Department+of+Materials+Science+and+Engineering
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Extremely Thin and Highly Flexible Graphene-Based Thermoacoustic Speakers
A joint research team led by Professors Jung-Woo Choi and Byung Jin Cho of the School of Electrical Engineering and Professor Sang Ouk Kim of the Material Science and Engineering Department, all on the faculty of the Korea Advanced Institute of Science and Technology (KAIST), has developed a simpler way to mass-produce ultra-thin graphene thermosacoustic speakers.
Their research results were published online on August 17, 2016 in a journal called Applied Materials & Interfaces. The IEEE Spectrum, a monthly magazine published by the Institute of Electrical and Electronics Engineers, reported on the research on September 9, 2016, in an article titled, “Graphene Enables Flat Speakers for Mobile Audio Systems.” The American Chemical Society also drew attention to the team’s work in its article dated September 7, 2016, “Bringing Graphene Speakers to the Mobile Market.”
Thermoacoustic speakers generate sound waves from temperature fluctuations by rapidly heating and cooling conducting materials. Unlike conventional voice-coil speakers, thermoacoustic speakers do not rely on vibrations to produce sound, and thus do not need bulky acoustic boxes to keep complicated mechanical parts for sound production. They also generate good quality sound in all directions, enabling them to be placed on any surface including curved ones without canceling out sounds generated from opposite sides.
Based on a two-step, template-free fabrication method that involved freeze-drying a solution of graphene oxide flakes and the reduction/doping of oxidized graphene to improve electrical properties, the research team produced a N-doped, three-dimensional (3D), reduced graphene oxide aerogel (N-rGOA) with a porous macroscopic structure that permitted easy modulation for many potential applications.
Using 3D graphene aerogels, the team succeeded in fabricating an array of loudspeakers that were able to withstand over 40 W input power and that showed excellent sound pressure level (SPL), comparable to those of previously reported 2D and 3D graphene loudspeakers.
Choong Sun Kim, the lead author of the research paper and a doctoral student in the School of Electrical Engineering at KAIST, said:
“Thermoacoustic speakers have a higher efficiency when conducting materials have a smaller heat capacity. Nanomaterials such as graphene are an ideal candidate for conductors, but they require a substrate to support their extremely thinness. The substrate’s tendency to lose heat lowers the speakers’ efficiency. Here, we developed 3D graphene aerogels without a substrate by using a simple two-step process. With graphene aerogels, we have fabricated an array of loudspeakers that demonstrated stable performance. This is a practical technology that will enable mass-production of thermosacoustic speakers including on mobile platforms.”
The research paper is entitled “Application of N-Doped Three-Dimensional Reduced Graphene Oxide Aerogel to Thin Film Loudspeaker.” (DOI: 10.1021/acsami.6b03618)
Figure 1: A Thermoacoustic Loudspeaker Consisted of an Array of 16 3D Graphene Aerogels
Figure 2: Two-step Fabrication Process of 3D Reduced Graphene Oxide Aerogel Using Freeze-Drying and Reduction/Doping
Figure 3: X-ray Photoelectron Spectroscopy Graph of the 3D Reduced Graphene Oxide Aerogel and Its Scanning Electron Microscope Image
2016.10.05 View 11867 -
President Steve Kang of KAIST Attends the 2014 Summer Davos Forum in Tianjin, China
President Steve Kang of KAIST will attend the 2014 Annual Meeting of the New Champions, the World Economic Forum (WEF), to be held on September 10-12, 2014 in Tianjin, China.
KAIST holds its own IdeasLab session on nanotechnology on September 12, 2014.
On September 10, 2014, President Steve Kang will participate in a private session hosted by the Global University Leaders Forum (GULF) community at WEF as a panelist.
In addition to President Kang, eight presidents from top global universities such as the National University of Singapore, Peking University, ETH Zurich (Swiss Federal Institute of Technology), University of Tokyo, and Carnegie Mellon University will join the panel discussion under the topic, “Increasing the Translational Impact of University Research.” Specifically, the presidents will address issues related to the importance of university-led technology transfer in Asia, key strategies and goals for technology transfer, and implementation approaches taken by each university to promote technology transfer from university to industry.
President Kang was invited to this GULF session, the only attendant from Korean universities, in recognition of his long time experience and expertise in education and research.
In 2006, WEF created the GULF, a small community of the presidents of top universities in the world, aiming to offer an open platform for high-level dialogues on issues of higher education and research with other sectors, as well as to foster collaboration between universities in areas of significance for global policy.
As of 2014, a total of 25 globally leading universities, including Harvard University, University of Cambridge, and Massachusetts Institute of Technology, are GULF members. KAIST, which joined the club this year, is the only Korean university.
The 2014 Annual Meeting of the New Champions, also known as the Summer Davos Forum, hosts numerous sessions under the theme of “Creating Value through Innovation.” At the Forum, a total of ten IdeasLab sessions will be hosted. KAIST was invited to run its own IdeasLab on nanotechnology on September 12, 2014.
Together with President Kang, Professors Sang Ouk Kim and Keon Jae Lee from the Department of Materials Science Engineering, KAIST, and Professors Sang Yup Lee and Hyunjoo Lee from the Department of Chemical and Biomolecular Engineering, KAIST, will present their own speeches on the topic entitled “From diagnostics to materials, how is nanotechnology changing lives?”
