Tech Front: Graphene-Based Light Detectors Add Thermal Vision to Contact Lenses
New research into graphene-based light detectors that can use the full infrared spectrum has the potential to put heat-vision technology into a contact lens or other devices. And unlike the mid- and far-infrared detectors currently on the market, the detector developed by University of Michigan (Ann Arbor, MI) engineering researchers doesn’t require bulky cooling equipment to work.
Thermal imaging is widely used today in military applications for night-vision goggles and cameras, and it’s even made some headway into high-end automotive systems, like the night-vision technology from BMW and other carmakers. Infrared light starts at wavelengths just longer than those of visible red light and stretches to wavelengths up to a millimeter long.
“We can make the entire design super-thin,” said Zhaohui Zhong, University of Michigan assistant professor of electrical and computer engineering. “It can be stacked on a contact lens or integrated with a cell phone.”
Defense applications for the technology include communications, IR imaging and detectors for heat-seeking missiles, said Zhong. “Currently, we are working on making an imaging camera using the graphene photodetector array, and I estimate a prototype camera within the next three years.”
Infrared vision may be best known for spotting people and animals in the dark and heat leaks in houses, but it can be used by doctors to monitor blood flow, to identify chemicals in the environment, or to allow seeing an artist’s original sketch under layers of paint.
Unlike the visible spectrum, which conventional cameras capture with a single chip, infrared imaging requires a combination of technologies to see near-, mid- and far-infrared radiation all at once. The mid-infrared and far-infrared sensors typically need to be at very cold temperatures. Graphene, a single layer of carbon atoms, could sense the whole infrared spectrum—plus visible and ultraviolet light—but until now, it hasn’t been viable for infrared detection because it can’t capture enough light to generate a detectable electrical signal. With one-atom thickness, it only absorbs about 2.3% of the light that hits it, and if the light can’t produce an electrical signal, graphene can’t be used as a sensor.
“The challenge for the current generation of graphene-based detectors is that their sensitivity is typically very poor,” Zhong said. “It’s a hundred to a thousand times lower than what a commercial device would require.”
Zhong and Ted Norris, the Gerard A. Mourou Professor of Electrical Engineering and Computer Science, worked with graduate students to design a new way of generating the electrical signal. Rather than trying to directly measure the electrons that are freed when light hits the graphene, they amplified the signal by looking instead at how the light-induced electrical charges in the graphene affect a nearby current. The device is described in a paper titled “Graphene photodetectors with ultra-broadband and high responsivity at room temperature,” which appears online in the journal Nature Nanotechnology (see http://tinyurl.com/GrapheneDetectors).
The research was supported by the National Science Foundation in part through Michigan Engineering’s Center for Photonic and Multiscale Nanomaterials, and was completed with help from electrical engineering and computer science doctoral students Chang-Hua Liu and You-Chia Chang.
“Our work pioneered a new way to detect light,” Zhong said. “We envision that people will be able to adopt this same mechanism in other material and device platforms.”
Although full-spectrum infrared detection likely will find application into military and scientific applications, it’s still unclear whether it will be used in the electronics market. “If we integrate it with a contact lens or other wearable electronics, it expands your vision,” Zhong said. “It provides you another way of interacting with your environment.”
For more information, go to www.eecs.umich.edu/zhonglab. ME
Laser Process Enables Micro-structural Control of Metals
Thin-film coating developer Picodeon Ltd. Oy (Il, Finland) has developed an ultra-short pulsed laser deposition (USPLD) surface coating technology that can create either porous or dense aluminium oxide (Al2O3) coatings on heat-sensitive substrates for use in a wide range of industrial applications.
Porous Al2O3 layers are used as filters and electrical insulation layers, while dense Al2O3 is used as a barrier layer and as an excellent optical coating with high transmittance properties. The Picodeon process enables precise micro-structural control of Al2O3 coating characteristics with management and maintenance of coating process parameters on Picodeon’s Coldab Series4 USPLD batch-process coating equipment.
