In broad terms, magnetic materials are classified as being either “hard” or “soft.” This distinction refers to the relative ease of magnetizing or demagnetizing these materials. Common magnets, like those on your refrigerator, are classified as hard magnetic materials because a very large externally applied magnetic field is required to magnetize them, and once they take on a magnetic charge they retain this magnetic field almost indefinitely. Conversely, soft magnetic materials are easily magnetized in the presence of even a weak external field and instantly lose their magnetic charge once the field is removed. Both types of materials have countless uses, and chief among the many useful applications is in the wide-ranging field of energy and power.
Soft magnetic materials are an essential part of many powered devices that we use every day, although their impact is not widely appreciated by those outside of specialized technical fields. Nevertheless, improving the performance of these materials is key to
- Improving the overall efficiency of our Nation’s electrical infrastructure
- Developing renewable energy sources
- Fully realizing NASA’s advanced technologies such as all-electric or hybrid vehicle systems, including aircraft
Uses of Soft Magnetic Alloys
Soft magnetic materials are the primary component of many alternating current (AC) distribution and conversion electrical systems. Transformers, motors, and alternators are common examples where these materials are used. One of the major contributors to the weight of a motor are the thin, soft magnetic “laminations” that couple electrical energy from the copper windings to the shaft. It is estimated that 45% of all worldwide electrical production is consumed by motors, so it is not difficult to understand how an improvement in the performance of soft magnetic materials would have huge economic benefits. These benefits will grow exponentially as the world moves toward a more electric society. On a smaller scale, electrical devices require that the components used to fabricate individual circuit boards, such as inductors, are as efficient as possible to perform optimally and to minimize unwanted waste heat. Many of these discrete components are also made from soft magnetic materials, and thus the soft magnetic material characteristics influence the overall performance of the larger system in numerous ways.
NASA Electrical System Needs
NASA requires efficient electrical systems for highly demanding applications in space but is also looking to leverage these technologies to enable new markets such as electrical propulsion in aviation. Low-loss power distribution and utilization are crucial to the efficient use of electrical power, and soft magnetic materials play a key role in both. One of NASA’s aeronautics strategic goals is to enable advanced propulsion options for commercial aircraft. Although numerous aircraft studies have outlined concepts that use electrical power distribution to enable substantial propulsion energy savings, all of these designs require considerable improvements in the power system components. The primary path to achieve increased power system performance is to increase the electrical operating frequency. New wide-band-gap semiconductors and pulse-width modulation schemes can provide these higher operating frequencies. Unfortunately, common soft magnetic materials are inefficient at higher frequencies, and because soft magnetic materials are crucial subcomponents of passive devices such as transformers and inductors, their inadequacies limit the overall system behavior. Therefore, the need for high frequencies and high efficiency has driven much of the research in soft magnetic materials. Although a new class of soft magnetic materials has shown potential for good performance at higher frequencies, these materials need to be transitioned from laboratory demonstrations into practical components.
Although soft magnetic materials have been around for centuries, the most commonly used versions have not changed significantly over the past 100 years. The electrical losses inherent in the use of these heritage materials could be substantially reduced through the development of new classes of iron- (Fe-) and cobalt- (Co-) based alloys called nanocomposite soft magnetic materials. These state-of-the-art materials are formed by cooling the alloy—almost instantaneously—from the molten state using a technique called rapid solidification. Casting in this manner followed by subsequent thermal treatments produces a material that contains very small grains embedded in a glassy matrix and is thus called a nanocomposite material. The material forms as thin continuous ribbons, resulting in two characteristics that make them desirable for power applications.
First, the material is naturally produced into the thin strips required for the motor laminations, generally on the order of 20 μm (finer than the diameter of a human hair). This eliminates a separate operation to mechanically form the material into the thin strips required for the motor laminations shown earlier in the figure of an electric motor. The thinner the material can be made, the lower the inherent AC electrical losses will be. Second, the rapid cooling produces the unique nanocomposite atomic structure in the material that imparts low losses for high-frequency AC applications. Common electrical steels become very inefficient at frequencies just greater than the conventional 60 Hz found in household applications, whereas these nanocomposite materials can operate up to 100,000 Hz.
NASA Glenn Magnetic Research Activities
New soft magnetic materials are key to developing smaller, lightweight power electronic components that operate efficiently at the higher frequencies commensurate with the capabilities of the new, wide-band-gap semiconductors. However, introducing recently developed nanocomposite alloys into relevant components requires the ability to cast ribbons with widths that are much greater than the standard 3 mm typically produced in research laboratories as well as the manufacturing skills to incorporate these ribbons into a specific application. Therefore, NASA is both developing new and more capable nanocomposite alloys as well as scaling up the production capabilities to the sizes and quantities necessary to support the production of relevant-sized components. Currently, ribbons as wide as 51 mm (2 in.) can be produced in lengths of over 600 m (2,000 ft) at the NASA Glenn Research Center. Key collaborations with industry are being developed to scale up processing even further. The goal is to move these alloys out of the laboratory and into devices that will enable a range of commercial and government applications such as electric and hybrid-electric propulsion systems, a more efficient national energy grid, and smaller, lower loss electrical circuits with less waste heat.
- Soft magnetic materials are primarily made from Fe, Ni, or Co and do not retain their own magnetizing field.
- Soft magnetic materials are used in a large variety of power-related applications.
- The primary path to substantial increase in power system performance is to increase the electrical operating frequency.
- Advanced soft magnetic materials allow for these higher frequencies, which in turn reduces wasted energy, enables new power systems, and has wide-ranging economic and societal benefits.
For more information, visit: NASA’s Magnetic Materials Lab Moves Evolution of Energy Conversion Forward