Surface Geometry
Inductive circuit elements produced as flat metallic spirals provide the necessary reactance for high-frequency filtering without the height of traditional wire-wound coils. A planar inductor relies on the surface area of the substrate to maintain a low profile in modern mobile or satellite communication hardware. The trace is typically etched into a copper layer on a printed circuit board or deposited onto a silicon wafer.
This configuration allows for the direct integration of magnetic components into the semiconductor manufacturing process.
Magnetic Flux
Current flowing through the spiral creates a magnetic field perpendicular to the surface. In a planar inductor, the proximity of the turns increases the mutual inductance but also raises the resistance. Designers use software to model the flux lines and optimize the shape for the highest efficiency.
Quality Factor
Performance is measured by the ratio of inductive reactance to the series resistance. A planar inductor with a high quality factor has lower energy loss and sharper resonance. This metric is verified using an impedance bridge at the design frequency.
Parasitic Capacitance
Capacitive coupling between the parallel traces of the spiral can limit the operating range. If the frequency is too high, the planar inductor behaves like a capacitor instead. This self-resonant frequency defines the upper boundary of the usable bandwidth.
