Improving Sensitivity and Resolution of Planar Magnetic Inductive Sensors by Optimizing Gap Between Magnetic Films

The sensitivity and resolution of the planar magnetic inductive sensors are enhanced by optimizing the gap between the upper and lower magnetic films. The tradeoff between the effect of the effective magnetic permeability and magnetic leakage of the magnetic films on the inductance of the sensor produces a gap that optimizes the sensor performance. This conclusion is verified theoretically and experimentally with the fabrication and testing of planar magnetic inductive sensors with given dimensions of magnetic films and planar spiral coil. From the analysis, the optimal gap ( $g$ ) for our manufactured sensors with given dimensions is four times the magnetic film thickness ( $t$ ). Experimentally, when $g\mathrm {/}t=4$ , the inductance value, inductance ratio, and voltage sensitivity of sensors are all the largest. The sensitivity and resolution of the sensor with $g\mathrm {/}t=4$ are 1.81 mV/Oe and 50.23 nT at 500 kHz. Compared with the prototype whose magnetic films and planar coil are stacked tightly together, the sensitivity is increased by 43.72% and the resolution is improved by 33.51%. It is universally applicable that there is a gap that optimizes the performance of the planar magnetic inductive sensor.