“We introduced some knowledge about acoustic wave filters in previous articles, from what are acoustic waves, to surface acoustic waves, to the structure of surface acoustic wave filters, of course, some bulk acoustic wave filters are also introduced here. Of course, it is a general discussion. We expect to start from the root of the device and analyze and explain it in detail. Of course, there is also an important principle missing here: piezoelectric effect and piezoelectric ceramics. This is the principle of how electromagnetic waves become sound waves. Today we try to unravel the mystery of the piezoelectric effect.
We introduced some knowledge about acoustic wave filters in previous articles, from what are acoustic waves, to surface acoustic waves, and then to the structure of surface acoustic wave filters. Of course, some bulk acoustic wave filters are also introduced here. Of course, it is a general discussion. We expect to start from the root of the device and analyze and explain it in detail. Of course, there is also an important principle missing here: piezoelectric effect and piezoelectric ceramics. This is the principle of how electromagnetic waves become sound waves. Today we try to unravel the mystery of the piezoelectric effect.
The piezoelectric effect has a rather awkward English name: Piezoelectric (pa?, izo? ‘lektr?k), which I can’t read yet. Fortunately, the Chinese gave it an image name: Piezoelectric, which contains pressure and electricity, which also vividly describes this feature, which generates current under pressure, as shown in the following figure:
It is enough to see the breadth and depth of Chinese characters. What about Piezo, which comes from Greece? If you want the standard one from the UK, it should be called: Press-electric, don’t you understand? In a nutshell: The piezoelectric effect is that when a crystal is squeezed, an electric current is generated, and in turn, when an electric current is applied to the crystal, the shape of the crystal changes.
Amazing isn’t it? Where is such a miraculous thing? In fact, piezoelectric crystals are all around us. Our daily quartz watches, speakers, and microphones contain piezoelectric crystals. Another is the most commonly used Electronic lighter in our lives, which uses piezoelectric crystals.
You might be wondering, how can something so miraculous be so common? Yes, how does a lighter work? Please see the picture below: When you press your hand, pressure is generated, then the piezoelectric crystal generates current, and an electric spark is generated at the open circuit, and the lighter is on.
When I was young, there must be many boys who took this to bully little girls. It really hurts to be hit by this.
After we briefly understand the piezoelectric effect, what is a piezoelectric crystal? As the name implies, piezoelectric crystals are crystals with piezoelectric effect. Let’s start with the structure of crystals. Regular crystals are defined by the organization and repeating structure of atoms held together by bonds, which is called a unit cell. Most crystals, such as iron, have symmetrical unit cells, which makes them unusable for piezoelectric purposes. As shown below:
But the piezoelectric crystal is special, its unit cell is asymmetric. But it can still exist in electrically neutral equilibrium. However, when you apply pressure on the surface of the crystal, the crystal structure deforms, the atoms push against each other, and an electric current can be generated, which completes the transformation from mechanical force to electricity. When you apply an electrical current to a piezoelectric crystal, the crystal expands and contracts, allowing the conversion of electrical current to mechanical energy.
There are many kinds of this piezoelectric material, the most commonly used in electronic design is quartz crystal, and some natural piezoelectric materials include sucrose, Rochelle salt, topaz, tourmaline, and even bone.
However, many applications of natural materials are limited, so people have made many artificial piezoelectric materials. For example, PZT is made of lead zirconate titanate, which can generate a higher voltage than quartz under the same mechanical pressure. PTZ piezoelectric material used in .
Barium titanate is a ceramic piezoelectric material discovered during World War II and known for its long-lasting durability.
Lithium niobate is a ceramic material that combines oxygen, lithium and lithium, and its properties are similar to barium titanate.
It is because of these piezoelectric materials that we can maximize the piezoelectric effect to make speakers and microphones.
Of course, there are hospital B-ultrasounds.
Of course, it also constitutes the physical basis of various acoustic filters.