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SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $72.50 12 issues (1 year): $135 24 issues (2 years): $255 Online subscription (Worldwide) 6 issues (6 months): $52.50 12 issues (1 year): $100 24 issues (2 years): $190 For overseas rates, see our website or email silicon<at>siliconchip.com.au * recommended & maximum price only Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Editorial Viewpoint What is ferrite? My editorial in the April 2025 issue was titled “Ferrite beads are not inductors”. It explained that while ferrite is used in both inductor cores and beads, their functions are different. In it, I wrote: “Ferrite is a ceramic material that contains iron oxide.” This is true, but it’s a very simplified explanation. In response, a reader wrote in to say: “Ferrite beads are very rarely iron oxide. They are, in the main, MnZn and NiZn, with other exotics being used. Also, you can buy iron powder beads (not an oxide), which are in fact used for their inductance, among other things.” This comment makes a few interesting points worth examining. First, are ferrite beads “rarely iron oxide”, and are they really made of “MnZn” or “NiZn”? In my editorial, I didn’t claim that ferrite is iron oxide; only that it contains it. That distinction is important. Ferrite refers to a family of ceramic materials with a particular crystal structure – the spinel structure – which incorporates iron (Fe) and oxygen (O), along with other metal ions like manganese (Mn), nickel (Ni), zinc (Zn), or cobalt (Co). The only pure-iron spinel is magnetite (Fe3O4), but it’s unsuitable for most magnetic core applications due to its relatively low resistivity and poor high-­ frequency performance. Commercial ferrites, by contrast, are mixed-metal oxides; engineered ceramics with general formulas like (Mn1-×Zn×)Fe2O4 or (Ni1-×Zn×)Fe2O4, where x typically ranges from 0.2 to 0.6. These additional metal ions are not just incidental. First, the spinel structure doesn’t form correctly without them. Second, they profoundly affect the material’s magnetic and electrical properties: permeability, losses, Curie temperature, resistivity and more. That’s why ferrites are tailored for specific roles, from switchmode transformers to EMI suppression. You may have noticed ferrite cores labelled with codes like N27, N49, N87, N90, N97 (TDK/EPCOS), 3C90, 3C94, 4A11, 4C65 (Ferroxcube), or #31, #43, #61, #77 (Fair-Rite). These designations reflect specific ferrite formulations and performance characteristics. Some are optimised for low core losses at 100kHz, others for high resistivity and EMI suppression into the MHz range. Designers don’t always need to understand the chemistry, but they must choose the right material by referring to the datasheet. So, in a sense, the reader is correct: ferrite is not just one compound, nor is it just “iron oxide”. It’s a highly engineered family of materials. As for powdered iron “beads”, I didn’t mention them in the previous editorial because their function is fundamentally different. Powdered iron is a metallic material (not a ceramic), with much lower resistivity and different loss characteristics. These components are usually used as inductors, not EMI suppression beads. They are relatively uncommon; I’ve never knowingly encountered one in a circuit, or if I did, it was indeed labelled as an inductor, which is appropriate. The bottom line is that ferrite is a fascinating and versatile material, and many people who use it – whether in beads or transformer cores – may not be fully aware of how varied and finely tuned its properties can be. Cover image: https://pixabay.com/photos/dji-farming-agriculture-drone-4223416/ by Nicholas Vinen Subscription Prices, effective 01/09/2025 New Prices Print (AU) Printing and Distribution: 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Combined (AU) Print (NZ) Combined (NZ) RoW 6-month $72.50 $82.50 $85 $95 $105 12-month $135 $155 $160 $180 $200 24-month $255 $280 $300 $335 $390 Australia's electronics magazine siliconchip.com.au