Tag Archives: piezoelectronics

Getting to know your piezoelectrics

It took me a couple of tries before I could see the butterfly in the neutron scattering image (on the left), which illustrates work undertaken in an attempt to better understand piezoelectrics (found in hard drives, loud speakers, etc.) by researchers at Simon Fraser University (Vancouver area, Canada) and the US National Institute of Standards and Technology.

These two neutron scattering images represent the nanoscale structures of single crystals of PMN and PZT. Because the atoms in PMN deviate slightly from their ideal positions, diffuse scattering results in a distinctive "butterfly" shape quite different from that of PZT, in which the atoms are more regularly spaced. Credit: NIST

These two neutron scattering images represent the nanoscale structures of single crystals of PMN and PZT. Because the atoms in PMN deviate slightly from their ideal positions, diffuse scattering results in a distinctive “butterfly” shape quite different from that of PZT, in which the atoms are more regularly spaced.
Credit: NIST

A Jan. 30, 2014 news release on EurekAlert (also found on on the NIST website where it’s dated Jan. 29, 2014) describes piezoelectrics,

Piezoelectrics—materials that can change mechanical stress to electricity and back again—are everywhere in modern life. Computer hard drives. Loud speakers. Medical ultrasound. Sonar. Though piezoelectrics are a widely used technology, there are major gaps in our understanding of how they work. Now researchers at the National Institute of Standards and Technology (NIST) and Canada’s Simon Fraser University believe they’ve learned why one of the main classes of these materials, known as relaxors, behaves in distinctly different ways from the rest and exhibit the largest piezoelectric effect. And the discovery comes in the shape of a butterfly. …

The news release goes on to explain piezoelectrics and provide details about how the researchers made their discovery,

The team examined two of the most commonly used piezoelectric compounds—the ferroelectric PZT and the relaxor PMN—which look very similar on a microscopic scale. Both are crystalline materials composed of cube-shaped unit cells (the basic building blocks of all crystals) that contain one lead atom and three oxygen atoms. The essential difference is found at the centers of the cells: in PZT these are randomly occupied by either one zirconium atom or one titanium atom, both of which have the same electric charge, but in PMN one finds either niobium or manganese, which have very different electric charges. The differently charged atoms produce strong electric fields that vary randomly from one unit cell to another in PMN and other relaxors, a situation absent in PZT.

“PMN-based relaxors and ferroelectric PZT have been known for decades, but it has been difficult to identify conclusively the origin of the behavioral differences between them because it has been impossible to grow sufficiently large single crystals of PZT,” says the NIST Center for Neutron Research (NCNR)’s Peter Gehring. “We’ve wanted a fundamental explanation of why relaxors exhibit the greatest piezoelectric effect for a long time because this would help guide efforts to optimize this technologically valuable property.”

A few years ago, scientists from Simon Fraser University found a way to make crystals of PZT large enough that PZT and PMN crystals could be examined with a single tool for the first time, permitting the first apples-to-apples comparison of relaxors and ferroelectrics. That tool was the NCNR’s neutron beams, which revealed new details about where the atoms in the unit cells were located. In PZT, the atoms sat more or less right where they were expected, but in the PMN, their locations deviated from their expected positions—a finding Gehring says could explain the essentials of relaxor behavior.

“The neutron beams scatter off the PMN crystals in a shape that resembles a butterfly,” Gehring says. “It gives a characteristic blurriness that reveals the nanoscale structure that exists in PMN—and in all other relaxors studied with this method as well—but does not exist in PZT. It’s our belief that this butterfly-shaped scattering might be a characteristic signature of relaxors.”

Additional tests the team performed showed that PMN-based relaxors are over 100 percent more sensitive to mechanical stimulation compared to PZT, another first-time measurement. Gehring says he hopes the findings will help materials scientists do more to optimize the behavior of piezoelectrics generally.

Here’s a citation for the researchers’ paper,

Role of random electric fields in relaxors by Daniel Phelan, Christopher Stock, Jose A. Rodriguez-Rivera, Songxue Chia, Juscelino Leão, Xifa Long, Yujuan Xie, Alexei A. Bokov, Zuo-Guang Ye, Panchapakesan Ganesh, and Peter M. Gehring. Proceedings of the National Academy of Sciences, Jan. 21, 2014. DOI:10.1073/pnas.1314780111

This paper is behind a paywall.

