Researchers at MIT have developed a very energy-efficient loudspeaker the thickness of a sheet of paper. The operation is based on tiny bubbles on a plastic and a piezoelectric layer. The material is simple and cheap to produce, according to the makers.
The loudspeaker developed by MIT weighs 2 grams and has a thickness of 120 micrometers. The sensitivity of the loudspeaker at a voltage of 25 volts is 86dB at a distance of 30 centimeters, regardless of the surface it is mounted on. The sheet needs only 100 milliwatts of power per square meter of surface for its operation.
The speakers can be used for mobile devices, among other things, the researchers think. They are also thinking of applications for the entertainment industry, to be able to immerse users in spatial sound by allowing large surfaces to serve as loudspeakers. They also mention applications for noise cancellation, where thin flexible loudspeakers can be used for anti-noise by canceling out annoying sounds with a reproduction in opposite phase.
Producing large surfaces would not be a problem and could also be done cheaply, the researchers say. They use a laser to make small holes in the layer of plastic. At the back they place a layer of piezoelectric material. By applying heat, the piezoelectric material works its way through the holes and forms bubbles on the other side. Those bumps stick out 15 micrometers and can vibrate up and down half a micrometer to produce sound. The researchers were able to easily test the optimal structure by making smaller or larger holes in the plastic to obtain bubbles of different sizes.
The researchers published their work in EEE Transactions of Industrial Electronics under the title An Ultra-Thin Flexible Loudspeaker Based on a Piezoelectric Micro-Dome Array.