New research from the Georgia Institute of Technology finds that elephants dilate their nostrils in order to create more space in their trunks, allowing them to store up to 5.5 liters of water. They can also suck up three liters per second — a speed 30 times faster than a human sneeze (150 meters per second/330 mph).

The Georgia Tech College of Engineering study sought to better understand the physics of how elephants use their trunks to move and manipulate air, water, food and other objects. They also sought to learn if the mechanics could inspire the creation of more efficient robots that use air motion to hold and move things.

While octopus use jets of water to move and archer fish shoot water above the surface to catch insects, the Georgia Tech researchers found that elephants are the only animals able to use suction on land and underwater.

The paper, “Suction feeding by elephants,” is published in the Journal of the Royal Society Interface.

“An elephant eats about 400 pounds of food a day, but very little is known about how they use their trunks to pick up lightweight food and water for 18 hours, every day,” said Georgia Tech mechanical engineering Ph.D. student Andrew Schulz, who led the study. “It turns out their trunks act like suitcases, capable of expanding when necessary.”

Schulz and the Georgia Tech team worked with veterinarians at Zoo Atlanta, studying elephants as they ate various foods. For large rutabaga cubes, for example, the animal grabbed and collected them. It sucked up smaller cubes and made a loud vacuuming sound, or the sound of a person slurping noodles, before transferring the vegetables to its mouth.

To learn more about suction, the researchers gave elephants a tortilla chip and measured the applied force. Sometimes the animal pressed down on the chip and breathed in, suspending the chip on the tip of trunk without breaking it. It was similar to a person inhaling a piece of paper onto their mouth. Other times the elephant applied suction from a distance, drawing the chip to the edge of its trunk.

“An elephant uses its trunk like a Swiss Army Knife,” said David Hu, Schulz’s advisor and a professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering. “It can detect scents and grab things. Other times it blows objects away like a leaf blower or sniffs them in like a vacuum.”

By watching elephants inhale liquid from an aquarium, the team was able to time the durations and measure volume. In just 1.5 seconds, the trunk sucked up 3.7 liters, the equivalent of 20 toilets flushing simultaneously.

An ultrasonic probe was used to take trunk wall measurements and see how the trunk’s inner muscles work. By contracting those muscles, the animal dilates its nostrils up to 30 percent. This decreases the thickness of the walls and expands nasal volume by 64 percent.

“At first it didn’t make sense: an elephant’s nasal passage is relatively small and it was inhaling more water than it should,” said Schulz. “It wasn’t until we saw the ultrasonographic images and watched the nostrils expand that we realized how they did it. Air makes the walls open, and the animal can store far more water than we originally estimated.”

Based on the pressures applied, Schulz and the team suggest that elephants inhale at speeds that are comparable to Japan’s 300-mph bullet trains.

Schulz said these unique characteristics have applications in soft robotics and conservation efforts.

“By investigating the mechanics and physics behind trunk muscle movements, we can apply the physical mechanisms — combinations of suction and grasping — to find new ways to build robots,” Schulz said. “In the meantime, the African elephant is now listed as endangered because of poaching and loss of habitat. Its trunk makes it a unique species to study. By learning more about them, we can learn how to better conserve elephants in the wild.”

The work was supported by the US Army Research Laboratory and the US Army Research Office 294 Mechanical Sciences Division, Complex Dynamics and Systems Program, under contract number 295 W911NF-12-R-0011. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the view of the sponsoring agency.

A room-temperature bonding technique for integrating wide bandgap materials such as gallium nitride (GaN) with thermally conducting materials such as diamond could boost the cooling effect on GaN devices and facilitate better performance through higher power levels, longer device lifetime, improved reliability, and reduced manufacturing costs. The technique could have applications for wireless transmitters, radars, satellite equipment, and other high-power and high-frequency electronic devices.

The technique, called surface-activated bonding, uses an ion source in a high-vacuum environment to first clean the surfaces of the GaN and diamond, which activates the surfaces by creating dangling bonds. Introducing small amounts of silicon into the ion beams facilitates forming strong atomic bonds at room temperature, allowing the direct bonding of the GaN and single-crystal diamond to fabricate high-electron-mobility transistors (HEMTs).

The resulting interface layer from GaN to single-crystal diamond is just four nanometers thick, allowing heat dissipation up to two times more efficient than in the state-of-the-art GaN-on-diamond HEMTs by eliminating the low-quality diamond left over from nanocrystalline diamond growth. Diamond is currently integrated with GaN using crystalline growth techniques that produce a thicker interface layer and low-quality nanocrystalline diamond near the interface. Additionally, the new process can be done at room temperature using surface-activated bonding techniques, reducing the thermal stress applied to the devices.

“This technique allows us to place high thermal conductivity materials much closer to the active device regions in gallium nitride,” said Samuel Graham, the Eugene C. Gwaltney Jr. School Chair and professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering. “The performance allows us to maximize the performance for gallium nitride on diamond systems. This will allow engineers to custom design future semiconductors for better multifunctional operation.”

The research, conducted in collaboration with scientists from Meisei University and Waseda University in Japan, was reported February 19 in the journal ACS Applied Materials and Interfaces. The work was supported by a multidisciplinary university research initiative (MURI) project from the U.S. Office of Naval Research (ONR).

