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  • richardmitnick 7:00 pm on March 21, 2019 Permalink | Reply
    Tags: "A Swiss cheese-like material’ that can solve equations", , , , Metamaterials,   

    From University of Pennsylvania: “A Swiss cheese-like material’ that can solve equations” 

    U Penn bloc

    From University of Pennsylvania

    March 21, 2019


    Evan Lerner, Gwyneth K. Shaw Media Contacts
    Eric Sucar Photographer

    Engineering professor Nader Engheta and his team have demonstrated a metamaterial device that can function as an analog computer, validating an earlier theory about ‘photonic calculus.’

    Nader Engheta (center), the H. Nedwill Ramsey Professor in the Department of Electrical and Systems Engineering, and lab members Brian Edwards and Nasim Mohammadi Estakhri conducted the pathbreaking work in Engheta’s lab.

    The field of metamaterials involves designing complicated, composite structures, some of which can manipulate electromagnetic waves in ways that are impossible in naturally occurring materials.

    For Nader Engheta of the School of Engineering and Applied Science, one of the loftier goals in this field has been to design metamaterials that can solve equations. This “photonic calculus” would work by encoding parameters into the properties of an incoming electromagnetic wave and sending it through a metamaterial device; once inside, the device’s unique structure would manipulate the wave in such a way that it would exit encoded with the solution to a pre-set integral equation for that arbitrary input.

    In a paper published in Science, Engheta and his team demonstrated such a device for the first time.

    Their proof-of-concept experiment was conducted with microwaves, as the long wavelengths allowed for an easier-to-construct macro-scale device. The principles behind their findings, however, can be scaled down to light waves, eventually fitting onto a microchip.

    Such metamaterial devices would function as analog computers that operate with light, rather than electricity. They could solve integral equations—ubiquitous problems in every branch of science and engineering—orders of magnitude faster than their digital counterparts, while using less power.

    The demonstration device is 2-foot-square, made of a milled type of polystyrene plastic.

    Engheta, the H. Nedwill Ramsey Professor in the Department of Electrical and Systems Engineering, conducted the study along with lab members Nasim Mohammadi Estakhri and Brian Edwards.

    This approach has its roots in analog computing. The first analog computers solved mathematical problems using physical elements, such as slide-rules and sets of gears, that were manipulated in precise ways to arrive at a solution. In the mid-20th century, electronic analog computers replaced the mechanical ones, with series of resistors, capacitors, inductors, and amplifiers replacing their predecessors’ clockworks.

    Such computers were state-of-the-art, as they could solve large tables of information all at once, but were limited to the class of problems they were pre-designed to handle. The advent of reconfigurable, programmable digital computers, starting with ENIAC, constructed at Penn in 1945, made them obsolete.

    As the field of metamaterials developed, Engheta and his team devised a way of bringing the concepts behind analog computing into the 21st century. Publishing a theoretical outline for “photonic calculus” in Science in 2014, they showed how a carefully designed metamaterial could perform mathematical operations on the profile of a wave passing thought it, such as finding its first or second derivative.

    Now, Engheta and his team have performed physical experiments validating this theory and expanding it to solve equations.

    “Our device contains a block of dielectric material that has a very specific distribution of air holes,” Engheta says. “Our team likes to call it ‘Swiss cheese.’”

    The Swiss cheese material is a kind of polystyrene plastic; its intricate shape is carved by a CNC milling machine.

    “Controlling the interactions of electromagnetic waves with this Swiss cheese metastructure is the key to solving the equation,” Estakhri says. “Once the system is properly assembled, what you get out of the system is the solution to an integral equation.”

    “This structure,” Edwards adds, “was calculated through a computational process known as ‘inverse design,’ which can be used to find shapes that no human would think of trying.”


    The pattern of hollow regions in the Swiss cheese is predetermined to solve an integral equation with a given “kernel,” the part of the equation that describes the relationship between two variables. This general class of such integral equations, known as “Fredholm integral equations of the second kind,” is a common way of describing different physical phenomena in a variety of scientific fields. The pre-set equation can be solved for any arbitrary inputs, which are represented by the phases and magnitudes of the waves that are introduced into the device.

