Reviewed by Lexie CornerAug 7 2024
In a study published in Nature Communications, researchers from North Carolina State University developed a method to restore the properties of piezoelectric materials at room temperature. This advancement makes it easier to repair devices that rely on these materials and paves the way for new ultrasound technologies.
Heat and pressure can impair the capabilities of piezoelectric materials used in cutting-edge ultrasound and sonar technologies. Traditionally, repairing this damage required dismantling devices and subjecting the materials to even higher temperatures.
Piezoelectric materials, essential for sonar and ultrasound wave creation and detection, must be "poled" to function effectively. Most piezoelectric materials in these applications are ferroelectric and exhibit spontaneous polarization, meaning they contain dipoles—pairs of positively and negatively charged ions.
Poling aligns all dipoles with an external electric field, enhancing their piezoelectric properties by orienting the dipoles uniformly. This alignment is crucial for the efficient emission of sonar and ultrasound waves.
If those dipoles aren’t in alignment, it’s difficult to generate targeted ultrasound waves with the amplitude needed for them to be practical.
Xiaoning Jiang, Study Corresponding Author and Dean F. Duncan Distinguished Professor, Mechanical and Aerospace Engineering, North Carolina State University
Jiang added, “Preserving the poling of piezoelectric-ferroelectric materials poses some significant challenges because the dipoles can begin losing their alignment when exposed to elevated temperatures or high pressures.”
“This is also a manufacturing problem because it limits which other materials and processes you can use when making ultrasound devices. And because the elevated temperatures aren’t even really that high – you can see alignment problems as low as 70 degrees Celsius – even shipping or storing these technologies can sometimes adversely affect the poling and the efficiency of the devices,” Jiang further noted.
He further stated, “What is more, extended use of some technologies can result in the device itself generating heat that risks depoling the piezoelectric-ferroelectric material.”
Furthermore, it is difficult to realign the dipoles in the material after they have deviated from their alignment. Before “repolling” and bringing the dipoles back into alignment, the piezoelectric-ferroelectric material must be removed from the device and subjected to extreme heat, 300 degrees Celsius or more.
Jiang added, “It’s important to re-use these piezoelectric-ferroelectric materials because they are usually expensive – you don’t want to just throw them away. But often, the material is retrieved, and the rest of the ultrasound device is discarded. We have developed a technique that allows us to depole and repole piezoelectric-ferroelectric materials at room temperature. That means we can pull the dipoles back into alignment without removing the material from the device – and this can be done repeatedly, as needed.”
To align the dipoles in a piezoelectric-ferroelectric material, which is essential to understanding the new methodology, two methods are commonly used. The most popular method involves applying a direct current (DC) electric field to push all the dipoles in the same direction.
Jiang noted, “This way works well for creating alignment, but it is virtually impossible to depole the material using only a DC field.”
The alternative method involves applying an alternating current (AC) electric field to the material, causing the dipoles to fluctuate in response to the field's waves. When the field is withdrawn, the dipoles lock into alignment.
“We found that we can also depole the material using an AC field, even at room temperature. If the material was originally poled using a DC field, we could remove much of the poling with an AC field–but not all of it. However, if the material was originally poled with an AC field, we found that could also completely depole the material using an AC field,” Jiang added.
The result has at least two important implications for ultrasound technology.
Jiang added, “If we can pole piezoelectric-ferroelectric materials at room temperature, it means we can alter the other materials and manufacturing processes we use when creating ultrasound devices to optimize their performance. We are no longer limited to materials and processes that won’t affect the polarization in the piezoelectric-ferroelectric components, because we can pole the material using an AC field after the device has been assembled.”
He concluded, “What’s more, it means that we can easily repole the materials in existing devices, hopefully giving us a long lifetime of peak performance for these technologies.”
The study’s first author, Hwang-Pill Kim, is a former postdoctoral researcher at NC State.
The study was co-authored by Huaiyu Wu, an Assistant Research Professor of Mechanical and Aerospace Engineering at NC State; Zhengze Xu and Sunho Moon, Ph.D. students at NC State; Sipan Liu, a Postdoctoral Researcher at NC State; Jong Eun Ryu, an Assistant Professor of Mechanical and Aerospace Engineering at NC State; Jun Liu, an Associate Professor of Mechanical and Aerospace Engineering at NC State; Yohachi Yamashita, an Adjunct Professor at NC State and Shonan Institute of Technology.
Mao-Hua Zhang and Long-Qing Chen of Pennsylvania State University, Bo Wang of Lawrence Livermore National Laboratory, and Shujun Zhang of the University of Wollongong also contributed to the study.
This study was supported by the Office of Naval Research (grant N00014-21-1-2058), the National Science Foundation (under grants 2011978, 2309184, and 2133373), and the US Department of Energy's Lawrence Livermore National Laboratory (contract DE-AC52-07NA27344).
Journal Reference:
Kim, H.-P., et. al. (2024) Electrical de-poling and re-poling of relaxor-PbTiO3 piezoelectric single crystals without heat treatment. Nature Communications. doi.org/10.1038/s41467-024-50847-3