Fixed inductors — Which option is NOT among the three major fixed-inductor core types commonly encountered in electronics?

Introduction:
Fixed inductors are built on a variety of cores optimized for frequency range, loss, and size. Recognizing standard core families helps with selection and expectations for Q factor and saturation characteristics.

Given Data / Assumptions:

• Focus on widely used fixed inductor types in RF and power electronics.
• Common categories include air core, ferrite core, and iron/iron-powder core.
• Exotic or nonmagnetic metals like magnesium do not serve as magnetic cores.

Concept / Approach:

Magnetic behavior hinges on permeability. Ferrite and iron-based cores provide high permeability; air cores have μ close to μ0 and are used at high frequencies to avoid core losses. Magnesium is non-ferromagnetic and is not used as a magnetic core in standard fixed inductors.

Step-by-Step Solution:

Verification / Alternative check:

Component catalogs categorize inductors by core as air, ferrite, and iron-powder among others. None list magnesium cores for inductors.

Why Other Options Are Wrong:

• air core / ferrite core / iron core / powdered iron: All standard and widely used.

Common Pitfalls:

• Confusing “iron core” with laminated transformer cores vs. iron-powder toroids; both are legitimate iron-based cores.
• Assuming any metal can be a magnetic core; only materials with suitable permeability and loss characteristics are used.

Final Answer:

magnesium core