    “For example,” Engheta says, “if you were trying to plan the acoustics of a concert hall, you could write an integral equation where the inputs represent the sources of the sound, such as the position of speakers or instruments, as well as how loudly they play. Other parts of the equation would represent the geometry of the room and the material its walls are made of. Solving that equation would give you the volume at different points in the concert hall.”

    In the integral equation that describes the relationship between sound sources, room shape and the volume at specific locations, the features of the room — the shape and material properties of its walls — can be represented by the equation’s kernel. This is the part the Penn Engineering researchers are able to represent in a physical way, through the precise arrangement of air holes in their metamaterial Swiss cheese.

    “Our system allows you to change the inputs that represent the locations of the sound sources by changing the properties of the wave you send into the system,” Engheta says, “but if you want to change the shape of the room, for example, you will have to make a new kernel.”

    The researchers conducted their experiment with microwaves; as such, their device was roughly two square feet, or about eight wavelengths wide and four wavelengths long.

    “Even at this proof-of-concept stage, our device is extremely fast compared to electronics,” Engheta says. “With microwaves, our analysis has shown that a solution can be obtained in hundreds of nanoseconds, and once we take it to optics the speed would be in picoseconds.”

    Scaling down the concept to the scale where it could operate on light waves and be placed on a microchip would not only make them more practical for computing, it would open the doors to other technologies that would enable them to be more like the multipurpose digital computers that first made analog computing obsolete decades ago.

    “We could use the technology behind rewritable CDs to make new Swiss cheese patterns as they’re needed,” Engheta says. “Some day you may be able to print your own reconfigurable analog computer at home!”

    Nader Engheta is the H. Nedwill Ramsey Professor in the Department of Electrical and Systems Engineering at the University of Pennsylvania’s School of Engineering and Applied Science.

    The research was supported by the Basic Research Office of the Assistant Secretary of Defense for Research and Engineering through its Vannevar Bush Faculty Fellowship program and by the Office of Naval Research through Grant N00014-16-1-2029.

    See the full article here .


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  • richardmitnick 10:03 am on August 15, 2015 Permalink | Reply
    Tags: , , Metamaterials,   

    From U Arizona: : Printing the Future of Engineering” 

    U Arizona bloc

    University of Arizona

    August 14, 2015
    Daniel Stolte

    Students in Hao Xin’s lab perform measurements on a 3-D printed prototype of a Lüneburg lens. (Image: Hao Xin)

    3-D printing is revolutionizing the ways engineers think about and make highly complicated devices, with applications ranging from wireless communication to air traffic control to earthquake-proof buildings.

    Lüneburg lenses are sought-after devices that could greatly advance wireless communications, among other applications. (Image: Hao Xin)

    Hao Xin opens the door to his lab and points to an object that looks like some kind of strange, synthetic sponge made by an alien race much more advanced than ours.

    “This is a prototype of a Lüneburg lens that we made,” Xin says.

    A lens?

    Never mind the fact that it’s neither transparent nor made of glass, but of a porous yet weirdly symmetric-looking, plasticky substance of oddly unappealing, pale gray color. Move your eyes closer, and your mind gets lost in a dazzling array of a myriad of tiny branchlets connected to each other at right angles, forming a thicket that gets denser toward the center of the object.

    “This lens is not made for light,” Xin says, “but for electromagnetic waves in the terahertz range, which is between microwaves and radio waves.”

    Hao Xin is an associate professor in the Department of Electrical and Computer Engineering in the UA’s College of Engineering.

    Now things make a bit more sense. Unlike light visible to humans, which is pretty picky and travels only through air, water or transparent things (for the most part), terahertz waves pass through anything from synthetics to textiles to cardboard. Because many biomolecules, proteins, explosives or narcotics absorb terahertz radiation in telltale ways, waves of this range can be used to detect such substances in airport security lanes, for example.

    Xin, a professor in electrical and computer engineering who heads the Millimeter Wave Circuits and Antennas Laboratory at the University of Arizona’s College of Engineering, is harnessing the possibilities of three-dimensional printing to create materials and structures that not too long ago would have been written off as science fiction.

    “By using 3-D printing and new design approaches, we are able to come up with components such as antennas, wave guides, lenses and holographic devices that are better than existing technology and haven’t been possible to make before,” he says.

