News Article | May 19, 2017
The levitating platform developed by Teo and co-workers contains arrays of permanent magnets floating above several coils of wire. The movement of the platform is controlled by varying the current in the coils. Credit: A*STAR Singapore Institute of Manufacturing Technology Magnetic levitation (Maglev) is well known for its use in high-speed rail networks, but could also be applied at smaller scales in medicine and electronics. To do so, researchers must be able to precisely control electromagnetic fields so that they can move and rotate objects without touching them. Now, Teo Tat Joo and co-workers at the Agency for Science, Technology and Research (A*STAR) Singapore Institute of Manufacturing Technology (SIMTech) and National University of Singapore have developed a Maglev system that can produce linear and rotational motion in all three dimensions. This system provides nanometer-scale precision in these movements, and is simpler and potentially less energy-intensive than other recent attempts. "Today's existing precision mechatronics systems can only be classified as having one micrometer positioning accuracy over one meter—one part-per-million or 1 PPM," says Teo. "On the other hand, Maglev technology has the potential to achieve a truly nanometer positioning system—0.001 PPM." To build their new Maglev system, Teo and co-workers employed a special arrangement of permanent magnets called a Halbach array, which produces a strong magnetic field on one side but not the other. They positioned four Halbach arrays on a square platform above several energized coils of wire (see image), and used analytical force modeling to work out how the magnets and coils would interact. Then, by carefully controlling the electrical current in different coils, they were able to move or rotate the square platform at several different speeds (see video), with a positional error of just 50 nanometers. "One of the main technical challenges we faced was that the large number of coils, with high electrical resistance, require a high power supply," says Teo. "We are currently developing a scheme that allows selective switching of the coils; this will improve the energy efficiency and significantly reduce the cost of the Maglev system." Perhaps the most promising uses of the Maglev system developed by the A*STAR team would be in processes that require a particle-free or vacuum environment, as Teo explains: "The contactless nature of Maglev ensures that no contaminating particles are generated from friction between surfaces. For example, future wafer lithography processes such as extreme UV lithography, which operates in a vacuum, will require a Maglev system to handle the wafer." Teo also suggests that Maglev technology could replace conventional conveyor belts in factories. Unlike traditional conveyors that can only move objects on pre-defined tracks, Maglev could move several objects simultaneously to different desired locations. More information: Haiyue Zhu et al. Design and Modeling of a Six-Degree-of-Freedom Magnetically Levitated Positioner Using Square Coils and 1-D Halbach Arrays, IEEE Transactions on Industrial Electronics (2017). DOI: 10.1109/TIE.2016.2598811
News Article | April 19, 2017
Carbon steel, an alloy made from iron and carbon, is the single largest class of alloys in use today. It's used to make a range of products from fences and springs to steel wires and pipelines, and for structural support in buildings, bridges, as well as nuclear power and fossil fuel power plants. The corrosion of carbon steel, however, is a huge cost to industry and is of enormous practical importance. One common corrosion inhibitor used in the construction industry, calcium nitrite, is quite toxic to humans, impairing the ability of red blood cells to transport oxygen. Seeking safer corrosion inhibitors, Yong Teck Tan and colleagues from the National University of Singapore and Singapore Institute of Manufacturing Technology investigated molybdate as a potential alternative and developed a technique to determine its suitability. Molybdate is non-toxic, and protects the carbon steel from corrosion by competitive adsorption against chloride on the passive film surface, and, in the presence of calcium cations, can also deposit a layer of calcium molybdate. "Our aim was to first determine the suitability of molybdate as a corrosion inhibitor for carbon steel in alkaline environments, and then to investigate its effect on the passivation of carbon steel," says Tan. "Previous studies using electrochemical techniques have focused on corrosion inhibition efficiency at a particular time, which provides a snapshot of the level of corrosion at that instant," explains Tan. "Depending on whether it was assessed over short or long timescales, different conclusions were drawn." So the research team took a longer look. They used an electrochemical method for estimating the extent of corrosion over the entire duration of the investigation, and could assess the overall effectiveness of molybdate. "Even though molybdate resulted in a slightly higher passive current in the later stages, faster passivation in the early stages resulted in a lower overall level of corrosion," says Tan. The researchers found that incomplete coverage of the carbon steel by the calcium molybdate led to slightly higher corrosion rates compared with untreated surfaces. By controlling the composition of the molybdate solution, however, the calcium molybdate film covered the entire surface, resulting in improved corrosion resistance. "Overall, molybdate proved to be an effective corrosion inhibitor," says Tan. "We will now explore its effectiveness in solutions containing other ions." Explore further: Improved corrosion protection with flake-type particles of zinc-phosphate More information: Yong Teck Tan et al. Effect of Molybdate on the Passivation of Carbon Steel in Alkaline Solutions under Open-Circuit Conditions, Journal of The Electrochemical Society (2016). DOI: 10.1149/2.0651610jes
News Article | February 20, 2017
