MIT engineers have developed a paper-thin loudspeaker that can turn any surface into an audio source.
The thin-film loudspeaker produces sound with minimal distortion while using a fraction of the energy required by a traditional loudspeaker.
The hand-sized loudspeaker, which weighs about as much as a cent, can generate high-quality sound no matter what surface the film is bonded to.
To achieve these properties, the researchers pioneered a deceptively simple fabrication technique, which requires only three basic steps and can be scaled up to produce ultra-thin loudspeakers large enough to cover the inside of an automobile or to wallpaper a room.
Used this way, the thin-film loudspeaker could provide active noise cancellation in clamorous environments, such as an airplane cockpit, by generating sound of the same amplitude but opposite phase; the two sounds cancel each other out.
The flexible device could also be used for immersive entertainment, perhaps by providing three-dimensional audio in a theater or theme park ride.
Because it is lightweight and requires such a small amount of power to operate, the device is well-suited for applications on smart devices where battery life is limited.
“It feels remarkable to take what looks like a slender sheet of paper, attach two clips to it, plug it into the headphone port of your computer, and start hearing sounds emanating from it. It can be used anywhere.
"You just needs a smidgeon of electrical power to run it,” says Vladimir Bulović, the Fariborz Maseeh chair in Emerging Technology, director of MIT.nano, and senior author of the paper.
Magnetic field
Bulović wrote the paper with lead author Jinchi Han, a ONE Lab postdoc, and co-senior author Jeffrey Lang, the Vitesse professor of Electrical Engineering.
A typical loudspeaker found in headphones or an audio system uses electric current inputs that pass through a coil of wire that generates a magnetic field, which moves a speaker membrane, that moves the air above it, that makes the sound we hear.
By contrast, the new loudspeaker simplifies the speaker design by using a thin film of a shaped piezoelectric material that moves when voltage is applied over it, which moves the air above it and generates sound.
Most thin-film loudspeakers are designed to be freestanding because the film must bend freely to produce sound. Mounting these loudspeakers onto a surface would impede the vibration and hamper their ability to generate sound.
To overcome this problem, the MIT team rethought the design of a thin-film loudspeaker. Rather than having the entire material vibrate, their design relies on tiny domes on a thin layer of piezoelectric material which each vibrate individually.
These domes, each only a few hair-widths across, are surrounded by spacer layers on the top and bottom of the film that protect them from the mounting surface while still enabling them to vibrate freely.
The same spacer layers protect the domes from abrasion and impact during day-to-day handling, enhancing the loudspeaker’s durability.
To build the loudspeaker, the researchers used a laser to cut tiny holes into a thin sheet of PET, which is a type of lightweight plastic. They laminated the underside of that perforated PET layer with a very thin film (as thin as 8 microns) of piezoelectric material, called PVDF.
Then they applied vacuum above the bonded sheets and a heat source, at 80 degrees Celsius, underneath them.
You can watch an example of the paper-thin loudspeaker below.
