Iron sulfide is a chemical compound (different from a mixture of Iron and Sulfur, show by its different physical and chemical properties). It is made of iron and sulfide ions.
A dielectric material (dielectric for short) is an electrical insulator that can be polarized by an applied electric field. dielectric resonator oscillator (DRO) is an electronic component that exhibits resonance of the polarization response for a narrow range of frequencies, generally in the microwave band. It consists of a puck of ceramic that has a large dielectric constant and a low dissipation factor.
Dielectric pads are simple pouches containing a highly conductive material that are placed between the patient and the receiver coil to reduce dielectric artifacts. The simplest pads contain a dilute solution or gel containing manganese chloride.