Tag Archives: piezoelectricity

Optical micrscopy images of (a) monoclinic and (b) tetragonal aggregate films of lysozyme. Credit: Nature Materials.

Squeezing crystals from plant waste generates electricity

Optical micrscopy images of (a) monoclinic and (b) tetragonal aggregate films of lysozyme. Credit: Nature Materials.

Optical microscopy images of (a) monoclinic and (b) tetragonal aggregate films of lysozyme. Credit: Nature Materials.

Scientists have identified a novel protein which generates electricity when mechanically stressed, such as when squeezed or tapped. The discovery suggests that plant waste could be turned into electricity in a more sustainable manner than current traditional methods, i.e. burning.

Squeezing juice

Everyone was very surprised by the amount of power this organelle called lysosome can generate. According to the Irish researchers at the University of Limerick, lysosomes could easily power electronics like smartphones, motion detectors, and all sorts of sensors.

Converting mechanical energy into electrical energy — a phenomenon called piezoelectricity (literally “pressing electricity”) — is nothing new. The phenomenon was first discovered and used in the 19th century and one of the most common application being electric cigarette lighters, which use piezoelectric crystals to create a flame. Another common application is the microphone you probably have incorporated in your laptop, whose piezoelectric crystals convert your voice (sound vibration) into electrical signals which are then processed by the computer. There’s even a dance club in San Francisco which uses this setup under its dance floor to power the lighting.

Previously, the team at the University of Limerick showed that applying pressure to lysosome crystals generates electricity. At the time, the researchers knew that this protein is found in egg white and tears. These are not the most productive sources of electricity unless you’re the kind of person that cries uncontrollably when the power is off.

In a new research published in the journal Nature Materialsthe team found that lysosomes can also be sourced from forestry residues, a natural material which can be produced extremely cheaply. According to the researchers, lysosome crystals can be produced at 1% of the cost of currently used piezoelectric materials, which are not only more expensive but often times toxic. Lysosomes, on the other hand, is biodegradable.

“It is really exciting that such a tiny molecule can generate so much electricity,” said Sarah Guerin, lead author and researcher at UL’s Bernal Institute.

Future applications may include controlling the release of drugs in vivo by using lysozyme as a physiologically mediated pump that scavenges energy from its surroundings. Lysozyme could also be used as a biodegradable, piezoelectric, and antimicrobial additive or coating to conventional implants.

California’s highways will generate electricity from cars driving over them

orange-county-road

California, home to some of the busiest highways in the world, will soon harvest energy from the millions of vehicles roaming its roads. As part of a pilot program approved by the California Energy Commission (CEC), several freeways will be covered in piezoelectric crystals that turn vibrations into electricity.

Harvesting roads for electricity

We often hear that we need more energy, but the truth is we’re already generating copious amounts. The problem is that most of it goes to waste. A petrol car, for instance, is only about 20 to 30 percent efficient depending on how new the vehicle is and the type of fuel used. The rest of the energy is lost to heat and friction.

The energy exchanged with the road by friction isn’t enormous but if you can capture just a fraction of it and turn it into usable electricity, the savings could be huge when you factor in tens of thousands of vehicles driving over a road on a daily basis.

To generate electricity from overhead vehicles, scientists in California are proposing using piezoelectric crystals which convert mechanical energy into electrical energy and vice versa. Piezoelectricity (literally “pressing electricity”) was first discovered and used in the 19th century, one of the most common application being electric cigarette lighters, which use piezoelectric crystals to create a flame. Another common application is the microphone you probably have incorporated in your laptop, which uses piezoelectric crystals to convert your voice (sound vibration) into electrical signals which are then processed by the computer. There’s even a dance club in San Francisco which uses this setup under its dance floor to power the lighting.

“If piezoelectric‐based technology has the potential to match the performance, reliability and costs of existing or emerging renewable energy sources, then it can potentially diversify California’s resource portfolio and ultimately increase grid reliability and reduce costs to ratepayers,” states a report prepared for the CEC in 2014

Piezoelectric walkways have been implemented in some parts of Europe or in East Japan Railway Company’s Tokyo station, and the first piezoelectric freeway opened in 2009 in Israel. The coastal road Route 4 in Israel consists of a ten-meter strip of asphalt which cover the piezoelectric generators beneath while batteries are located nearby to store the 2,000 watt-hours of electricity which this setup generates.

It was Route 4 that provided the inspiration for U.S. officials to first propose a similar project back home five years ago, but the state’s Governor first wanted a research team formed that would study the technology. Now, CEC announced it would be finally funding multiple piezoelectric pilot projects throughout California.

