The laptop talks!

Liquid crystals produce sounds. Will we have tiny speakers?

Published: Tuesday 30 November 1999

for their unique optical properties, liquid crystals are finding increasing applications in displays of computer laptops, flat-screen televisions and other products. Now, physicists Jay S Patel and Y J Kim of the Pennsylvania State University, usa , report acoustic properties of liquid crystals. The duo discovered that during electrical switching of liquid crystals, they give out sound waves that can be heard by the human ear.

Potential uses of this novel phenomenon include tiny speakers and circuit components. Though these applications could still be sometime into the future, the researchers feel that they have discovered a new area of research that might lead to a better understanding of molecular dynamics in liquid crystals.

Liquid crystals -- their very name is an oxymoron -- blend structures and properties of the usually disparate liquid and crystalline solid states. Liquids can flow, while solids cannot. And crystalline solids possess special symmetry properties that liquids lack. As ice melts to water, ordinary solids melt into ordi nary liquids as the temperature increases. Between the crystalline solid at low temperatures and the ordinary liquid state at high temperatures lies an intermediate state: the liquid crystal.

Liquid crystals flows like liquids and displays symmetries inherited from crystalline solids. Most liquid crystals consist of rod-shaped molecules with the ability to polarise light. This amazing property is what makes them useful: an applied voltage lines up the rods and shuts off or turns on transmitted light. What Patel and Kim found was that on applying an electrical voltage to a particular kind of crystal, it switches from one state to another, accompanied by a faint sound ( Applied Physics Letters , Vol 75, No 13).

The researchers say the energy imparted to the rod-shaped molecules in turn causes the cavity in which the liquid crystal resides to vibrate, which can be heard by the unaided ear. The same phenomenon applies to a string instrument like the sitar, in which the vibration of the string causes the cavity to resonate.

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