X-MINING What are Magnetostrictive Materials? Exploring Their Use in Power Generation Devices and Potential of Vibration Power Generation × IoT

Magnetostriction and Magnetostrictive Materials

Magnetic materials, such as iron and nickel, contain microregions called magnetic domains, where the magnetic direction is uniformly aligned. When an external magnetic field is applied, their magnetic domains align with the direction of the external magnetic field, causing a slight change in their shape. This phenomenon is called magnetostriction or magnetostrictive effect.

Conversely, when an external force that slightly changes the shape of a magnetic material is applied, the magnetic direction of magnetic domains inside the magnetic material changes according to the direction of the applied force, altering the ease of magnetic flow within the magnetic material (i.e., permeability). This is known as inverse magnetostrictive effect.

Materials that exhibit significant magnetostrictive effects are called giant magnetostrictive materials and are utilized in a wide range of fields, including magnetostrictive sensors and oscillators.

Fig1. Magnetostrictive effect and Inverse Magnetostrictive effect

Fe-Ga Magnetostrictive Alloy

Fe-Ga magnetostrictive alloy is one of the iron-based magnetostrictive materials, possessing both significant magnetostrictive effects and high mechanical properties. In recent years, it has gained attention for use in magnetostrictive vibration energy harvesting applications. The main characteristics of Fe-Ga magnetostrictive alloy are listed below.

Sumitomo Metal Mining has been manufacturing and selling crystal materials for various applications. Based on extensive and abundant experiences, we have developed Fe-Ga magnetostrictive alloy single crystals suitable for magnetostrictive vibration power generation for IoT.

We have developed a technology for growing Fe-Ga magnetostrictive alloy single crystals using Vertical Bridgman (VB) method(Fig.2). The magnetostrictive performance of Fe-Ga magnetostrictive alloy is greatly affected by the variation in Ga concentration within the alloy. VB method contributes to keep the variation of Ga concentration low. Furthermore, special post-processing makes it possible to keep the direction of magnetic domains within the material aligned, thus creating magnetostrictive materials with high magnetostriction constant and less variance. (Fig.3)

At this point, we have successfully grown single crystal rectangular prisms up to approximately 66mm x 100mm. Magnetostrictive materials of various of sizes and shapes can be produced from single crystals.

Here are some examples of power generation devices that utilize Fe-Ga magnetostrictive alloy single crystals:

Reference: Vibration Power Generation Research Laboratory, Kanazawa University – Magnetostrictive Vibration Power Generation Device (V-GENERATOR)

The structure of the device is shown in Figure 4. U-shaped steel frame is fitted with a Fe-Ga magnetostrictive alloy plate, around which copper wire is wound, and a permanent magnet is placed under the end of the Fe-Ga magnetostrictive alloy plate. This configuration forms a closed magnetic circuit, as indicated by the red line in Figure 4. When a weight is attached to the end of the frame and the device is fixed to a vibration source, the weight moves up and down due to the inertial force acting on it. This causes the frame to deform, and both tensile and compressive forces are alternately applied to the Fe-Ga magnetostrictive alloy plate attached to the frame. This changes the ease with which magnetism flows (i.e., permeability) inside the Fe-Ga alloy due to the inverse magnetostriction effect, resulting in a magnetic change within the coil and generating voltage through electromagnetic induction. The generated voltage can be extracted as direct current power through an electrical circuit and used as an independent power source for IoT (Internet of Things) and other applications.

Fig.4 Structure and Power Generation Principle of the Magnetostrictive Vibration Power Generation Device (V-GENERATOR)

Reference: Magnetostrictive self powered bridge sensor device, KANSAI UNIVERSITY, Koganezawa laboratory (JAPANESE PAGE)

The structure of the device is shown in Figure 5. The vibration sensor device has a structure where a coil is wound around a cylindrical Fe-Ga magnetostrictive alloy, magnets are placed around it to apply an external magnetic field, and a yoke (a circuit to magnetically connect the magnets) is formed with SS400 (rolled steel plate) and covered with SS400. This device is used by being placed between the bridge girder and the bridge pier. When a vehicle passes over the bridge, the girder moves up and down, and this deformation applies compressive stress in the vertical direction to the cylindrical magnetostrictive material, changing the ease with which magnetic flux flows (i.e., permeability). As a result, a change in magnetic flux density occurs within the coil, generating voltage through electromagnetic induction. The generated voltage can be utilized as direct current power by rectifying and storing it. Additionally, since there is a correlation between the magnitude of the generated voltage and the vibration of the bridge, analyzing this voltage signal as vibration information of the bridge can help in diagnosing the health of the bridge. By storing the electricity generated from the bridge’s vibrations in secondary batteries and periodically acquiring and analyzing vibration information to diagnose the bridge’s health, and then sending the results to a server via wireless communication, it is expected to automate the inspection and health diagnosis of bridges, which has traditionally relied on manual labor.

Fig.5 The structure and operational concept of a magnetostrictive self-powered vibration sensor

The combination of vibration power generation and IoT offers limitless possibilities. For example, using the energy generated from vibrations to continuously operate remote sensors can allow for the real-time collection of data on weather, environment, movement and location of people and objects, and the health of structures and equipment. This reduces the need for battery replacements, thus lowering maintenance burdens and reducing waste. The utilization of vibration power generation is expected to create new value in various fields such as industry, transportation, logistics, healthcare, welfare, infrastructure, environment, lifestyle, and entertainment.

Fig.6 The Potential Applications of Vibration Energy Harvesting

Sumitomo Metal Mining has successfully developed high-quality Fe-Ga magnetostrictive alloy single crystals through its unique single crystal growth and processing technologies. Through open innovation with device manufacturers, universities, and others, we are contributing to the realization of devices and applications that leverage the characteristics of high-quality single crystal magnetostrictive materials, creating new value in various fields.