July 25, 2012
One physical phenomenon, especially annoying to small children, is the electrical spark that jumps from their finger to switchplates in low humidity, usually in the winter. Winter is also the time when they are likely to have socks, slippers, or shoes on their feet, and that's important to the process. It's the rubbing of the dissimilar materials of their foot covering and the room carpet that generates an electrical charge in their body by the triboelectric effect.
I wrote about the triboelectric effect in two previous articles (Triboelectricity, July 17, 2007, and William Duddell's Singing Sparks, May 15, 2012. The triboelectric effect was known in ancient Greece, where Thales of Miletus (c. 600 BC) made the first written record, and the triboelectricity of amber was mentioned by Theophrastus in his book, "On Stones" (see figure).
The Greek's noted that rabbit fur and amber make a good triboelectric couple; in fact, the name of the negative charge carrier, the electron, comes from the Greek word for amber, ηλεκτρον. The word triboelectric comes from the Greek verb for rubbing, tribo, (τριβω), but actual rubbing is not required. What's required is that the materials contact each other, and then separate. The physical mechanism is that chemical bonds form between the materials, and separating the materials will also separate a charge. Rubbing helps by increasing the contact area.
It took quite a few centuries for triboelectricity to go from a novelty to an accessible source of continuous electricity. James Wimshurst (1832-1903), a nineteenth century British engineer designed and built his Wimshurst machine (see figure). The Wimshurst machine rubbed two disks together to generate a static electrical charge that was collected by metal patches and directed to electrodes.
Although Michael Faraday's electrical generator and electromagnetic dynamos replaced generators such as the Wimshurst machine as voltage sources for most applications, they weren't very good for high voltage generation.
Princeton University physics professor, Robert Van de Graaff(1901-1967), developed the eponymous Van de Graaff generator for such high voltage applications. This triboelectric generator is very simple, as the figure shows. It's an improved topology of the Wimshurst machine, and it was an inexpensive means of generating millions of volts for early nuclear physics experiments.
|The Winshurst machine. Left image, a scan by Andy Dingley from the 1903, Electrical Installations (Volumes V) by Rankin Kennedy, Caxton Press, London. Right image, a modern replica. Images from Wikimedia Commons.|
Scientists from the Georgia Institute of Technology (Atlanta, GA) have developed a new triboelectric generator using transparent polymers that's suitable for some environmental energy-harvesting applications.[2-3] The secret ingredient, of course, is nanotechnology. Zhong Lin Wang, professor of Materials Science and Engineering at the Georgia Tech, explains that "this generator can convert random mechanical energy from our environment into electric energy."
The generator is made from a sheet of polyester, a electron donor, that rubs against a sheet of polydimethylsiloxane, an electron acceptor. The polymer surfaces rub together, and produce a charge when separated. Continually rubbing and separating the sheets generates a small alternating current. The current production is enhanced by micropatterning the surfaces (see photograph). Pyramidal shapes seemed to be optimum, with as much as 18 volts at about 0.13 microamps per square centimeter being generated.[2-3]
Any good physical effect can easily be turned into a sensor, and this triboelectric device can be used as a pressure sensor. The sensitivity is quite good, since it can detect an 8 milligram water droplet (3.6 Pa contact pressure); or, a 20 milligram falling feather (0.4 Pa in contact pressure). The lower limit of pressure detection is 13 millipascals.[2-3] These devices have been tested for more than 100,000 operating cycles.
This research was funded by the National Science Foundation, the Department of Energy and the U.S. Air Force. Details were reported in the June issue of the journal, Nano Letters.
|Diagram of a Van De Graaf generator|
The triboelectric version of this device has a pulley acting as one member of a triboelectric couple with an insulating belt.
Charge is transferred through a small gap between the belt and the brushes.
(Via Wikimedia Commons, modified).
- Earle Radcliffe Caley and John F.C. Richards, "Theophrastus on Stones: Introduction, Greek Text, English Translation, and Commentary," Ohio State University (Columbus, Ohio, 1956). Greek text, p. 23; English translation, p. 51, as follows:
"... And since amber is also a stone—for the kind that is dug up is found in Liguria—the power of attraction would belong to this too. The stone that attracts iron is the most remarkable and conspicuous example. This also is rare and occurs in few places. This stone too should be listed as having a similar power."
- John Toon, "Plastic Power: Triboelectric Generator Produces Electricity by Harnessing Frictional Forces Between Transparent Polymer Surfaces," Georgia Tech Press Release, July 9, 2012.
- Feng-Ru Fan, Long Lin, Guang Zhu, Wenzhuo Wu, Rui Zhang, and Zhong Lin Wang, "Transparent Triboelectric Nanogenerators and Self-Powered Pressure Sensors Based on Micropatterned Plastic Films," Nano Letters, vol. 12, no. 6 (June 13, 2012), pp. 3109-3114.
