In this blog post, we will look at how piezoelectric materials work and examples of their use in everyday life to understand why this technology is attracting attention as a future eco-friendly energy source.

Basic principles of piezoelectric materials

In the photo below, a gentle breeze is blowing. The grass in the meadow is swaying in the breeze, and among the grass, a unique tree is swaying as well. There are wires connected to the tree, and these wires are connected to a battery to charge it. There is no strong wind or complicated machinery, but electricity is being produced from the tree. This tree is called a ‘piezo tree.’ The principle behind how this piezo tree generates electricity comes from ‘piezoelectricity.’
Piezoelectricity is derived from the Greek word ‘piezein,’ which means ‘to press.’ Electric means electricity, so piezoelectricity can be interpreted as ‘electricity produced by pressing.’ In other words, piezoelectricity is the phenomenon of electricity being generated when mechanical force or deformation is applied, and objects with this characteristic are called piezoelectric materials. Conversely, when electricity is applied to a piezoelectric material, mechanical deformation occurs, 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 Pierre Curie and Jacques Curie. The brothers experimentally proved that electrical signals are generated in some materials in response to temperature changes. The following year, in 1881, Gabriel Lippmann mathematically deduced this phenomenon, and the Curie brothers succeeded in calculating the electrical changes in piezoelectric crystals arithmetically.
By 1910, piezoelectric crystals had been classified into about 20 types based on their material properties, and piezoelectric constants were derived to indicate the degree of piezoelectric effect of materials based on this classification.

Principle of piezoelectric effect

The piezoelectric effect is caused by electric dipoles within a material. Most materials are electrically neutral, but some materials have positive and negative charges that are slightly misaligned, forming electric dipoles. When these electric dipoles are subjected to mechanical force, the crystal structure changes, causing a change in the electric field. This structural change causes the piezoelectric effect.

Types of piezoelectric materials

Materials with piezoelectric properties are found in various fields, such as metals, ceramics, and polymers. The most widely known is a material called Lead Zirconate Titanate (PZT), which has a crystal structure composed of metal, oxygen, zirconium, or titanium. When the centre atom moves due to an external force, it forms an electric dipole, which causes the piezoelectric effect.
Among polymers, polyvinylidene fluoride (PVDF) also has piezoelectric properties. Compared to metals and ceramics, polymer materials are lightweight and highly processable, offering a wide range of applications. However, they have the disadvantage of being less durable, and research is ongoing to improve this.

Applications of piezoelectric materials

Piezoelectric materials are commonly found in everyday life. The most representative example is electric lighters. When the spring button on a lighter is pressed, a small hammer inside strikes the piezoelectric material, generating a spark that ignites the gas in the lighter. Another example is sensors. Piezoelectric materials can convert sound waves into electrical signals and are used in microphones and non-destructive testing equipment for medical use.

New research and potential applications of piezoelectric materials

Recently, the potential applications of piezoelectric materials have expanded into various fields. In particular, piezoelectric materials are expected to play an important role in wearable devices and IoT (Internet of Things) devices. Smart clothing and accessories utilising piezoelectric materials can convert the minute vibrations generated by the user’s physical activity into electricity to charge or operate low-power sensors and devices. For example, technology is being developed to charge smart watches and health monitoring devices using vibrations generated during exercise.
In addition, piezoelectric materials can play a major role in environmental monitoring systems. Sensors equipped with piezoelectric power generation technology can operate semi-permanently without an external energy source and can be used in forest fire detection and air pollution detection sensors. Such technologies can be an environmentally friendly solution that can operate continuously in areas with limited energy resources, as well as preventing natural disasters.
Research into piezoelectric materials will play an important role in improving sustainability and energy efficiency, and is expected to demonstrate its potential in many more applications in the future.

Limitations and 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 power supply for small electronic devices and sensors. In particular, piezoelectric materials are expected to become a core technology for smart cities and automated systems.
Currently, research is actively underway to develop bags and shoes that use piezoelectric materials to charge smartphones through human movement, and once these technologies are commercialised, they will become more widely used in everyday life.