Smartphones are now the biggest piece of the mobile device market, and users want to download more data every year — sending photos, streaming videos and logging on to social networks. But there’s a limit to the wireless network, the amount of radio spectrum, any given phone carrier such as Verizon or Sprint can offer its customers.
But MIT researchers may have a solution. They built a kind of filter that would allow a radio receiver, like those on a smartphone, for example, to pick out a certain radio frequency easily, while blocking out unwanted noise. That means phones and tablets could use the radio spectrum allotted with less need for “empty” frequencies between channels, as well as hop to signal bands they don’t currently use. (This is one reason phones from the U.S. don’t work in countries like Japan; the radio in the phone isn’t geared to working with the frequency of the local network).
In work to be presented in June at the International Conference on Solid-State Sensors, Actuators and Microsystems, Dana Weinstein, professor of electrical engineering and computer science, and Laura Popa, a graduate student in physics, built a resonator that converts radio signal to vibrations and back to an electrical signal with a gallium nitride transistor.
Resonators are part of every radio-enabled electronic device, and they are the “filters” that allow a phone conversation to be heard without hearing all the other conversations on nearby frequency bands.
Weinstein and Popa’s resonator does a better job of filtering out noise than current technologies. That’s because the switch that turns it on and off is built into the circuit.
All resonators have to be switched on and off with a separate transistor. That switching makes “noise” that degrades the signal quality. The new technology has the transistor built in. So when it turns on and off, there isn’t the noise added to the signal. Since there’s no noise, it’s easier to for it to “hear” higher-frequency radio transmissions.
Most resonators only work with a narrow frequency range. It’s possible to add more resonators to a phone that are tuned to more frequencies, but that means adding more bulk. Gallium nitride is sensitive to a much wider range than conventional materials. And since the whole thing fits on a single processor, the switching between frequencies is faster.
It may be a while before this device is commercially available in a phone, but Weistein told Discovery News that the technology is patented and there’s interest from phone manufacturers and even the Department of Defense. If nothing else, it might mean fewer complaints that crowds of other people are slowing down your favorite movie download.
Weinstein and Popa’s paper will be presented in June at the International Conference on Solid-State Sensors, Actuators and Microsystems, in Barcelona, Spain.
Credit: M. Scott Brauer / MIT