Permanent Link to this article
Linked Keywords: Physical phenomenon; child; children; electrical spark; finger; light switch; switchplate; low humidity; winter; sock; slipper; shoe; foot; feet; material; carpet; electrical charge; triboelectric effect; ancient Greece; Thales of Miletus (c. 600 BC); amber; Theophrastus; On Stones; mineral; rabbit fur; charge carrier; electron; Greek language; Greek word; chemical bond; contact area; electricity; James Wimshurst (1832-1903); nineteenth century; British; engineer; Wimshurst machine; metal; electrode; Rankin Kennedy; Electrical Installations; Wikimedia Commons; Michael Faraday; electrical generator; electromagnetic; dynamo; voltage; high voltage; Princeton University; Robert Van de Graaff(1901-1967); Van de Graaff generator; nuclear physics; scientist; Georgia Institute of Technology (Atlanta, GA); transparent; polymer; environmental energy-harvesting; secret ingredient; nanotechnology; Zhong Lin Wang; Materials Science and Engineering; polyester; polydimethylsiloxane; alternating current; micropatterning; pyramidal; volt; microamp; square centimeter; sensor; pressure sensor; milligram; water droplet; pascal; Pa; feather; National Science Foundation; Department of Energy; U.S. Air Force; Nano Letters.
Latest Books by Dev Gualtieri
Thanks to Cory Doctorow of BoingBoing for his favorable review of Secret Codes!
Blog Article Directory on a Single Page
- J. Robert Oppenheimer and Black Holes - April 24, 2017
- Modeling Leaf Mass - April 20, 2017
- Easter, Chicks and Eggs - April 13, 2017
- You, Robot - April 10, 2017
- Collisions - April 6, 2017
- Eugene Garfield (1925-2017) - April 3, 2017
- Old Fossils - March 30, 2017
- Levitation - March 27, 2017
- Soybean Graphene - March 23, 2017
- Income Inequality and Geometrical Frustration - March 20, 2017
- Wireless Power - March 16, 2017
- Trilobite Sex - March 13, 2017
- Freezing, Outside-In - March 9, 2017
- Ammonia Synthesis - March 6, 2017
- High Altitude Radiation - March 2, 2017
- C.N. Yang - February 27, 2017
- VOC Detection with Nanocrystals - February 23, 2017
- Molecular Fountains - February 20, 2017
- Jet Lag - February 16, 2017
- Highly Flexible Conductors - February 13, 2017
- Graphene Friction - February 9, 2017
- Dynamic Range - February 6, 2017
- Robert Boyle's To-Do List for Science - February 2, 2017
- Nanowire Ink - January 30, 2017
- Random Triangles - January 26, 2017
- Torricelli's law - January 23, 2017
- Magnetic Memory - January 19, 2017
- Graphene Putty - January 16, 2017
- Seahorse Genome - January 12, 2017
- Infinite c - January 9, 2017
- 150 Years of Transatlantic Telegraphy - January 5, 2017
- Cold Work on the Nanoscale - January 2, 2017
- Holidays 2016 - December 22, 2016
- Ballistics - December 19, 2016
- Salted Frogs - December 15, 2016
- Negative Thermal Expansion - December 12, 2016
- Verbal Cues and Stereotypes - December 8, 2016
- Capacitance Sensing - December 5, 2016
- Gallium Nitride Tribology - December 1, 2016
- Lunar Origin - November 27, 2016
- Pumpkin Propagation - November 24, 2016
- Math Anxiety - November 21, 2016
- Borophene - November 17, 2016
- Forced Innovation - November 14, 2016
- Combating Glare - November 10, 2016
- Solar Tilt and Planet Nine - November 7, 2016
- The Proton Size Problem - November 3, 2016
- Coffee Acoustics and Espresso Foam - October 31, 2016
- SnIP - An Inorganic Double Helix - October 27, 2016
- Seymour Papert (1928-2016) - October 24, 2016
- Mapping the Milky Way - October 20, 2016
- Electromagnetic Shielding - October 17, 2016
- The Lunacy of the Cows - October 13, 2016
- Random Coprimes and Pi - October 10, 2016
- James Cronin (1931-2016) - October 6, 2016
- The Ubiquitous Helix - October 3, 2016
- The Five-Second Rule - September 29, 2016
- Resistor Networks - September 26, 2016
- Brown Dwarfs - September 22, 2016
- Intrusion Rheology - September 19, 2016
- Falsifiability - September 15, 2016
- Fifth Force - September 12, 2016
- Renal Crystal Growth - September 8, 2016
- The Normality of Pi - September 5, 2016
- Metering Electrical Power - September 1, 2016
Deep Archive 2006-2008