Cellphones that seamlessly work on any network would make lives easier for international travelers. At Cornell University, Alyssa Apsel, PhD ’03, is designing inexpensive, flexible radio systems to help make that possible.
Every country has standardized frequency bands set aside for different forms of radio communication, whether it’s Wi-Fi, cellular, or Bluetooth. The components in today’s radios are designed to work for those specific frequencies.
Spurred by recent research advances, however, manufacturers are slowly moving toward making radios more flexible. Components like amplifiers and mixers are being made reconfigurable so they can operate at different frequencies.
One component that has resisted this transformation is a duplexer: a device that allows radios to both transmit and receive signals at the same time. The emitted signal is usually 1 billion times stronger than the signal being received and would drown out the receiver, so the two signals need to be isolated from each other. But today’s duplexers can only do this at a single frequency. They are also expensive magnetic devices that are notoriously difficult to integrate onto silicon chips along with other radio components.
Apsel has figured out a way to make a duplexer on a chip that can be tuned across a wide range of frequencies. “We completely rearchitected the transmitter and receiver,” she says. A standard radio has a signal power amplifier and a receiver. “We cut the amplifier into pieces and distributed it along the transmission line.” As the staggered amplifier stages emit signals, they add up in one direction and cancel each other out in the other direction so they can be transmitted without interfering with the received signal flowing in the other direction.
Those pieces also add noise, so Apsel and her Cornell collaborators have developed hardware-based methods to suppress the noise. The design could make cellphones less expensive and easy to quickly reprogram so they work anywhere in the world. Apsel was named the new director of the School of Electrical and Computer Engineering at Cornell in January. She takes over that post in July.