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MIT Technology Review

Squeal Stopper

A material that expands when voltage is applied could silence an automobile’s brakes.

Brakes-even new ones-are plagued with the problem of squeal, a major cause of consumer complaint and warranty repairs. The exact cause is unclear, but according to one theory, the rotor and pads vibrate from the friction of rubbing together, creating a high-pitched screech that squeal suppression tactics such as replacing the pads don’t always cure. Ken Cunefare, a mechanical engineer at the Georgia Institute of Technology, says he has a better solution: a small cylinder housed inside each brake piston. The device holds several layers of a piezoceramic material that stretches when a voltage is applied across it. Every time the driver hits the brakes, a varying voltage is applied to the device, and the material grows or shrinks a few hundredths of a millimeter-changing the force with which it presses against the steel plate on the back of the brake pad. The pulsing pressure causes the brake to vibrate at a higher, inaudible frequency. Cunefare has done lab tests and is looking for a corporate partner to help him build a second-generation prototype that he could road-test on cars.