How to squeeze electricity out of crystals - Ashwini Bharathula

譯者: Lilian Chiu 審譯者: Ann Chen

This is a crystal of sugar.

這是糖的結晶

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

如果去擠壓它，它會產生出電力

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

為何這麼簡單的結晶 能像小型電源一樣？

Because sugar is piezoelectric.

因為糖有壓電特性

Piezoelectric materials turn mechanical stress,

壓電材料能把機械應力

like pressure,

如壓力

sound waves,

聲波

and other vibrations

及其他振動

into electricity and vice versa.

轉變為電力，反之亦然

This odd phenomenon was first discovered

這個奇特現象最早在

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

1880 年由物理學家皮埃爾·居禮 和他的哥哥雅各發現

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

他們發現，如果他們 擠壓某些結晶的薄片

positive and negative charges would appear on opposite faces.

正電荷與負電荷 會出現在相對的表面上

This difference in charge, or voltage,

電荷或電壓的差異

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

意味著壓縮結晶 可以讓電流透過迴路流動

like a battery.

就像電池

And it worked the other way around, too.

這現象也可以倒轉過來

Running electricity through these crystals made them change shape.

讓電通過這些結晶 會讓結晶改變形狀

Both of these results,

這兩項結果：

turning mechanical energy into electrical,

將機械能轉為電能

and electrical energy into mechanical,

以及將電能轉為機械能

were remarkable.

都是很了不起的結果

But the discovery went uncelebrated for several decades.

但這發現數十年都沒有被公開讚揚

The first practical application was in sonar instruments

最先的實際應用 是用在聲納儀器上

used to detect German submarines during World War I.

在第一次世界大戰時 用來偵測德國潛艇

Piezoelectric quartz crystals in the sonar's transmitter

聲納發射器中的壓電石英結晶

vibrated when they were subjected to alternating voltage.

會在受到交流電壓時振動

That sent ultrasound waves through the water.

接著會透過水發送出超音波

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

測量超音波碰到物體再反彈回來 要花多少時間

revealed how far away it was.

就能算出物體的距離多遠

For the opposite transformation,

至於反向的轉換

converting mechanical energy to electrical,

將機械能轉為電能

consider the lights that turn on when you clap.

想想當你拍手時就會亮起來的燈

Clapping your hands send sound vibrations through the air

拍手會透過空氣發送聲振

and causes the piezo element to bend back and forth.

導致壓電元素開始前後彎曲

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

就會形成電壓 產生足夠電流使燈發亮

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

不過燈能持續發光 還是要靠一般電源

So what makes a material piezoelectric?

怎樣的材料會是壓電材料？

The answer depends on two factors:

這取決於兩個因子：

the materials atomic structure,

材料的原子結構

and how electric charge is distributed within it.

以及電荷在其中的分佈

Many materials are crystalline,

很多材料都是結晶狀的

meaning they're made of atoms or ions

意味著它們是由原子或電子組成

arranged in an orderly three-dimensional pattern.

且原子或電子是以三維形式排列

That pattern has a building block called a unit cell

這個排列形式的基礎單位 稱為「單位晶格」

that repeats over and over.

晶格會不斷重覆排列

In most non-piezoelectric crystalline materials,

在大部份非壓電的材料中

the atoms in their unit cells are distributed symmetrically

單位晶格中的原子 是繞著一個中心點對稱性的分佈

around a central point.

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

但有些結晶材料並沒有對稱的中心

making them candidates for piezoelectricity.

它們可能就會有壓電效應

Let's look at quartz,

咱們來看看石英

a piezoelectric material made of silicon and oxygen.

它是矽和氧所組成的壓電材料

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

氧有些微的負電荷 矽有些微的正電荷

creating a separation of charge,

創造出電荷的分離

or a dipole along each bond.

或是每個鍵結的雙極

Normally, these dipoles cancel each other out,

正常來說，這些雙極會彼此抵消

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

所以在單位晶格中不會有電荷分離

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

但如果石英結晶 被延著某個方向擠壓

the atoms shift.

原子會轉移

Because of the resulting asymmetry in charge distribution,

造成電荷分佈不對稱

the dipoles no longer cancel each other out.

雙極不再能彼此抵消

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

最後，被拉伸的晶格 其中一端會有淨負電荷

and a net positive on the other.

另一端會有淨正電荷

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

這種電荷不平衡 不斷傳遍於整個材料當中

and opposite charges collect on opposite faces of the crystal.

相反的電荷 會在結晶的相反面上結集

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

這就會造成電壓 讓電流通過迴路流動

Piezoelectric materials can have different structures.

壓電材料可能會有不同的結構

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

但它們有個共通性： 單位晶格沒有對稱中心

And the stronger the compression on piezoelectric materials,

對壓電材料做越強的壓縮

the larger the voltage generated.

產生的電壓就會越大

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

若改為拉伸結晶，電壓就會切換

making current flow the other way.

讓電流反向流動

More materials are piezoelectric than you might think.

壓電材料比你想像的還多

DNA,

去氧核糖核酸

bone,

骨頭

and silk

絲

all have this ability to turn mechanical energy into electrical.

都有將機械能轉為電能的能力

Scientists have created a variety of synthetic piezoelectric materials

科學家創造了各種合成壓電材料

and found applications for them in everything from medical imaging

在各種事物當中都可以應用

從醫學影像到噴墨印表機都可以

to ink jet printers.

Piezoelectricity is responsible for the rhythmic oscillations

壓電會造成石英的節奏性振盪

of the quartz crystals that keep watches running on time,

因而手錶能一直準時地運行

the speakers of musical birthday cards,

其他應用包括音樂生日卡的蜂鳴片

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

及某些烤肉架點火器只要一撥開關

when you flick the switch.

就有火花能點燃瓦斯

And piezoelectric devices may become even more common

壓電裝置可能會變得更常見

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

因為電力需求很大 而機械能是很充足的

There are already train stations that use passengers' footsteps

已經有火車站利用乘客的腳步

to power the ticket gates and displays

來供電給驗票閘門和電子顯示板

and a dance club where piezoelectricity helps power the lights.

有間跳舞俱樂部 用壓電來輔助供電給燈光

Could basketball players running back and forth power the scoreboard?

籃球員在場上來回跑 能否供電給計分板？

Or might walking down the street charge your electronic devices?

在街上行走 能否將你的電子裝置充電？

What's next for piezoelectricity?

壓電的下一步發展會是什麼呢？