Hearing Microwaves

Listening out for mysterious microwave messages - The Telegraph

The BT Tower, originally the Post Office Tower, opened in 1965 and, for many years, exchanged microwave messages with its partners across the UK, using a collection of dishes, horns and trumpets. In these digital days of fibre optics and satellites, that technology is out of date. It is deaf to the microwaves that still criss-cross the capital, because, over the past weeks, its transmitters and receivers have been stripped off on safety grounds. It is now the Pointless Tower of London.

We have an unexpected aural talent: the ability to sense bursts of microwave energy as if they are sounds. The odd illusion was first reported during the Second World War by people working close to radar transmitters who claimed to hear mysterious noises or even messages from within their own heads. Patients inside a magnetic resonance imaging machine, with powerful and pulsing microwaves, sometimes complain of the same thing – and their own bodies, too, are acting as receivers.

The effect does not arise through the normal mechanisms of hearing. Instead, the energy of the waves heats up soft tissues in the head by a fraction of a degree. As the flesh expands and contracts with each burst of wave energy, it sends physical pulses through the bone. These travel to the inner ear, the section that transforms the vibrations of a liquid into nerve impulses. That structure is fooled by the signal and interprets it as a normal sound; a click for a single pulse, or a note or even a tune if a series arrives in rapid succession.