tag:theconversation.com,2011:/ca/topics/metamaterials-25076/articlesMetamaterials – The Conversation2017-10-26T21:22:44Ztag:theconversation.com,2011:article/863782017-10-26T21:22:44Z2017-10-26T21:22:44ZHow quantum materials may soon make Star Trek technology reality<figure><img src="https://images.theconversation.com/files/192105/original/file-20171026-13298-9jyeex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Strange new materials that propel the fictional Star Trek universe are being developed by scientists in reality today. Above, the USS Discovery accelerates to warp speed in an artist's rendition for the TV series Star Trek Discovery.
</span> <span class="attribution"><span class="source">(Handout)</span></span></figcaption></figure><p>If you think technologies from Star Trek seem far-fetched, think again. Many of the <a href="https://tricorder.xprize.org/">devices</a> from the acclaimed television series are slowly becoming a <a href="https://www.theguardian.com/technology/gallery/2009/may/15/star-trek-technology">reality</a>. While we may not be <a href="http://www.bbc.com/news/science-environment-40594387">teleporting</a> people from starships to a planet’s surface anytime soon, we are getting closer to developing other tools essential for future space travel endeavours.</p>
<p>I am a lifelong Star Trek fan, but I am also a researcher that specializes in creating new magnetic materials. The field of <a href="https://www.physics.utoronto.ca/research/condensed-matter-physics">condensed-matter physics</a> encompasses all new solid and liquid phases of matter, and its study has led to nearly every technological advance of the last century, from computers to cellphones to solar cells.</p>
<p>My approach to looking for new phenomena in materials comes from a chemistry perspective: How can we create materials that have new properties that can change our world, and eventually be used to explore “strange, new worlds”? I believe an understanding of so-called “quantum materials” in particular is essential to make science-fiction science fact. </p>
<h2>Quantum materials</h2>
<p>What makes a substance a quantum material? Quantum materials have unusual and fantastic properties that arise from enormous numbers of particles acting in a concerted way.</p>
<p>Think of a conductor directing a symphony: without some order brought to the music, all you have is noise. The more musicians you have performing out of step, the more noise you will have.</p>
<p>A quantum material has all of the constituent musicians — in this case, the electrons or atoms in a material, which amounts to billions upon billions of particles — acting in a certain way according to quantum rules, or the “sheet music,” if you will.</p>
<p>Instead of noise from random electronic and atomic motions, with a conductor you get music — or in the case of new materials, a new property that emerges. The use of these new properties for devices is what is driving the technological revolutions that we are seeing today.</p>
<h2>Magnetic fields and shields</h2>
<p>So, how can these new materials be used in the spacecraft of tomorrow? One example might be the force-shields that protect ships in Star Trek. High magnetic fields could be used to protect bodies from incoming projectiles, especially if the projectiles have an electric charge.</p>
<p>How do you create large magnetic fields? One way is to use a superconducting magnet. Superconductors have electrons that conduct electricity with no resistance to flow. One of the consequences of this is that large magnetic fields can be generated — the current supported by a superconductor that generates the magnetic field can be huge without destroying the superconductivity itself.</p>
<p>These superconductors are used every day to create large magnetic fields in places such as hospitals for MRI (magnetic resonance imaging) devices to see inside the body.</p>
<p>Advanced superconductors might have new applications as magnetic shields for spacecraft. Imagine your spaceship coated in a superconductor that can generate a large magnetic field with a flick of a switch to get the current flowing, creating a magnetic force shield. </p>
<p>This is exactly what scientists at the European Organization for Nuclear Research, <a href="http://home.cern/about/updates/2015/08/superconducting-shield-astronauts">CERN, are investigating</a>: a new <a href="http://www.popularmechanics.com/space/moon-mars/a16757/cern-spaceship-shields/">magnetic shield for spacecraft</a> — superconducting magnesium diboride, or MgB₂.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/y-0z6_yVSAw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Physicist and science writer Ian O'Neill discusses CERN’s plan to create a superconducting cosmic radiation shield for astronauts.</span></figcaption>
</figure>
<h2>Superconductors on spaceships</h2>
<p>A spaceship coated in superconducting magnets would generate a “magnetosphere” around the craft which could be used to deflect harmful projectiles. While we don’t have to worry about <a href="http://www.startrek.com/database_article/klingons">Klingon</a> torpedoes just yet, we do have to worry about harmful cosmic rays in outer space for future space travel.</p>
