Metamaterials Make Waves Do What They Shouldn’t 

Time for science that just doesn’t make sense. 

We’re talking about metamaterials. Meta, from the Greek word meaning “beyond” or “after,” and materia, the Latin word meaning “matter” or “material.” 

Metamaterials don’t occur naturally. They are human-engineered structures designed to interact with waves (electromagnetic waves, acoustic waves, magnetic waves, etc.) in specific ways. For example, metamaterials could help us design antennas that better receive radio frequencies or create special hyperlenses that increase the power of microscopes. 

The important thing to remember is that when creating metamaterials, scientists first determine the result they want and then look at the properties of the material as well as the shape they arrange it in to achieve the desired outcome. 

Whatever metamaterial is being tested, the structure must be smaller than the wavelength. That means these synthetic materials can interact with waves in ways that natural materials do not. 

Yep, metamaterials are “beyond matter.” 

First, a quick review 

To really appreciate what all this means, you need to step back. 

You might have learned in science class that everything in the world—living and nonliving—is made of matter. You probably also learned that atoms are the building blocks of matter. 

Let’s build on those concepts. Matter is put together to make materials. When waves of light, energy, sound, etc., hit that material, they react in predictable ways depending on the matter that makes up the material. For example, sound waves reflect off hard surfaces and are absorbed in softer materials. 

“So, there’s this wave–matter interaction,” said Duke physicist David Smith in an article in Duke Magazine. Smith explains that the interaction is defined by the atomic makeup of the material. The material is characterized by how the waves interact with it. 

Metamaterials don’t change the chemistry of the material, but they are designed to make waves do things they normally wouldn’t do. 

It all began with invisibility 

Smith’s work with metamaterials began with invisibility. 

In 2006, Smith and a team at Duke published a paper about an experiment they conducted to test the idea of “invisibility.” Can this new concept of materials make something invisible? 

They used concentric circles of copper etched with geometric patterns as metamaterials. Then they aimed microwaves at the material. The key point here is that the patterns were smaller than the microwaves. 

The materials directed the microwaves around the object so that when the waves hit the material, instead of reacting and bouncing off it, the waves looked almost the same as when they were first sent out. 

Think of a stream. If the rocks are shaped and aligned in the same direction as the water, it’s difficult to notice them. If the rocks have an odd shape or block the water, they are easy to spot. 

That’s essentially what happened in the experiment. While the object was still visible to the eye, with everything aligned, the object wasn’t really “seen” by the microwaves; it was, in a sense, invisible. 

Invisibility cloak, the press announced. 

“Despite all the caveats,” Smith told the magazine, “Despite writing a paper that said, ‘This is not going to be Harry Potter’s cloak,’ the exact opposite happened.” Smith and the project became a media sensation. 

But it demonstrated the possibilities that metamaterials can provide. 

Life has calmed down, and scientific research has continued. There are now multiple labs at Duke working with metamaterials and spinning off companies from the work in Smith’s lab. It’s unclear what the future holds because nobody knows what new materials might be created and what applications those materials might be used for.  

“You’d like to believe that the work you’re working on has impact,” said Smith. “And certainly, the people we’re training here have been pivotal in those companies.”