“This development has enormous potential for new applications of dense and porous aluminium oxide coatings on heat sensitive materials,” said Marko Mylläri, Picodeon vice president, sales and business development. “It is currently very difficult to achieve these results using physical vapor deposition [PVD], sputtering or chemical vapor deposition [CVD] surface coating technologies.”
Applications include sensors, optical devices, lithium-ion batteries and PLD coatings such as complex oxides used in superconductors. The company’s recently-developed Coldab Series4 equipment has built-in online plasma monitoring and laser power measurement that enable very precise management of coating process parameters, as well as PC-controlled automation that records the actions of the coating process. The metrics provided by these systems mean that the coating process, and especially the thin-film quality, can be controlled with great accuracy to achieve coating characteristics within highly targeted parameters.
Production tests showed that the system could improve the porosity of a 3-µm Al2O3 coating from 10 to 45% by tuning the scanning speed and laser power repetition rate.
For more information, visit www.picodeon.com. ME
Playing with 3D Imaging
Motion-sensing input devices are getting play time in applications far beyond game consoles, as described in two new papers published in the Journal of Manufacturing Systems (JMS) (http://tinyurl.com/d8unzjn). In one paper, fast, high-quality results have been achieved for observation-oriented, silhouette-aware body tracking (http://tinyurl.com/ntjfaj9) using a single-depth camera, for example, MiTech Front: Graphene-Based Light Detectors Add Thermal Vision to Contact Lensescrosoft Kinect, which is for Xbox and Xbox One consoles. The approach fits a 3D morphable human model to an actual body shape, with benefits for virtual try-on, full human body scanning and applications in manufacturing systems.
In another JMS paper, a system for fast capture of a personalized 3D avatar (http://tinyurl.com/p8jzndz) uses two calibrated Kinects to capture three partial scans of a person in a moment’s time (3 sec). The discrepancy between the scans caused by body movement is negligible, saving the effort of nonrigid alignment. The final reconstructed mesh model demonstrates good fidelity against the person with unique details of hairstyle, face and cloth wrinkles.
Modeling Medical Applications
More than 80 papers in the SME Technical Paper library address 3D scanning/imaging and solid modeling topics and applications. As presented at several Rapid events (www.sme.org/rapid), a narrower slice of papers focuses on the compelling potential of these technologies in medical device design, biomedical modeling and medical treatment planning.
Two of the papers deal with imaging for production and customization of medical devices. Authors O. Harrysson, O. Cansizoglu and D. Marcellin-Little in TP09PUB10 discuss how detailed visualization assists manufacturers in choosing a fabrication method, such as laser-based vs. electron beam-based direct metal fabrication, that best fits their needs in terms of build time, surface quality, feature size and cost.
A framework for design and manufacturing optimization of medical devices is outlined in TP09PUB13 by F. McBagonluri, R. Varadarajan and T. Fang. Taking advantage of the broad intersection of art and mathematical modeling in 3D models provides the capability of total virtual product development from concept through launch and delivery to the customer.
Another paper, TP13PUB83 by A. Sirinterlikci, summarizes efforts to streamline the use of biomedical engineering software tools, reverse engineering tools and rapid prototyping systems, in addition to Mastercam and Haas machining tools, for real-world projects designed to improve student preparation for employability in the medical device field. In TP09PUB9, authors G. Grant et al. favorably compare the accuracy of captured images from cone beam computerized tomography with conventional CT images for use with rapid prototyping of models and medical treatment planning software. The authors, from the Naval Postgraduate Dental School (Bethesda, MD), discuss the application of this technology in surgical reconstruction of war-related traumatic head and neck injuries.
TechFront is edited by Senior Editors Patrick Waurzyniak, firstname.lastname@example.org, and Ellen Kehoe, email@example.com.
This article was first published in the May 2014 edition of Manufacturing Engineering magazine. Click here for PDF.
Published Date : 5/1/2014