Manufacturing Bits: Sept. 26

Electrical twisted yarn; hybrid 3D printing; liquid metal chips.

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Electrical twisted yarn
The U.S. Air Force Research Laboratory (AFRL), the University of Texas at Dallas and Hanyan University in South Korea have developed a twisted yarn technology that can be used to generate or harvest electrical energy.

The technology, dubbed “twistron” yarn, incorporates twisted bundles of tiny coiled carbon nanotubes. The nanotube-based twistron yarn works in conjunction with an ionic material, thereby transforming these materials into supercapacitors. And once the yarn is stretched, it generates electrical power.

Carbon nanotube-based twistron yarn ((U.S. Air Force photo/Matt Lucas)

Typically, the industry uses piezoelectric devices for power generation and harvesting. Piezoelectrics generate power using an external charge. But they are harder materials, thereby limiting this technology to capture energy when deformed.

In comparison, twistron yarn captures energy even if they it is deformed. The yarn can be submerged in an electrolyte, ocean water or human sweat. This, in turn, charges the yarn, enabling energy output, according to researchers.

The flexibility of twistron yarn, which can harvest mechanical energy, can be used to power flexible devices and wearables. “Technologies like this do not yet exist,” said Lawrence Drummy, a senior materials engineer at the AFRL, on the agency’s Web site. “These are energy harvesters for mechanical energy, and they could potentially eliminate the need for external power supplies, such as batteries, on a host of wearable devices. The potential application space is enormous.”

Benji Maruyama, the flexible materials and processes team lead at AFRL, added: “Humans move a lot, so in order to have something that interfaces well between the human and machine, it has to move like a human and be able to stretch a lot—like skin. The superior properties of these yarns which can twist and pull and generate their own voltage and power, open the potential for generating power through a human’s movement and even by using their own sweat.”

Hybrid 3D printing
The AFRL and Harvard University have developed a new technology called hybrid 3D printing.

The technology combines 3D printing of stretchable conductive inks with pick-and-place of electronic components for use in making flexible, wearable sensors.

In the flow, a 3D printer is used to deposit stretchable conductive ink on a surface. The ink is based on thermoplastic polyurethane (TPU). TPI is a flexible plastic that is mixed with silver flakes. The inks are used to develop the conductive traces on the surface. The traces are deposited in a set pattern.

The 3D printer system also incorporates a separate vacuum nozzle. The nozzle then picks up components and places them on the surface in a pick-and-place process. Then, LEDs are mounted on the surface.

“With this technique, we can print the electronic sensor directly onto the material, digitally pick-and-place electronic components, and print the conductive interconnects that complete the electronic circuitry required to read the sensor’s data signal in one fell swoop,” said Alex Valentine, a former staff engineer at the Wyss Institute for Biologically Inspired Engineering at Harvard, on the university’s Web site. Valentine is now a medical student at Boston University.

Will Boley, a postdoctoral researcher at Harvard, added: “Because the ink and substrate are 3D-printed, we have complete control over where the conductive features are patterned, and can design circuits to create soft electronic devices of nearly every size and shape.”

Liquid metal chips
The AFRL has recently demonstrated a line of non-toxic liquid metals that are capable of creating multi-functional, reconfigurable electronic devices.

In the lab, researchers developed non-toxic, conductive gallium liquid metal alloys. The metals are flowed through channels embedded into an airframe of a system. The metals behave as reconfigurable radio frequency antennas.

The liquid metal antennas can be reconfigured within the airframe to operate at new frequency ranges and provide additional operational directivity. “Essentially, we showed that you can rewire a system for a new mission set. By flowing liquid metals through channels in a system, you can change the frequency and function by simply removing the metal and patterning it in a new place,” said Christopher Tabor, a research scientist in the Nanoelectronics Branch of AFRL’s Materials and Manufacturing Directorate. “This can add multiple functions to a single platform, ultimately enhancing mission capabilities.”