NFT technology uses two coils, a transmitter and a receiver. Typically, the receiver coil is close to the transmitter coil, taking advantage of the transmitter’s near-field zone - that is, the zone where the magnetic field from the transmitter coil induces strong eddy currents, axially and radially, in the tube wall.

NFT probes operate within the same frequency range as remote-field testing (RFT) probes.

NFT is specifically suited to detecting corrosion, erosion, and pitting inside diameter of carbon steel tubing. NFT is perfect for fin-fan tube heat exchangers because eddy currents do not go through the wall of the tube. NFT is also much more sensitive to defects close to structures such as support plates and tube sheets.