Research Bits: April 10

Meminductor identified; semiconductor-free origami robots; solid-state thermal transistor.


Meminductor identified

Researchers at Texas A&M University identified the meminductor circuit unit. Similar to the memristor and the memcapacitor, a meminductor has a memory-like nature where its properties are dependent on previous values.

The resistor, capacitor, and inductor comprise the three classical circuit elements. The memristor and the memcapacitor, while earlier theorized, have only been demonstrated fairly recently.

“Those two discoveries set the world a little bit on its head as far as electrical engineering,” said H. Rusty Harris, associate professor in the Department of Electrical and Computer Engineering at Texas A&M University. “All of the sudden, we thought we had three, but now we found these two others. And so that led us to think, ‘OK, there’s got to be more then, but how do we understand what they are? How do we map all of these things relative to each other?’ And it turns out, there is a relationship between each of the resistors and its family and each of the capacitors and its family.”

To demonstrate physical evidence of meminductance, the researchers created a two-terminal passive system comprised primarily of an electromagnet interacting with a pair of permanent magnets. This allowed them to examine the magnetic flux density and magnetizing field strength of the inductor circuit element and prove the existence of the pinched hysteresis curve within the inductor leading to its mem- state, or memory-like nature, by the same definition that the memristor and memcapacitor were realized.

Semiconductor-free origami robots

Researchers from University of California Los Angeles (UCLA), Massachusetts Institute of Technology (MIT), and Tsinghua University created fully foldable robots that can perform a variety of complex tasks without relying on semiconductors through a fabrication technique inspired by origami and kirigami.

By embedding flexible and electrically conductive materials into a pre-cut, thin polyester film sheet, the researchers created a system of transistors that can be integrated with sensors and actuators. They then programmed the sheet with simple computer analogical functions that emulate those of semiconductors. Once cut, folded, and assembled, the sheet transformed into an autonomous robot that can sense, analyze, and act in response to their environments with precision.

The so-called OrigaMechs use a combination of mechanical origami multiplexed switches created by the folds and programmed Boolean logic commands. The switches enabled a mechanism that selectively output electrical signals based on the variable pressure and heat input into the system.

The team created three unique robots: an insect-like walking robot that reverses direction when either of its antennae senses an obstacle, a Venus flytrap-like robot that envelops a “prey” when both of its jaw sensors detect an object, and a reprogrammable two-wheeled robot that can move along pre-designed paths of different geometric patterns.

While the robots were tethered to a power source for the demonstration, the researchers said the long-term goal would be to outfit the autonomous origami robots with an embedded energy storage system powered by thin-film lithium batteries. They envision creating robots capable of working in extreme environments — strong radiative or magnetic fields, and places with intense radio frequency signals or high electrostatic discharges — where traditional semiconductor-based electronics might fail to function.

“These types of dangerous or unpredictable scenarios, such as during a natural or manmade disaster, could be where origami robots proved to be especially useful,” said Ankur Mehta, an assistant professor of electrical and computer engineering and director of UCLA’s Laboratory for Embedded Machines and Ubiquitous Robots.

Solid-state thermal transistor

Researchers from Hokkaido University developed a solid-state electrochemical thermal transistor, a device that can be used to control heat flow with electrical signals.

“A thermal transistor consists broadly of two materials, the active material and the switching material,” said Hiromichi Ohta, a professor at the Research Institute for Electronic Science at Hokkaido University. “The active material has changeable thermal conductivity (), and the switching material is used to control the thermal conductivity of the active material.”

The team constructed their thermal transistor on a yttrium oxide-stabilized zirconium oxide base, which also functioned as the switching material, and used strontium cobalt oxide as the active material. Platinum electrodes were used to supply the power required to control the transistor.

The thermal conductivity of the active material in the “on” state was comparable to some liquid-state thermal transistors. In general, thermal conductivity of the active material was four times higher in the “on” state compared to the “off” state. Additionally, the transistor was stable over 10 use cycles, better than some current liquid-state thermal transistors. This behavior was tested across more than 20 separately fabricated thermal transistors, ensuring the results were reproducible. The major drawback was the operating temperature of around 300°C.

“Our findings show that solid-state electrochemical thermal transistors have the potential to be just as effective as liquid-state electrochemical thermal transistors, with none of their limitations,” said Ohta. “The main hurdle to developing practical thermal transistors is the high resistance of the switching material, and hence a high operating temperature. This will be the focus of our future research.”

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