麻省理工学院物理科研感受

原标题:麻省理工学院物理科研感受

每年约有24万人因雷击而受伤。根据美国国家海洋和大气管理局(national ocean and atmospheric administration)的数据,在过去20年里,美国平均每年发生51起雷击死亡事故,位居第二,仅次于洪水造成的致命天气。

一道闪电所携带的能量相对较大。超过10微秒的50亿焦耳等于5×1014(或500万亿)瓦。闪电背后的机制是因为水滴由于与云中其他水滴和冰的接触而带负电荷。

当液滴中的净电荷超过空气的分解电荷密度并接近地面时,就会产生闪电。导致水从摩擦中获得净电荷的是摩擦电效应(te),它表明材料在相互接触后变得带电。

About 240,000 people are injured by lightning strikes each year. According to the National Oceanic and Atmospheric Administration, over the last 20 years, the United States averaged 51 annual lightning strike fatalities, placing it in the second position, just behind floods for deadly weather.

A single bolt of lightning carries a relatively large amount of energy. 5 billion joules over 10 microseconds is equal to 5×1014 (or 500 trillion) watts.

The mechanism behind lightnings is because water droplets became negatively charged from the contacts with other water droplets and ice in the clouds.

As the net charge in the droplets exceeds the air break-down charge density and come close to the ground, lightnings were produced.

What causes the water to gain a net charge from friction is the triboelectric effect (TE) which suggests materials become electrically charged after they were in contact with each other.

摩擦电效应在我们的生活中非常普遍,但它也非常不可预测,因此在许多技术中通常是避免的。然而,近年来,纳米发电机被发明出来。它利用摩擦电效应将机械能转化为电能。

Triboelectric nano generators是由两层不同的介质膜面对面构成的,在叠层结构的上下表面分别沉积有电极。两个介电薄膜之间的物理接触产生了相反的带电表面。一旦两个表面在外力的作用下被一个小间隙隔开,就会产生一个电位降。

如果两个电极通过负载电连接,一个电极中的自由电子将流向另一个电极,形成相反的电势,以平衡静电场。一旦间隙闭合,摩擦电荷产生的电位消失,电子回流。

The triboelectric effect is very common in our lives but it’s also very unpredictable, so it is generally avoided in many technologies.

However, in recent years, nanogenerator is invented. It uses triboelectric effect to convert mechanical energy into electricity.

The TENG (Triboelectric Nanogenerators) consists of two dissimilar dielectric films face with each other, and there are electrodes being deposited on the top and the bottom surfaces of the stacked structure.

A physical contact between the two dielectric films creates oppositely charged surfaces. Once the two surfaces are separated by a small gap under the lifting of an external force, a potential drop is created.

If the two electrodes are electrically connected by a load, free electrons in one electrode would flow to the other electrode to build an opposite potential in order to balance the electrostatic field.

Once the gap is closed, the triboelectric charge created potential disappears, the electrons flow back.

虽然这是一种常见的现象,也有一些技术是利用这一现象发展起来的,但两种材料在物理接触中一次带电的基本机理。

王教授利用开尔文探针显微镜对te的作用机理进行了研究。开尔文探针显微镜具有在原子或分子尺度上观察表面工作功能的能力。

他们使用kpfm在不同的条件下观察两种电介质,电介质金属和金属对金属。他们的结论是te“必须是一个电子主导的转变过程”

Although we TE is a common phenomenon and there are technologies developed using such phenomenon, the fundamental mechanism of why two materials become charged once in physical contact.

Studies conducted by Professor Wang of the mechanism of the TE uses Kelvin probe microscopy. The Kelvin Probe microscopy has the ability of observing the work function of surfaces at atomic or molecular scales is important.

They use KPFM to observe the in different conditions between two dielectric, dielectric-metal and metal to metal. Their conclusion was that the TE “has to be an electron-dominated transition process”

为了能够更准确地模拟和预测闪电,我们需要更多关于两种液体物质之间te行为的信息,特别是水分子。王教授的团队利用滕的概念发明了一种新型的纳米发电机,这种发电机直接从两种液体材料中提取。

这种液态滕(L-L滕)的目标是从雨滴中收集电能。它使用一个内置电线的框架来固定一个液膜,液膜收集雨滴,从而收集雨滴与膜接触产生的静电。

In order to be able to more accurately model and predict lightnings, we need more information on the behavior of TE between two liquid material especially water molecules.

Professor Wang’s team using the concept of TENG to invent a new kind of nanogenerators which harvests directly from two liquid materials.

This Liquid-Liquid TENG (L-L TENG) is aiming at harvesting electricity from rain droplets.

It uses a frame built in with wires to hold a liquid membrane which collects rain droplets and therefore collects electrostatic electricity from the contact of rain droplets and the membrane.

这项技术的概念是理解液-液材料的关键,因为它实际上是在液体之间使用te,这在其他方法中是不可能的。由于绝缘体比导体更有效地保持电荷,因此其执行te的能力和效率更好。

像水这样的液体很容易导电,因此很难获得足够的电荷使te变得重要。然而,我们知道在极端条件下的雷暴,其影响是相当重要的观察。L-L Teng是一种很有前途的方法,可以用来调查闪电发生的条件。

它从以前接触空气的水滴中收集电荷。控制每个液滴的体积可以改变其表面积。在比表面积较大的情况下,液滴的电荷密度可能较大。

要对产生闪电的雷云进行建模,需要了解云中水滴的电荷密度,才能准确地知道闪电发生的时间。

The concept of this technology is key to understanding liquid to liquid material because it actually utilizes TE in between liquids which has not been possible in other methods.

Since insulators are more effective to hold electric charge than conductors, its ability and efficiency of performing TE is better.

Liquids such as water conducts electricity easily therefore it is hard to gain enough charge for TE to become significant. However, we know in extreme conditions of thunderstorms, the effect is quite significant to observe.

L-L TENG is a promise way of investigating into what conditions it has to have for lightning to occur. It collects charges from water drops from previous contact with air. Manipulating the volume of each droplet could change its surface area.

With a larger surface area, a droplet could have a larger charge density.

To model a thundercloud that produces lightning, information of the charge density of water droplets in the cloud is a requirement for knowing when exactly lightnings occurs.

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