1. How Can Squeezing a Ceramic Make Electricity?
Some materials produce a voltage when they are squeezed or struck. This is called the piezoelectric effect. The first careful experiments were published in 1880 by the French brothers Pierre and Jacques Curie. They put crystals under mechanical stress, including tourmaline, quartz, topaz, cane sugar and Rochelle salt, and measured electric charge appearing on their surfaces. They did it with tinfoil, glue, wire, magnets and a jeweler's saw [4].
Lighters today do not usually use a cut crystal. During the Second World War, research groups in the United States, Japan and the Soviet Union found ceramics, made by baking metal-oxide powders, that opened up new possibilities. One of their properties, the dielectric constant, was up to 100 times higher than in common cut crystals, and the same class of materials (called ferroelectrics) showed similar improvements in piezoelectric properties. Later came lead zirconate titanate, known as PZT [4].
Here is how one of the earliest piezoelectric lighters used it. A US patent filed in January 1963 describes two small ceramic rods made of PZT-4, squeezed by a lever when you press the fingerpiece. The patent says this material can generate a potential of 3000 volts when compressed, that the voltage grows with the pressure, and that it appears almost instantly. The voltage is held briefly on metal-coated ends of the rods, which act like the plates of a small capacitor, and then it discharges across a gap beside the wick or gas outlet. That spark lights the fuel. The patent states its aim plainly: a lighter that works "without the use of flint, batteries, induction coils or catalysts" [2].
2. Where Did Push-Button Igniters Come From, and What About Japan?
The 1963 patent above was American. In Japan, the same idea reached ordinary homes at about the same time. The 1973 journal article (Hitachi Hyoron, a monthly engineering magazine from the Hitachi company) says that spark ignition using piezoelectric ceramics was put to practical use "from about 1963" in household gas appliances and in gas lighters for cigarettes [1]. A history from a piezoelectric-ceramics manufacturer adds that Japanese manufacturers, who began seeing commercial returns from 1965, developed ceramic igniters for natural gas and butane appliances [4].
So when you hear a "click-click" from a gas grill or a kitchen gas burner and see it light without any battery, a piezoelectric igniter may well be at work. Not every igniter is made this way. Some are powered by batteries or by a wall socket, so this article cannot say which kind your own appliance uses. The instruction manual is the best place to check.
3. Why Does a Lighter Strike the Ceramic with a Spring-Driven Hammer?
You can press a lighter button slowly and the click still happens at the same moment. The reason is a small mechanism inside. The Hitachi article says that there are two ways to give the ceramic its squeeze, a steady pressure or a sudden impact, and that for gas appliances the piezoelectric unit is commonly built inside an impact mechanism [1].
A patent for a gas-lighter mechanism shows how such a unit can be built. Inside, the piezoelectric element sits between a metal anvil and a stop piece. A firing hammer rests away from the element, held back by a catch. As you push the body of the lighter, a spring is compressed. At the very end of the stroke, the catch lets go, and the hammer flies forward and strikes the stop piece, which delivers the impact to the element. Only then does the spark appear [3]. The sharp "click" you hear is this hammer hitting.
The patent does not explain why a hammer is better than slow pressure. One simple way to picture it is this: with a catch and a spring, the strike is the same each time, however slowly or clumsily your thumb moves. That is our reading of the design, not something the patent says.
4. How Many Volts Does a Piezoelectric Igniter Really Make?
The numbers depend on the ceramic and the design. The 1963 patent speaks of about 3000 volts for its PZT-4 rods [2]. The Hitachi article opens by saying that piezoelectric ignition devices generate 10,000 volts or more [1]. When Hitachi's engineers measured one commercial unit, called HPSU-1, the voltage reading used for the spark phase was 8.7 kilovolts, which is 8,700 volts [1]. These values are from different devices and measured in different ways, so they should not be compared as if they were the same quantity. They all fall in the range of thousands of volts, many times the 120 volts of an American wall outlet or the 230 volts of a European one.
5. If the Voltage Is So High, Why Is the Spark So Weak?
Voltage and energy are different things. Think of a tiny drop of water falling from a great height: the height is large, but the amount of water is small. A piezoelectric spark is like that.
In the Hitachi measurements, the spark had two phases. First came a very sudden spark discharge, a short burst that lasts less than 100 billionths of a second. In that burst the unit released about 0.5 millijoules. Then came a longer glow discharge of about 1.5 millijoules. The total was about 2 millijoules [1]. A millijoule is one thousandth of a joule. Lifting a 100-gram object by 1 meter takes roughly 1 joule, so 2 millijoules is about the energy needed to lift that object by 2 millimeters.
Small as it is, this is enough for a flammable gas. The Hitachi article quotes a literature value of 0.2 millijoules as the smallest spark energy that ignites methane in still air. It adds that gas flowing past a real igniter behaves differently, so the engineers tested real igniters in flowing methane-air mixtures instead [1]. In their tests, three commercial igniters with discharge energies of about 0.9 to 1.2 millijoules and a 4-millimeter electrode gap lit the mixture only within a band of methane concentration. The lower limit was 6% for all three, and the upper limit was between 10.5% and 12.5% depending on the igniter [1]. The spark does not have to be strong. It only has to start the flame in the right mixture of gas and air.
6. Does a Piezoelectric Igniter Light Every Kind of Gas Equally Well?
No. The same article explains that changing the gas can change how easy ignition is. In 1970, Tokyo Gas began studying piezoelectric ignition afresh. Japan was planning to switch city gas to natural gas, and the company's staff saw reasons why piezoelectric ignition might become harder with the new fuel, so the old standards needed a second look [1]. The company wanted a spark unit with higher performance and more safety. That is why the article measured the spark's energy directly. Until then, the energy had been estimated from the capacitance and the voltage of the element, rather than measured [1].
That is also a good reminder about the piezoelectric igniter: it is a small, cheap device, but the details of its spark were studied carefully when the fuel changed.
7. How Can You Look into This Yourself, Safely?
Do not take apart a lighter or test igniters to see what happens. Only adults should handle lighters, fuel or ignition parts. Here are safer ways to explore:
- Ask an adult to show you a lighter's click from a safe distance, and do not handle it or go near the flame. Can you hear a click, and does it come at the same moment each time, however slowly the button is pressed?
- Search for a patent drawing of a piezoelectric lighter, such as the two patents listed below, and find the hammer, the spring and the element [3].
- Compare the voltage claims. The 1963 patent says about 3000 volts, while the Hitachi article says 10,000 volts or more. What might explain the difference?
- Read the Curie brothers' story at [4] and ask: why did the first experiments need so little equipment, and why did it take decades for the effect to be used in everyday objects?