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Pulsed power is an exciting and emerging technology with a variety of industrial and Bioelectrics applications, such as water treatment.

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Nuclear Fusion reactions power the Sun and other stars. In a fusion reaction, two light nucleimerge to form a single heavier nucleus. The process releases energy because the total mass of the resulting single nucleus is less than the mass of the two original nuclei. The leftover mass becomes energy. Einstein's equation (E=mc ²), which says in part that mass and energy can be converted into each other, explains why this process occurs. If scientists develop a way to harness energy from fusion in machines on Earth, it could be an important method of energy production.

Fusion can involve many different elements in the periodic table. However, researchers working on fusion energy applications are especially interested in the deuterium-tritium (DT) fusion reaction. DT fusion produces a neutron and a helium nucleus. In the process, it also releases much more energy than most fusion reactions. In a potential future fusion power plant such as a tokamak or stellarator, neutrons from DT reactions would generate power for our use. Researchers focus on DT reactions both because they produce large amounts of energy and they occur at lower temperatures than other elements.

DOE Office of Science & Fusion Reactions

The Department of Energy Office of Science, Fusion Energy Sciences (FES) program seeks to develop a practical fusion energy source. To do so, FES partners with other Office of Science programs. They work with the Advanced Scientific Computing Research program to use scientific computing to advance fusion science as well as the Nuclear Physics program on nuclear reaction databases, generation of nuclear isotopes, and research in nucleosynthesis. FES also partners with the DOE's National Nuclear Security Administration to pursue fundamental research on fusion reactions in support of DOE's nuclear stockpile stewardship mission.

Fusion Reaction Facts

The ITER international fusion energy experiment will be scientists' first attempt at creating a self-sustained fusion reaction for long durations. "Burning plasmas" in ITER will be heated by the fusion reactions occurring in the plasma itself.

Fusion reaction experiments at the DOE's National Ignition Facility at the Lawrence Livermore National Laboratory require 192 laser beams to align on a DT target smaller than a pea. This is like throwing a perfect strike in baseball from a pitcher's mound 350 miles away from the plate.

Resources and Related Terms

Acknowledgements
Matthew Lanctot (U.S. DOE Office of Science) Scientific terms can be confusing. DOE Explains offers straightforward explanations of key words and concepts in fundamental science. It also describes how these concepts apply to the work that the Department of Energy's Office of Science conducts as it helps the United States excel in research across the scientific spectrum.

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Nuclear Fusion reactions power the Sun and other stars. In a fusion reaction, two light nucleimerge to form a single heavier nucleus. The process releases energy because the total mass of the resulting single nucleus is less than the mass of the two original nuclei. The leftover mass becomes energy.

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What is Fusion, and Why Is It So Difficult to Achieve?

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It is expected that fusion could meet humanity's energy needs for millions of years. Fusion fuel is plentiful and easily accessible: deuterium can be extracted inexpensively from seawater, and tritium can be produced from naturally abundant lithium. Future fusion reactors will not produce high activity, long lived nuclear waste, and a meltdown at a fusion reactor is practically impossible.

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Controlled Nuclear Fission. To maintain a sustained controlled reaction, for every 2 or 3 neutrons released, only one must be allowed to strike another uranium nucleus. If this ratio is less than one then the reaction will die out; if it is greater than one it will grow uncontrolled (an atomic explo…

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Fission and Fusion: What is the Difference?

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Learn the difference between fission and fusion - two physical processes that produce massive amounts of energy from atoms.

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Fission and Fusion: What is the Difference?

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Learn the difference between fission and fusion - two physical processes that produce massive amounts of energy from atoms.

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Reactors use uranium for nuclear fuel. The uranium is processed into small ceramic pellets and stacked together into sealed metal tubes called fuel rods. Typically, more than 200 of these rods are bundled together to form a fuel assembly. A reactor core is typically made up of a couple hundred assemblies, depending on power level.

Inside the reactor vessel, the fuel rods are immersed in water which acts as both a coolant and moderator. The moderator helps slow down the neutrons produced by fission to sustain the chain reaction.

Control rods can then be inserted into the reactor core to reduce the reaction rate or withdrawn to increase it.

The heat created by fission turns the water into steam, which spins a turbine to produce carbon-free electricity.

Types of Light-water Reactors in the United States

All commercial nuclear reactors in the United States are light-water reactors. This means they use normal water as both a coolant and neutron moderator.

