Can piezoelectricity harness wasted energy?

In this blog post, we’ll explain how piezoelectricity works to utilize wasted energy.

 

When you take the subway, you’ll often come across a curious staircase: as you go up or down, a piano key sounds and the number of people who have climbed the stairs so far is displayed on the screen, accumulating donations. How does it work, and can we use this principle in real life? For example, could we generate our own power from the energy we expend when we touch our phones or exercise?
The scientific principle at work in this case is piezoelectricity. The piezoelectric effect is the generation of electrical energy when pressure is applied. There is a forward and a reverse effect. The former is called the primary piezoelectric effect (positive piezoelectricity), and the latter is called the secondary piezoelectric effect (negative piezoelectricity). Here’s how it works Most materials are electrically neutral, but in materials with a crystalline structure, positive and negative charges can be misplaced, creating an electric field within the structure that is not canceled out by neutrality, called an electric dipole. Piezoelectric materials all have this crystal structure of electric dipoles.
When a piezoelectric material is subjected to a force, the crystal structure becomes more misaligned, causing a state change and a change in the size of the electric dipole, which changes the electric field. This change is generated as electricity in a connected circuit. In the case of piezoelectricity, applying an electric field to a substance changes its structure by randomly arranging the dipoles. In other words, the structural aspects due to the position of the charges are subjected to mechanical changes such as compression or tension, which changes the properties of the electric field. Tension is the stretching of an object when a force acts outward, parallel to the object’s central axis. It is divided into simple tension and eccentric tension depending on whether the line of action of the force coincides with the central axis.
This piezoelectric effect was discovered by the Curie brothers in the 19th century. They used an experimental and inductive method to show that a change in temperature generates electricity. In fact, the mechanical deformation of expansion and contraction due to temperature changes enabled the generation of electricity, but they did not recognize it and did not predict the reverse reaction. This was mathematically deduced a year later by Lippmann. Later, the Curie brothers made the degree of energy conversion calculable. Nowadays, piezoelectric crystals have been derived and divided into piezoelectric constants according to more than 20 different material crystallographic classifications. The piezoelectric effect can now be summarized mathematically and visually.
Devices or components that contain piezoelectric effects are called piezoelectric devices and are used in everyday life. Examples include airbags, quartz watches, lighters, and gas stoves. Piezoelectric devices are categorized into primary and secondary depending on the type of piezoelectric effect. Primary devices include lighters, airbags, and microphones, while secondary devices include filters, speakers, and motors. The forward and reverse elements are like the relationship between a motor and a generator. However, piezoelectric devices are between electrical energy and mechanical energy, while motors and generators are between kinetic energy and electrical energy.
The advantages of piezoelectric devices are intuitiveness and speed. If most energy conversion involves turning heat energy into kinetic energy by turning a turbine, the piezoelectric effect is a simpler and more intuitive energy conversion. An object that epitomizes this intuitiveness and immediacy is the airbag. In a collision with a vehicle, the element under pressure immediately creates energy to deploy the airbag. The airbag senses the collision within 0.03 seconds of impact and inflates at a speed of about 300 kilometers per hour. It’s not a lot of energy, but the source of this instantaneous burst of force is the piezoelectric in the acceleration sensor. These thin piezoelectrics in the airbag estimate the acceleration from the voltage at impact and inflate with nitrogen gas from the explosion of sodium azide, which is made up of sodium and nitrogen.
The airbag example suggests a myriad of possibilities for piezoelectric devices to act as sensors. Like our body’s reflexes. It’s like David in the art of fighting, using his opponent’s strength to overpower him. There are many types of pressure signals. Among them, microphones and ultrasonic vibrators utilize sound waves. The microphone itself is a sensor that converts microscopic voice signals into electrical signals. What if a piezoelectric element, which is a versatile device that can detect changes in a single place and transmit them as electrical signals at the same time, is used in a communication circuit? The true meaning of communication is to inform someone who is far away of a change, and isn’t it easy to do this quickly and easily while generating electric energy? Ultrasonic vibrators are inverse devices that generate ultrasonic waves by evaporating water through vibration. In addition, piezoelectric elements can be used to operate ultra-fast camera shutters or other devices that require quick thinking. Whether it’s a sprayer, shutter, or x-ray shutter, the circuit can be modified to produce the desired amount of power by adapting to minute changes that would otherwise be invisible to the human eye. Large pressures are more detectable, so there are many applications for military sensors. It can also be applied to medical or industrial non-destructive sensors that utilize a lot of energy, such as ultrasound.
On the other hand, a pacemaker has recently been developed that inserts a flexible piezoelectric element into the heart. The principle is that electricity is supplied as long as the heart doesn’t stop beating, and whenever a patient at risk of hypertension or arrhythmia fails to beat properly, this electricity is used to force the heart to beat. Both reactions, forward and reverse, are carried out through a single element. Isn’t this true self-power? In the field of piezoelectric device research, it has become possible to produce piezoelectric polymers, which are high molecular materials, and transparent piezoelectric films are being manufactured in Korea, and the functionality and efficiency of the materials themselves are being developed. Due to its intuitive nature, it has many potential applications in the fields of music and art, learning, and medicine.
The disadvantages are low efficiency and a one-time current is generated in the case of a static element. In addition, it does not generate a one-time signal just because there is pressure, but a change in pressure or a change in shape is required to generate a one-time signal.
Despite these limitations, the value of primary and secondary piezoelectric elements is that they collect and use small energy that would otherwise be wasted, like sweeping up fallen leaves. The idea of “a thousand miles a day, a step at a time” will resonate loud and clear in energy conservation. Anyone who has experienced this energy will surely feel the need to save and conserve energy. Primary and secondary piezoelectric devices are small but strong components that show that a small David can win over a big Goliath.