By Christian Fell, VP of Technology and Custom Solutions, FRABA B.V.
Achieving Energy Harvesting
with the Wiegand Effect
Generating energy from mechanical motion has potential for new generation of sensors.
With the growing interest in small distributed sensors and other electronic devices aimed at collecting data
for new applications—including the Internet of Things
(Io T)—more attention is being paid to technologies for
energy harvesting. Engineers and scientists are looking
for ways to enable stand-alone devices that collect
small amounts of energy from the surrounding physical
environment, to power a tiny electronic circuit.
Several energy harvesting technologies are in use today.
Thermocouple effects, for example, can be harnessed to
provide electrical energy (although these require strong
temperature gradients in the region of the device to provide
significant power levels). Piezoelectric transduction,
electromagnetic induction, and capacitive energy harvesting
all rely on conversion of mechanical energy from a vibrating
component into electrical energy. The Wiegand effect
is another energy harvesting technology that generates
electrical energy from mechanical motion, in this case,
rotations or oscillating motions. Wiegand effect energy
harvesting is reliable, efficient, and capable of producing
consistent levels of energy, even when the underlying
motions occur very slowly.
The Wiegand Effect
The “Wiegand effect” was first discovered in the 1970s by
John Wiegand, a German-American musician and inventor
who became interested in the use of magnetic effects in
audio equipment.
Wiegand found that when a specially prepared piece
of ferromagnetic alloy (the Wiegand wire) is subject
to a reversing external magnetic field, it will retain its
magnetic polarity up to a certain point, then suddenly
‘flip’ to the opposite polarity. This change in magnetic
polarity occurs within a few microseconds. This sudden
change of magnetic polarity can generate a pulse of
current in a copper coil positioned close to the Wiegand
wire. The strength and duration of this current pulse is
independent of the rate at which the external magnetic
“Wiegand wire” is produced through a process
involving the annealing of a Vicalloy spool wire (an alloy
of vanadium, iron, and cobalt), then simultaneously
stretching and twisting the wire to form a strain-
hardened outer layer on the wire, surrounding a soft
inner core. The wire is then aged under controlled
conditions to stabilize its crystalline structure. The
machine they developed to produce Wiegand wire
features a series of rotating frames that twist and un-
twist the wire at various rates (Figure 1).
Application of the Wiegand Effect
An early commercial application of the Wiegand effect
was with access cards for security systems. Several short
lengths of Wiegand wire were embedded side-by-side
in the plastic body of each card. The spacing between
these pieces of wire would be unique for each card
manufactured. In use, a card would be swiped through
a reader that contained permanent magnets arranged to
cause polarity flips in the Wiegand wires. By detecting
these polarity reversals, the device could read the coded
number built into the card (based on the wire spacing)
and decide whether the card holder should be granted
access. This technology has been gradually replaced by
newer RFID technology.
Energy Harvesting from Rotary Motion
Another main application for the Wiegand effect has
been to provide power for rotation counters in water and
Figure 1: The machine used to produce Wiegand wire features
a series of rotating frames that twist and un-twist the wire at
various rates.