There are two types of light-water reactors operating in America.

Pressurized water reactors

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NUCLEAR 101: How Does a Nuclear Reactor Work?

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Learn how boiling and pressurized light-water reactors work.

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MIT News | Massachusetts Institute of Technology

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With the world's energy needs growing rapidly, can zero-carbon energy options be scaled up enough to make a significant difference? How much of a dent can these alternatives make in the world's total energy usage over the next half-century? As the MIT Energy Initiative approaches its fifth anniversary next month, this five-part series takes a broad view of the likely scalable energy candidates.

The sunlight that reaches Earth every day dwarfs all the planet's other energy sources. This solar energy is clearly sufficient in scale to meet all of mankind's energy needs - if it can be harnessed and stored in a cost-effective way.

Unfortunately, that's where the technology lags: Except in certain specific cases, solar energy is still too expensive to compete. But that could change if new technologies can tip the balance of solar economics.

The potential is enormous, says MIT physics professor Washington Taylor, who co-teaches a course on the physics of energy. A total of 173,000 terawatts (trillions of watts) of solar energy strikes the Earth continuously. That's more than 10,000 times the world's total energy use. And that energy is completely renewable - at least, for the lifetime of the sun. "It's finite, but we're talking billions of years," Taylor says.

Since solar energy is, at least in theory, sufficient to meet all of humanity's energy needs, the question becomes: "How big is the engineering challenge to get all our energy from solar?" Taylor says.

Solar thermal systems covering 10 percent of the world's deserts - about 1.5 percent of the planet's total land area - could generate about 15 terawatts of energy, given a total efficiency of 2 percent. This amount is roughly equal to the projected growth in worldwide energy demand over the next half-century.

Such grand-scale installations have been seriously proposed. For example, there are suggestions for solar installations in the Sahara, connected to Europe via cables under the Mediterranean, that could meet all of that continent's electricity needs.
Because solar installations of all types are modular, the experience gained from working with smaller arrays translates directly into what can be expected for much larger applications. "I'm a big fan of large-scale solar thermal," says Robert Jaffe, the Otto (1939) and Jane Morningstar Professor of Physics. "It may be the only renewable technology that can be deployed at very large scale."

And we do know how to harness solar energy, even at a colossal scale. "There's no showstopper, it's just a matter of price," says Daniel Nocera, the Henry Dreyfus Professor of Energy at MIT.

Nocera foresees a time when every home could have its own self-contained system: For instance, photovoltaic panels on the roof could run an electrolyzer in the basement, producing hydrogen to feed a fuel cell that generates power. All the necessary ingredients already exist, he says: "I can go on Google right now, and I can put that system together." Nocera's own invention, a low-cost system for producing hydrogen from water, could help over the next few years to make such systems cost-competitive.

In principle, we know multiple ways of generating electricity from the sun (direct photovoltaic, or solar thermal energy used to drive a turbine); of storing that energy (in batteries, by pumping water uphill, or by separating water into hydrogen and oxygen using an electrolyzer); and of converting that stored energy into electricity when it's needed (using fuel cells powered by hydrogen, for example). Some kinds of solar power are already cost-competitive, at least in some settings, and prices have been moving steadily downward.

"Costs have come down very dramatically" for solar power, says Ernest J. Moniz, the Cecil and Ida Green Distinguished Professor of Physics and Engineering Systems and director of the MIT Energy Initiative, "but it's still not that cheap." And even as the price of solar panels themselves has dropped, there has been little reduction in the costs associated with installing them.

Like nuclear power, Moniz says, solar is characterized by high initial costs, but very low operating costs. But one significant advantage solar has over nuclear is "you can do it in smaller bites," rather than needing to build multibillion-dollar plants.

Solar energy is a vibrant research topic, attracting scientists interested in many different approaches. For example, MIT researchers Angela Belcher and Paula Hammond are exploring approaches to solar power that would harness the power of biological organisms to create solar devices; Penny Chisholm and Shuguang Zhen are looking into the possibility of directly harnessing the photosynthesis done by plants or single-celled organisms; and various researchers including Vladimir Bulovic, Michael Strano, Tonio Buonassisi, Jeffrey Grossman and Yang Shao-Horn, among others, are working on ways of improving the efficiency or lowering the costs of solar photovoltaic cells.

