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A Real-World ‘Invisibility Cloak’? Research Teams See Progress

 
For decades—since the first season of the original Star Trek series, at least—the world has wondered if something like a “cloaking device” to create functional invisibility would ever be feasible. Now, after a long wait, real progress was reported from two separate sources within a week of each other.

First, scientists at the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California Berkeley reported that they’ve devised an ultra-thin invisibility covering they call a “skin cloak” that can conform to the shape of an object and conceal it from detection with visible light. Although this cloak is only microscopic in size, the principles behind the technology should enable it to be scaled-up to conceal macroscopic items as well, they say.A 3D illustration of a metasurface skin cloak made from an ultrathin layer of nanoantennas—gold blocks—covering an arbitrarily shaped object. Light (red arrows) reflects off the cloak  as if it were reflecting off a flat mirror.

Working with brick-like blocks of gold nanoantennas, the Berkeley researchers fashioned a skin cloak barely 80 nanometers in thickness, which was wrapped around a three-dimensional object about the size of a few biological cells and arbitrarily shaped with multiple bumps and dents. The surface of the skin cloak was engineered to reroute reflected light waves so that the object was rendered invisible to optical detection when the cloak is activated.

“This is the first time a 3D object of arbitrary shape has been cloaked from visible light,” said Xiang Zhang, director of Berkeley Lab’s Materials Sciences Division and an authority on metamaterials—artificial nanostructures engineered with electromagnetic properties not found in nature. “Our ultra-thin cloak … is easy to design and implement, and is potentially scalable for hiding macroscopic objects.” For the past 10 years, Zhang and his research group have been pushing the boundaries of how light interacts with metamaterials, managing to curve the path of light or bend it backwards, phenomena not seen in natural materials, and to render objects optically undetectable.

Just days after Berkeley Labs announced their success, the Army Times reported that the US military was interested in “a major breakthrough in the quest for invisibility” made by researchers at another West Coast institution. Boubacar Kante and fellow scientists at the University of California San Diego have successfully tested what they call a “dielectric metasurface cloak”—a very thin, nonmetallic covering that influences electromagnetic waves. Their cloak is made of a layer of Teflon substrate with ceramic cylinders embedded into it.

Previous versions of this cloaking material needed to be 10 times thicker that the electromagnetic wavelength being manipulated; the new stuff can work at only a tenth of the wavelength’s thickness. Kante and his team still have a ways to go: their test used light hitting the cloak at 45°—and was effective at only ±6° of that angle, Army Times reported. But it’s progress.

Whichever team of West Coast scientists succeeds in producing a workable large-scale cloaking device first, we hope the competition remains friendly. Anything else would be unsightly.
 

Cancer Patient Receives Customized 3D Printed Ribs, Sternum

A patient in Spain suffering from cancer in the chest has received a customized 3D printed titanium sternum and rib implant that was designed and manufactured by Melbourne, Australia-based medical device company Anatomics, which specializes in the manufacture of patient-specific implants. The device was 3D-printed at the titanium 3D printing facility of CSIRO—Australia’s national science agency, the Commonwealth Scientific and Industrial Research Organisation. Illustration of how the 3D-printed sternum and rib cage fit inside the patient’s body.

The surgical team in Spain, Dr. José Aranda, Dr. Marcelo Jimene and Dr. Gonzalo Varela from Salamanca University Hospital, faced a challenging surgery due to the complicated geometries involved in the chest cavity. “We thought, maybe we could create a new type of implant that we could fully customize to replicate the intricate structures of the sternum and ribs,” Aranda said. “We wanted to provide a safer option for our patient, and improve their recovery post-surgery.”

That’s when the surgeons turned to Anatomics. After assessing the complexity of the requirements, Anatomics CEO Andrew Batty said, the solution lay in the complex design of the part. “We wanted to 3D print the implant from titanium because of its complex geometry and design,” Batty said. “While titanium implants have previously been used in chest surgery, designs have not considered the issues surrounding long-term fixation. Flat and plate implants rely on screws for rigid fixation that may come loose over time. This can increase the risk of complications and the possibility of reoperation.”