“I still get stopped on the street by people who ask what happened to the idea of using our roads to generate electricity,” said Mike Gatto, a Los Angeles assemblyman, in a statement. “California is the car capital of the world and we recycle just about everything. So why not capture the energy from road vibrations and put it to good use?”

Scientists estimate the energy generated from a 10 mile stretch of four-lane roadway can power the entire City of Burbank, which has a population numbering 105,000 people.

“Thirty years ago, no one would have believed that black silicon panels in the desert could generate ‘solar’ power,” said Gatto.  “Piezoelectric technology is real, and I am glad the state has finally acknowledged its potential in becoming an energy source.”

An atomically thin material, molybdenum disulfide (MoS2), shown, could be the basis for unique electric generator and mechanosensation devices that are optically transparent, extremely light, and very bendable and stretchable. —Image courtesy of Rob Felt/Georgia Tech

This electric generator is only a few atoms thin

Researchers from Columbia Engineering and the Georgia Institute of Technology report the first experimental proof of piezoelectricity and the piezotronic effect in an atomically thin material, molybdenum disulfide (MoS2). This makes it the thinnest electrical generator in the world. The resulting generator is optically transparent, extremely light weight, as well as very bendable and stretchable. In the future, such generators could be used to power extremely tiny devices harnessing energy from the environment, be them remote sensors or nanotech that travels through your bloodstream.

The world’s thinnest electrical generator

Positive and negative polarized charges are squeezed from a single layer of atoms, as it is being stretched. —Image courtesy of Lei Wang/Columbia Engineering

Positive and negative polarized charges are squeezed from a single layer of atoms, as it is being stretched.
—Image courtesy of Lei Wang/Columbia Engineering

Piezoelectricity is a well documented form of energy conversion  in which stretching or compressing a material causes it to generate an electrical voltage, or viceversa — an electrical current is applied to cause expansion or contraction in a material. This effect has been harnessed for various applications, some more practical than others, like a notebook that can be powered by typing (a piezoelectric transducer converts the pressure used to press the keys into electricity). This is the first time, however, that piezoelectricity has been demonstrated at the scale of only a few atoms of thickness.

“This material—just a single layer of atoms—could be made as a wearable device, perhaps integrated into clothing, to convert energy from your body movement to electricity and power wearable sensors or medical devices, or perhaps supply enough energy to charge your cell phone in your pocket,” says James Hone, professor of mechanical engineering at Columbia and co-leader of the research.

“Proof of the piezoelectric effect and piezotronic effect adds new functionalities to these two-dimensional materials,” says Zhong Lin Wang, Regents’ Professor in Georgia Tech’s School of Materials Science and Engineering and a co-leader of the research. “The materials community is excited about molybdenum disulfide, and demonstrating the piezoelectric effect in it adds a new facet to the material.”

Generating power in 2-D

An atomically thin material, molybdenum disulfide (MoS2), shown, could be the basis for unique electric generator and mechanosensation devices that are optically transparent, extremely light, and very bendable and stretchable. —Image courtesy of Rob Felt/Georgia Tech

An atomically thin material, molybdenum disulfide (MoS2), shown, could be the basis for unique electric generator and mechanosensation devices that are optically transparent, extremely light, and very bendable and stretchable.
—Image courtesy of Rob Felt/Georgia Tech

You might remember Hone as being part of a research group that proved in 2008 that graphene — a 2-D form of carbon arranged in a hexagon geometry — is the strongest material in the world. Since then, Hone and colleagues have been exploring the novel properties of 2D materials like graphene and MoS2 as they are stretched and compressed.

Because MoS2 is highly polar, an even number of layers cancels out the piezoelectric effect, so if the material is to be effective at generating current an odd number of layers need to be used and flexed in the proper direction. The fact that  the material’s crystalline structure also is piezoelectric in only certain crystalline orientations made matters even more challenging.

Hone’s team placed thin flakes of MoS2 on flexible plastic substrates, then  patterned metal electrodes onto the flakes.  Wang’s group installed measurement electrodes on samples provided by Hone’s group, then measured current flows as the samples were mechanically deformed. As the material was deformed, voltage and current outputs were measured, as seen in the paper published in Nature.

“This is the first experimental work in this area and is an elegant example of how the world becomes different when the size of material shrinks to the scale of a single atom,” Hone adds. “With what we’re learning, we’re eager to build useful devices for all kinds of applications.”