For high-power electronic applications using materials such as GaN in miniaturized devices, heat dissipation can be a limiting factor in power densities imposed on the devices. By adding a layer of diamond, which conducts heat five times better than copper, engineers have tried to spread and dissipate the thermal energy. 

However, when diamond films are grown on GaN, they must be seeded with nanocrystalline particles around 30 nanometers in diameter, and this layer of nanocrystalline diamond has low thermal conductivity – which adds resistance to the flow of heat into the bulk diamond film. In addition, the growth takes place at high temperatures, which can create stress-producing cracks in the resulting transistors.

“In the currently used growth technique, you don’t really reach the high thermal conductivity properties of the microcrystalline diamond layer until you are a few microns away from the interface,” Graham said. “The materials near the interface just don’t have good thermal properties. This bonding technique allows us to start with ultra-high thermal conductivity diamond right at the interface.” 

By creating a thinner interface, the surface-activated bonding technique moves the thermal dissipation closer to the GaN heat source.

“Our bonding technique brings high thermal conductivity single crystal diamond closer to the hotspots in the GaN devices, which has the potential to reshape the way these devices are cooled,” said Zhe Cheng, a recent Georgia Tech Ph.D. graduate who is the paper’s first author. “And because the bonding takes place near room temperature, we can avoid thermal stresses that can damage the devices.”

That reduction in thermal stress can be significant, going from as much as 900 megapascals (MPa) to less than 100 MPa with the room temperature technique. “This low stress bonding allows for thick layers of diamond to be integrated with the GaN and provides a method for diamond integration with other semiconductor materials,” Graham said.

Beyond the GaN and diamond, the technique can be used with other semiconductors, such as gallium oxide, and other thermal conductors, such as silicon carbide. Graham said the technique has broad applications to bond electronic materials where thin interfacial layers are advantageous.

“This new pathway gives us the ability to mix and match materials,” he said. “This can provide us with great electrical properties, but the clear advantage is a vastly superior thermal interface. We believe this will prove to be the best technology available so far for integrating wide bandgap materials with thermally conducting substrates.”

In future work, the researchers plan to study other ion sources and evaluate other materials that could be integrated using the technique. 

“We have the ability to choose processing conditions as well as the substrate and semiconductor material to engineer heterogenous substrates for wide bandgap devices,” Graham said. “That allows us to choose the materials and integrate them to maximize electrical, thermal, and mechanical properties.”

In addition to the researchers already mentioned, the paper included co-corresponding author Fengwen Mu from Meisei University and Waseda University in Japan, Luke Yates from Georgia Tech, and Tadatomo Suga from Meisei University.

This research was supported by the U.S. Office of Naval Research (ONR) through MURI Grant No. N00014-18-1-2429. Any findings, conclusions, and recommendations are those of the authors and not necessarily of the Office of Naval Research.

CITATION: Zhe Cheng, Fengwen Mu, Luke Yates, Tadatomo Suga and Samuel Graham, “Interfacial Thermal Conductance across Room-Temperature-Bonded GaN/Diamond Interfaces for GaN-on-Diamond Devices” (ACS Appl. Mater. Interfaces, 2020, 12, 8376?8384). https://doi.org/10.1021/acsami.9b16959

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Meet Oliver Brand, executive director of the Institute for Electronics and Nanotechnology (IEN) at Georgia Tech.

IEN is one of Georgia Tech's 10 interdisciplinary research institutes (IRIs) within the Georgia Tech Research enterprise.

What is your field of expertise and why did you choose it?

My research is in the area of Micro Electro Mechanical Systems or MEMS and, in particular, the development of micro-scale physical, chemical and biological sensors, which are fabricated using processes similar to the ones used to make integrated circuits. I was first introduced to this area at the beginning of my Ph.D. in the early 1990s and was initially fascinated by images of these micrometer-sized devices. We quickly learned that these beautiful, tiny structures and devices can have many useful applications. 
 
What makes the way in which your IRI enables campus research unique? 
My field of research MEMS and micro/nanotechnology in general rely on expensive equipment to fabricate these tiny devices and systems. To enable research in this area, IEN maintains extensive core facilities for fabrication and characterization at the micro- and nanoscale. These facilities are not only used by Georgia Tech researchers, but by dozens of companies and other academic institutions. Many of these companies are start-ups that couldn’t do the work they do without access to these facilities. In addition, nanotechnology is a highly interdisciplinary field and the IRIs help bring together the interdisciplinary teams to tackle big problems. 
 
What couldn’t have happened without your IRI? 
IEN supports an incredibly talented team of research faculty and staff that have the goal of enabling nanotechnology research, development and commercialization done by Georgia Tech faculty, students, and external partners. Many nanotechnology research accomplishments at Georgia Tech and beyond could have simply not happened without the dedication of this team. 
 
What impact is your research having on the world? 
Let me pick a timely example, the development of COVID-19 tests. Many of these tests have nanotechnology components in order to detect the virus that has nanometer dimensions by itself. Over the past year, we have been heavily involved in an NIH-funded program called Rapid Acceleration of Diagnostics or RADx, where we assist project teams developing novel tests with engineering expertise but also access to the core facilities I mentioned earlier. Some of the tests we have supported now already are commercially available. 

Learn more about IEN.