Developing self-powered batteries for pacemakers

Imagine having your chest cracked open every time your pacemaker needs to have its battery changed? It’s not a pleasant thought and researchers are working on a number of approaches to change that situation.  Scientists from the University of Michigan have presented the results from some preliminary testing of a device that harvests energy from heartbeats (from the Nov. 4, 2012 news release on EurekAlert),

In a preliminary study, researchers tested an energy-harvesting device that uses piezoelectricity — electrical charge generated from motion. The approach is a promising technological solution for pacemakers, because they require only small amounts of power to operate, said M. Amin Karami, Ph.D., lead author of the study and research fellow in the Department of Aerospace Engineering at the University of Michigan in Ann Arbor.

Piezoelectricity might also power other implantable cardiac devices like defibrillators, which also have minimal energy needs, he said.

Today’s pacemakers must be replaced every five to seven years when their batteries run out, which is costly and inconvenient, Karami said.

A University of Michigan at Ann Arbor March 2, 2012 news release provides more technical detail about this energy-harvesting battery which the researchers had not then tested,

… A hundredth-of-an-inch thin slice of a special “piezoelectric” ceramic material would essentially catch heartbeat vibrations and briefly expand in response. Piezoelectric materials’ claim to fame is that they can convert mechanical stress (which causes them to expand) into an electric voltage.

Karami and his colleague Daniel Inman, chair of Aerospace Engineering at U-M, have precisely engineered the ceramic layer to a shape that can harvest vibrations across a broad range of frequencies. They also incorporated magnets, whose additional force field can drastically boost the electric signal that results from the vibrations.

The new device could generate 10 microwatts of power, which is about eight times the amount a pacemaker needs to operate, Karami said. It always generates more energy than the pacemaker requires, and it performs at heart rates from 7 to 700 beats per minute. That’s well below and above the normal range.

Karami and Inman originally designed the harvester for light unmanned airplanes, where it could generate power from wing vibrations.

Since March 2012, the researchers have tested the prototype (from the Nov. 4, 2012 news release on EurekAlert),

Researchers measured heartbeat-induced vibrations in the chest. Then, they used a “shaker” to reproduce the vibrations in the laboratory and connected it to a prototype cardiac energy harvester they developed. Measurements of the prototype’s performance, based on sets of 100 simulated heartbeats at various heart rates, showed the energy harvester performed as the scientists had predicted — generating more than 10 times the power than modern pacemakers require. The next step will be implanting the energy harvester, which is about half the size of batteries now used in pacemakers, Karami said. Researchers hope to integrate their technology into commercial pacemakers.

There are other teams working on energy-harvesting batteries, in my July 12, 2010 posting I mentioned a team led by Professor Zhong Lin Wang at Georgia Tech (Georgia Institute of Technology in the US) which is working on batteries that harvest energy from biomechanical motion such as heart beats, finger tapping, breathing, etc.

Dem bones, dem bones, dem dry bones

Making sounds with bones—but not as you might imagine.

Image from slideshow of Transjuicer exhibit in Science Gallery, Dublin, 2011 and John Curtin Gallery, Perth 2010

Christopher Mims in his Dec. 27, 2011 (?) article for Fast Company explains what artist Boo Chapple is doing with her Transjuicer installation of speakers made from bone tissue,

Turned on its head, bone’s response to physical stress can be used to produce music—or at least musical tones. That’s what artist Boo Chapple discovered during the course of a year-long collaboration at the University of Western Australia’s SymbioticA lab, the only research facility in the world devoted to providing access to wet labs to artists and artistically minded researchers.

When Chapple began this project, she knew that extensive scientific literature suggested bone had what are known as piezoelectric properties. Basically, when a piezoelectric material is bent, compressed, or otherwise physically stressed, it generates an electric charge. Conversely, applying an electric charge to a piezoelectric material can change its shape. This has made piezoelectrics the backbone of countless environmental sensors and tiny actuators.

Poring through this literature, Chapple realized that applying a current to bone at just the right frequency should make it vibrate like the diaphragm in an audio speaker. And because bone retains its piezoelectric properties even when it’s no longer living, it should be fairly straightforward to transform any old bone into the world’s most outre audio component.

Because Chapple is an artist and not a technologist, her goal wasn’t to pursue this technique until it yielded a new product. Rather, the point was to accomplish what all good art can: “making strange” otherwise familiar objects.

