Shanghai, April 27 (Editor Huang Junzhi) According to media reports recently, engineers at the Massachusetts Institute of Technology (MIT) have developed a speaker as thin as paper that can turn any surface into an active sound source.
This membrane speaker produces very little sound distortion and uses only a fraction of the energy required by conventional speakers.
The team showcased palm-sized speakers that weighed about the equivalent of a dime. No matter what surface the film is glued to, it produces a high-quality sound. To achieve these extraordinary properties, the researchers pioneered a deceptively simple manufacturing technique that involves only three basic steps to make ultra-thin speakers, and that can be large enough to cover the interior of a car or paste wallpaper in a room.
Membrane speakers can provide active noise cancellation in noisy environments, such as the cockpit of an airplane, by producing sound of the same amplitude but opposite phases. This flexible device can also be used for immersive entertainment, perhaps providing three-dimensional audio in a theater or amusement park ride. And, since it is so light that it requires minimal power to operate, the device is well suited for smart devices with limited battery life.
It is understood that in headphones or audio systems, typical speakers use current inputs, which generate a magnetic field through the coil, and the magnetic field can move the speaker film, so that the air above it moves, thereby producing sound. In contrast, this new type of speaker simplifies the design of the loudspeaker by using a molded piezoelectric film material. When a voltage is applied to the film, the film moves, moving the air above it and producing sound.
Specifically, to make such speakers, the researchers used lasers to cut small holes in the SHEET, a lightweight plastic. They laid a very thin piezoelectric material PVDF film (only 8 microns thick) on the bottom of the perforated PET layer. They then apply a vacuum above the bonded flakes and a heat source of 80 degrees Celsius below the flakes.
Since the PVDF layer is too thin, the pressure difference caused by the vacuum and the heat source causes it to expand. PVDF cannot forcibly pass through the PET layer, so in places where there is no PET obstruction, tiny domes protrude. These protrusions can self-align the holes in the PET layer. The researchers then laid another PET layer on the other side of the PVDF as a spacer between the dome and the binding surface.
Instead of making the entire material vibrate, their design relies on tiny domes on a thin layer of piezoelectric material, each vibrating individually. These domes, each only a few hairs wide, are surrounded by spacers at the top and bottom of the film, protecting them from the mounting surface while still allowing them to vibrate freely. The same spacer layer protects the dome from wear and shock during daily operation, enhancing the durability of the speakers.
The researchers say, "It's a very simple, straightforward process. If we can combine it with the roll-to-roll process in the future, we can produce these speakers in a high-throughput way. This means it can be manufactured in large quantities, covering the interior of a wall, car or airplane like wallpaper. ”