magnetic wood
n. Wood packed with magnetic particles that absorb microwave radio signals, particularly those emitted by cell phones.

Example Citations:
Americans seeking a legal way to jam cell phones can look into passive jamming technologies. For instance, lining your office in lead should ensure that no signals get in or out. But if lead is too industrial to suit your decor, a more genteel alternative exists: You could install magnetic wood paneling throughout. A Japanese scientist, Hideo Oka, has invented a new kind of building material, saturated with magnetic particles made of nickel-zinc ferrite that supposedly deflect 97 percent of mobile-phone signals.
—David S. Bennahum, "Hope You Like Jamming, Too," Slate Magazine, December 5, 2003

Magnetic wood that silences mobile phones could prevent mobile use in cinemas, restaurants, theatres or anywhere it is installed.
—Michelle Pountney, "Inventions defy belief," Herald Sun (Melbourne, Australia), December 14, 2002

Earliest Citation:
Magnetic wood could be a major plank in the battle against noisy cellphone users. The high-tech material absorbs microwave radio signals, making it impossible to use a mobile phone in any room lined with it. Or a radio for that matter. So theatres and restaurants, for example, can stop people using cellphones on their premises without resorting to signal jammers.
—Ian Sample, "Magnetic wood blocks mobile phone signals," New Scientist, June 27, 2002

The earliest media citation for magnetic wood is from 2002 (see below), but the phrase was in use before that. Here's a excerpt from an abstract of a 1999 technical article that tantalizingly suggests that the concept (if not the phrase) has been around since 1991:

Magnetic wood, wood which demonstrates magnetic characteristics, was introduced by the Oka group in 1991.
—Hideo Oka and Hiromitu Fujita, "Experimental study on magnetic and heating characteristics of magnetic wood," Journal of Applied Physics, April 15, 1999

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