Microwaves are highly sensitive to water molecules. When penetrating the measured material the microwaves cause a rotation of the free water molecules. As a result the velocity of the microwave is slowed down (phase shift) and their intensity is weakened (attenuation). Both effects are measured, allowing for a very stable measurement. Phase shift and attenuation are a direct measure for the water content, out of which concentration or dry substance is indicated.
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. With the microwave transmission principle used by Berthold, the whole material cross-section is penetrated. Therefore the measurement is highly accurate and representative. Factors such as colour, viscosity, inhomogeneous composition or dust have no or only a negligible effect on the measurement performance.