Research Bits: March 21

Micropatterning with sugar

A scientist at the National Institute of Standards and Technology (NIST) discovered a transfer printing process that can deposit microcircuit patterns on curved and textured surfaces using sugar candy.

Transfer printing methods, such as flexible tapes, are often used for surfaces that are difficult to directly print on. But they have difficulty with conforming to certain surfaces or with accuracy.

The new method uses a combination of caramelized sugar and corn syrup, the basis for hard candy.

When dissolved in a small amount of water, this sugar mixture can be poured over micropatterns on a flat surface. Once the water evaporates, the candy hardens and can be lifted away with the pattern embedded.

The candy with the print is then placed over the new surface and melted. The sugar/corn syrup combination maintains a high viscosity as it melts, letting the pattern maintain its arrangement as it flows over curves and edges. Then, using water, the sugar can be washed away, leaving just the pattern behind.

Using this technique, called REFLEX (REflow-driven FLExible Xfer), microcircuit patterns could be transferred like a stencil to allow scientists or manufacturers to etch and fill the materials they need in the right places. Or, patterned materials could be transferred from their original chip onto fibers or microbeads for potential biomedical or microrobotics studies, or over sharp or curved surfaces within new devices.

The technique proved successful for a large range of surfaces, including printing onto the sharp point of a pin, and writing the word “NIST” in microscale gold lettering onto a single strand of human hair. In another example, 1-micrometer-diameter magnetic disks were successfully transferred onto a floss fiber of a milkweed seed. In the presence of a magnet, the magnetically printed fiber reacted, showing the transfer had worked.

“The semiconductor industry has spent billions of dollars perfecting the printing techniques to create chips we rely on,” said Gary Zabow, a NIST scientist that discovered the method. “Wouldn’t it be nice if we could leverage some of those technologies, expanding the reach of those prints with something as simple and inexpensive as a piece of candy?”

3D printed mmWave antennas

Researchers at the University of Sheffield created 3D-printed mmWave radio antennas with performance that matches those produced using conventional manufacturing techniques. They believe the antennas could speed up the development of new 5G and 6G infrastructure as well as bring access to remote areas.

The antennas use silver nanoparticles, which have excellent electrical properties for radio frequency, and have been tested at various frequencies used by 5G and 6G networks, up to 48 GHz. Their gain and time domain response – affecting the direction and strength of signal they can receive and transmit – is almost indistinguishable from those manufactured traditionally.

“This 3D-printed design could be a game changer for the telecommunications industry. It enables us to prototype and produce antennas for 5G and 6G networks at a far lower cost and much quicker than the current manufacturing techniques. The design could also be used to produce antennas on a much larger scale and therefore have the capability to cover more areas and bring the fastest mobile networks to parts of the world that have not yet had access,” said Eddie Ball, Reader in radio frequency engineering at the University of Sheffield

Human antenna for energy harvesting

Researchers from the University of Massachusetts Amherst and Delft University of Technology found a low-cost way to harvest the waste energy from Visible Light Communication (VLC) by using the human body as an antenna. This waste energy could potentially be used to power wearable sensors.

“VLC is quite simple and interesting,” says Jie Xiong, professor of information and computer sciences at UMass Amherst. “Instead of using radio signals to send information wirelessly, it uses the light from LEDs that can turn on and off, up to one million times per second. Anything with a camera, like our smartphones, tablets or laptops, could be the receiver.”

VLC would use the already-existing infrastructure of LED bulbs in homes and offices to transmit data.

Researchers at UMass Amherst previously found that there’s significant “leakage” of energy in VLC systems, because the LEDs also emit side-channel RF signals. As the first step of harvesting this leaked RF energy, the team designed an antenna out of coiled copper wire. They found that the efficiency of the antenna varied according to what the antenna touched. They tried resting the coil on plastic, cardboard, wood, and steel, as well as touching it to walls of different thicknesses, phones powered on and off, and laptops.

They also put it in contact with a human body, which turned out to be the best medium for amplifying the coil’s ability to collect leaked RF energy, up to ten times more than the bare coil alone.

The team then experimented with different designs, finding that a simple coil of copper wire worn as a bracelet on the upper forearm provided a good balance of power harvesting and wearability.

“The design is cheap—less than fifty cents,” note the authors. “But Bracelet+ can reach up to micro-watts, enough to support many sensors such as on-body health monitoring sensors that require little power to work owing to their low sampling frequency and long sleep-mode duration.”

“Ultimately,” said Xiong, “we want to be able to harvest waste energy from all sorts of sources in order to power future technology.”