Still others are pursuing a variety of approaches to solar thermal energy: using the sun's heat to power turbines or to heat homes or water. A significant breakthrough in any of these areas could make solar power an economically viable option for the world's energy needs. This year, for example, Alexander Slocum and others published a proposal for a solar thermal system that could provide steady, 24/7 baseload power for utility companies, helping to make it cost-competitive with other sources.

Other researchers are studying ways to make effective solar-power systems using common, inexpensive materials. For example, cadmium telluride is a very promising material for solar cells. But it turns out that tellurium, one of its ingredients, is "rarer than gold," Jaffe says. "We need to be able to make solar cells out of common materials, or at least things that are not exquisitely rare," he adds.

Tomorrow: There are many sources that can make a contribution to our energy supply, but likely not at a major scale in the near future.

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With the world's energy needs growing rapidly, can zero-carbon energy options be scaled up enough to make a significant difference? How much of a dent can these alternatives make in the world's total energy usage over the next half-century?

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A revised and updated version of this post is at Opportunities for solar energy In this post I’ll talk about some of the science behind this interesting fact and I’ll also discuss how solar energy…

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Meeting the world's ever-growing energy demands in an environmentally responsible and sustainable manner is one of the most pressing issues facing us. Solar energy-sunlight-is an abundant, clean, safe and free resource, providing approximately 1,000 watts of power per square meter to Earth's surface on a sunny day. In fact, the total amount of solar energy that hits Earth in just two hours is more than enough to meet current global energy consumption for an entire year.

How can we most effectively capture, convert and store this tremendous natural resource? First, it is important to recognize that sunlight consists of a spectrum of wavelengths. About half of it is lower energy infrared radiation that we cannot see, but we feel as heat. The rest is higher energy visible light or ultraviolet light. Some technologies for harnessing solar energy target the entire spectrum, while others use only a portion of the available wavelengths.

One of the first technologies that comes to mind when discussing solar energy is the growing use of solar cells, also known as photovoltaics, which convert sunlight directly into electricity. Solar cells are silent, non-polluting and long-lived devices that typically convert 10 to 15 percent of the energy received into energy that can be used.

They are not the only way to get electricity from solar energy, though. Sunlight can also be intensely focused onto a small area, using an array of mirrors or lenses to heat water and create steam. High-pressure steam can be driven through a turbine to generate electricity.

When the sun shines, we can store the electricity generated by solar cells or steam-driven turbines by using batteries (technically energy stored as electrochemical potential) or supercapacitors (energy stored in an electric field, due to the spatial separation of positive and negative charges). Then we can release electrical energy when it is cloudy or at night.

There are at least two other ways to store solar energy for use later. First, the thermal energy of concentrated sunlight can be stored in the heat capacity of a molten salt (the liquid form of an ionic compound like sodium chloride) at a high temperature. When electricity is needed later, heat is transferred from the molten salt to water, using a heat exchanger to generate steam to drive a turbine.

A second method of harnessing and storing solar energy is to employ sunlight to produce a fuel. For example, a photoelectrochemical cell uses solar energy to split water into hydrogen and oxygen gases, which can be stored as fuels. These gases are then recombined to generate electricity in a device known as a fuel cell. An attractive feature of this approach is that the byproduct of the fuel cell reaction is simply water.

We should not forget that sunlight can also be used to directly heat a tank of water located outside the home, and that solar heated water can be used for washing or showering; this is common in parts of the developing world.

While many of the technologies described here are in use on a small scale today, we must continue to develop innovative methods of storing solar energy and promote sustainable energy policies that benefit generations to come.
Submit a question to "Ask the Expert." Previous "Ask the Expert" questions: How can I help my child cope with a tragic event? Is it safe to exercise while undergoing cancer treatment? How can parents tell the difference between normal teenage mood swings and possible mental illness? Is dieting or exercise better for losing weight? How can I help my child learn a second language?

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How can we effectively store solar energy?

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Meeting the world's ever-growing energy demands in an environmentally responsible and sustainable manner is one of the most pressing issues facing us. Solar energy-sunlight-is an abundant, clean, safe and free resource, providing approximately 1,000 watts of power per square meter to Earth's surface on a sunny day.

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(Image credit: <a href="http://www.shutterstock.com/pic-108308282/stock-photo-volcanic-landscape-on-the-reykjanes-peninsula-in-iceland-near-the-blue-lagoon-viewed-from-the-road.html">Reykjanes Peninsula image</a> via Shutterstock)

It's not every day that scientists can study a volcano up close, but researchers investigating the feasibility of volcano-powered electricity successfully drilled into the core of one in Iceland.

