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Q&A with Metamagnetics’ Experts

Q: Aren’t ferrites old news?

Q: What are some advantages to ferrites?

Q: What are some notable characteristics to keep in mind when picking ferrites?

Q: What does it mean for a ferrite to have “nonlinear” properties?

Q: What are power cores?

Q: What types/classes of materials are used for power cores production?

Q: What does “magnetically tunable” mean?

Q: What are the benefits of analogue phase shifters and filters?

Q: Aren’t ferrites old news?
A: Natural ferrites such as magnetite have been used as magnets for thousands of years. Synthetic ferrites were invented in the 1930s; however, very little research has been done to improve upon them since then. Universities in the US no longer have education programs about ferrite magnetics, so there are virtually no new experts in the field. Very few people know how to work with ferrites and design ferrite-based products. Metamagnetics is the one place that does have the experts on ferrites who continue to build upon the century-old knowledge base and create unique products with this unique expertise. Because ferrites are so abundant in all the electronics in our lives, any improvements make a huge impact.

- Anton Geiler, PhD, President of Metamagnetics

Q: What are some advantages to ferrites?
A: Ferrites are often compared to silicon semiconductor chips, which have developed very quickly in recent decades compared to the lack of research on ferrites. While semiconductors have limited capabilities, ferrites are passive devices that provide a useful functionality without a lot of loss. Ferrites are a domestically available, low-cost material with a well established manufacturing base. Ferrites are non-toxic and electrically insulating. A special property of ferrites is non-reciprocity—signals going in one direction can be different than the signals going in the opposite direction—that allows them to be used as control devices. Ferrites used to be big, heavy, and have limited bandwidth. Metamagnetics innovates where no one else has for decades.

- Anton Geiler, PhD, President of Metamagnetics

Q: What are some notable characteristics to keep in mind when picking ferrites?
A: Desired operating frequency: Ferrites have electromagnetic properties that are strongly frequency dependent. It is very important to choose the right material(s) for each application. It is hard to make very broadband devices with ferrites because you often have to use multiple compositions of ferrite materials.

Radiation Hardness: Ferrites are inherently radiation proof. This makes them an excellent choice for space applications where other materials would require special shielding to protect them from hazardous radiation in space.

High Power Handling: Ferrites are insulators so they can handle high average power levels, which both makes them more robust as well as easier to integrate into systems because they can be used in the front end of a receiver (low power) as well as in high power sections of a given RF system.

Temperature stability: The EM properties of ferrites are often strongly dependent on temperature. For this reason, one often has to incorporate temperature compensation systems into devices.

Small: Ferrites typically have a high dielectric constant that allows them to be smaller than semiconductor devices.

Passive: Ferrite devices can often be passive, which means they require no power or control circuitry to operate. Metamagnetics’ self-biased circulators and Auto-Tune Filters are two such examples. The devices consume no electricity so they are cheaper to operate and design.

Maturity of manufacturing processes: Although some certain ferrites have become almost a standard material in RF (radio frequency) microwave fabrication, the processes are nowhere near as matured and refined as those of semiconductors like silicon, GaN (gallium nitride) and GaAs (gallium arsenide). This means that there are often extra challenges in manufacturing devices on ferrites (such as lapping, polishing, cutting, metallization and circuit patterning).

Advanced materials: Ferrites are ceramic materials, which means they can be made very cheaply using pretty old technology (powder processing). It’s very cheap and you can tailor the composition of the ferrite to your needs. They can also be grown as high quality single crystal substrates, or deposited as thin films using pulsed laser deposition (PLD). In recent years many advances have been made allowing a greater flexibility and control in ferrite material properties. Ferrites were kind of a niche technology in the early days of electromagnetics. They had a few uses and they were great for that, but beyond that people kind of lost interest as the semiconductor industry started to take off. However, researchers kept plugging away all these years and now there is more and more interest in ferrites because of their unique exotic properties.

- Michael Geiler, Senior Research Technician

Q: What does it mean for a ferrite to have “nonlinear” properties?
A: All materials have nonlinear properties. They usually become apparent at the upper end of the power handling capability of a device, at the extremes of the frequency range, or both. This means the device stops operating the way it is supposed to (loss goes up, phase becomes distorted, etc). From a theoretical point of view, a perfectly linear system would look like this:

Output A = Input A + Gain (on a graph this would be a straight line). The gain would remain constant while Input changes. When it is non linear the “Gain” part changes depending on what the Input is (this would not be a straight line).

