Piezoelectric materials have the property of generating electricity through external pressure or deformation, and are utilized in various applications such as electric lighters, sensors, and wearable devices. In particular, they are expected to gain more attention in the future as an energy source for environmental monitoring systems and small electronic devices.

Basic principles of piezoelectric materials

In the picture below, a gentle breeze is blowing. The grass in the meadow is swaying in the breeze, and a tree with a special shape is swaying among the grass. There are wires running around the tree, and these wires are connected to a battery, which is charging the battery. There is no strong wind, no complicated machinery, but electricity is being generated by the tree. This tree is called a ‘piezo-tree’. The principle of how this piezo-tree generates electricity comes from piezoelectricity.
Piezoelectricity is called “piezo-electric” in English, where the prefix Piezo comes from the Greek word Piezein, which means “to press”. Electric means electricity, so piezoelectricity is interpreted as “electricity by pressing.” In other words, an electrical phenomenon that occurs when mechanical force or deformation is applied is called piezoelectricity, and an object with this property is called a piezoelectric body. Conversely, applying electricity to a piezoelectric body causes mechanical deformation, which is called the ‘secondary piezoelectric effect’ or ‘reverse piezoelectric effect’.

Discovery and history of piezoelectric materials

The piezoelectric effect was first discovered in 1880 by brothers Pierre and Jacques Curie. The brothers experimentally demonstrated that several materials generated electrical signals in response to changes in temperature. The following year, in 1881, it was mathematically deduced by Gabriel Lippmann, and again by the Curie brothers, who succeeded in mathematically calculating the electrical changes in piezoelectric crystals.
By 1910, piezoelectric crystals had been divided into more than 20 material crystallographic classifications, from which the piezoelectric constant, which describes the degree of piezoelectric effect of a material, was derived.

How piezoelectricity works

Piezoelectricity is caused by electric dipoles in a material. Most materials are electrically neutral, but some materials have a slight misalignment of positive and negative charge positions, forming an electric dipole. When these electric dipoles are subjected to a mechanical force, their crystal structure changes, resulting in a change in the electric field. This structural change is what creates the piezoelectric effect.

Types of piezoelectric materials

Materials with piezoelectric properties are found in a variety of fields, including metals, ceramics, and polymers. The most widely known is Lead Zirconate Titanate (PZT), which has a crystalline structure made up of metals and oxygen, zirconium, or titanium. An external force causes the central atom to move and form an electric dipole, which creates a piezoelectric effect.
Polyvinylidene Fluoride (PVDF) is also piezoelectric. Compared to metals and ceramics, polymer materials are lightweight and highly processable, offering a wide range of application possibilities. However, they have the disadvantage of being less durable, so research is ongoing.

Applications of piezoelectric materials

Piezoelectric materials are common in everyday life. The most typical example is an electric lighter. When you press the spring button on the lighter, a small hammer inside strikes the piezoelectric material and creates a spark, which ignites the gas in the lighter. Another example is sensors. Piezoelectric materials can convert sound wave signals into electrical signals, which is why they are used in microphones and medical non-destructive testing equipment.

New research and application possibilities for piezoelectric materials

In recent years, the applications of piezoelectric materials have expanded into many different fields. In particular, piezoelectric materials are expected to play an important role in wearable devices and IoT (Internet of Things) devices. Smart clothing or accessories that utilize piezoelectric materials can convert tiny vibrations from a user’s physical activity into electricity to charge or operate low-power sensors or devices. For example, technologies are being developed to charge smart watches or health monitoring devices using the vibrations generated during exercise.
Piezoelectric materials can also play a big role in environmental monitoring systems. Sensors equipped with piezoelectric power generation technology can operate semi-permanently without an external energy source, which can be utilized in sensors for detecting forest fires or air pollution. This technology could be an eco-friendly solution to preventing natural disasters, as well as providing continuous operation in areas where energy is scarce.
Research into piezoelectric materials will play an important role in promoting sustainability and energy efficiency, and their potential is expected to be realized in many more applications in the future.

Limitations and the future of piezoelectric materials

Piezoelectric materials have limitations that make them unsuitable for large-scale power generation, such as solar or wind power. However, they have great potential in areas such as powering small electronic devices and sensors. In particular, piezoelectric materials are expected to become a key technology for smart cities and automation systems.
Currently, research is underway to charge smartphones using human movement through bags or shoes with piezoelectric materials, and once these technologies are commercialized, they will become more widely used in everyday life.