I have two boxes of SMD r.f. inductors. One lot are wire wound, and the others are ceramic chip. What is the difference in construction? From peering at them with a microscope I see that the wire wound ones are, umm, wound with wire. But how are the ceramic chip ones made? What do they look like inside? I notice that the \$Q\$ for the wire wound ones is higher. Are there any other important differences in usage?
The internal structure is similar to that of a multilayer ceramic capacitor:
The wirewound type has less capacitance between windings, leading to a higher self-resonant frequency. Also lower DC resistance (so higher Q) and a higher DC current rating. The multilayer type can support higher inductance in a small package.
Either type can be made with 'air' (actually ceramic, but it has similar magnetic properties but higher dielectric constant) or ferrite, with the former suitable for very low inductances.