical
source to improve the LUS
imaging depth, bandwidth
and resolution, the parallelization
of optical sources and
receivers could enable optical
transmit and receive beam
forming techniques. This
combined with modern computer
vision techniques such
as 3D imaging and tracking
could make large-volume LUS
imaging and optical beam
forming feasible, note the
authors.
With optical spot tracking and a sufficiently fast data acquisition
and coverage, LUS systems could enable the simultaneous
3D imaging of both the external and internal tissue geometries,
the paper concludes. Indeed, a lot of the technologies required
for such 3D acquisitions has already been developed for lidars,
with chip-scale steerable laser technology used in autonomous
cars.
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