Army researchers make progress on more efficient battlefield power re-supply

October 25, 2019

By U.S. Army CCDC Army Research Laboratory Public Affairs

ADELPHI, Md. (Oct. 25, 2019) -- When a new, exciting material is discovered, researchers at the Army's corporate research laboratory ask, "What can it do for the Army and the Soldier?"

This was exactly the case when researchers discovered a set of properties called ferroelectricity in materials based on hafnium oxide in 2011, which has led to research that will allow for intelligent and seamless power re-supply for Soldiers on the battlefield.

"Ferroelectric materials are incredibly versatile; they exhibit electronic memory, sensitivity to mechanical force and sensitivity to heat," said Dr. Brendan Hanrahan, materials engineer for the U.S. Army Combat Capabilities Development Command's Army Research Laboratory. "The discovery of ferroelectricity in hafnium oxide, or HFO, in 2011 by German researchers was a shocking surprise to the field, considering the standard material, Lead Zirconate Titanate, or PZT, was discovered in 1952."

For the past year, Hanrahan has endeavored to understand if these materials could help the Army, particularly in the areas of energy harvesting and power beaming.

"The main source of excitement around ferroelectric HFO is that the material is already integrated into large-scale semiconductor manufacturing, so the transition path should be more straight-forward than other ferroelectrics, like PZT, which contain lead," Hanrahan said.

The material is grown in the lab's cleanroom using a technique called atomic layer deposition, which can create nanometer-thick functional materials as well as perfectly-coated 3-D surfaces.

The laboratory's studies have focused on the set of properties called pyroelectricity, where the material generates charge when it is heated or cooled.

The first of two studies, which was published this month, dealt with the theoretical understanding of pyroelectricity in HFO.

The paper, "Origin of pyroelectricity in ferroelectric HfO2," shows, through simulation, that the pyroelectric coefficient in these materials has a curious origin, he said.

"Rather than arising primarily from a temperature-induced internal electrical change, it is actually more of a product of the thermal expansion of the material," Hanrahan said. "All materials show some change in size based on heating and cooling, which we take advantage of when, for example, you run a stuck lid under hot water, but HFO materials expand in specific directions, which changes their internal electrical properties called polarization."

This study, published in Physical Review Applied and highlighted by the editor, is the first to point out this curious property, which can guide further device development.

The second study, which was featured on the cover of Energy Technology, shows pyroelectric Hafnia performance within a real device.

"Since HFO can be deposited on undulating surfaces and the amount of energy is relative to the total area, a collaboration between ARL and Fraunhofer in Germany deposited pyroelectric Hafnia on an undulating surface, similar to accordion-folding a map," Hanrahan said. "This way, there is more Hafnia in a smaller space."

Hanrahan met the Fraunhofer group at an international conference after they attended one of his talks, and after speaking, they decided the ARL team would be able to create a wireless power test from the group's microchip.

The team tested thermal power beaming on the accordion devices, which was the first time that these materials have been used in real energy conversion applications.

"The collaboration showed that these materials can be both the most efficient theoretically and can face challenges arising from the fabrication techniques," Hanrahan said.

This collaboration has also led to a foreign technology assessment, or FTAS, which funds science and research for preliminary assessment of technologies that, if proven successful, may be transitioned into a laboratory project or other research program.

Together, Hanrahan said, these two studies significantly advance the state of knowledge for Hafnia in pyroelectric energy conversion applications, supporting Army technologies like power beaming.

"We envision a future for the Army where re-supply is intelligent and seamless," Hanrahan said. "Getting energy around the battlefield is a mission-limiting challenge, and beaming power, from a protected to hard-to-reach place, or even between squad mates, is part of that vision."

Hanrahan said that this research opens up new device architectures for wireless power receivers as well as offshoots on low-power sensors and high-density energy storage.

"Now that we've gained a theoretical-to-device level understanding of these materials for power beaming, we are going to look at other energy applications such as devices that do both energy creation and storage," Hanrahan said.

The laboratory, through Hanrahan's research, has a world-recognized capability to assess pyroelectric devices, and through the theoretical paper, the lab brought this assessment capability to the table, which helped confirm their theory, he said.

The CCDC Army Research Laboratory (ARL) is an element of the U.S. Army Combat Capabilities Development Command. As the Army's corporate research laboratory, ARL discovers, innovates and transitions science and technology to ensure dominant strategic land power. Through collaboration across the command's core technical competencies, CCDC leads in the discovery, development and delivery of the technology-based capabilities required to make Soldiers more lethal to win our Nation's wars and come home safely. CCDC is a major subordinate command of the U.S. Army Futures Command.


Last Update / Reviewed: October 25, 2019