Braiding technique enables antennae fabrication for next-gen devices

Antennae that work at frequencies needed for next generation phones and wireless devices can be fabricated with a machine developed in the US.

This simple machine uses the surface tension of water to grab and manipulate microscopic objects
This simple machine uses the surface tension of water to grab and manipulate microscopic objects - Manoharan Lab/Harvard SEAS

These devices will require antennae that work at tens of gigahertz but making them will require braided filaments of about one micrometre in diameter.

Now a team of researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) has developed a simple machine that uses the surface tension of water to grab and manipulate microscopic objects, offering a potentially powerful tool for nanoscopic manufacturing. The research is published in Nature.

“Our work offers a potentially inexpensive way to manufacture microstructured and possibly nanostructured materials,” said Vinothan Manoharan, the Wagner Family Professor of Chemical Engineering and Professor of Physics at SEAS and senior author of the paper. “Unlike other micromanipulation methods, like laser tweezers, our machines can be made easily. We use a tank of water and a 3D printer, like the ones found at many public libraries.”

The machine is a 3D-printed plastic rectangle and its interior is carved with channels that intersect. Each channel – with hydrophilic walls - has wide and narrow sections.

Through a series of simulations and experiments, the researchers found that when they submerged the device in water and placed a millimetre-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 moved to a wide section where it could float as far away from the walls as possible.

Once in a wide section of the channel, the float would be trapped in the centre, held in place by the repulsive forces between the walls and float. As 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, it may find itself in a narrow channel as the water level falls and need to move to the left or right to find a wider spot.

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

The researchers then attached microscopic fibres to the floats; as the water level changed and the floats moved to the left or right within the channels, the fibres twisted around each other.

“It was a shout-out-loud-in-joy moment when - on our first try - we crossed two fibres using only a piece of plastic, a water tank, and a stage that moves up and down,” Faaborg said in a statement.


According to SEAS, the team then added a third float with a fibre and designed a series of channels to move the floats in a braiding pattern. During this iteration the team successfully braided micrometre-scale fibres of Kevlar.

The researchers then showed that the floats themselves could be microscopic. They made machines that could trap and move colloidal particles 10 micrometres in size, despite the machines being a thousand times bigger.

“We weren’t sure it would work, but our calculations showed that it was possible,” said Ahmed Sherif, a PhD student at SEAS and a 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 tiny objects, even with a machine big enough to fit in your hand.”

Next, the team aims to design devices that can simultaneously manipulate many fibres, with the goal of making high-frequency conductors. They also plan to design other machines for micromanufacturing applications, such as building materials for optical devices from microspheres.