This study presents a comparative investigation of two inductive circuit configurations employing planar coils for magnetic particle detection. The sensor element was a flat PCB coil, which proved to be effective while maintaining a compact design. The first circuit, based on a Colpitts oscillator, has relatively low sensitivity, however, offers the possibility of digital detection through frequency variation. In contrast, the second configuration, a modified Maxwell bridge composed of resonant second-order differential filters, exhibited significantly higher sensitivity and a linear response for small inductance variations. Experimental validation with magnetic samples of varying magnetic iron content confirmed that both circuits are capable of correlating voltage variations with the content iron.
Acuna et al. (2025) studied this question.