Fujifilm Corp developed a film that can be use as the diaphragm (vibrating plate) of a speaker and unveiled it at nano tech 2013, a trade show that runs from Jan 30 to Feb 1, 2013, in Tokyo.
By using the diaphragm, which Fujifilm calls "Beat," it becomes possible to realize a speaker that can be bent and folded. At the trade show, the company exhibited a slim speaker, retractable speaker and Japanese fan (sensu)-like speaker.
To realize a bendable diaphragm, a soft material is required. However, because soft materials absorb vibration, it is difficult to ensure a flexibility and high acoustic characteristics at the same time. This time, Fujifilm ensured both of them by using a viscoelastic polymer that hardens in the audible range (20Hz to 20kHz) and softens in the range for bending it by hand (several hertz).
Fujifilm mixed the viscoelastic polymer with piezoelectric ceramics to make a piezoelectric composite and packaged it with a protection layer after sandwiching it with electrodes. When a voltage is applied to the electrodes, the piezoelectric ceramics vibrates, and the viscoelastic polymer functions as a diaphragm.
The strain energy generated by bending the film by hand is released as heat, preventing cracks, peel-off, etc. In the audible range, the film keeps an internal loss appropriate for a diaphragm. The viscoelastic polymer was developed based on materials that Fujifilm developed in the past.