Through high-resolution CT data, the Anatomics team was able to create a 3D reconstruction of the chest wall and tumor, allowing the surgeons to plan and accurately define resection margins. “From this, we were able to design an implant with a rigid sternal core and semi-flexible titanium rods to act as prosthetic ribs attached to the sternum,” Batty said. Once the prosthesis was complete it was couriered to Spain and implanted into the patient.

“The operation was very successful,” Aranda said. “We were able to create a body part that was fully customized and fitted like a glove.” A description of the procedure has been published in the European Journal of Cardio-Thoracic Surgery.  
 

Kirigami Solar Cells Track the Sun

Solar cells capture up to 40% more energy when they can track the sun across the sky, but conventional, motorized trackers are too heavy and bulky for pitched rooftops and vehicle surfaces.

Talk about cutting-edge research: Now, by borrowing from kirigami, the ancient Japanese art of paper cutting, researchers at the University of Michigan have developed solar cells that can have it both ways.  By borrowing from kirigami, the Japanese art of paper cutting, U-M researchers developed solar cells that can track the sun.

“The design takes what a large tracking solar panel does and condenses it into something that is essentially flat,” said Aaron Lamoureux, a doctoral student in materials science and engineering.

A team of engineers and an artist developed an array of small solar cells that can tilt within a larger panel, keeping their surfaces more perpendicular to the sun’s rays.

“From the standpoint of the person who’s putting this panel up, nothing would really change,” said Max Shtein, associate professor of materials science and engineering. “But inside ... the solar cell would split into tiny segments that would follow the position of the sun in unison.” By designing an array that tilts and spreads apart when the sun’s rays are coming in at lower angles, they raise the effective area that is soaking up sunlight.

To explore patterns, the team of engineers worked with paper artist Matthew Shlian, a lecturer in the U-M School of Art and Design. Shlian showed Lamoureux and Shtein how to create them in paper using a plotter cutter. Lamoureux then made more precise patterns in Kapton, a space-grade plastic, using a CO2 laser.

To make the solar array, Kyusang Lee, a doctoral student in electrical engineering, built custom solar cells. He and Lamoureux attached them to an uncut piece of Kapton, leaving spaces for the cuts. Then, Lamoureux patterned the Kapton with the laser cutter.

The optimized design is effective because it stretches easily, allowing a lot of tilt without losing much width. According to the team’s simulations of solar power generation during the summer solstice in Arizona, it is almost as good as a conventional single-axis tracker, offering a 36% improvement over a stationary panel. 
 

Magnetic Field Assists Plasma Micromachining

Laser Induced Plasma Micro-Machining (LIPMM) has better micromachining capabilities than conventional pulsed laser micromachining. Ishan Saxena, Sarah Wolff and Jian Cao, all of Northwestern University’s Department of Mechanical Engineering, report a process modification in LIPMM by which an external unidirectional magnetic field is used to alter the characteristics of the plasma, which in turn yields a higher material removal rate on a 304L steel workpiece, than does regular LIPMM.

A commercially available Lumera Lasers Nd-YVO4 laser emitting linearly polarized pulses was used for conducting the experiments. A rare-earth (Neodymium) permanent magnet (N52) with a surface field of 5400 Gauss (both in longitudinal and transverse directions) was used to create external magnetic fields. The plasma was created within four different magnetic field configurations.

Their study, which is published in SME’s Manufacturing Letters journal, indicates that the plasma energy can increase by about 70% by applying a field of 5400 Gauss in either the longitudinal or transverse direction. Correspondingly, the depth of micro-features obtained in the presence of such a field is approximately 50% greater. This technique can potentially be applied to create high-aspect ratio micro-features, with higher throughput, in various materials. Read the entire study, free of charge, at http://tinyurl.com/Techfront-ML-11-2015)

 

Tech Front welcomes your manufacturing research-related news releases: Please email them to Tech Front editor Michael Anderson at manderson@sme.org. 

 

This article was first published in the November 2015 edition of Manufacturing Engineering Magazine. Click here for PDF.

 


Published Date : 11/1/2015

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