Scientists studied the volcanic system at Reykjanes Peninsula in Iceland, which has been dormant for more than 700 years, according to a hazard assessment by Verkis Consulting Engineers for Invest in Inceland.

The depths of Reykjanes' geothermal field - an area with high heat flow - had never been explored, researchers with the Iceland Deep Drilling Project (IDDP) said in a statement. Beginning in August 2016, the IDDP spent 168 days drilling into the volcanic belly of Reykjanes. This well was completed on Jan. 25, reaching a record-breaking depth of nearly 3 miles (4.8 kilometers). [ The 11 Biggest Volcanic Eruptions in History]

At this depth, the hole does not enter the magma chamber but does penetrate the rock surrounding it, which the researchers measured to be about 800 degrees Fahrenheit (427 degrees Celsius).

Geothermal energy uses the heat trapped beneath the Earth's surface to generate electricity. Conventional geothermal energy utilizes steam from natural sources such as geysers, or by drawing water from the hot, high-pressue depths of the Earth. The hot vapors are then used to drive electric turbines.

In the case of volcanic geothermal energy, the heat comes from "supercritical water." The researchers explained that energy from so-called supercritical water is much higher than conventional geothermal steam. When molten rock and water meet, the extreme heat and pressure bring water to a "supercritical" state, where it is neither liquid nor gas. In this form, the water can carry more energy than normal steam, which could create up to 10 timesthe power output of other geothermal sources.

Research will continue through 2018 to explore how the volcano's thermal energy could be used, including as a form of alternative energy, according to IDDP scientists.

"If deep supercritical wells, here and elsewhere in the world, can produce more power than conventional geothermal wells, fewer wells would be needed to produce the same power output, leading to less environmental impact and improved economics," IDDP researchers said in the statement.

Geothermal energy is a major source of energy in Iceland, with about 25 percent of the country's electricity generated from tapping the Earth's heat, according to the National Energy Authority of Iceland. About 90 percent of Icelandic households are heated with geothermal energy.

In its 2016 power production report, the Geothermal Energy Association (GEA) found that only 6 to 7 percent of global geothermal power potential has been tapped. However, production is on the rise and the GEA predicts global geothermal energy production will more than double by 2030.
Original article on Live Science.

Kacey Deamer is a journalist for Live Science, covering planet earth and innovation. She has previously reported for Mother Jones, the Reporter's Committee for Freedom of the Press, Neon Tommy and more. After completing her undergraduate degree in journalism and environmental studies at Ithaca College, Kacey pursued her master's in Specialized Journalism: Climate Change at USC Annenberg. Follow Kacey on Twitter.

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Magma Power: Scientists Drill into Volcano to Harness its Energy

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(Image credit: Reykjanes Peninsula image via Shutterstock) It's not every day that scientists can study a volcano up close, but researchers investigating the feasibility of volcano-powered electricity successfully drilled into the core of one in Iceland.

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Still searing from the formation of the solar system, the core of Earth is a nuclear reactor generating heat from the breakdown of radioactive elements like uranium, thorium, and potassium. Scientists have been harnessing that heat for decades by drilling deep wells to power turbines. But now researchers have been able to tap into even greater energy by drilling into volcanoes and exploiting the heat of molten rock. If current geothermal wells are replaced with the new technology, it could provide 30% more power than current renewable energy sources.

The idea of tapping the energy of magma came from a pair of accidents. In 1985, workers drilling for a geothermal well in Iceland ran into a sudden and uncontrollable blast of high-pressure steam. Scientists think the steam originated from a reservoir of water that's under such pressure that as it begins to boil, the water cannot expand enough to become vapor and remains in a liquidlike state. Water in such a "supercritical state" contains enormous amounts of energy. Water reaches this state once it reaches 222 bars of pressure and 374°C or above, and flashes into steam when the pressure drops as the water rises to the surface.

For the next 2 decades, researchers dreamed of capturing superhot steam from supercritical fluids and turning it into electricity. Whereas a typical geothermal well produces 5 to 10 MW of electricity, geologist Wilfred Elders, an emeritus professor at the University of California, Riverside, says supercritical wells could potentially yield 10 times that much.

