Electromagnetic vs. piezoelectric
vibration energy harvesting
What is the difference?
Introduction
Now that we have learned what Energy Harvesting is, it’s time to take a closer look into the different types of vibration energy harvesting.
There are several different ways to capture energy from vibrations and kinetic movement and turn it into electricity. Out of these, the two that are most commonly used in commercial applications are piezoelectric materials and electromagnetic induction. In this article, we will cover the following:
- What is Piezoelectric Vibration Energy Harvesting?
- What is Electromagnetic Vibration Energy Harvesting?
- Piezoelectric vs. Electromagnetic Energy Harvesting: Differences and Similarities
What is Piezoelectric Vibration Energy Harvesting?
Some materials have the ability to generate an electric charge when subjected to mechanical stress. This phenomenon is called the Piezoelectric effect, and it is being utilized in many different applications ranging from doorbells and cigarette lighters to printers and amplifiers.
It is also possible to use a piezoelectric material as a transducer to convert mechanical strain or movement into useful electric voltage or current. Such generators are often based on a cantilever beam or a membrane that oscillates at the same frequency as the vibration source, but it is also possible to generate electricity by applying pressure to the material (and thus harvesting energy from e.g. floor tiles or shoe soles).
Piezoelectric energy harvesters are primarily used to power Internet of Things (IoT) applications and low-power wireless sensor systems.
What is Electromagnetic Vibration Energy Harvesting?
According to Faraday’s law of induction, an electric current is induced when an electric conductor moves through an electric field, or if the magnetic field surrounding the conductor changes. This is called electromagnetic induction and is used by electromagnetic vibration energy harvesters to convert vibrations into electricity. This is the same principle that is used in e.g. transformers and electric motors.
Electromagnetic energy harvesting devices are typically designed as a system of springs, magnets and coils, where the magnet and the coil move relative to each other. This movement creates a change in the magnetic flux which produces an electromagnetic force.
Just as piezoelectric energy harvesters, electromagnetic energy harvesters are used as an “perpetual power source” to replace batteries and cables in wireless sensor networks and IoT applications.
Piezoelectric vs. Electromagnetic Energy Harvesting: Differences and Similarities
Both piezoelectric and electromagnetic energy harvesters rely on resonance. This means that the harvester in some way needs to be tuned to a specific resonance frequency, which matches the dominant frequency of the vibration in the intended application. Both principles also generate an unregulated AC voltage, and need to be paired with rectification and power management electronics in order to produce any useful power output.
One benefit with piezoelectric energy harvesters is the possibility of miniaturization and MEMS integration. Also, the simple design with very few moving parts makes it easy to produce cost-efficient in high volumes. The main drawback is a lower power output compared to electromagnetic energy harvesters. Also, as piezoelectric materials tend to be brittle and degrade over time, they are unsuitable in harsh environments and for applications with high demands on durability.
The main benefit with electromagnetic energy harvesters is the high power output compared to piezoelectric energy harvesters, which makes the principle more useful in a wider range of applications. Moreover, it is easier to design electromagnetic energy harvesters for a long service life in harsh environments, which is often a requirement for vibration energy harvesting systems.
Piezoelectric energy harvesting has for a long time been seen as a promising future technology to power IoT systems and it has been widely researched. Due to the low power output of piezoelectric energy harvesters, however, electromagnetic energy harvesting has been the main alternative for commercial applications.
