  In this paper, an electromagnetic sensor which can operate simultaneously in
capacitive and inductive modalities with sensitivities to permittivity,
conductivity, and permeability is developed, and a novel measurement strategy
is proposed accordingly. The sensor is composed of two planar spiral coils with
a track width of 4 mm, which promotes its capacitive mode. The capacitive
coupling is measured in common mode, while the inductive coupling is measured
in differential mode. In capacitive mode, the sensor is sensitive to changes in
permittivity, i.e., the dielectric material distribution; while in inductive
mode, it is sensitive to magnetically permeable material and electrically
conductive material. Furthermore, it is demonstrated that the sensor can
simultaneously measure dielectric and conductive materials. This novel sensing
element has been designed and implemented. Experimental results verified its
effectiveness in dual modality measurement.
