Magnetic Testing and Evaluation

Modern technology depends to an unprecedented degree on the phenomenon of magnetism. Magnetic effects are made use of in every electric motor, every electrical transformer or power supply, every radio, every microwave, most every electric circuit, and in switches, sensors, compasses, and much, much, more.

How a magnetic field interacts with a ferromagnetic material is essential to the proper function of many apparatus. The properties which describe the interaction of a ferromagnetic material with magnetism include:

• Permeability
• Coercive Force
• Remanence
• Saturation Magnetization

Permeability is a measure analogous to electrical conductivity: it measures the ability of a material to conduct magnetic flux. It is measured by the slope of the magnetization curve plotting magnetic flux in a material vs. magnetizing force. Materials with high permeability are used for focusing and concentrating magnetic forces in electromagnets, transformers, and electric motors. In many cases where the function of a device depends on its permeability, materials must be tested to ensure adequate permeability. High permeability materials like Mu-metal and Permalloy, which have an approximately 80:20 ratio of iron to nickel, are also useful for magnetic shielding enclosure construction, where they form the path of least resistance for magnetic flux to travel around an enclosed volume. This reduces significantly the amount of magnetic flux that crosses the shielded boundary. In cases where very strong magnets need to be shielded, or where a region must be made free of all magnetic influences, including the earth’s ubiquitous magnetic field, multiple shielding enclosures are nested within each other to increase shielding efficiency. Shielding is much more effective if the shielding high-permeability material is divided into several separated layers, rather than thickening a single layer. Permeability is strongly affected by alloy chemistry and grain structure, and can be affected by annealing, heat treatment or cold working, and other modifications.

Coercive force or Coercivity is a measure of how permanent a magnet is, ie. what amount of magnetic force it takes to reverse its magnetization. Materials with high coercive force require high magnetizing H fields to become magnetized or demagnetized. Coercive force is defined as that amount of magnetizing H-field needed to return the magnetization B of a magnet to zero, after it has been magnetized. Coercive force also varies with material composition and grain structure, and may be modified by annealing or cold working.

Remanence: When a ferromagnetic material is magnetized in one direction, it will not relax back to zero magnetization (B) when the imposed magnetizing field (H) is removed. Remanence is a measure of how strong a magnetization remains in a material after an externally applied magnetizing force is removed remains in a material after an externally applied magnetizing force is removed.

High values of remanence and coercivity are sought for permanent magnets, so that the magnets will retain a strong field and not be demagnetized in response to external magnetic interactions. Materials with high remanence and coercivity are known as magnetically “hard”, and are contrasted against materials with low coercivity and remanence which are known as magnetically “soft”. Magnetically soft materials are preferred for transformer cores and inductors because they require less energy to magnetize and demagnetize. This is desirable in transformers, inductors, and other AC magnetic devices because less energy is irretrievably lost as heat in the process of re-orienting the magnetic domains, which is done once every cycle of the applied AC power. Consequently, such transformers are more efficient.

Coercivity and remanence of some common permanent magnet materials are detailed in the below table. Besides coercivity and remanence, a quality factor for permanent magnets is the quantity (BB₀/μ₀)_max. A high value for this quantity implies that the required magnetic flux can be obtained with a smaller volume of the material, making the device lighter and more compact.

Saturation Magnetization: When the magnetizing force applied to a sample is increased, there comes a point when it cannot be magnetized further. All the magnetic domains in the material are then aligned maximally with the applied magnetic field. This is referred to as saturation.

We offer testing in accordance with existing standards; examples are shown below. Or, we can design a test-up that specifically addresses your needs.

Examples of Projects :

• Testing of small solenoidal mechanical actuators used for guided missile fuses, which may not work properly if the materials are not adequately permeable.
• Failure analysis of a pipe that became so magnetized that it could not be arc-welded to: “arc blow” phenomenon.
• Testing of mechanical wristwatches for the ability to withstand magnetic fields and continue operating accurately.
• Testing of magnetic packages, such as magnetrons from a particle accelerator, for air-shipment to determine if the magnetic field emitted from the packages will interfere with aircraft magnetic compasses..
• Design and evaluation of shielding enclosures for high power magnetrons in order to reduce their interference with aircraft navigational equipment.
• Measurement of AC electric fields near power lines for homeowners, schools, and hospitals.
• Measurement of microwave power at a housing development near an experimental RADAR research station to determine whether occupants were being irradiated.

Our team of scientists, engineers and electronics specialists has the knowledge you need to test, evaluate and improve your magnetic system, product, or production line. We have evaluated magnetic materials and components for major industrial, commercial and medical companies. We have started down the road to the twenty-first century. Now is the time to envision, design, create, and implement new magnetic technologies. MATCO Services, Inc. has the team needed to make these processes happen. Give us a call or send us an e-mail to discuss your specific testing requirement.

We Value Our Customers... Throughout the years, we have noticed that much of our business comes from repeat customers. Our expertise and well-equipped lab can account for much of this, but we believe there is something more to it. We attribute it to the fact that we promote an open and friendly environment that is never too busy to meet your needs.

At MATCO, we value your business whether you are a large corporation or a small enterprise. We will provide you with the attention you need and deserve. We invite you to visit us and get to know our staff, and share in the learning experience. Why Choose MATCO Services? As one of the premier testing and failure analysis firms featuring state of the art equipment, MATCO Services is able to provide a unique and diverse blend of services. Thousands of investigations have been performed at MATCO Services, ranging from jet engines and boiler tubes, to computer components and implants. Projects are not only conducted on your schedule from initiation to completion with competent and experienced personnel, and conducted in a discrete manner that ensures confidentiality as well.