Filter promises better cellphone performance

West Lafayette, Ind. – Researchers have developed a new type of band-pass filter for use in cellphones and other devices.

The new resonators – tiny mechanical devices containing vibrating, hair-thin structures – vibrate in specific patterns, and are therefore able to cancel out certain frequencies and allow others to pass, improving transmission efficiency. Incoming signals generate voltage to produce the electrostatic force that causes the vibration.

The band-pass filter design promises higher performance than previous technology because it more sharply defines which frequencies can pass and which are rejected. The new design may also be more robust.

Jeffrey Rhoads, an assistant professor of mechanical engineering at Purdue University, said it represents a potential way to further miniaturize band-pass filters while improving their performance and reducing power use.
The devices are made of silicon and are manufactured using a “silicon-on-insulator” procedure commonly used in the electronics industry to make computer chips and electronic circuits. The small, vibrating mechanical structures contain beams about 10 microns in diameter, which can be connected mechanically, like tiny springs, or linked using electric fields and magnetic attractions.

Researchers have previously proposed linking the beams in straight chains, but Rhoads has pursued a different approach, arranging the structures in rings and other shapes. One prototype resembles spokes attached to a wheel’s hub, and is about 160 microns in diameter.

In addition to their use as cell phone filters, such resonators could also could be used for advanced chemical and biological sensors in medical and military applications – even, says Rhoads, for a new type of “mechanical memory element” that harnesses vibration patterns to store information.

“The potential computer-memory application is the most long term and challenging,” Rhoads said. “We are talking about the possibility of creating complex behaviors out of relatively simple substructures.”

Findings are detailed in a research paper to be presented on September 2 during the American Society of Mechanical Engineers’ Third International Conference on Micro and Nano Systems.