<p><a href="https://home.cern/about/physics/cosmic-rays-particles-outer-space">Cosmic rays</a>) are typically charged particles that can interfere with the electronics of a spacecraft, and more importantly, give astronauts a lethal dose of radiation during long space flights.</p>
<p>Protecting future spacecraft from these rays is crucially important for the future of any space program, including trips to Mars in the next few decades. And who knows, with the superconducting magnet shields you might be able to escape a <a href="http://www.startrek.com/database_article/romulans">Romulan</a> attack on the way.</p>
<h2>Technical hurdles</h2>
<p>There is a catch, however. Superconductors do not work at high temperatures and there is no room-temperature superconductor. Above a certain temperature called the “critical temperature,” the superconductor becomes “normal” and the electrons experience a resistance to flow again. For magnesium diboride, this occurs at a very cold temperature — around -248°C. This is actually fine for interstellar space where the background temperature is a much colder -270°C or so but it is not conducive to spacecraft visiting other warmer planets.</p>
<p>Scientists like me are searching for “room temperature” superconductors that would enable these shields to work at much higher temperatures. This would also enable new advances to society such as cheaper health care, for example, since one wouldn’t need low temperatures for MRI instruments to work.</p>
<p>However, high temperature superconductivity has been a mystery for decades, and progress is in slow increments. As someone who works on the border between physics and chemistry, I believe that the answer will be found in the discovery of new materials. Historically, this is where progress has been made to raise the critical temperature to one above the liquid nitrogen boiling point of -196°C.</p>
<p>These superconductors would be great to use as magnetic shield devices if you were exploring many areas of the galaxy. But they wouldn’t work on warmer planets such as Mars without significant amounts of cryogens to keep the magnets cold.</p>
<h2>Quantum computers and societal revolution</h2>
<p>Superconducting technology would also have a variety of other uses aboard starships. <a href="https://uwaterloo.ca/institute-for-quantum-computing/quantum-computing-101">Quantum computers</a> can perform operations orders of magnitude faster than conventional computers, and would undoubtedly be used on a modern starship. Need to send an encrypted message to Starfleet? If the Klingons have a quantum computer, they might be able to intercept and hack your message, so you had better make sure that you understand the technology.</p>
<p>And superconducting electrical systems would naturally be used for the most efficient devices, from starship engines down to tricorders used in away missions. The emergence of room temperature superconductors would spark a transformation of our society that would rival the silicon age of modern electronics. Their discovery is an essential hurdle to cross for the next part of our evolution as a species to a new technological age.</p>
<p>It would be highly logical to continue our search for a room temperature superconductor. If only we could make it so. Quantum materials offer strange new worlds of discovery and perhaps most exciting are the technologies we haven’t discovered yet — that will exploit quantum effects on scale that humans can easily see.</p><img src="https://counter.theconversation.com/content/86378/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher Wiebe receives funding from the Natural Science and Engineering Research Council of Canada (NSERC), the Canadian Foundation for Innovation (CFI), the Canada Research Chairs Program (CRC), and the Canadian Institute for Advanced Research (CIFAR).</span></em></p>Advanced materials that seem like they come from Star Trek are becoming reality today.Christopher Wiebe, Professor and Canada Research Chair in Quantum Materials Discovery, University of WinnipegLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/708722017-01-19T15:07:11Z2017-01-19T15:07:11ZWe’ve created a new vibration-proof ‘metamaterial’ that could save premature babies’ lives<figure><img src="https://images.theconversation.com/files/153244/original/image-20170118-3927-i87vz1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>There are <a href="http://www.bliss.org.uk/neonataltransport">16,000 transfers</a> of premature babies to medical facilities each year in the UK alone. The babies are often transported over large distances from rural to city locations over significant periods of time, in some cases two hours or more. The ambulances, helicopters or aircraft used are miniaturised intensive care units, containing all the equipment required to keep the baby alive.</p>
<p>But mechanical vibrations and noise from the equipment and transfer vehicle can provide significant, even life-threatening stress to the most vulnerable and delicate human lives. As we discovered when speaking to clinicians, transfers are sometimes aborted as a result of the stress that develops in the baby. These vehicles need materials and structures to reduce the noise and vibrations to tolerable levels.</p>
