The speaker works by rapidly heating and cooling air, and because it doesn’t require a box to create vibrations, it can exist as a flat or even curved surface. Researchers from the Korea Advanced Institute of Science and Technology (KAIST) developed a two-step (freeze-drying and reduction/doping) technique for producing the graphene aerogel. An array of these aerogels was then aligned in a 4x4 configuration to form a 40W speaker. The work, which was supported by the Samsung Research Funding Center for Future Technology and the National Research Foundation of Korea, is described in the journal ACS Applied Materials & Interfaces.
MOF captures hot CO2 from industrial exhaust streams
How much so-called "hot" exhaust could be usefully captured for other heating purposes (domestic/commercial) or for growing crops?