A simple 3D printed device can pave the way for much more powerful cell phones and WIFI

This simple machine that uses the surface tension of water to grasp and manipulate microscopic objects. Credit: Manoharan Lab / Harvard SEAS

A 3D printed device in a water tank intertwines the nanowires and displaces the microparticles.

The next generation of wireless phones and devices will require new antennas to access ever higher frequency ranges. One way to make antennas that operate at tens of gigahertz – the frequencies needed for 5G and higher devices – is to weave filaments about 1 micrometer in diameter. However, today’s industrial manufacturing techniques don’t work on such small fibers.

“It was a moment of great joy when, on our first try, we crossed two fibers using just a piece of plastic, a water tank and a stage that moves up and down.” – Maya Faaborg

Now a team of engineers and scientists from Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) has developed a simple machine that uses the surface tension of water to grasp and manipulate microscopic objects. This extraordinary innovation offers a potentially powerful tool for nanoscopic manufacturing.

The research was published in the journal Nature on October 26.

“Our work offers a potentially cost-effective way to produce microstructured and possibly nanostructured materials,” said Vinothan Manoharan, professor of chemical engineering and professor of physics in the Wagner family at SEAS and senior author of the paper. “Unlike other micromanipulation methods, such as laser tweezers, our machines can be made easily. We use a water tank and a 3D printer, like those found in many public libraries ”.

The machine is a 3D printed plastic rectangle the size of an old Nintendo cartridge. The interior of the device is sculpted with intersecting channels. Each canal has wide and narrow stretches, similar to a river that expands in some parts and narrows in others. The canal walls are hydrophilic, which means they attract water.

Through a series of simulations and experiments, the scientists found that when they immersed the device in water and placed a millimeter-sized plastic float in the channel, the surface tension of the water caused the wall to repel the float. If the float was in a narrow section of the channel, it would move to a wide section, where it could float as far away from the walls as possible.

Once in a large section of the channel, the float would be trapped in the center, held in place by the repulsive forces between the walls and the float. When the device is lifted out of the water, the repulsive forces change as the shape of the channel changes. If the float was in a wide channel to start with, it may be in a narrow channel when the water level drops and you will need to move left or right to find a wider spot.

“The eureka moment came when we discovered that we could move objects by changing the cross section of our capture channels,” said Maya Faaborg, SEAS associate and co-first author of the paper.

“The amazing thing about surface tension is that it produces forces that are gentle enough to grab small objects, even with a machine large enough to hold.” – Ahmed Sheriff

Next, the researchers attached microscopic fibers to the floats. As the water level changed and the floats moved left or right within the channels, the fibers twisted around each other.

“It was a moment of great joy when, on our first try, we crossed two fibers using just a piece of plastic, a water tank and a stage that moves up and down,” said Faaborg.

The team then added a third float with a fiber and designed a series of channels to move the floats in a braided pattern. They successfully woven micrometer-scale fibers of the synthetic Kevlar material. The braid was just like a traditional three strand hair braid, except that each fiber was 10 times smaller than a single human hair.

Next, investigators showed that the floats themselves could be microscopic. They built machines capable of trapping and moving colloidal particles as small as 10 micrometers in size, even though the machines were a thousand times larger.

“We weren’t sure it would work, but our calculations showed it was possible,” said Ahmed Sherif, a doctoral student at SEAS and co-author of the paper. “So we tried it and it worked. The amazing thing about surface tension is that it produces forces that are gentle enough to grab small objects, even with a machine large enough to hold. “

Next, the team aims to design devices capable of simultaneously manipulating many fibers, with the aim of making high-frequency conductors. They also plan to design other machines for microproduction applications, such as building materials for optical bead devices.

Reference: “3D Printed Machines Manipulating Microscopic Objects Using Capillary Forces” by Cheng Zeng, Maya Winters Faaborg, Ahmed Sherif, Martin J. Falk, Rozhin Hajian, Ming Xiao, Kara Hartig, Yohai Bar-Sinai, Michael P. Brenner and Vinothan N. Manoharan, October 26, 2022, Nature.
DOI: 10.1038 / s41586-022-05234-7

The research was co-authored by Cheng Zeng, Ahmed Sherif, Martin J. Falk, Rozhin Hajian, Ming Xiao, Kara Hartig, Yohai Bar-Sinai and Michael Brenner, Michael F. Cronin Professor of Applied Mathematics and Applied Physics and Professor of Physics at SEAS. It was supported in part by the Defense Advanced Research Projects Agency ([{” attribute=””>DARPA), under grant FA8650-15-C-7543; the National Science Foundation through the Harvard University Materials Research Science and Engineering Center, under grant DMR-2011754 and ECCS-1541959; and the Office of Naval Research under grant N00014-17-1-3029.

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