<p>Our team has recently developed a special “metamaterial” inspired by a nuclear reactor design that offers a double whammy of protection by combining two unusual properties known to dampen vibrations to a much greater degree than existing materials. Once we’ve tested and adapted the material, it could be used to help make safer neonatal transfer vehicles. And it could even be used in much bigger structures, for example to help prevent earthquake damage in buildings.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/153418/original/image-20170119-26585-16vjl03.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/153418/original/image-20170119-26585-16vjl03.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=658&fit=crop&dpr=1 600w, https://images.theconversation.com/files/153418/original/image-20170119-26585-16vjl03.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=658&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/153418/original/image-20170119-26585-16vjl03.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=658&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/153418/original/image-20170119-26585-16vjl03.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=826&fit=crop&dpr=1 754w, https://images.theconversation.com/files/153418/original/image-20170119-26585-16vjl03.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=826&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/153418/original/image-20170119-26585-16vjl03.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=826&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">How it works.</span>
<span class="attribution"><span class="source">Andy Alderson/Sheffield Hallam University</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p><a href="http://www.azom.com/article.aspx?ArticleID=11450">Auxetic materials</a> <a href="http://www.bbc.co.uk/programmes/p02jfq9q">can dampen vibrations</a>. They have what’s called a negative Poisson’s ratio, which means that they become thicker when stretched along their length, unlike an elastic band, which becomes thinner. Imagine stretching a crumpled or folded sheet of paper. The unfolding of the paper as it is stretched causes the sheet to become both longer and wider. This is the auxetic effect. </p>
<p>There are also other unusual materials that contract (rather than stretch) along their length when pulled lengthwise (<a href="http://silver.neep.wisc.edu/%7Elakes/NegStfPRL.pdf">negative stiffness</a>), which also have dramatic vibration damping properties when used as part of a composite material.</p>
<p>If you stand a ruler on its end and push it down from the top it will bend into a C shape. If you then push sideways against the mid-point of the outer edge of the C, initially the ruler will offer resistance to the sideways push. That’s positive stiffness. But keep increasing the force and the bend in the ruler snaps through to the other side, creating an inverted C shape. During the snap-through period, the ruler is working with the force, not resisting it. So in this transition phase it displays what is called negative stiffness.</p>
<p>One way of achieving such unusual properties is to develop mechanical metamaterials. These are made from a particular geometric arrangement of smaller building blocks that give the materials their <a href="http://iopscience.iop.org/article/10.1088/0034-4885/76/12/126501/meta">special mechanical properties</a>. We have developed “double negative” mechanical metamaterials that combine both negative Poisson’s ratio and negative stiffness properties simultaneously.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/frOqArygsAU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p><a href="http://onlinelibrary.wiley.com/doi/10.1002/adma.201603959/abstract;jsessionid=5827525BB34384F0035422891D1D9C39.f04t01">Our metamaterials</a> comprise interlocking hexagon building blocks that move together in all directions when compressed, by sliding along the interlocks that connect adjacent hexagons. This creates an auxetic effect.</p>
<p>These were in part inspired by the graphite core interlocking structures of some nuclear reactors designed and built in the 1950s and 1960s, which are auxetic and were specifically designed to withstand seismic vibrations during earthquakes. We have also added three negative stiffness elements – foam inserts, buckled beam inserts and an arrangement of magnets – between the interlocking blocks.</p>
<h2>Stopping bad vibes</h2>
<p>We expect the combination of both auxetic and negative stiffness properties in the bulk metamaterial will give it better vibration damping ability than if it just had one of these properties. And through careful design, we expect it to be able to dampen vibrations at many different frequencies.</p>
<p>Because the technology can be scaled up or down – and once we have determined exactly how good it is at dampening vibrations – it could be used in lots of different applications, from ambulances to buildings.</p>
<p>We also think the principle of combining these two properties could be used in other materials. For example, you could use collapsible auxetic truss structures as <a href="http://www.google.com/patents/US20130322955">rapidly deployable tents and shelters</a> in military and disaster-relief situations. Building negative stiffness into such structures would enable them to provide protection from severe vibrations, such as earthquakes.</p>