The coiled thread on a screw is among the 'chiral' structures' whose mirror image is different from the original. When reduced to the nanometer scale, these structures could have an important role in nanosensor technology. However, making a screw out of a straight wire is no small task, even in the macroscopic world. Making it on the nanoscale has previously used bottom-up methods that grow or assemble the structure in a gas or solution. But such approaches can be complicated, slow and expensive. Jun Wei from A*STAR's Singapore Institute of Manufacturing Technology and co-workers from the A*STAR Institute of Materials Research and Engineering, Nanyang Technological University and Nanjing Tech University in China, developed a simpler method that uses etching techniques to convert a straight nanowire into a screw. The team created 10-micrometer silver nanowires, 80 nanometers in diameter and with five sides. The structures were attached to a silicon substrate and then placed into a solution of silver nitride in ethylene glycol at 80 degrees Celsius for 20 minutes. The sample was then rinsed clean and the process repeated five times. When the resultant wires were imaged using a scanning transmission electron microscope the team observed smooth ridges and grooves reminiscent of screw threads. Interestingly, such a structure was not evident when a single-step etch was used. Etching usually works along specific crystallographic directions, leading to symmetric structures, so the team wanted to know how equivalent crystal facets could be etched in an anisotropic way. They propose that this unusual etching mode might begin with the creation of pits at the boundaries between the five crystallographic regions that make up the pentagonal nanowire. These pits merge at an angle, driven by the propensity to minimize the surface energy, and thus create ridges and grooves that spiral around the nanowire. "This selective etching is driven by a faster etching rate at some defect locations on the silver nanowire," says Wei. "Thus, we can convert a regular structure into non-symmetrical one." Such chiral nanostructures have a much larger surface area than a straight nanowire of similar size. This makes them potentially useful for sensing applications. "We next hope to use the nanoscrews in the fabrication of sensors and transparent conductors," says Wei. The A*STAR-affiliated researchers contributing to this research are from the Singapore Institute of Manufacturing Technology and the Institute of Materials Research and Engineering. More information: Rachel Lee Siew Tan et al. Nanoscrews: Asymmetrical Etching of Silver Nanowires, Journal of the American Chemical Society (2016). DOI: 10.1021/jacs.6b06250
News Article | November 2, 2016
The team developed an all-fiber laser, constructed similarly to a fiber-optic cable. The key component is a glass tube, whose core is doped with atoms that act as a gain medium—a material from which energy is transferred to boost the output power of the laser—through which light particles, or 'photons', travel. The doping atoms are selected according to the specific wavelengths of light that they will absorb, store and then release, creating an efficient, controllable output beam. "To date, most tunable all-fiber pulsed lasers achieve a maximum tuning range of about 50 nanometers," says Xia Yu from the A*STAR Singapore Institute of Manufacturing Technology, who worked on the project with her team and her collaborator Qijie Wang from Nanyang Technological University. "We have achieved a widely-tunable laser in the mid-infrared wavelength band, with a range of 136 nanometers (from 1,842 to 1,978 nanometers). We used thulium as the doping atom; this generates a laser that operates in the eye-safe range, meaning it could have medical and military applications." The researchers combined two techniques to create their laser and ensure the output was tunable. They used nonlinear polarization evolution, a filtering effect that picks out pulses of light at the desired wavelength and channels them into the output beam. This simultaneously ensures that the output can be adjusted to a specific wavelength while generating ultrafast pulsed light. They also used bidirectional pumping—injecting energy into the gain medium from both ends of the fiber—to ensure a high optical power for as wide a range of wavelengths as possible. The gain occurs when thulium ions are excited to higher-energy states; they then release more photons when they return to lower-energy states. "This is the state-of-the-art, widely-tunable all-fiber laser with pulsed output at this wavelength," says Yu. "We have shown that every parameter, from the pumping scheme to the use of nonlinear polarization evolution, is critical to the final output." Yu's team believe that their simple, inexpensive and compact laser could one day be used in combination with high power amplifiers to generate other forms of laser, including extreme ultraviolet and soft X-ray beams. Explore further: Researchers nearly double the continuous output power of a type of terahertz laser
Genevet P.,Harvard University |
Genevet P.,Singapore Institute of Manufacturing Technology |
Capasso F.,Harvard University
Reports on Progress in Physics | Year: 2015
In this article, we review recent developments in the field of surface electromagnetic wave holography. The holography principle is used as a tool to solve an inverse engineering problem consisting of designing novel plasmonic interfaces to excite either surface waves or free-space beams with any desirable field distributions. Leveraging on the new nanotechnologies to carve subwavelength features within the large diffracting apertures of conventional holograms, it is now possible to create binary holographic interfaces to shape both amplitude phase and polarization of light. The ability of the new generation of ultrathin and compact holographic optical devices to fully address light properties could find widespread applications in photonics. © 2015 IOP Publishing Ltd.
