TECH KNOWLEDGEY
EVENTS, ADVANCES, AND NEWS
2011
■ BY JEFF ECKERT
ADVANCED TECHNOLOGY
■ Innowattech's piezoelectric railway pads can
produce up to 120 k Wh
of power.
HARVESTING WASTED VEHICLE POWER
Most of the electrical energy-harvesting concepts that have emerged lately have worked on a relatively small scale, such as wireless sensor networks, wearable electronics,
and so forth. A range of energy sources have been tapped, including thermal gradients,
vibration, blood sugar, and even trees, with various degrees of success. However, an Israeli
company called Innowattech ( www.innowattech.co.il) has been working on large-scale
applications of piezoelectric technology to generate more than just incidental currents.
For those who are unfamiliar with the piezoelectric effect, we note that, way back in 1880
the Curie brothers discovered that certain crystals generate an electric current when
deformed under pressure (known as the "direct effect"). Naturally occurring examples are quartz,
rochelle salt, topaz, and even cane sugar. Not all that much deformation is required, either.
Lead zirconate titanate crystals, for example, will generate measurable piezoelectricity
when deformed by as little as 0.1 percent. In addition, when an electric current is
applied to the materials they will undergo deformation as a result (the "converse effect").
In any event, Innowattech has developed a special breed of piezoelectric devices —
dubbed Innowattech Piezoelectric Generators (IPEGs) — that are designed to harvest wasted
energy from moving vehicles. Last year, the company introduced a version designed to be embedded just below the surface of
asphalt highways to tap into the energy of cars and trucks. One might suppose that it would be a parasitic process; after all, if it
involved increased deformation of the roadway, it would take a bit more energy to propel the vehicles. The company insists, however,
that IPEGs do not increase asphalt deformation and thus do not increase fuel consumption in vehicles traveling over it.
The latest twist on the concept is applying it to railroad tracks. Working with Israel's National Railway Company,
Innowattech has replaced 32 existing railroad pads with their own electricity-generating ones in a test. Preliminary
results suggest that if a particular section of track handles between 10 and 20 ten-car trains per hour, this will produce
120 k Wh during the same period. This can be used to help power trains or signals, or can be routed to the power grid
for general purposes. The company also offers pedestrial tiles for use in places like train stations, subways, shopping
malls, and so forth, and a product to be placed in factories that use heavy press machinery. No information about the
cost was provided, so the return on investment is still an open question. The installations have no moving parts and are
rated to work for about 30 years, so the long-term numbers could be favorable. ▲
KILLER LASER TECHNOLOGY
You're probably familiar with zinc oxide as an additive in things like plastics, ceramics, cement, skin creams, and so n. But how about making lasers out of it? Apparently, some folks at the University of California, Riverside's Bourns
College of Engineering ( www.engr.ucr.edu) have figured out a way to do it, with killer results — literally. Because the
devices — being constructed from ZnO nanowires — are very small and emit short-wavelength ultraviolet light, they
might be useful for killing viruses, among other functions.
According to Prof. Jianlin Liu, researchers have spent a decade or so trying to find a replacement for UV
semiconductor diode lasers based on gallium nitride, as they are expensive and difficult to manufacture. Zinc oxide has
long been considered a good candidate except for one little problem: the material was well suited to act as the n-type
diode element but couldn't work as the p-type one. However, Liu and associates solved the problem by doping the
ZnO with antimony, transforming it into a p-type material. When you connect the two, you get a p-n junction diode
which emits laser light from the ends of the nanowires.
Because the devices emit wavelengths down in the 340 nm range, they may provide for two or three times greater
storage capacities for DVDs. And because the nanowires are so thin, it may be possible to poke one into a living cell
and use the laser beam to kill unwanted cells or viruses, or even change the nature of the cell.
As usual, more research is needed, specifically in terms of the p-type material's reliability. Liu believes, "This
discovery is likely to stimulate the whole field to push the technology further." ▲
10
September 2011
