Super-Skinny, Metal Filaments Best Shields Against Electromagnetic Radiation

BUFFALO, N.Y. -- As cellular telephones and all kinds of electronic systems become ubiquitous, the problem of electromagnetic interference increasingly concerns manufacturers.

Radiofrequency waves from wireless devices, such as cellular phones, tend to interfere with those from digital computers and devices, such as calculators. That can result in problems ranging from minor disruptions in electronic performance to disastrous losses of information.

Those problems are being addressed by engineers at the University at Buffalo who have developed a new material out of skinny, nickel filaments that provides better shielding against electromagnetic interference than any materials currently on the market.

A patent application has been filed.

The UB researchers have developed a composite material in which skinny, nickel-coated carbon filaments are embedded in a polymer matrix.

By reflecting and absorbing radiation, composite materials can shield electronic systems from electromagnetic interference.

The researchers note that when filaments are used in these materials, they are most effective when they are very thin and demonstrate low electrical resistivity.

"By using nickel to coat carbon filaments that are less than a micron -- one millionth of a meter -- in diameter, we have developed skinny filaments that shield as effectively as solid copper," said Deborah D.L. Chung, Ph.D., professor of mechanical and aerospace engineering, Niagara Mohawk Chair of Materials Research at UB, and principal investigator.

The thinnest nickel filaments for shielding materials currently available are 2 microns in diameter.

"We've managed to make these filaments super-skinny," she said, "and at a low price, too, less than $20 per pound."

According to Chung, the higher frequencies of electromagnetic radiation only interact with the near surface region, or the perimeter, of a filament in a shielding material. Therefore, conducting units in the best shielding materials have a high surface area.

A filament with a smaller diameter will be more effective at shielding than a filament with a larger diameter with equal volume, Chung explained.

"Only the outer region of the filament does the shielding, so you get more shielding effectiveness out of the same volume of fiber with a smaller diameter," she said. "The finer diameter of our filament gives it more surface area per unit volume, which makes it more effective."

The filaments comprise seven percent of the total volume of the composite material developed by the UB researchers.

The material shields at an electromagnetic frequency of 1 Gigahertz (GHz), or one billion cycles per second, in contrast to the frequency of 60 cycles per second found in household electrical outlets, of 90 dB (decibels of radiation attenuation). In other words, Chung explained, what does get transmitted is only one billionth of the electromagnetic power, with the rest being absorbed or reflected.

In comparison, nickel filaments considered state-of-the-art today shield at about 1GHz of 60 dB with seven percent volume.

Another advantage of Chung's skinny filaments is the method used to make them.

She explained that in order to get the 2-micron filaments down to the diameter of the new filaments, they would have to undergo expensive processes, such as metal-working and melt-drawing.

The skinny nickel filaments developed at UB are created by taking very thin carbon filaments and coating them with nickel in an electroplating bath, a common and inexpensive industrial practice.

The result is a filament with 94 percent volume nickel and six percent volume carbon.

The filaments are embedded in polymer matrices, the plastic material that houses electronic systems, from calculators to cellular phones.

Chung conducted the research with UB doctoral candidate Xiaoping Shui. The work was supported by the Defense Department's Advanced Research Projects Agency and the UB Center for Electronic and Electro-Optic Materials.