In its most basic form — the single-element eddy current testing probe — a copper wire is excited with an alternating electrical current. This wire produces a magnetic field around itself in the direction ascertained by the right-hand rule. This magnetic field oscillates at the same frequency as the current running through the coil. When the coil approaches a conductive material, currents opposed to the ones in the coil are induced in the material — eddy currents.

When a copper coil is excited with an alternating electrical current, the coil produces a magnetic field around itself. This magnetic field oscillates at the same frequency as the current passing through the coil. The magnetic field follows the direction ascertained by the right hand rule.

The probe sensor consists of two coils, differentially connected in a bridge circuit. When an alternating current is applied, the sensor generates a magnetic field (Primary magnetic field), when this field approaches the tube wall of a conductive material, currents opposed to the ones in the coils are induced (Eddy Currents). The Eddy Current field again generates a secondary magnetic alternating field which is opposite to the primary field.