What is a piezoelectric crystal?

There is a very interesting type of crystal. When you squeeze or stretch it, different charges will be generated at its two ends. This effect is called the piezoelectric effect. Crystals that can produce piezoelectric effect are called piezoelectric crystals. Crystal (α-quartz) is a famous piezoelectric crystal.

If pressure is applied to a thin slice cut from a crystal in a certain direction, an electric charge will be generated on the slice. If the slice is stretched in the opposite direction, an electric charge will also appear on the slice, but the sign is opposite. The greater the force of squeezing or stretching, the more electric charge will be on the crystal. If electrodes are plated on both ends of the slice and an alternating current is passed through it, the slice will periodically extend or shorten, i.e., begin to vibrate. This inverse piezoelectric effect has been widely used in science and technology. Piezoelectric quartz slices can be made from crystal, with an area of ​​only a few square millimeters and a thickness of only a few tenths of a millimeter. Don't underestimate this small chip, it plays a huge role in radio technology. As mentioned earlier, in an alternating electric field, the vibration frequency of this slice does not change at all. This stable and unchanging vibration is exactly what is necessary for controlling frequency in radio technology. Many electrical appliances such as the color TV in your home have filters made of piezoelectric chips to ensure the clarity of images and sounds. The core component of the quartz electronic watch you wear is called a quartz oscillator. It is this key component that ensures that quartz watches have higher time accuracy than other mechanical watches.

Instruments equipped with piezoelectric crystal elements have made it possible for technicians to study the changes in pressure in steam engines, internal combustion engines, and various chemical equipment. Piezoelectric crystals can even measure the pressure of fluids in pipes, the pressure on cannon barrels when firing shells, and the instantaneous pressure when bombs explode.

Piezoelectric crystals are also widely used in the reproduction, recording and transmission of sound. The piezoelectric chip installed on the microphone will convert the vibration of sound into changes in electric current. Once the sound wave hits the piezoelectric thin film, it will generate charges on the electrodes at both ends of the thin film, and its size and sign will change with the change of sound. The change of charge on this piezoelectric chip can be converted into radio waves and transmitted to distant places through electronic devices. These radio waves are received by the radio, and through the vibration of the piezoelectric crystal thin film installed on the radio speaker, it becomes sound and reverberates in the air. Can it be said that the piezoelectric chip in the microphone can "hear" the sound, while the piezoelectric crystal thin film on the speaker can "speak" or "sing".