Patent of the Month – Negative Refractive Index Meta-Materials
Kobus Cilliers | On 15, Mar 2020
Patent of the month this month takes into another foray into the realm of so-called ‘negative materials’. Or, as seems to be becoming more popular, ‘left-handed materials’. Which has a certain ring to it, if you happen to be lefthanded. US10,431,897 was granted to a trio of inventors at the University of Arizona on October 1.
Negative refractive index (NRI) materials were first suggested following pioneering theoretical work in the late 1960s in Russia. The materials, if producible, were deemed to be attractive because of applications such as super lens and electromagnetic invisibility. As is so often the case, however, theory is one thing and practical reality quite another. In the real world, the Second Law of Thermodynamics tells us that things are never as good as you think they ought to be. And this is certainly the case when it comes to early meta-material attempts to create NRI materials. They produce energy loss. Too much to make NRIs anything other than a nice theory. Prior to the present invention, the ‘impossibility’ of constructing an artificial material having a negative refractive index (NRI) and acceptable energy loss was taken as a ‘law of nature’. Now it seems, not only has the loss been eliminated, but energy gain has also been demonstrated. I think that is what is known as a win-win solution.
Here’s what the basic NRI versus energy-loss conflict looks like when mapped on to the Contradiction Matrix:
And here’s how the US10,431,897 inventors claim to have solved the problem:
A microwave gain medium having a negative refractive index adapted to be placed in a rectangular waveguide to form a volumetric structure, the medium comprising: (a) a unit cell comprising a substrate; (b) a linear sub-wavelength wire printed on the substrate of the unit cell; (c) a circular-shaped split ring resonator printed on the substrate of the unit cell, the circular-shaped split ring resonator overlays the linear sub-wavelength wire ); (d) a first negative resistance device being embedded at a horizontal symmetry axis of the linear sub-wavelength wire, which causes the sub-wavelength wire to exhibit a negative permittivity; (e) a second negative resistance device being embedded at an opposite end of a split point on the split ring resonator, which causes the split ring resonator to exhibit a negative permeability.
Okay, I grant you, not the easiest text in the world to decipher unless you spend several hours a day poring through the patent literature. A couple of obvious things, however, can be seen: the ‘circular-shaped split ring resonator’ makes for a good illustration of Principle 14, Spheroidality; the ‘sub-wavelength wire’ makes for a good illustration of Principle 35, Parameter Changes; ‘embedding’ = Principle 7, Nested Doll.
Lead inventor, Professor Hao Xin further elaborated in a Nature Communications paper that the above description includes in effect a 3D (Principle 17) tunnel-diode.
Still not the simplest set of ideas to grasp, I imagine, but if it fits with TRIZ and also opens the world up to the possibility of invisibility shields and super-resolution molecular microscopes, its probably okay to offer up a little domain expert jargon leeway.