ASU Researchers Develop New Filter Technology

Arizona State University announced New research could offer better cell reception at lower cost. The secret is a ceramic filter material developed by Nathan Newman and graduate student Lingtao Liu at ASU's Ira A. Fulton Schools of Engineering that can maintain frequency stability without special cooling. This makes them easier to use in cellphone base stations.

“They need a very precise filter to listen to each particular channel in a very busy network,” Newman said.”The better the quality of those filters, the more cellphones a tower can support. The number of dropped calls also declines as quality goes up.”

Filters are typically made from oxide ceramics, but the oxide ceramics currently used in filters do not have angular rigidity. Newman compared them to a room full of bowling balls.

“If you stood on them, you’d fall right through because the bowling balls slide right past each other,” he said. “As microwaves pass through the filter, atoms in the filter material vibrate against each other and the signal loses energy. But if certain chemicals are substituted, the material becomes stronger. No one knew why until now.”

Newman and Liu found that the special bond acted like Tinker Toys rather than bowling balls.

“Some of the electrons in the inner shells, those that typically do not take part in bonding, transfer from one atom to the other to form rigid structures,” said Newman. “This is called directional d-electroni bonding, similar to the covalent bonds that make diamonds so hard. This finding allowed Newman and Liu to chose the appropriate starting material for the filter and investigate additives to keep the filter on frequency even with temperature changes. Chemicals containing electrons with a magnetic component made the best additive.”

He explained that some of the electrons in the inner shells which do not typically take part in the bonding process can transfer from one atom to the other to create rigid structures. He noted that when this happens, “filter performance jumps to record high levels.”

While the obvious use is in cellphone base stations, as spectrum becomes more congested, better filters are needed in other RF applications, such as defense. “We’ve already started to give them to defense contractors who are going to try and use them for listening beyond our borders,” Newman said. “Right now, the enemy thinks we can only hear so far away, but not if we use super high-performance materials.”

Doug Lung

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.