President Kang will give the opening speech at the KAIST IdeasLab.
He said that an invitation from WEF to join the IdeasLab spoke well for KAIST:
“KAIST is the first and the only Korean university ever invited to run its own IdeasLab at the World Economic Forum. The IdeasLab is an expert group meeting, conducted only by the world’s most prestigious universities and research institutes. At the IdeasLab sessions, global leaders from different sectors identify major issues facing higher education and humanity and explore solutions through science and technology innovation. Holding our own IdeasLab on one of our strongest fields, nanotechnology, is indeed an excellent opportunity for KAIST to show its strength in academic and research excellence on the global stage.”
2014.09.08 View 12659 -
News Article on the Development of Synthesis Process for Graphene Quantum Dots
Before It's News, an international online news agency, highlighted the recent research conducted by KAIST professors (Seokwoo Jeon of the Department of Materials Science and Engineering, Yong-Hoon Cho of the Department of Physics, and Seunghyup Yoo of the Department of Electrical Engineering) on the development of synthesis process for graphene quantum dots, nanometer-sized round semiconductor nanoparticles that are very efficient at emitting photons. If commercialized, this synthetic technology will lead the way to the development of paper-thin displays in the future.
For the article, please go to the link below:
Before It’s News, September 3, 2014“Graphene quantum dots prove highly efficient in emitting light”
http://beforeitsnews.com/science-and-technology/2014/09/graphene-quantum-dots-prove-highly-efficient-in-emitting-light-2718190.html
2014.09.07 View 11702 -
A KAIST startup, YBrain, builds a wearable device to cure Alzheimer's
A group of KAIST graduates from the Departments of Bio and Brain Engineering, Computer Science, Materials Science Engineering, and Industrial Design created a startup called YBrain (http://ybrain.com/). YBrain develops a wearable neuroscience technology to treat or reduce the symptoms of degenerative brain diseases such as dementia and Alzheimer’s. Their recent technological developments were covered in e27, one of the leading blogs based in Singapore. The blog covers topics like the latest technology innovation, startups, and entrepreneurship in Asia. A news article follows below:
e27, June 24, 2014
“This wearable tech may be able to combat effects of Alzheimer’s”
http://e27.co/this-wearable-tech-may-be-able-combat-effects-of-alzheimers-20140624/
2014.06.25 View 10857 -
Ultra-High Strength Metamaterial Developed Using Graphene
New metamaterial has been developed, exhibiting hundreds of times greater strength than pure metals.
Professor Seung Min, Han and Yoo Sung, Jeong (Graduate School of Energy, Environment, Water, and Sustainability (EEWS)) and Professor Seok Woo, Jeon (Department of Material Science and Engineering) have developed a composite nanomaterial. The nanomaterial consists of graphene inserted in copper and nickel and exhibits strengths 500 times and 180 times, respectively, greater than that of pure metals. The result of the research was published on the July 2nd online edition in Nature Communications journal.
Graphene displays strengths 200 times greater than that of steel, is stretchable, and is flexible. The U.S. Army Armaments Research, Development and Engineering Center developed a graphene-metal nanomaterial but failed to drastically improve the strength of the material.
To maximize the strength increased by the addition of graphene, the KAIST research team created a layered structure of metal and graphene. Using CVD (Chemical Vapor Deposition), the team grew a single layer of graphene on a metal deposited substrate and then deposited another metal layer. They repeated this process to produce a metal-graphene multilayer composite material, utilizing a single layer of graphene. Micro-compression tests within Transmission Electronic Microscope and Molecular Dynamics simulations effectively showed the strength enhancing effect and the dislocation movement in grain boundaries of graphene on an atomic level.
The mechanical characteristics of the graphene layer within the metal-graphene composite material successfully blocked the dislocations and cracks from external damage from traveling inwards. Therefore the composite material displayed strength beyond conventional metal-metal multilayer materials. The copper-graphene multilayer material with an interplanar distance of 70nm exhibited 500 times greater (1.5GPa) strength than pure copper. Nickel-graphene multilayer material with an interplanar distance of 100nm showed 180 times greater (4.0GPa) strength than pure nickel.
It was found that there is a clear relationship between the interplanar distance and the strength of the multilayer material. A smaller interplanar distance made the dislocation movement more difficult and therefore increased the strength of the material. Professor Han, who led the research, commented, “the result is astounding as 0.00004% in weight of graphene increased the strength of the materials by hundreds of times” and “improvements based on this success, especially mass production with roll-to-roll process or metal sintering process in the production of ultra-high strength, lightweight parts for automobile and spacecraft, may become possible.” In addition, Professor Han mentioned that “the new material can be applied to coating materials for nuclear reactor construction or other structural materials requiring high reliability.”
The research project received support from National Research Foundation, Global Frontier Program, KAIST EEWS-KINC Program and KISTI Supercomputer and was a collaborative effort with KISTI (Korea Institute of Science and Technology Information), KBSI (Korea Basic Science Institute), Stanford University, and Columbia University.
A schematic diagram shows the structure of metal-graphene multi-layers. The metal-graphene multi-layered composite materials, containing a single-layered graphene, block the dislocation movement of graphene layers, resulting in a greater strength in the materials.
2013.08.23 View 14260