    In one line of research, Hao Xin’s team is developing 3-D printing solutions to the challenges of combining different materials, as in this coplanar waveguide, a device that is used to transmit microwave-frequency signals. (Image: Hao Xin)

    As computers, communication devices and other IT applications get smaller and can do ever more amazing things, engineers have to overcome ever greater challenges in designing and building the components that make them work.

    Some applications require the invention of new materials. Some require new ways of manufacturing. And some require both.

    Xin’s group is one of the first to adopt 3-D printing approaches to make so-called metamaterials, engineered materials with properties not found in nature. Unlike conventional materials such as metals or plastics, metamaterials consist of assemblies of elements made from conventional materials, usually in repeating patterns. Their special properties arise not so much from the properties of their ingredients, but from the shape, geometry and orientation of their subunits. They can be designed to affect electromagnetic waves, sound and even the shockwaves of an earthquake in ways that would be impossible to achieve with traditional materials.

    This horn antenna (used to focus beams of terahertz radiation) made by a 3-D printer in Xin’s lab is another example of fabricating sophisticated devices more simply and cost-effectively than conventional processes. (Image: Hao Xin)

    “Traditionally, it has been very difficult to make those three-dimensional, periodic structures,” Xin explains. “Oftentimes, someone produces a two-dimensional prototype of a three-dimensional object to demonstrate some desired property, but those aren’t very practical, nor do they have all the properties they need in order to work for application in question.”

    Xin’s team has successfully created highly complicated structures using 3-D printing, such as the Lüneburg lens, which has applications ranging from microwave antennas to radar calibration devices.

    “A Lüneburg lens makes a fantastic antenna that can be used for wireless communication and radar installations,” Xin says, “but traditionally it is built manually, which is not cost-effective, and you can’t make it very precise. Now we can make it at much lower cost and more precise.”

    Xin’s lab also uses 3-D printers to make a range of conventional things, such as regular antennas and integrated circuits. It is one of the first to apply the approach to metamaterials to build innovative electromagnetic applications, and it has support from the National Science Foundation, the U.S. Air Force Office of Research, Raytheon and even Google.

    Earlier this year, the team made waves when it published the first successful attempt at designing what many consider the holy grail of metamaterials: a negative refraction metamaterial that not only bends electromagnetic waves (in this case, microwaves) backward but also does not diminish energy in the process. All previous designs suffered from the fact that the waves lost a large portion of their energy when passing through the material.

    Xin’s accomplishment could bring negative refraction metamaterials closer to applications aiming at manipulating electromagnetic radiation in new ways.

    One of them is a so-called phased array, a sophisticated assembly of antennas capable of focusing and pointing a beam of electromagnetic radiation. Used in radar applications for a long time, such arrays form a vital part of the next generation of wireless communication such as the 5G network.

    “Unlike rotating radar antennas that you see at airports, which are limited to rotating speeds based on mechanical parts, a phased array doesn’t move and has no moving parts that can fail,” Xin explains. “Plus, the antenna can scan as fast as microseconds and in any direction you want.

    “But for traditional phased arrays, the manufacturing cost and the mechanical assembly are quite expensive, and sometimes problematic. So if we use a 3-D printer where we can print a vertically integrated phased array, it is cheaper and offers better performance in a smaller footprint.”

    Therein lies the main advantage of 3-D printing over traditional assembly, according to Xin: It becomes possible to build extremely complex and intricate structures consisting of different materials in three-dimensional space rather than by stacking two-dimensional components, each made from one material.

    “Take the way we design electronic components, for example,” Xin says. “Traditionally, everything is printed on a flat circuit board, and if you need vertical integration, you have to make another board, and another, and then you connect them together. That is a costly process.”

    On the other hand, 3-D printing allows putting one material with one property in one location, and a material with a different property in another location, Xin explains.

    “It doesn’t matter how complicated the structure you’re building,” he says. “You can even think more futuristically. Your smartphone is essentially a three-dimensional block made of metal, glass, semiconductors and plastics. Of course, today we can’t yet do this, but if 3-D printing technology becomes sufficiently advanced, we may be able to print the whole cellphone at once.”

    See the full article here.

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    Where else in the world can you find an astronomical observatory mirror lab under a football stadium? An entire ecosystem under a glass dome? Visit our campus, just once, and you’ll quickly understand why the UA is a university unlike any other.

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