12 | New Scientist | 27 February 2021
News
TransportMatthew SparkesELECTRIC cars are becoming more
popular, but until the infrastructure
to keep them charged expands,
there is the potential for very long
waits to top up batteries at public
chargers. A computer model can
help. By taking information about
electric vehicle journeys, it can slash
waiting times by 97 per cent.
Sven Schönberg at Paderborn
University and Falko Dressler at
the Berlin Institute of Technology,
both in Germany, simulated 5000
electric cars each undertaking a trip
of 500 kilometres in a single day on
Germany’s roads. The average wait
to charge was over 6 hours.
To improve on this, the pair first
calculated the most efficient routes
between nearby charging stations
on the road network. They think
electric cars’ on-board computers
can create an optimal route by
using a string of these.
The researchers also propose a
central database to which drivers
upload their planned routes and
charging stops – like pilots filing
a flight plan to an aviation
administration. An algorithm
can then process all this to
maximise journey efficiency.
For instance, using information
from the algorithm, a car’s
navigation system might suggest
going at a slower and more efficient
speed if it knows there will be a wait
at a charging station. Doing so can
reduce total journey time: travelling
more slowly is more energy efficient
and so when the car does stop to
charge, the driver won’t have to lose
as much time. “It is easy to find the
fastest route or the most energy
efficient route,” says Schönberg.
“But sometimes the optimal
solution is somewhere in between.”
When the researchers reran the
simulation of 5000 electric vehicles
using the database and algorithm,
they found the average wait to
charge fell to just 11 minutes
(arxiv.org/abs/2102.06503). ❚Smart system can
dramatically cut wait
to charge electric carMilitary technologyDavid HamblingTHE US Army is building a laser
weapon over a million times
more powerful than any used
before – although because it
delivers short pulses, the overall
energy hitting the target is low.
Existing laser weapons
produce a continuous beam
that is held on a target, such
as a drone or missile, until it
melts. The first was deployed
by the US Navy in 2014. The
new weapon, known as theTactical Ultrashort Pulsed
Laser for Army Platforms, would
be more like science-fiction
movie lasers, firing bullet-like
pulses of light.
Such ultrashort laser pulses
carry extreme power over
vanishingly short lengths of
time: the project is aiming for
a terawatt pulse lasting just
200 femtoseconds (2 x 10⁻¹³ s),
compared with a maximum
of 150 kilowatts for previous
systems.
The laser would produce
between 20 and 50 pulses
per second, for an overall
power rating of 20 to 50 watts,
about 10 times more than
an LED light bulb.
Ultrashort lasers this
powerful are already used
in laboratories and factories,
but the US Army wants a
compact, rugged version that
can be aimed at distant targets.
Normal lasers are ineffective
over long distances because
the beam spreads out, but
ultrashort pulses can be shaped
into self-focusing light pulses
called solitons that turn the air
itself into a lens, continually
refocusing the pulse.Such a weapon would
produce dramatic effects. The
rapid temperature rise from
the ultrashort pulse would
vaporise the surface of a target
rather than melting it, a
technique used industrially
to cut precise holes through
metal. The resulting rapid
expansion of gas can also
produce a powerful blast wave.
In addition, the US Army
hopes the laser will create an
electromagnetic pulse (EMP)
effect. On striking a metal
target, the laser pulse rapidly
accelerates electrons, and the
moving charges produce a
burst of radio-frequency energy
powerful enough to disturb
nearby electronics. This is
a known problem in lab
settings, where EMPs can
affect measuring instruments.
A sufficiently powerful EMP
could bring down drones
or missiles by disrupting
their control systems.
Contractor Aqwest in
Larkspur, Colorado, is
developing a ceramic disc laser
for the project. The design is a
variation of the thin-disc laser
invented in Germany in 1992.The original lasing disc was
just 0.1 millimetres thick and
was attached to a heat sink
to disperse waste heat.
Aqwest’s version is thicker
and can deliver proportionately
more energy in each pulse.
The firm declined to comment
on the work.
Building this kind of laser
weapon is possible with current
technology, says Derryck Reid
at Heriot-Watt University in
Edinburgh, UK. “This is not
science fiction.”
Reid sees the self-focusing
effect as the key benefit of the
new laser. Although the amount
of energy is low compared
with a continuous beam laser,
delivering it rapidly to a small
enough area could be effective.
“You could certainly do some
damage with these power
levels,” he says.
Laser weapons are generally
intended for use against small,
fast-moving, airborne targets.
If used to target a human, it
would cause unpleasant burns,
but would generally be less
harmful than conventional
weaponry.
The International Committee
of the Red Cross, which has
worked to develop international
law around laser weapons,
declined to comment on the
specifics of the weapon, but
notes that the only current
restriction on such arms is a
1995 treaty prohibiting the use
of lasers intended to blind.
Aqwest’s contract states
that the prototype ultrashort
pulse laser weapon will be
demonstrated by August next
year, after which the US Army
will decide whether to go ahead
with further development.
This could lead to laser
blasters mounted on ground
vehicles and helicopters. ❚US Army laser weapon
to be most powerful ever
JOHN^ F.^ W
ILLIAMS/U.S.^NA
VYThe US Navy has
previously deployed
laser weapons1
Power of a laser pulse from
the new weapon, in terawatts