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A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 2 0 1 4 METAMATERIAL VIBRATES UNIDIRECTIONALLY A group of physicists from the Uni- versity of Amsterdam, the Netherlands, has designed a metamaterial that can transmit vibrations in one direction. The material could be extremely useful for many applications, such as building earthquake-resistant structures. Each building block of this ma- terial acts as a tiny robot that is able to sense and act upon the behavior of its neighbors through local feedback loops. The researchers have used these programmable feedback loops to break the symmetry of motion. As a result, a given building block does not react the same way to the dis- placement of its left-hand neighbor as it does to the one on the right. By putting several of these build- ing blocks together, the researchers as- sembled a metamaterial with a unique property: waves propagating through this material are dissipated when prop- agating in one direction but are ampli- fied when they propagate in the oppo- site direction. This robotic material is key to the development of new wave guiding sys- tems that can focus undesired vibra- tions on strong parts of structures. Be- sides building solid structures, the uni- directional amplification could, for ex- ample, beused toharness energy or per- form high-quality measurements with- out affecting their surroundings. www. uva.nl/en. GREEN APPROACH TO CARBON CAPTURE Researchers at Kyoto University and the University of Tokyo, Japan, along with colleagues at Jiangsu Nor- mal University in China have designed a new material that can capture carbon dioxide (CO 2 ) molecules and efficient- ly convert them into useful organic materials. EMERGING TECHNOLOGY The ExOne Company, North Huntingdon, Pa., the global leader in industrial sand and metal 3D printers using binder jetting technology, and Global Tungsten & Powders, Towanda, Pa., international manufacturer of tungsten metal powders, are collaborating to advance tungsten-based metal 3D printing using binder jet- ting. Binder jetting is a 3D printing process that uses a digital file to inkjet a bonding agent into a bed of powder parti- cles, creating a solid part, one layer at a time. Compared to other 3D printing processes, binder jetting delivers preci- sion parts at a high rate of speed, making it an ideal approach for serial production. exone.com , globaltungsten.com . BRIEF The material is a porous coordina- tion polymer (PCP) with a framework consisting of zinc metal ions. The re- searchers tested a sample using x-ray structural analysis and found that it can selectively capture only CO 2 molecules with 10 times more efficiency than oth- er PCPs. The material has an organic com- ponent with a propeller-like molecular structure, and as CO 2 molecules ap- proach the structure, they rotate and rearrange to permit CO 2 trapping, re- sulting in slight changes to the molecu- lar channels within the PCP. This allows the material to act as a molecular sieve that can recognize molecules by size and shape. The PCP is also recyclable; the efficiency of the catalyst did not de- crease even after 10 reaction cycles. “One of the greenest approaches to carbon capture is to recycle the car- bon dioxide into high-value chemicals, such as cyclic carbonates, which can be used in petrochemicals and pharma- ceuticals,” says Kyoto University chem- ist Susumu Kitagawa. After capturing thecarbon, thecon- verted substance can be used to make polyurethane, amaterial with a wide va- riety of applications including clothing, domestic appliances, and packaging. This work highlights the po- tential of porous coordination poly- mers for trapping carbon dioxide and converting it into useful materials, opening an avenue for future research into carbon capture materials. www. kyoto-u.ac.jp/en , www.u-tokyo.ac.jp/en , www.en.jsnu.edu.cn. Metamaterial featuring one-way amplification. Courtesy of Business Wire. This new porous coordination polymer selectively captures carbon dioxide. Courtesy of Mindy Takamiya.