The second unexpected event happened in 2009. The Icelandic Deep Drilling Project (IDDP), a consortium of energy companies and scientists, including Elders, had begun drilling for the theorized supercritical fluid wells when they hit a pocket of magma. The molten rock ruined their equipment, but the team realized that the intense heat could actually boost the production capability of the well. The higher the temperature, the easier it becomes for water to enter a supercritical state, and the magma pouring into their well was hotter than 900°C. "There is an enormous energy potential, orders of magnitude greater than can be produced from conventional geothermal systems at 200 to 300°C," Elders says.

To use the magma for energy, workers wouldn't drill directly into it. Instead, they could either tap into superhot water in nearby magma-heated rock and use its steam to turn turbines, or make artificial steam by injecting water from the surface. In 2011, the researchers finished the well just above the magma, where the temperature didn't quite reach 900°C. Even so, the well generated superheated steam and 35 MW of electricity at 500°C, Elders and his colleagues report in the current issue of Geothermics. For the first time, researchers proved it was possible to create supercritical geothermal wells enhanced by magma.

It isn't so simple though. IDDP's 2011 well suffered from mechanical failure after only 2 years of use, and tools are still being developed to withstand such extreme conditions. Location is a problem, too: Magma-heated systems require active volcanoes, and even there it's exceedingly hard to find magma to drill into. It's "a bit like finding a needle in a haystack," says Bruce Marsh, a professor at Johns Hopkins University's Department of Earth and Planetary Sciences, who wasn't involved in the work. These types of wells won't be easily replicable, but Marsh is hopeful. "Maybe after we find a few of these things, we'll know how to look for them," he says.

Power aside, Marsh says he is excited about the wells' scientific value. Magma is hard to study, he notes. Researchers usually analyze it as solid rock that has come to the surface or as solid drill cores. But now scientists might be able to study it from where it is inside the crust and begin understanding what drives systems in Earth's interior. "We've got a tiger by the tail," Marsh says. "It's the difference between studying something in the zoo and studying it in the wild."

IDDP, meanwhile, is moving forward with other supercritical geothermal wells in Iceland soon, and similar projects are under way in New Zealand and Japan. "There's enormous potential out there," Marsh says.

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Still searing from the formation of the solar system, the core of Earth is a nuclear reactor generating heat from the breakdown of radioactive elements like uranium, thorium, and potassium. Scientists have been harnessing that heat for decades by drilling deep wells to power turbines.

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One benefit of California’s volcanoes? Geothermal energy | U.S. Geological Survey

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Nearly all of California’s geothermal electric power generation comes from areas where eruptions occurred in the past tens of thousands of years

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How Piezoelectricity Works | EAGLE | Blog

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Learn how piezoelectricity works to produce an electric charge by applying mechanical stress to a piezoelectric material, called the piezoelectric effect.

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Crystals which acquire a charge when compressed, twisted or distorted are said to be piezoelectric. This provides a convenient transducer effect between electrical and mechanical oscillations. Quartz demonstrates this property and is extremely stable. Quartz crystals are used for watch crystals and for precise frequency reference crystals for radio transmitters. Rochelle salt produces a comparatively large voltage upon compression and was used in early crystal microphones. Barium titanate, lead zirconate, and lead titanate are ceramic materials which exhibit piezoelectricity and are used in ultrasonic transducers as well as microphones. If an electrical oscillation is applied to such ceramic wafers, they will respond with mechanical vibrations which provide the ultrasonic sound source. The standard piezoelectric material for medical imaging processes has been lead zirconate titanate (PZT). Piezoelectric ceramic materials have found use in producing motions on the order of nanometers in the control of scanning tunneling microscopes.

The word piezo is Greek for "push". The effect known as piezoelectricity was discovered by brothers Pierre and Jacques Curie when they were 21 and 24 years old in 1880.

There is a magnetic analog where ferromagnetic materials respond mechanically to magnetic fields. This effect, called magnetostriction, is responsible for the familiar hum of transformers and other AC devices containing iron cores.

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Crystals which acquire a charge when compressed, twisted or distorted are said to be piezoelectric. This provides a convenient transducer effect between electrical and mechanical oscillations. Quartz demonstrates this property and is extremely stable. Quartz crystals are used for watch crystals and for precise frequency reference crystals for radio transmitters.

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Piezoelectricity - an overview | ScienceDirect Topics

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Piezoelectricity is the ability of a material to generate an internal electric field when subjected to mechanical stress or strain (Berlincourt, 1971).

