Motorola has found a way to make the keypad on a cellphone give tactile feedback without wasting space on bulky vibration motors (patent application EP 1503272).
The company’s answer is to coat the phone’s buttons with an electroactive polymer – a soft rubber with carbon nanotubes embedded in it. Applying a voltage induces stresses and strains in the bonds between the nanotubes and the rubber molecules, which can be felt. In Motorola’s phone, the keys are fed a varying voltage that makes them vibrate gently to give tactile feedback.
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