A single monolayer flake strained by 0.53% generates a peak output of 15 mV and 20 pA, corresponding to a power density of 2 mW m−2 and a 5.08% mechanical-to-electrical energy conversion efficiency. Of course, for most applications this sort of power output is useless, but even a few milliwatts of power can sustain tiny micrometer devices. This study also reveals the piezotronic effect in two-dimensional materials for the first time and considering MoS2 is just one of a group of 2D semiconducting materials known as transition metal dichalcogenides, there’s no telling what kind of breakthrough can be achieved in the future once more materials are probed for piezoelectricity.

Harvesting wasted electricity: the triboelectric generators

With just one footstep, you can illuminate a thousand LED bulbs – with no batteries or power cord; the energy comes from rubbing two different materials together to create static electricity. A researcher called Zhong Lin Wang has finally learned how to harvest this power and put it to work.

Triboelectricity? What’s that ?!

A professor at the Georgia Institute of Technology, Wang is using what is called the triboelectric effect – a type of contact in which certain materials become electrically charged after they come into contact with another different material through friction. For example, when you rub glass with fur, or a comb through the hair, you are building triboelectricity. This has been known for a long time, nothing new here – but harvesting it… that’s an entirely different story, but Zhong figured it out.

He believes his discovery could potentially power mobile devices such as sensors and smartphones by capturing the otherwise wasted mechanical energy from walking, wind, and even rain. This is why, besides from powering electric devices, the technology could lead to a new generation of sensors, detecting vibrations, motion, water leaks, explosions, etc.

“We are able to deliver small amounts of portable power for today’s mobile and sensor applications,” said Wang, a Regents professor in Georgia Tech’s School of Materials Science and Engineering. “This opens up a source of energy by harvesting power from activities of all kinds.”

How it works

In its simplest form, a triboelectric generator works like this: you have 2 different materials – an electron donor and other an electron acceptor. Electrons flow from the donor to the acceptor. If the sheets are separated, one sheet holds an electrical charge isolated by the gap. If the electrical load is then connected to two electrodes placed at the outer edges of the two surfaces, a small current will flow to equalize the charges. If you continuously repeat this process (like in rubbing), you can generate an alternative current.

“The fact that an electric charge can be produced through triboelectrification is well known,” Wang explained. “What we have introduced is a gap separation technique that produces a voltage drop, which leads to a current flow in the external load, allowing the charge to be used. This generator can convert random mechanical energy from our environment into electric energy.”

When they initially started out, the energy out put was negligible. Since then, they managed to increase the power output density of their triboelectric generator by a factor of 100,000! This translates into a square meter of single-layer material producing as much as 300 watts.

“When two materials are in physical contact, the triboelectrification occurs,” said Wang, who holds the Hightower Chair in the Georgia Tech School of Materials Science and Engineering. “When they are moved apart, there is a gap distance created. To equalize the local charge, electrons have to flow. We are getting surprisingly high voltage and current flow from this. As of now, we have discovered four basic modes of triboelectric generators.”

Wang and his team accidentally discovered the power generating potential of the triboelectric effect while working on piezoelectric generators, which use an entirely different technology. The output from one of the piezoelectric device was way higher than expected – and this increased effect was found to be caused by triboelectricity.

Via Georgia Tech.

Graphene allows nano-engineering control for the first time

The amazing properties of graphene are being put to use more and more, as Evan Reed and Mitchell Ong from the Stanford School of Engineering have described a new way of engineering piezoelectrics into graphene. The study was published in the ACS Nano Journal.

When you apply a mechanical stress to certain materials, such as crystals, ceramics, or even biological materials, they become electrically charged, and this property is called piezoelectricity – basically, it is electricity resulting from pressure. Using this effect, their work extends engineering control to the nanoscale for the first time. Reed explained that the proportions of the applied pressure directly varies with the electrical field, and this approach might be the key to manipulating electronics at the nanoscale, and this phenomenon can bring a revolution in the field of straintronics. This is where graphene steps in.

Graphene, which is basically a one-atom thick layer of carbon may offer an unprecedented degree of control over optical, electrical and mechanical properties for applications such as nanoscale transistors and touchscreens. In order to measure the piezoelectric field of graphene, they simulated graphene doped with fluorine, potassium, hydrogen, lithium and combinations of fluorine and lithium and fluorine and hydrogen on either sides. Researchers were absolutely surprised with the results, reporting that the effect of the 2D graphene were practically similar to those of 3D materials.

Based on these positive results, scientists hope they can continue their studies, which can have a number of applications in a number of fields, including electronics, chemical sensing, energy harvesting, photonics and many, many more.

Via AZonano