Zhang X.,Singapore Institute of Manufacturing Technology
Journal of Luminescence | Year: 2010
In this paper, ligand effect of several bi-dental oxygen (O) and nitrogen (N) ligands on the red luminescence properties of europium ion (Eu3+) was studied comprehensively. Absorption, emission, and excitation spectral properties of ternary europium complexes with different combinations of ligands including thenoyl trifluoroacetone (TTA), naphthyl trifluoroacetone (NTA), 2,2′-bipyridyl (bpy) and phenanthroline (Phen) were investigated. Efficient Eu3+ red emission was observed with all the combinations of the above mentioned ligands. The most intense emission was found with the all nitrogen coordinated complex Eu(bpy)2(Phen)2 while the longest wavelength excitation band was recorded with oxygen-nitrogen mixed NTA-bpy complex Eu(NTA)1(bpy)3. With change of the ligands combination and ratio, the Eu3+ emission peak changes slightly from 612 to 618 nm. The absorption and excitation spectra of the europium complexes were compared and analyzed referring to the individual absorption spectral properties of the ligands. The relation between ligand-to-metal charge transfer states and luminescence intensities for different complexes was studied. © 2010 Elsevier B.V. All rights reserved.
Ko J.H.,Singapore Institute of Manufacturing Technology
International Journal of Machine Tools and Manufacture | Year: 2015
This article proposes a time domain model for predicting an end milling stability considering process damping caused by a variety of cross edge radiuses and flank profiles. The time domain model of calculating indentation areas, as well as regenerative dynamic uncut chips, is formulated for the prediction of the stabilizing effect induced by interference areas between the edge profiles and undulation left on a workpiece. The interference area generates forces against the vibration motion, which acts as a damping effect. In the model, the present and previous angular position of cross radiuses and flank edge profiles are located to calculate the dynamic uncut chip as well as indentation area based on a time history of the dynamic cutter center position. The phenomenon that chatter is damped according to cross edge radiuses and flank edge profiles is successfully simulated with the proposed dynamic model and validated through the extensive experimental tests. © 2014 Elsevier Ltd. All rights reserved.
Liu T.,Singapore Institute of Manufacturing Technology
NDT and E International | Year: 2012
All traditional CT reconstruction algorithms define the reconstruction slices as perpendicular to the axis of rotation. This leads to a significant inefficiency when reconstructing and visualizing multilayered planar objects such as stacked IC and MEMS devices. This paper reports an alternative solution to the planar CT reconstruction technologies that are published previously, based on a modified version of the widely used FDK cone-beam reconstruction algorithm. The present method distinguishes itself to the existing planar CT technologies and all other traditional CT reconstructions by defining the reconstruction slices along the exact orientation of the planar object in the scan. This new method still possesses the advantages of the previous planar CT technologies such as efficient reconstruction in terms of computation time and resources saving, higher reconstruction resolution in preferred direction, easy visualization, and so on. But it also has better performance than the existing ones by providing an analytical solution to the low-efficiency problem of the traditional FDK algorithm, further reducing the reconstruction volume, and eliminating the interpolation error induced by an image rotation process that is required by the previous planar CT methods. © 2011 Elsevier Ltd. All rights reserved.
