"Click" ~ "Click" ~ "Click"...How does a lighter ignite?

The earliest use of fire by humans can be traced back to 1.8 million years ago. From Yuanmou Man to Peking Man, archaeologists have found traces of their use of fire, although they used natural fire at that time.

But primitive people have realized that fire is a powerful natural force, so they began to explore ways to make fire artificially. From drilling wood to making fire to using flint, and then to today's various fire-making tools, humans' ways of making fire have become more diverse.

Lighters have been widely used by the public because of their lightness, durability and stable fire-generating ability.

Currently, most disposable lighters on the market use butane as fuel. Because butane becomes liquid under high pressure and can quickly become gas after decompression , it is very suitable for storage in the small fuel tank of the lighter.

When we press the "ignition button" of the lighter, wisps of butane in the small tank overflow with gas, and then come into contact with the electric spark generated by the ignition device to produce a bright flame.

Speaking of the ignition device, it is actually the long black object inside the lighter, which should be familiar to everyone. Because it is such a small thing, when I was a kid, I used it to hit my friend's back of the hand (please do not imitate me), and I felt a slight electric shock.

However, where does this electricity come from? There is no independent power supply, no small magnets to generate magnetic fields, let alone any metal cutting magnetic flux lines. It only has a set of "striking and being struck devices", which is in line with the Chinese saying "Zhou Yu fights Huang Gai, one is willing to fight and the other is willing to be beaten".

When we press the trigger down, pressure is applied to the spring inside. A small hammer is connected under the spring. When the applied pressure reaches the threshold, the spring will bounce back to the origin and release energy. At this time, the connected small hammer will fall down hard and hit the piezoelectric crystal (or piezoelectric ceramic) below.

When a piezoelectric crystal is impacted, its surface will dent slightly, causing a potential difference (voltage) across the crystal.

Piezoelectric effect

Some of you may wonder why piezoelectric crystals can generate voltage?

This is actually caused by the piezoelectric effect. The word piezoelectricity comes from the Greek word piezein, which literally means: squeeze and press to generate electricity? In fact, it is almost the same.

In 1880, French physicists the Curie brothers discovered in an experiment that when certain natural crystals are stretched or squeezed by mechanical force, equal amounts of opposite charges will appear on the two opposite surfaces of the crystal. Scientists call this phenomenon the piezoelectric effect.

The Curie brothers' experimental equipment

The medium that exhibits piezoelectric phenomenon is called piezoelectric material.

In fact, most crystals in nature have piezoelectric effect, but the effect is very weak. With the deepening of research on materials, people have found that quartz crystals, barium titanate, tourmaline and other materials are all piezoelectric materials with excellent performance.

One of the important reasons for becoming a piezoelectric material is that it has a central asymmetric structure. Take quartz crystal as an example. In ionic crystals, positive and negative ions are regularly interlaced to form a crystal lattice.

In this way, an inherent electric moment is formed on the surface of the quartz crystal and polarized charges are generated, but these charges cannot leave the crystal surface . Because the crystal is exposed to the air, these polar charges will combine with the opposite charges in the air, so the crystal still exists in an electrically neutral and balanced way .

However, if mechanical pressure is applied to the quartz crystal, the crystal structure will change and the electric moment will change accordingly. The value of the polarized charge on the crystal surface is proportional to the strength of the external force and the size of the contact surface. The greater the external force and the contact surface, the more charge will appear.

The sign of the surface charge of the crystal is related to the external force. If it is in a stretched state, the charge on the top is positive and the charge on the bottom is negative; if it is in a compressed state, the opposite is true.

If electrodes are installed at both ends of the crystal and connected with wires, these charges will be transferred from one plate to the other, forming an electric current, which is the electric spark we see in a lighter.

Inverse piezoelectric effect

Another special thing about the piezoelectric effect is that this process is reversible. When mechanical stress is applied to a piezoelectric material, mechanical energy can be converted into electrical energy, which is a positive piezoelectric effect. Conversely, when an electric field is applied to a piezoelectric material, it will produce mechanical deformation (elongation or contraction).

Compared with the direct piezoelectric effect, the inverse piezoelectric effect has a wider range of applications. For example, when the common speakers we see are powered on, the piezoelectric ceramics inside are affected by the electric field, causing the ceramics to vibrate the air in the form of sound waves and make a louder sound.

In today's electronic world, piezoelectricity is everywhere, and with the development of science and technology, the pace of piezoelectric technology will continue to advance. There may be infinite possibilities in the future. For example, the energy generated by the piezoelectric effect can be collected.

Imagine if the batteries of future smart devices have piezoelectric materials, then you can activate the piezoelectric materials through simple body movements to charge your devices.

Even more impressive, a piezoelectric system can be embedded under the road. When a car passes by on the road, the system below can be activated, and the collected energy can then be used for public facilities on both sides, such as street lights, billboards, etc.

No matter which possibility it is, the development of science and technology is always fascinating and desirable.