The Discovery of the Meminductor Brings the Number of Fundamental Circuit Elements to Six

Researchers at the Department of Electrical and Computer Engineering at Texas A&M University have come up with a sixth circuit element, dubbed the meminductor, bringing memory-like properties to the classic inductor — and completing a series of discoveries spanning more than 50 years.

The meminductor joins the memristor, first described by Leon Chua in 1971, and memcapacitor as relatively-newly discovered fundamental elements of electronic circuits alongside the resistor, the capacitor, and the inductor. Where the memristor was, the name implies, a memory-resistor, and the memcapacitor a memory-capacity, meminductor is a memory-inductor — completing the circle and bringing the total number of fundamental circuit elements to six. All the three mem-prefixed elements have one thing in common: their properties vary depending on current or voltage changes over time, hence their being described as having "memories."

"Those two discoveries [the memristor and memcapacitor] set the world a little bit on its head as far as electrical engineering [goes]," H. Rusty Harris, associate professor at Texas A&M and the discoverer of the meminductor, explains. "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."

"[This] new discovery is very exciting," Harris says. "And the student-professor interaction on this project was beautiful. During our brainstorming sessions, we fed off each other — I learned new things based on my discussion with him and he learned new things based on my experience."

While the theoretical existence of the memristor dates back to Chua's work in 1971, it wasn't until 2008 that the first intentional memristor was fabricated — and the world wouldn't see a working memcapacitor until 2019. The existence of a meminductor follows logically from the creation of the other two mem-variants of existing circuit elements, but it took Harris and colleagues Abhiram Dinavahi and Alexandre Yamamoto to actually prove its existence, using a two-terminal passive system made of an electromagnet in interaction with two permanent magnets to monitor magnetic flux density and magnetizing field strength from an inductor.

As with the memristor before it, though, it could be some time before anyone builds a functional true meminductor and puts it to practical use: the team found that the meminductance properties are hidden behind a much more dominant resistive component, which would need to be tamed to create a "true" meminductor.

"Operating the element in a cryogenic environment below the superconducting temperature of the winding appears the most feasible technique to eliminate series resistance in the configuration discussed," the researchers propose. "At room temperature, combating series resistance would require strengthening the inductive component through higher frequency operation; hence, replacing electromechanical means of varying instantaneous inductance with electronic phenomena is worth pursuing."

The team's work has been published in the journal Scientific Reports under open-access terms.