A magnetostrictive system in wearable devices converts vibrations into electrical power through a process known as the magnetostrictive effect. The magnetostrictive effect refers to the property of certain materials to change their shape or dimensions when subjected to a magnetic field. This effect is reversible, meaning that when the magnetic field changes, the material's shape returns to its original state.
Here's how a magnetostrictive system typically works to convert vibrations into electrical power in wearable devices:
Selection of Materials: The system uses materials that exhibit the magnetostrictive effect, such as certain alloys or compounds. Terfenol-D (a magnetostrictive alloy) is a common choice due to its strong magnetostrictive properties.
Mechanical Vibration: The wearable device is designed to capture mechanical vibrations, which could be generated from movements of the wearer's body, ambient vibrations, or specific activities. These vibrations cause the magnetostrictive material to change its shape slightly.
Magnetic Field: A magnetic field is applied to the magnetostrictive material. This can be achieved using a permanent magnet or an electromagnet placed in proximity to the magnetostrictive material.
Magnetostrictive Effect: As the material vibrates due to the mechanical vibrations, its dimensions change in response to the applied magnetic field. This phenomenon is called the magnetostrictive effect. The material undergoes small deformations that result in mechanical stress within the material.
Conversion to Electrical Power: The mechanical stress within the magnetostrictive material generates a voltage across it, according to the magnetostrictive effect. This voltage can be captured using appropriate electrodes placed on or near the material. The changing voltage can then be collected and converted into usable electrical power.
Rectification and Storage: The generated voltage is usually an alternating current (AC). To make it useful for most applications, such as charging batteries or powering electronic components, it needs to be converted into direct current (DC) using rectification circuits. The rectified DC voltage can then be used to charge a battery or directly power components in the wearable device.
It's important to note that while magnetostrictive systems can convert vibrations into electrical power, the efficiency of this conversion process is generally lower compared to other energy harvesting methods such as piezoelectric or triboelectric systems. The amount of power generated depends on factors like the material properties, the strength of the magnetic field, and the intensity of the vibrations.
Magnetostrictive systems might not be as common as other energy harvesting methods in wearable devices due to their lower efficiency and certain technical challenges, but they still offer an alternative way to scavenge energy from the environment.