Thanks for some good info on ferrites. The video brought 2 questions to mind: 1. You mentioned gluing ferrites together. What glue should be used? If a ferrite has cracked or broken, can it be glued to return it to service until a replacement is obtained? 2. What would be the effect of using a toroid that is bigger in size (but of proper mix) than is needed rather than an appropriate size toroid? Thanks R.E. - K1AUS
For adhesives, cyanoacrylate works very well on ferrite cores. Gluing a broken core back can work with a few caveats. If the fracture or break is running across the magnetic path (O.D.-I.D. on a toroid for example), there is going to be some loss of effective permeability. This loss will be proportionately larger on higher permeability materials than lower ones. Whether or not the core remains functional really depends on what it's being used for and how sensitive the application is to values like inductance, coupling coefficient, impedance, etc... As far as larger than needed cores, it again will depend on what it is being used for. Large cores will have higher inductance values typically and produce lower core losses due to the reduction in flux density from the greater cross sectional area. Windings can be spaced apart further leading to lower interwinding capacitance (can be good or bad). A negative is that ferrites (all ferrites) are prone to dimensional resonance beyond some frequency when the cross section gets too massive leading to higher relative losses and reduced bandwidth than a smaller toroid of the same material. That last one isn't yet well quantified and it's significance will vary a lot by size, material, and frequency.
Aside from the difficulty of showing the small cores on video, will you go into the details of smaller cores? I am curious about the multi-aperture cores you guys offer and how they compare to a traditional toroid, both come in very small sizes!
Particle accelerators eg SLAC use large ferrite rings and maybe 10 inches dia and 1 inch thick. These are stacked to make typical pulsed magnets , eg kicker magnets.These ferrites are sometimes used as saturating magnetic swithces. This is highly dependent on the materials.
One trick would be to use several smaller cores stacked together or in parallel. Lower cross-section cores will typically provide lower losses over a wider range of frequencies (to a point) but, they cannot handle the same sort of flux density as a large core. The ideal core would be something like a long tube shape. Thin walls but, high length the get the cross section number back up. A stack of small cores can be used for a similar effect.
They definitely use geometric tricks to manipulate and dissipate the fields that hit the walls. The ferrites in these are generally just flat absorbers behind the e field absorber foam )typically where the fun geometries come in. In ferrites, we usually talk about dimensional resonance in the sense of standing wave generation inside the magnetic cross section. This is still an area of a lot of research to better understand but, the effect seems somewhat similar to skin effect in conductors.
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Excellent. Informative.
Thanks for some good info on ferrites. The video brought 2 questions to mind:
1. You mentioned gluing ferrites together. What glue should be used? If a ferrite has cracked or broken, can it be glued to return it to service until a replacement is obtained?
2. What would be the effect of using a toroid that is bigger in size (but of proper mix) than is needed rather than an appropriate size toroid?
Thanks
R.E. - K1AUS
For adhesives, cyanoacrylate works very well on ferrite cores. Gluing a broken core back can work with a few caveats. If the fracture or break is running across the magnetic path (O.D.-I.D. on a toroid for example), there is going to be some loss of effective permeability. This loss will be proportionately larger on higher permeability materials than lower ones. Whether or not the core remains functional really depends on what it's being used for and how sensitive the application is to values like inductance, coupling coefficient, impedance, etc... As far as larger than needed cores, it again will depend on what it is being used for. Large cores will have higher inductance values typically and produce lower core losses due to the reduction in flux density from the greater cross sectional area. Windings can be spaced apart further leading to lower interwinding capacitance (can be good or bad). A negative is that ferrites (all ferrites) are prone to dimensional resonance beyond some frequency when the cross section gets too massive leading to higher relative losses and reduced bandwidth than a smaller toroid of the same material. That last one isn't yet well quantified and it's significance will vary a lot by size, material, and frequency.
Aside from the difficulty of showing the small cores on video, will you go into the details of smaller cores? I am curious about the multi-aperture cores you guys offer and how they compare to a traditional toroid, both come in very small sizes!
Particle accelerators eg SLAC use large ferrite rings and maybe 10 inches dia and 1 inch thick. These are stacked to make typical pulsed magnets , eg kicker magnets.These ferrites are sometimes used as saturating magnetic swithces. This is highly dependent on the materials.
What are the largest types 43, 52 and 61 cores available? I'm Looking for cores larger than the FT290 series.
In broadband (RF) transformers, how do you get higher power handling and wide bandwidth at the same time?
One trick would be to use several smaller cores stacked together or in parallel. Lower cross-section cores will typically provide lower losses over a wider range of frequencies (to a point) but, they cannot handle the same sort of flux density as a large core. The ideal core would be something like a long tube shape. Thin walls but, high length the get the cross section number back up. A stack of small cores can be used for a similar effect.
Ferrite tiles in EMC chambers actually use dimensional resonance, right?
They definitely use geometric tricks to manipulate and dissipate the fields that hit the walls. The ferrites in these are generally just flat absorbers behind the e field absorber foam )typically where the fun geometries come in. In ferrites, we usually talk about dimensional resonance in the sense of standing wave generation inside the magnetic cross section. This is still an area of a lot of research to better understand but, the effect seems somewhat similar to skin effect in conductors.