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by Chris Woodford. Last updated: August 21, 2018.

You've probably used piezoelectricity (pronounced "pee-ay-zo-electricity") quite a few times today. If you've got a quartz watch, piezoelectricity is what helps it keep regular time. If you've been writing a letter or an essay on your computer with the help of voice recognition software, the microphone you spoke into probably used piezoelectricity to turn the sound energy in your voice into electrical signals your computer could interpret. If you're a bit of an audiophile and like listening to music on vinyl, your gramophone would have been using piezoelectricity to "read" the sounds from your LP records. Piezoelectricity (literally, "pressing electricity") is much simpler than it sounds: it just means using crystals to convert mechanical energy into electricity or vice-versa. Let's take a closer look at how it works and why it's so useful!

Photo: A piezoelectric actuator used by NASA for various kinds of testing. Photo by courtesy of NASA Langley Research Center (NASA-LaRC).

What is piezoelectricity?

Squeeze certain crystals (such as quartz) and you can make electricity flow through them. The reverse is usually true as well: if you pass electricity through the same crystals, they "squeeze themselves" by vibrating back and forth. That's pretty much piezoelectricity in a nutshell but, for the sake of science, let's have a formal definition:

Piezoelectricity (also called the piezoelectric effect) is the appearance of an electrical potential (a voltage, in other words) across the sides of a crystal when you subject it to mechanical stress (by squeezing it).

In practice, the crystal becomes a kind of tiny battery with a positive charge on one face and a negative charge on the opposite face; current flows if we connect the two faces together to make a circuit. In the reverse piezoelectric effect, a crystal becomes mechanically stressed (deformed in shape) when a voltage is applied across its opposite faces.

What causes piezoelectricity?

Think of a crystal and you probably picture balls ( atoms) mounted on bars (the bonds that hold them together), a bit like a climbing frame. Now, by crystals, scientists don't necessarily mean intriguing bits of rock you find in gift shops: a crystal is the scientific name for any solid whose atoms or molecules are arranged in a very orderly way based on endless repetitions of the same basic atomic building block (called the unit cell). So a lump of iron is just as much of a crystal as a piece of quartz. In a crystal, what we have is actually less like a climbing frame (which doesn't necessarily have an orderly, repeating structure) and more like three-dimensional, patterned wallpaper.

Artwork: What scientists mean by a crystal: the regular, repeating arrangement of atoms in a solid. The atoms are essentially fixed in place but can vibrate slightly.

In most crystals (such as metals), the unit cell (the basic repeating unit) is symmetrical; in piezoelectric crystals, it isn't. Normally, piezoelectric crystals are electrically neutral: the atoms inside them may not be symmetrically arranged, but their electrical charges are perfectly balanced: a positive charge in one place cancels out a negative charge nearby. However, if you squeeze or stretch a piezoelectric crystal, you deform the structure, pushing some of the atoms closer together or further apart, upsetting the balance of positive and negative, and causing net electrical charges to appear. This effect carries through the whole structure so net positive and negative charges appear on opposite, outer faces of the crystal.

The reverse-piezoelectric effect occurs in the opposite way. Put a voltage across a piezoelectric crystal and you're subjecting the atoms inside it to "electrical pressure." They have to move to rebalance themselves-and that's what causes piezoelectric crystals to deform (slightly change shape) when you put a voltage across them.

How piezoelectricity works

Here's a quick animation showing how piezoelectricity occurs. It's somewhat simplified, but it gives you the basic idea:

1. Normally, the charges in a piezoelectric crystal are exactly balanced, even if they're not symmetrically arranged.

2. The effects of the charges exactly cancel out, leaving no net charge on the crystal faces. (More specifically, the electric dipole moments-vector lines separating opposite charges-exactly cancel one another out.)

3. If you squeeze the crystal (massively exaggerated in this picture!), you force the charges out of balance.

4. Now the effects of the charges (their dipole moments) no longer cancel one another out and net positive and negative charges appear on opposite crystal faces. By squeezing the crystal, you've produced a voltage across its opposite faces-and that's piezoelectricity!

What is piezoelectricity used for?

Photo: A typical piezoelectric transducer. This one is the ringer inside my landline telephone: it makes a particularly shrill and horrible chirping noise when the phone rings!

