Microwaves penetrate the bulk material, causing a rotation of the free water molecules. As a result the velocity of the microwaves is slowed down (phase shift) and their intensity is weakened (attenuation). Both effects are measured and used as a direct indication of the moisture content.

These measuring effects are already achieved by using very small microwave transmission power – typically 0.1 mW. Consequently the measured material is neither warmed nor modified. Factors such as color, viscosity, inhomogeneous composition or dust have no or only a negligible effect on the measurement performance.

Fast neutrons are slowed down by scattering the hydrogen nuclei. But they are hardly affected by scattering other material components.

The measurement system comprises a source, emitting a cloud of fast neutrons. After their interaction with the water molecules within the measured material, the attenuated neutrons are measured with a specific detector that is sensitive to slow neutrons only. As the number of slow neutrons corresponds to the hydrogen content, the neutron technology is a extremely reliable measure for the product moisture. 

It is not affected by temperature, pressure, conductivity or varying particle sizes and even frozen water can be measured reliably.