News Article | February 22, 2017
Hyperlens devices—composed of thin stacks of alternate metal and plastic layers—have raised prospects for capturing living biological processes in action with high-speed optics. Key to their operation are oscillating electrons, known as surface plasmons, that resonate with and enhance evanescent waves that appear when photons strike a solid object. The narrow wavelengths of evanescent beams give nanoscale resolution to images when the hyperlens propagates the images to a standard microscope. Mass-production of current hyperlenses has stalled however because of their intricate fabrication— up to 18 different layer depositions may be required, each with stringent requirements to avoid signal degradation. "For perfect imaging, these layers need precisely controlled thickness and purity," says Linda Wu, from the A*STAR Singapore Institute of Manufacturing Technology. "Otherwise, it's hard to magnify the object sufficiently for a conventional microscope to pick up." Wu and her co-workers proposed a different type of hyperlens that eliminates the need for multiple interfaces in the light propagation direction—a major source of energy loss and image distortion. The team's concept embeds a hemispherical array of nanorods into a central insulating core, giving the hyperlens a shape similar to a thorny sea urchin. This geometry enables more efficient harvesting of evanescent waves, as well as improved image projection. "For the sea urchin geometry, the nano-sized metallic structures align in the same direction of the light propagation direction, and they are much smaller than the wavelength of applied infrared light," explains Wu. "Therefore the light doesn't 'see' any obstacles, and propagates effectively and naturally, without loss." The researchers' simulations revealed the spiky hyperlens could separate the complex wave information into its component frequencies, and then transmit this data to the microscope as an intense, easy-to-spot band. This approach was also efficient – it proved capable of resolving intricate objects, 50 to 100 nanometers wide, without the need for image post-processing. Wu notes that fabricating sea urchin hyperlenses should be much simpler than multi-layered structures. "The nano-sized metallic structures could be formed using pores and templates into flexible lenses, with no real size limitations," she says. "This hyperlens could be an important tool for real-time bio-molecular imaging." Explore further: Goal of nanoscale optical imaging gets boost with new hyperlens More information: Ankit Bisht et al. Hyperlensing at NIR frequencies using a hemispherical metallic nanowire lens in a sea-urchin geometry, Nanoscale (2016). DOI: 10.1039/c5nr09135g
News Article | April 7, 2016
A more accurate method of modeling heat generation and transfer in electromagnetic machines could lead to more efficient electric motors An improved method to track and control heat generation in electric motors for cars, or power generators, such as those in wind turbines, has been developed by A*STAR researchers in collaboration with colleagues from the UK. The scientists devised a numerical model that can predict the thermal properties of these energy conversion machines, which includes heat transfer across multiple device components (see image). For permanent magnet electric machines, a precise knowledge of the temperature distribution is important, as excessively high temperatures can degrade their magnets and electrical windings, and can even lead to a complete failure of the machine. A detailed understanding of heat creation and distribution is crucial for their design, says Jonathan Hey, from the A*STAR Singapore Institute of Manufacturing Technology (SIMTech) who conducted the study along with colleagues from the Imperial College, London. “These machines are often constructed from an assembly of multiple components, and complex heat transfer mechanisms between the components make it difficult to model the process accurately.” Previous models either have modeled heat conduction within individual components, or studied heat convection on a larger device scale, but failed to consider the specifics of heat transfer across individual component parts. To solve the issue of simulating the heat transfer between components, the model added a virtual thin material between the simulated parts. A mathematical optimization process was used to determine the thermal properties of the virtual thin material such that it best describes the heat transfer across the interface. Other components of the machines, such as the heat generated by the permanent magnet, are modeled using a similar inverse modeling method. The computations reveal that the imperfect contacts between components contribute considerably to the thermal properties of the entire machine. However, by including the modeled interfaces into the simulation, and by using experimentally determined parameters, the numerical modeling technique achieves a realistic model of the heat distribution. The model is so accurate that it differs to the measured one by a mere 2.4 percent. In future research, the goal is to apply this model to machines of different size and configuration, adds Hey. “Part of the development is to translate the modeling technique into a software tool that can be used by a machine designer. Such a software tool could improve the power density and reliability of next-generation high-performance electric machines.” Using these computer models, the software tool could reliably model the properties of a broad range of devices, and therefore help develop prototypes of more efficient energy generation machines. The A*STAR-affiliated researchers contributing to this research are from the Singapore Institute of Manufacturing Technology Citation: Hey, J., Malloy, A.C, Martinez-Botas, R. & Lamperth, M. Conjugate heat transfer analysis of an energy conversion device with an updated numerical model obtained through inverse identification. Energy Conversion and Management 94, 198–209 (2015).| Article