<p>We still need to turn the prototype technology into designed and manufactured products, but this metamaterial could have a vibrant future ahead of it.</p><img src="https://counter.theconversation.com/content/70872/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andy Alderson received support for preliminary work leading to the eventual double negative mechanical metamaterial concept in a collaboration with The University of Texas at Austin, funded by the US Army Research Office.</span></em></p><p class="fine-print"><em><span>Fabrizio Scarpa does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>This special dampening material could also protect buildings from earthquakes.Andy Alderson, Professor of Smart Materials and Structures, Sheffield Hallam UniversityFabrizio Scarpa, Professor of Smart Materials & Structures, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/546322016-02-26T11:07:33Z2016-02-26T11:07:33ZBeyond invisibility: engineering light with metamaterials<figure><img src="https://images.theconversation.com/files/112804/original/image-20160224-15614-15i3r6d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Drawing and reality: designing a metamaterial pattern. On the left is the plan; on the right is the actual object.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/pennstatelive/14110596902/in/photolist-dV6Brj-eDDW8E-9eQDJP-9eQDU2-9eTLMJ-9eTLJu-9eTLF7-9eTLA1-nuUuRu-e6Mn6y-e6Mn9f-e6FH1x-8TSPid-9eTM5E-eDDVrW-eDxMm6-7DjBL6-ebyCV4-nvdbdo-pUxdqm-eXJzst-dkddbE-e6FSqc-ptBgnS-q6eAkm-qk2yCH-pW1j1t-qak6N4-pQUqfX-o4pbdC-pSkfF8-pg3JM8-q9H9D6-oTyPhn-pQYXpn-pbEy8F-ndFJNM-pRS9oc-qiTZUZ-sgMppt-pcynik-sgQe1F-rXvaiD-sTKiCz-rXvarV-sgFmD1-rk2zuH-9sde6n-fkMdur-cQTuas">Bossard/Penn State/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p>Since ancient times, people have experimented with light, cherishing shiny metals like gold and cutting gemstones to brighten their sparkles. Today we are far more advanced in how we work with this ubiquitous energy.</p>
<p>Starting with 19th-century <a href="https://www.theguardian.com/science/life-and-physics/2015/nov/22/maxwells-equations-150-years-of-light">experimentation</a>, we began to explore controlling how light interacts with matter.</p>
<p>Combining multiple materials in complex structures let us use light in new ways. We crafted lenses and mirrors to make telescopes to peer out into the universe, and microscopes to explore the world of the small.</p>
<p>Today this work continues, on a much more detailed level. <a href="http://scitation.aip.org/content/aip/journal/apl/104/20/10.1063/1.4878849">My own research</a> into what are called “<a href="http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1845620">metamaterials</a>” explores how we can construct materials in ways that do amazing – and previously impossible – things.</p>
<p>We can build metamaterials to respond in particular ways to certain frequencies of light. For example, we can create a smart filter for infrared cameras that allows the user to easily determine if the white powder in an envelope is baking soda or anthrax, determine if a skin melanoma is benign or malignant and find the sewer pipe in your basement without breaking through the concrete. These are just a few applications for one device; metamaterials in general are far more powerful. </p>
<h2>Working with light</h2>
<p>What scientists call “light” is not just what we can see, but all <a href="http://www.qrg.northwestern.edu/projects/vss/docs/space-environment/2-what-is-electromagnetic-radiation.html">electromagnetic radiation</a> – from low-frequency radio waves to high-frequency X-rays.</p>
<p>Normally, light moves through a material at a slower speed. For example, visible light travels through glass about 33 percent slower than it does through air. A material’s fundamental resistance to the transmission of light at a particular frequency is called its “index of refraction.” While this number changes with the light’s frequency, it starts at 1 – the index of refraction for a vacuum – and goes up. The higher the index, the slower the light moves, and the more its path bends. This can be seen when looking at a <a href="https://www.highlightskids.com/science-questions/why-does-straw-look-bent">straw in a cup of water</a> (see below) and is the basis of how we make lenses for eyeglasses, telescopes and other optics.</p>
<p>Scientists have long wondered if they could make a material with a negative index of refraction at any given frequency. That would mean, for example, that light would bend in the opposite direction when entering the material allowing for new types of lenses to be made. Nothing in nature fits into this category. The <a href="https://www3.nd.edu/%7Edjena/ee358/veselago_original_paper.pdf">properties of such a material</a> – were it to exist – were predicted by <a href="https://nanohub.org/resources/2792/play?resid=2793">Victor Veselago</a> in 1967.</p>
<p>These odd materials have properties that look very strange compared with our everyday experiences. In the picture below, we see two cups of water, each with a straw in it. The picture on the left is what happens normally – the section of the straw in the water appears disconnected from the part of the straw that is in the air. The image is displaced because air and water refract light differently. </p>
