Flat Inductor
Electromagnetic elements fabricated on flat substrates replace traditional wire-wound coils in compact sensor designs. Utilizing planar coils reduces the physical height of inductive displacement and proximity sensors. These components are usually integrated directly onto printed circuit boards or ceramic substrates.
Magnetic Field
Spatial distribution of the magnetic flux is determined by the geometry of the flat conductors. The field is concentrated near the surface of the substrate and decays rapidly with distance. This decay profile limits the effective sensing range to a fraction of the coil diameter.
Fabrication Process
Photolithography methods etch copper traces on the substrate with high dimensional accuracy and repeatability. This manufacturing process produces highly consistent coil inductances across different production runs, which reduces the need for individual sensor calibration. Multi-layer boards can connect multiple planar spirals in series to increase the total inductance without increasing the sensor footprint.
The trace width and spacing are optimized to minimize resistance and parasitic capacitance.
Temperature Sensitivity
Thermal expansion of the substrate shifts the trace geometry and alters the coil inductance over the operating range. Utilizing low-expansion materials such as ceramic or FR4 reduces this thermal drift. High-precision designs include reference coils on the same substrate to cancel out these thermal effects.