There are all kinds of situations where we need to convert mechanical energy (pressure or movement of some kind) into electrical signals or vice-versa. Often we can do that with a piezoelectric transducer. A transducer is simply a device that converts small amounts of energy from one kind into another (for example, converting light, sound, or mechanical pressure into electrical signals).

In ultrasound equipment, a piezoelectric transducer converts electrical energy into extremely rapid mechanical vibrations-so fast, in fact, that it makes sounds, but ones too high-pitched for our ears to hear. These ultrasound vibrations can be used for scanning, cleaning, and all kinds of other things.

In a microphone, we need to convert sound energy (waves of pressure traveling through the air) into electrical energy-and that's something piezoelectric crystals can help us with. Simply stick the vibrating part of the microphone to a crystal and, as pressure waves from your voice arrive, they'll make the crystal move back and forth, generating corresponding electrical signals. The "needle" in a gramophone (sometimes called a record player) works in the opposite way. As the diamond-tipped needle rides along the spiral groove in your LP, it bumps up and down. These vibrations push and pull on a lightweight piezoelectric crystal, producing electrical signals that your stereo then converts back into audible sounds.

Photo: Record-player stylus (photographed from underneath): If you're still playing LP records, you'll use a stylus like this to convert the mechanical bumps on the record into sounds you can hear. The stylus (silver horizontal bar) contains a tiny diamond crystal (the little dot on the end at the right) that bounces up and down in the record groove. The vibrations distort a piezoelectric crystal inside the yellow cartridge that produces electrical signals, which are amplified to make the sounds you can hear.

In a quartz clock or watch, the reverse-piezoelectric effect is used to keep time very precisely. Electrical energy from a battery is fed into a crystal to make it oscillate thousands of times a second. The watch then uses an electronic circuit to turn that into slower, once-per-second beats that a tiny motor and some precision gears use to drive the second, minute, and hour hands around the clock-face.

Piezoelectricity is also used, much more crudely, in spark lighters for gas stoves and barbecues. Press a lighter switch and you'll hear a clicking sound and see sparks appear. What you're doing, when you press the switch, is squeezing a piezoelectric crystal, generating a voltage, and making a spark fly across a small gap.

If you've got an inkjet printer sitting on your desk, it's using precision "syringes" to squirt droplets of ink onto the paper. Some inkjets squirt their syringes using electronically controlled piezoelectric crystals, which squeeze their "plungers" in and out; Canon Bubble Jets fire their ink by heating it instead. (You'll find more details of both methods in our article about inkjet printers.)

Energy harvesting with piezoelectricity?

If you can make a tiny bit of electricity by pressing one piezoelectric crystal once, could you make a significant amount by pressing many crystals over and over again? What if we buried crystals under city streets and pavements to capture energy as cars and people passed by? This idea, which is known as energy harvesting, has caught many people's interest. Inventors have proposed all kinds of ideas for storing energy with hidden piezoelectric devices, from shoes that convert your walking movements into heat to keep your feet warm, and cellphones that charge themselves from your body movements, to roads that power streetlights, contact lenses that capture energy when you blink, and even gadgets that make energy from the pressure of falling rain.

Artwork: Energy harvesting? Inventors have been filing lots of patents for wearable gadgets that will generate small amounts of electricity from your body movements. This example is a shoe with a built-in piezoelectric transducer (1) that springs up and down as you walk, sending electricity to a circuit (2) and then storing it in a battery (3).

Is energy harvesting a good idea? At first sight, anything that minimizes waste energy and improves efficiency sounds really sensible. If you could use the floor of a grocery store to capture energy from the feet of hurrying shoppers pushing their heavy carts, and use that to power the store's lights or its chiller cabinets, surely that must be a good thing? Sometimes energy harvesting can indeed provide a decent, if rather modest, amount of power.

The trouble is, however, that energy harvesting schemes can be a big distraction from better ideas. Consider, for example, the concept of building streets with piezoelectric "rumble strips" that soak up energy from passing traffic. Cars are extremely inefficient machines and only a small amount (15 percent or so) of the energy in their fuel powers you down the road. Only a fraction of this fraction is available for recovery from the road-and you wouldn't be able to recover all that fraction with 100 percent efficiency. So the amount of energy you could practically recover, and the efficiency gain you would make for the money you spent, would be minuscule. If you really want to save energy from cars, the sensible way to do it is to address the inefficiencies of car transportation much earlier in the process; for example, by designing engines that are more efficient, encouraging people to car share, swapping from gasoline engines to electric cars, and things of that sort.

