Scientists discover crystal that records / repeats sound...

[Guest guest]

Hi All,

 

Hope this is okay to post here - as it is SO fascinating & crystal-

related, thought you all would enjoy it (from Rense.com)...

 

Hugs

Jan

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Rense.com

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Scientists Discover Crystal

Remembers, Repeats Sounds

By Philip Ball

Nature.com

9-26-2

 

Scientists have discovered a crystal that answers back. They sent a

sound wave into the material, there was a quiet pause, then it

suddenly emitted the same sound.

 

The material, lithium niobate, is used in information technology. Its

acoustic memory might help manufacturers to assess crystal quality,

suggest its discoverers, Mack Breazeale and co-workers at the

University of Mississippi.

 

This acoustic quirk of lithium niobate might be connected to its

other unusual and useful electrical properties. It is piezoelectric,

producing an electric field when squeezed, and electric fields change

the way light passes through it. This makes it suitable for use in

fibre-optic telecommunications and holographic memories, where laser

beams read information in and out.

 

Each lithium niobate crystal is a patchwork of so-called

ferroelectric domains. Breazeale's team suspects that the frequency

of the delayed echoes a crystal produces is related to the size of

these domains, which determine the material's suitability for various

applications.

 

Sound idea

 

Lithium niobate seems to store acoustic energy temporarily, rather

like a compressed spring stores mechanical energy.

 

How is not clear, but the researchers reckon the acoustic wave

squeezes the material as it passes through. This produces electric

fields within the crystal, which in turn move the electrically

charged atoms that the solid contains - just as a breeze passing

through a cornfield stores energy by bending all the stems.

 

When the acoustic input stops, the ions move back, but not all in the

same direction - the movement is divided into domains, separated by

boundaries where the direction changes.

 

As the ions spring back, they release the stored energy as a delayed

acoustic wave. This causes each domain to ring like a bell. The

strongest echo corresponds to the resonant frequency of the domains,

which, like that of a bell, depends on size.

 

 

References McPherson, M. S., Ostrovskii, I. & Breazeale, M. A.

Observation of acoustical memory in LiNbO3. Physical Review Letters,

89, 115506, (2002). |Article|

© Nature News Service / Macmillan Magazines Ltd 2002

http://www.nature.com/nsu/020916/020916-19.html

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