SEPTEMBER/OCTOBER 2019
.
DISCOVER 41
L
E
F
T
:
R
O
B
F
E
L
T
/
G
E
O
R
G
I
A
T
E
C
H
.
R
I
G
H
T
:
E
M
R
I
T
E
R
I
M
/
S
H
U
T
T
E
R
S
T
O
C
K
produce a current. The
concept is simple, but
it’s the kind of engi-
neering simplicity that
nevertheless requires
decades of research
and trial and error, and
error, and error, and
error. Such a generator,
Wang says, can enable
that keyboard to harvest
energy from keystrokes,
or turn clothing into a
mini power plant.
Wang’s idea is new in
the sense that research-
ers have only begun to
explore and understand it, but in another
sense, it’s quite old. He uses what is called
the triboelectric effect. You already know
about triboelectricity, if not necessarily
by name. It’s how we explain why clothes
stick together after tumbling inside a
dryer, or why unexpected shocks zap us
in the winter.
Triboelectricity’s more common name
is static electricity.
HARVESTING SPARKS
The “triboelectric effect” describes what
happens when two dissimilar materials
rub against each other and exchange
charges, leaving one more positive and
the other more negative. (Tr ib o- comes
from the Greek word for “to rub.”) It’s
the spark that flies from your fingertip to
the doorknob after you shuffle across the
carpet in socks on a cold, dry day.
“The idea is to harvest those sparks,”
says micro-engineer Jürgen Brugger
of the École Polytechnique Fédérale de
Lausanne, in Switzerland. He began
researching energy-
harvesting schemes using
triboelectric materials
about two years ago, after
hearing about Wang’s work.
The ancient Greeks
observed that after rub-
bing a piece of amber with
animal fur, the hardened
tree sap would attract dust
and other small particles.
The word electric, coined
by Elizabethan scientist
William Gilbert, speaks
to these origins: It traces
back to elektron, Greek for
amber. Schoolteachers use
the same amber-on-fur demonstration to
introduce the fundamentals of electricity,
showing that two rubbed amber rods will
repel each other. Bored kids at birthday
parties rub their heads with balloons to
make their hair stand up, and to get the
balloons to stick to walls.
The marvel of static electricity once
seemed a promising way forward in the
great electrification of the world. In 1663,
Prussian scientist Otto von Guericke,
who was also the mayor of Magdeburg,
generated eerie yellow sparks by rubbing
a spinning sulfur ball with his hands.
His invention is often recognized as the
first electrostatic generator, and some
Magdeburgians reportedly believed
their mayor capable of magic. In the
following centuries, people used elec-
trostatic generators for a wide variety of
sometimes dubious applications, from
“electric baths” as medical treatment for
movement disorders and lead poison-
ing, to electrifying — some might say
electrocuting — plants.
For the last decade
and a half, Wang, an
electrical engineer
and nanotechnologist,
has sought ways to
scavenge energy
from the movements
of ordinary life.
The zap you might get
from a doorknob on a
dry day is a result of
the triboelectric effect
— better known as
static electricity.
Zhong Lin Wang’s
pioneering work with
triboelectricity has led to
inventions like the small
generator powering this
array of 1,000 LED lights,
activated by a tap of the foot.