<p>The image on the right indicates what the straw would look like if the fluid were a material with a negative index of refraction. Since the light bends in the opposite direction, the image is reversed, creating the observed illusion. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/112983/original/image-20160225-15179-oredon.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/112983/original/image-20160225-15179-oredon.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/112983/original/image-20160225-15179-oredon.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/112983/original/image-20160225-15179-oredon.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/112983/original/image-20160225-15179-oredon.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/112983/original/image-20160225-15179-oredon.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/112983/original/image-20160225-15179-oredon.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/112983/original/image-20160225-15179-oredon.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">At left: normal refraction. At right: with simulated negative refraction.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-107122541/stock-photo-water-glass-with-a-blue-straw-on-white-background.html">Water glass with straw (normal) from shutterstock.com</a></span>
</figcaption>
</figure>
<p>While Veselago could imagine these materials in the late 1960s, he could not conceive of a way to create them. It took an additional 30 years before <a href="http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_22-5-2013-11-25-22">John Pendry</a> published papers in <a href="http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.76.4773">1996</a>, <a href="https://iopscience.iop.org/article/10.1088/0953-8984/10/22/007/pdf">1998</a> and <a href="http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=798002">1999</a> describing how to make a composite man-made material, which he called a metamaterial. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/112765/original/image-20160224-16455-13wcr13.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/112765/original/image-20160224-16455-13wcr13.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/112765/original/image-20160224-16455-13wcr13.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=406&fit=crop&dpr=1 600w, https://images.theconversation.com/files/112765/original/image-20160224-16455-13wcr13.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=406&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/112765/original/image-20160224-16455-13wcr13.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=406&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/112765/original/image-20160224-16455-13wcr13.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=510&fit=crop&dpr=1 754w, https://images.theconversation.com/files/112765/original/image-20160224-16455-13wcr13.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=510&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/112765/original/image-20160224-16455-13wcr13.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=510&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An early metamaterial using repeating elements of copper split-rings and copper wires.</span>
<span class="attribution"><a class="source" href="https://www2.bc.edu/~padillaw/PDF/Smith_NATO-ASI_2000b.pdf">D. R. Smith et al., Left-handed Metamaterials, in Photonic Crystals and Light Localization, ed. C. M. Soukoulis (Kluwer, Netherlands, 2000).</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Making metamaterials</h2>
<p>This work was followed up experimentally by <a href="http://muri.lci.kent.edu/References/NIM_Papers/Nanoparticle_Theory_Experiment/2000_SRR_Properties.pdf">David R. Smith’s group in 2000</a>, which created a metamaterial using copper split-rings on circuit boards and lengths of copper wires as repeating elements. The picture below shows one such example produced by his group. The size and shape of the split-rings and copper posts determines what frequency of light the metamaterial is tuned to. The combination of these components interacts with the incident light, creating a region with an fully engineered effective index of refraction. </p>
<p>At present, we are only able to construct metamaterials that manage interactions with very specific parts of the electromagnetic spectrum.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/112414/original/image-20160222-25888-1a1k4gf.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/112414/original/image-20160222-25888-1a1k4gf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/112414/original/image-20160222-25888-1a1k4gf.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=321&fit=crop&dpr=1 600w, https://images.theconversation.com/files/112414/original/image-20160222-25888-1a1k4gf.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=321&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/112414/original/image-20160222-25888-1a1k4gf.