Rahul Sarpeshkar - Drawing inspiration from nature to build a better radio
New radio chip mimics human ear, could enable universal radio
Anne Trafton, News Office
June 3, 2009
MIT engineers have built a fast, ultra-broadband, low-power radio chip,
modeled on the human inner ear, that could enable wireless devices
capable of receiving cell phone, Internet, radio and television signals.
Rahul Sarpeshkar, associate professor of electrical engineering and
computer science, and his graduate student, Soumyajit Mandal, designed
the chip to mimic the inner ear, or cochlea. The chip is faster than any
human-designed radio-frequency spectrum analyzer and also operates at
much lower power.
"The cochlea quickly gets the big picture of what's going on in the sound
spectrum," said Sarpeshkar. "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 to be published 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.
Copying the cochlea
The RF cochlea mimics the structure and function of the biological cochlea,
which uses fluid mechanics, piezoelectrics and neural signal processing to
convert sound waves into electrical signals that are sent to the brain.
As sound waves enter the cochlea, they create mechanical waves in the cochlear membrane and the fluid of the inner ear, activating hair cells (cells
that cause electrical signals to be sent to the brain). The cochlea can
perceive a 100-fold range of frequencies -- in humans, from 100 to 10,000
Hz. Sarpeshkar used the same design principles in the RF cochlea to create
a device that can perceive signals at million-fold higher frequencies, which
includes radio signals for most commercial wireless applications.
The device demonstrates what can happen when researchers take
inspiration from fields outside their own, says Sarpeshkar.
"Somebody who works in radio would never think of this, and somebody
who works in hearing would never think of it, but when you put the two
together, each one provides insight into the other," he says. For example, in
addition to its use for radio applications, the work provides an analysis of
why cochlear spectrum analysis is faster than any known spectrum-analysis
algorithm. Thus, it sheds light on the mechanism of hearing as well.
The RF cochlea, embedded on a silicon chip measuring 1.5 mm by 3 mm,
works as an analog spectrum analyzer, detecting the composition of any
electromagnetic waves within its perception range. Electromagnetic waves
travel through electronic inductors and capacitors (analogous to the
biological cochlea's fluid and membrane). Electronic transistors play the role
of the cochlea's hair cells.
The analog RF cochlea chip is faster than any other RF spectrum analyzer
and consumes about 100 times less power than what would be required for direct digitization of the entire bandwidth. That makes it desirable as a
component of a universal or "cognitive" radio, which could receive a broad
range of frequencies and select which ones to attend to.
This is not the first time Sarpeshkar has drawn on biology for inspiration in
designing electronic devices. Trained as an engineer but also a student of
biology, he has found many similar patterns in the natural and man-made
worlds (http://www.rle.mit.edu/avbs). For example, Sarpeshkar's group, in
MIT's Research Laboratory of Electronics, has also developed an analog
speech-synthesis chip inspired by the human vocal tract and a novel
analysis-by-synthesis technique based on the vocal tract. The chip's
potential for robust speech recognition in noise and its potential for voice
identification have several applications in portable devices and security
The researchers have built circuits that can analyze heart rhythms for
wireless heart monitoring, and are also working on projects inspired by
signal processing in cells. In the past, his group has worked on hybrid
analog-digital signal processors inspired by neurons in the brain.
Sarpeshkar says that engineers can learn a great deal from studying
biological systems that have evolved over hundreds of millions of years to
perform sensory and motor tasks very efficiently in noisy environments while
using very little power.
"Humans have a long way to go before their architectures will successfully
compete with those in nature, especially in situations where ultra-energyefficient
or ultra-low-power operation are paramount," he said. Nevertheless,"We can mine the intellectual resources of nature to create devices useful to
humans, just as we have mined her physical resources in the past.
A version of this article appeared in MIT Tech Talk on April 15, 2009. MIT News article with video.