Engineers at the University of Michigan have micromachined a life-sized cochlea that could one day translate acoustic vibrations into electrical signals the brain would interpret as sound. The device is 3-cm long, as long as a normal cochlea if it were unwound from its spiral.

Sound strikes an input membrane and generates a wave in a fluid-filled duct etched into a silicon chip. The wave interacts with a tapered membrane, separating the sound wave into different frequencies. (This is done by hairs on the cochlea in an organic ear.) The next step will be to hook up an array of sensors to the tapered membrane so that different portions of the membrane send electrical signals to the brain, making the cochlear implant act as a microphone. The engineers would also like to use it with cochlear implants, which take outside sound, convert it to electrical signals, and transmit them inside the cochlea via an array of electrodes.

Researchers say the device has several advantages over other artificial-ear designs. It's life sized, so it should be implantable. It uses conventional semiconductor manufacturing methods, so it can be inexpensively mass-produced. And its mechanical design uses little power to handle acoustic signal processing. The last point also makes the design a candidate for low-power sensors for military and commercial applications.