These are usually things we want to avoid! However, if you really understand the mechanisms behind the nonlinearity, you can use it to your advantage and do things that would otherwise require very sophisticated systems requiring multiple components and complex circuit networks. A great example of this is Metamagnetics’ AtF.

The reason we can do this is because we have a tremendous amount of knowledge and expertise in electromagnetism and in particular, in ferrites. There is a very small community of people who know about ferrites and an even smaller community of people that are experts in them. This makes us unique.

- Michael Geiler, Senior Research Technician

Q: What are power cores?
A: A power core is that which provides a common magnetic path between the windings of a power transformer, thus enabling effective flux linkage between the windings. It is the main component of the transformer and as such the performance specifications of the core material components, such as insertion loss, isolation, power handling, and temperature stability, is vital to the overall system performance. Metamagnetics specializes in the design and optimization of power core for high frequency usage.

- Ogheneyunume (Yunume) Obi, PhD, Materials Scientist

Q: What types/classes of materials are used for power cores production?
A: Power cores are typically made of ceramic ferrimagnetic, conducting laminated or pressed powder-metallic magnetic materials. For high-frequency operation with low power loss insulating, ferrimagnetic materials offer superior performance. The ferrite materials currently dominating industrial applications include Manganese-Zinc (MnZn) and Nickel-Zinc (NiZn) ferrites. MnZn ferrites with soft magnetic properties, low loss, and high permeability values, have been the material of choice for medium and high-frequency power electronics for several decades. Usually they are designed to exhibit optimum magnetic performance up to 1 MHz, above which they introduce losses in the form of unwanted heat in the device. Heat can alter the performance of the device and surrounding devices to the point that they do not meet requirements. Cooling systems that require energy, space and ultimately increase the upfront and operational costs of the device and or system are needed to eliminate this unwanted heat. To reduce cost and improve power conversion, designers desire low loss, high permeability magnetics over a wide frequency range. At frequencies greater than 1MHz, NiZn ferrites are typically used. However, NiZn ferrites are low permeability ferrites.

Metamagnetics has designed and developed grain boundary engineered, low loss, high permeability ferrite cores composite material using nanotechnology to enable a cost effective solution for higher efficiency magnetics in power electronics components. Our technology enables the ferrite to operate from 1 MHz to 14 MHz by extending its frequency of operation.

- Ogheneyunume (Yunume) Obi, PhD, Materials Scientist

Q: What dooes magnetically tunable mean?
A: The term “magnetically tunable” means that properties of a material can be altered by applying a magnetic field. Nearly all materials are affected by magnetic fields, which can change material properties from the atomic through macro scale in ways that may be readily apparent or hidden to the naked eye. Certain types of materials, such a magnetostrictives, react to magnetic fields by changing size. Another type of material, known as magnetoelectrics, generate electric fields as a reaction to applied magnetic fields. Ferrite materials are of significant interest for use in electronics due to a property called “permeability”, which can be controlled using an applied magnetic field. Permeability is a fundamental material property that dictates how an electromagnetic wave propagates. Controlling permeability via an applied magnetic field enables magnetically tunable devices capable of various functions such as shifting wave phase, frequency response, attenuation, and more. Magnetically tunable devices offer many unique functions and novel modes of operation compared to digital voltage controlled counterparts.

- Scott Gillette, PhD, RF Engineer

Q: What are the benefits of analogue phase shifters and filters?
A: Analog phase shifters and filters offer smooth continuous tuning of phase and passband, respectively, over their specified range of operation. Unlike digital devices, analog devices have infinite tuning resolution. For example, a 360° analog phase shifter can be tuned to provide a phase shift of any angle between 0 and 360° whereas a 360° 4-bit digital phase shifter has 16 states and is able to provide phase shift from 0 – 360° in discreet steps of 22.5°. For low resolution applications, digital devices suffice, but for high-resolution applications such as radar, imaging, active filtering, directed energy, and other beam-steering platforms, analog devices are required. Another benefit to analog-based devices is that they can always be tuned using either analog or digital control circuitry, where digital-based devices are limited to digital control. Metamagnetics’ analog phase shifters and filters are low-loss, high-speed, require low tuning power, and offer a fail-safe mode of operation such that if the control circuit becomes compromised, the transmission line is unaffected.

- Scott Gillette, PhD, RF Engineer

For more information, call us at (617) 833-2950