Oka tested each wood in turn by putting collars of each material over a short antenna that broadcasts radio waves at the typical GSM mobile phone frequencies of 900 megahertz and 1.8 gigahertz.Keeping incoming cell phone signals out of cinemas is great for the general public, but even more exciting is the material's potential for insulating a business' wireless network. Is this the end of WarDriving? If the panels become available as widely and cheaply as their creators desire, it just might.
The antenna can also broadcast at frequencies up to 2.5 gigahertz, which covers the range commonly used for wireless networks like Bluetooth and the emerging IEEE 802.11 standard, better known as Wi-Fi. A receiver measured the strength of the radio waves transmitted through the material.
In the end, Oka found that ferrite sandwiched between thin sheets of wood performed best. Further tests showed that a 4-millimetre-thick sandwich absorbed the most microwave radiation, cutting the wave's power by 97 per cent. Increasing the thickness of the outer wooden sheets of the sandwich increased the frequency of radio waves that the shield would absorb.