I first heard about the SymbioticA lab when they showed their Fish & Chips project (the report I’ve linked to is undated) at the 2001 Ars Electronic annual event in Linz, Austria. I never did get to see the performance (fish neurons grown on silicon chips and hooked up to software and musical instruments) but their work remains a source of great interest to me. (I last mentioned SymbioticA in my July 5, 2011 posting where they were scheduled for the same session that I was, at the 2011 ISEA conference in Istanbul.)

Here’s a bit more about the SymbioticA lab at the University of Western Australia (from their home page),

SymbioticA is a research facility dedicated to artistic inquiry into knowledge and technology in the life sciences.

Our research embodies:

  • identifying and developing new materials and subjects for artistic manipulation
  • researching strategies and implications of presenting living-art in different contexts
  • developing technologies and protocols as artistic tool kits.

Having access to scientific laboratories and tools, SymbioticA is in a unique position to offer these resources for artistic research. Therefore, SymbioticA encourages and favours research projects that involve hands on development of technical skills and the use of scientific tools.

The research undertaken at SymbioticA is speculative in nature. SymbioticA strives to support non-utilitarian, curiosity based and philosophically motivated research.

Boo Chapple, a resident at the SymbioticA Lab, had this to say about her installation, Transjuicer, and science when it was at Dublin’s Science Gallery (excerpted from the Visceral Interview),

Do you think that work like yours helps to open up science to public discussion and debate; and does this interest you?

I’m not sure that Transjuicer is so much about science as it is about belief, the economy of human-animal relations, and the politics of material transformation. These are all things that are inherent to the practice of science but perhaps not what one might think of when one thinks of public debate around particular scientific discoveries, or technologies.

While I am interested in the philosophical parameters of these debates, I do not see my art practice as an instrument of communication in this respect, nor is Transjuicer engaged with any hot topics of the moment, or designed in such a way as to reveal the technical processes that were employed in making the bone audio speakers.

The work being done at the SymbioticA lab is provocative in the best sense, i.e., meant to provoke thought and discussion.

Noisy new world with clothing that sings and records and varnishes that ring alarms

They’re called functional fibres and a team at MIT (Massachusetts Institute of Technology) has taken another step forward in achieving fibres that can produce and detect sound. From the news item on physorg.com,

For centuries, “man-made fibers” meant the raw stuff of clothes and ropes; in the information age, it’s come to mean the filaments of glass that carry data in communications networks. But to Yoel Fink, an Associate professor of Materials Science and principal investigator at MIT’s Research Lab of Electronics, the threads used in textiles and even optical fibers are much too passive. For the past decade, his lab has been working to develop fibers with ever more sophisticated properties, to enable fabrics that can interact with their environment.

… Applications could include clothes that are themselves sensitive microphones, for capturing speech or monitoring bodily functions, and tiny filaments that could measure blood flow in capillaries or pressure in the brain. The paper, whose authors also include Shunji Egusa, a former postdoc in Fink’s lab, and current lab members Noémie Chocat and Zheng Wang, appeared on Nature Materials‘ website on July 11, and the work it describes was supported by MIT’s Institute for Soldier Nanotechnologies, the National Science Foundation and the U.S. Defense Department’s Defense Advanced Research Projects Agency. [emphases mine]

Interesting to note all of the military interest.

The heart of the new acoustic fibers is a plastic commonly used in microphones. By playing with the plastic’s fluorine content, the researchers were able to ensure that its molecules remain lopsided — with fluorine atoms lined up on one side and hydrogen atoms on the other — even during heating and drawing. The asymmetry of the molecules is what makes the plastic “piezoelectric,” meaning that it changes shape when an electric field is applied to it.

I’m not sure how this fits with Professor Zhong Lin Wang’s work in the field of piezotronics  (July 12, 2010 posting) and I’m not looking at the technical aspect so much as the social impact of clothing made of fibres that can harvest biomechanical energy and/or record sound and/or produce sound. In other words, what’s the social impact? In all the talk about developing new products and getting them to market,  I haven’t found that much discussion about whether people are going to adopt products that are constantly monitoring their health or given to making a sound for one reason or another. When you add in the other work on such things as varnishes that emit sounds as they cool or heat (Feb. 3, 2010, 2nd excerpt, last paragraph), you have to come to the conclusion that at the very least it’s going to be a very noisy world in the future. Questions that come to mind include: will these fibres that can monitor our health or record sounds or the varnishes that sound alarms have an off button? What happens if they malfunction?