Knock on wood [cell-phone jamming device]

TLDR: Oda et al. as mentioned in this paper used wood magnetic material to panel a room to shield it from cell-phone signals in order to provide a "quiet zone" for restaurant or theater owners.

Abstract: Some time ago, actor Laurence Fishburne interrupted a Broadway performance to give a piece of his mind to a member of the audience whose cell phone had gone off during the show. I am sure that, at one point or another, you have been similarly annoyed in a public place by an inconsiderate cell-phone user. How can a restaurant or theater owner provide a "quiet zone" for its customers? IEEE member Hideo Oda of Iwate University (Japan) and his colleagues have been perfecting another line of defense against irresponsible cell-phone users in public places. Based on a patented design, wood magnetic material (1994), Dr. Oda's magnetic wood can be used to panel a room to shield it from cell-phone signals. The Japanese investigators settled on wood because "it offers more natural, aesthetic options to interior design".