Sarpeshkar mimics nature's ear to build new 'RF cochlea'

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June 16, 2009

Associate Professor of Electrical Engineering Rahul Sarpeshkar, left, and Soumyajit Mandal display their RF (radio frequency) cochlea, a low-power, ultra-broadband radio chip. The chip, held by Mandal, is attached to an antenna, held by Sarpeshkar. The diagram on the computer monitor shows the wiring layout of the chip.  Photo / Donna Coveney

Rahul Sarpeshkar, associate professor of electrical engineering and computer science, and his graduate student, Soumyajit Mandal, have designed a chip to mimic the inner ear, known as the cochlea. The chip is faster than any human-designed radio-frequency spectrum analyzer and also operates at much lower power.

In what has become a pattern of understanding nature's sophisticated and highly evolved engineering to improve current human engineering practices, Sarpeshkar and his group at the Analog VLSI and Biological Systems Group, part of the Research Laboratory of Electronics (RLE) have repeatedly taken away lessons learned from studying biological systems to create newly engineered devices. He related to the MIT News Office, for a June 3, 2009 article: "The cochlea quickly gets the big picture of what's going on in the sound spectrum. The more I started to look at the ear, the more I realized it's like a super radio with 3,500 parallel channels."

Sarpeshkar and his students describe their new chip, which they have dubbed the "radio frequency (RF) cochlea," in a paper now appearing in the June issue of the IEEE Journal of Solid-State Circuits. They have also filed for a patent to incorporate the RF cochlea in a universal or software radio architecture that is designed to efficiently process a broad spectrum of signals including cellular phone, wireless Internet, FM, and other signals.

Just as the cochlea perceives a 100-fold range of frequencies through use of fluid mechanics, piezoelectrics and neural signal-processing to convert sound waves into electrical signals sent to the brain, Sarpeshkar and his team have created in the RF cochlea a device that perceives signals at a million-fold higher frequencies, including radio signals for most commercial wireless applications. By embedding the RF cochlea into a silicon chip measuring 1.5mm by 3mm, the device acts as an analog spectrum analyzer, detecting the composition of any electromagnetic waves within its perception range. Analogous to sound waves traveling through the biological cochlea's fluid and membranes in the inner ear, electromagnetic waves travel through electronic inductors and capacitors while electronic transistors play the role of the cochlea's hair cells 'perceiving' and transmitting the signals.

The analog RF cochlear chip is faster than any other RF spectrum analyzer, consuming nearly 100 times less power than required for direct digitization of the entire bandwidth. This fact, makes it a strong candidate as a component in a universal or 'cognitive' radio--one able to receive a broad range of frequencies and selectively focus on specific frequency inputs.

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