Name: How to squeeze electricity out of crystals - Ashwini Bharathula
Uploaded: 2020-07-03T06:11:02.000Z
Duration: 4 min 56 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

If you press on it, it will actually generate its own electricity.

How can this simple crystal  act like a tiny power source?

Piezoelectric materials  turn mechanical stress,

by the physicist Pierre Curie  and his brother Jacques in 1880.

They discovered that if they compressed thin slices of certain crystals,

positive and negative charges would appear on opposite faces.

meant that the compressed crystal could drive current through a circuit,

Running electricity through these crystals made them change shape.

turning mechanical energy into electrical,

But the discovery went uncelebrated for several decades.

The first practical application was in sonar instruments

used to detect German submarines during World War I.

Piezoelectric quartz crystals  in the sonar's transmitter

vibrated when they were subjected to alternating voltage.

That sent ultrasound waves through the water.

Measuring how long it took these waves to bounce back from an object

converting mechanical energy  to electrical,

consider the lights that turn on when you clap.

Clapping your hands send sound vibrations through the air

and causes the piezo element to bend back and forth.

This creates a voltage that can drive enough current to light up the LEDs,

though it's conventional sources  of electricity that keep them on.

and how electric charge is distributed within it.

arranged in an orderly  three-dimensional pattern.

That pattern has a building block called a unit cell

In most non-piezoelectric  crystalline materials,

the atoms in their unit cells are distributed symmetrically

But some crystalline materials don't possess a center of symmetry

making them candidates  for piezoelectricity.

a piezoelectric material  made of silicon and oxygen.

The oxygens have a slight negative charge and silicons have a slight positive,

Normally, these dipoles  cancel each other out,

so there's no net separation of charge in the unit cell.

But if a quartz crystal is squeezed along a certain direction,

Because of the resulting asymmetry in charge distribution,

the dipoles no longer cancel each other out.

The stretched cell ends up with a net negative charge on one side

This charge imbalance is repeated all the way through the material,

and opposite charges collect on opposite faces of the crystal.

This results in a voltage that can drive electricity through a circuit.

Piezoelectric materials can  have different structures.

But what they all have in common is unit cells which lack a center of symmetry.

And the stronger the compression on piezoelectric materials,

Stretch the crystal, instead, and the voltage will switch,

More materials are piezoelectric than you might think.

all have this ability to turn mechanical energy into electrical.

Scientists have created a variety of synthetic piezoelectric materials

and found applications for them in everything from medical imaging

Piezoelectricity is responsible for  the rhythmic oscillations

of the quartz crystals that keep watches running on time,

and the spark that ignites the gas  in some barbecue grill lighters

And piezoelectric devices may become even more common

since electricity is in high demand and mechanical energy is abundant.

There are already train stations that use passengers' footsteps

and a dance club where piezoelectricity helps power the lights.

Could basketball players running back and forth power the scoreboard?

Or might walking down the street charge your electronic devices?

Subtitles ListPlay Video

How to squeeze electricity out of crystals - Ashwini Bharathula

phenomenon

material

reveal

stretch