https://www.google.com/search?q=ferrite https://en.wikipedia.org/wiki/Ferrite_(magnet) https://www.tdk.com/en/tech-mag/ferrite02/001#:~:text=In%20other%20words%2C%20ferrite%20is,allow%20current%20to%20flow%20easily.
https://en.wikipedia.org/wiki/Ferrite_core
examples: https://en.wikipedia.org/wiki/Ferrite_(magnet)#/media/File:Ferrite_cores.jpg
#/media/File:Ferrite_cores.jpg){kind=link}
https://en.wikipedia.org/wiki/Ferrite_core#/media/File:Ferrite_antenna.jpg