That's not to say that energy harvesting has no place; it could be really useful for charging mobile devices using energy that would otherwise go to waste. Imagine a cellphone that charged itself automatically every time it jiggled around in your pocket, for example. Even so, when it comes to saving energy, we should always consider the bigger picture and make sure the time and money we invest is producing the best possible results.

Who discovered piezoelectricity?

The piezoelectric effect was discovered in 1880 by two French physicists, brothers Pierre and Paul-Jacques Curie, in crystals of quartz, tourmaline, and Rochelle salt (potassium sodium tartrate). They took the name from the Greek work piezein, which means "to press."

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On this website

Practical demonstrations

Articles

A Fitbit for the Stomach by Megan Scudellari. IEEE Spectrum, 11 October, 2017. Researchers develop a piezoelectric stomach sensor.

Good Vibrations? California to Test Using Road Rumbles as a Power Source by Philip E. Ross. IEEE Spectrum, 19 April 2017. Could piezoelectric rumble-strips generate useful amounts of power? Given how much energy cars waste in converting fuel to motion, thinking about harvesting a tiny fraction of this energy could, itself, be a waste of (mental) energy.

Energy harvesting fibre invented at University of Bolton: BBC News, 28 June, 2011. Flexible, piezoelectric fibers could be sewn into your clothes to charge your MP3 player or cellphone as you move around!

Future Helicopters Get SMART: NASA, 25 February 2009. NASA scientists think piezoelectric blades could make helicopters quieter and more economical.

A step closer to self-powered kit: BBC News, 4 December, 2008. Describes how small, piezoelectric generators could be used to make a variety of self-powered gadgets.

Implant may help deaf hear music: BBC News, 19 October 2005. How piezoelectric materials are being used in new cochlear implants to improve deaf people's hearing.

Books

Piezoelectric Materials: Applications in SHM, Energy Harvesting and Biomechanics by Suresh Bhalla, Sumedha Moharana, Naveet Kaur, and Visalakshi Talakokula. Wiley/Athena, 2017. An up-to-date introduction that connects theoretical aspects of piezoelectricity with practical applications in medicine and energy production.

Piezoelectric Ceramics: Principles and Applications: APC International, Ltd. 2011. A pithy (114-page) introduction to the principles of piezoelectricity and how it's used in different kinds of generators, sensors, actuators, and transducers.

The Beginnings of Piezoelectricity: A Study in Mundane Physics by Shaul Katzir. Springer, 2011. A fascinating historical account of how the piezoelectric effect was discovered and explained by a variety of different theories and models.

Piezoelectricity: Evolution and Future of a Technology by Walter Heywang, Karl Lubitz, and Wolfram Wersing. Springer, 2008. What is piezoelectricity and how can we apply it in medicine, defense, and other important areas of society?

Patents

Inventors have been dreaming up all kinds of imaginative uses for piezoelectricity for years. Here are a few examples from the US Patent and Trademark Office database:

US Patent: US 20140128753 A1: Piezoelectric heart rate sensing for wearable devices or mobile devices by Michael Edward Smith Luna et al, 8 May 2014. A cutting-edge sensor that can monitor your heart and send details to your cellphone (or similar mobile device).

US Patent: 8,087,186: Piezoelectric-based toe-heaters for frostbite protection by ‎Jahangir S. Rastegar, 3 January 2012. These shoes use piezoelectric materials to convert the repeated squashing and stretching of your shoes into electrical energy that can warm your feet.

US Patent: 20050127677: Roadway generating electrical power by incorporating piezoelectric materials by Jeffrey Luttrull, 16 June 2005. Describes a method of harvesting energy from roads. US Patent: 8,278,800: Multi-layer piezoelectric generator by Haim Abramovich et al, Innowattech, 2 October 2010, is a variation on the same basic idea with more details of how road generators would actually work.

US Patent: 4,685,296: Ocean wave energy conversion using piezoelectric material members by Joseph R. Burns, 11 August 1987. In this invention, piezoelectric materials generate electricity from the up-and-down movements of ocean waves.

US Patent: 5,598,196: Piezoelectric ink jet print head and method of making by Hilarion Braun, Eastman Kodak, 28 January 1987. An inkjet print head that squirts precise droplets of ink using piezoelectric materials.

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Piezoelectricity - How does it work? | What is it used for?

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A really easy-to-understand introduction to how piezoelectricity works and what we can use it for