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=321&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/112414/original/image-20160222-25888-1a1k4gf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=404&fit=crop&dpr=1 754w, https://images.theconversation.com/files/112414/original/image-20160222-25888-1a1k4gf.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=404&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/112414/original/image-20160222-25888-1a1k4gf.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=404&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The electromagnetic spectrum, showing all types of light, including the narrow band of visible light.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:EM_spectrum.svg">Philip Ronan</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Smith’s group worked initially in the microwave portion of the spectrum, because working with larger wavelengths makes metamaterial construction easier, as multiple copies of the split-rings and pins must fit into the space of one wavelength of the light. As researchers work with shorter wavelengths, metamaterial components need to be much smaller, which is more challenging to build.</p>
<p>Since the first experiments, multiple research groups have made metamaterials that work in the infrared; some are skirting the fringe of the visible portion of the spectrum. For these short wavelengths, circuit boards, copper wires and pins are far too large. Instead the structures have to use micro- and nano-fabrication techniques similar to what is used to make computer chips.</p>
<h2>Creating ‘invisibility’</h2>
<p>Soon after the first metamaterials were fabricated, researchers began engineering applications for which they would be useful. One application that got a lot of press was the creation of an “<a href="http://time.com/4042506/invisibility-cloak/">invisibility cloak</a>.” </p>
<p>Normally if a microwave radar were aimed at an object, some of the radiation would absorb and some would reflect off. Sensors can detect those disturbances and reconstruct what the object must have looked like. If an object is surrounded by the metamaterial cloak, then the radar signal bends around the object, neither being absorbed nor reflected – as if the object were never there.</p>
<p>By creating a metamaterial layer on the surface of an object, you can change what happens to the light that hits the object. Why is this important? When you look at a still pool of water, it is not surprising to see your reflection. When you point a flashlight at a pond at night, some of that light beam bounces off onto the trees beyond. </p>
<p>Now imagine you could coat the surface of that pond with a metamaterial that worked for all the visible spectrum. That would remove all reflection – you wouldn’t see your own reflection, nor any light bouncing into the woods. </p>
<p>This type of control is very useful for determining specifically what type of light can enter or exit a material or a device. For example, solar cells could be coated with metamaterials that would admit only specific (e.g., visible) frequencies of light for conversion to electricity, and would reflect all other light to another device that collects the remaining energy as heat.</p>
<h2>The future of wave engineering</h2>
<p>Engineers are now creating metamaterials with what is called a dynamic response, meaning its properties vary depending on how much electricity is passing through it, or what light is aimed at it. For example, a dynamic metamaterial filter might allow passage of light only in the near infrared, until electricity is applied, at which point it lets through only mid-infrared light. This ability to “tune” the responsiveness of metamaterials has great potential for future applications, including uses we can’t yet imagine.</p>
<p>The amazing thing about all of the wondrous possibilities of metamaterials’ interaction with light is that the principle works much more broadly. The same mathematics that predict the structure needed to produce these effects for light can be applied to the interaction of materials with any type of waves. </p>
<p>A group in Germany has successfully created a <a href="http://www.sci-news.com/physics/article01074-invisibility-cloak.html">thermal cloak</a>, preventing an area from heating by bending the heat flow around it – just as an invisibility cloak bends light. The principle has also been used for sound waves and has even been discussed for seismic vibrations. That opens the potential for making a building “invisible” to earthquakes! We are only beginning to discover how else we might use metamaterials and their underlying principles.</p><img src="https://counter.theconversation.com/content/54632/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thomas Vandervelde receives funding from the National Science Foundation, the Air Force Office of Scientific Research, the Office of Naval Research, the Intelligence Community, the Alexander Von Humboldt Foundation, and Tufts University. </span></em></p>We are beginning to be able to control very precisely how light interacts with matter, creating opportunities for invisibility, soundproofing and even earthquake damage prevention.Thomas Vandervelde, Associate Professor of Electrical and Computer Engineering, Tufts UniversityLicensed as Creative Commons – attribution, no derivatives.