A team of Japanese engineers has come up with a way of blocking mobile phone signals using wood panels containing magnetic material.

The panels would be useful in cinemas, theatres, or anywhere where ringing mobile phones cause exasperation.

They work by sandwiching a layer of nickel-zinc ferrite between thin slices of wood, New Scientist magazine reports.

The magnetic ferrite absorbs much of the energy of the radio signal, cutting the phone dead in most cases.

Stopping power

Hideo Oka and his colleagues at Iwata University in Morioka, Japan, tested the composite panels by placing them over antennae used to transmit radio signals at frequencies typical for GSM mobiles, Bluetooth and Wi-Fi computer networks.

He chose wood as a natural material which could be used for furnishing.

Tests showed a four-millimetre sandwich of wood and ferrite stopped 97% of the power of a test microwave signal.

Mr Oka hopes the shielding panels will eventually be sold in hardware stores.

They could be used to build doors, walls and rooms in which it would be impossible to carry out a mobile phone conversation.

They might also be useful to shield wireless computer networks from each other.

Mr Oka told New Scientist he wanted to make the panels cheaply and cut their cost even further by using recycled materials.

In many public places in Japan - such as trains and cinemas - customers are asked to switch off their mobile phones or put them on silent tone. However, until now, there has been no way of enforcing silence.