Water molecules are strong dipoles. When an electromagnetic field is produced, the water molecules adjust themselves according to the field's polarity, due to their positive and negative ends.
If the field changes its polarity rapidly, only the water molecules can follow this change in direction as they are small and have a strong dipole.
This movement requires energy, which is drawn from the electromagnetic field. This loss of energy, which depends on the number of water molecules, is detected.
However, the number of water molecules in the measuring volume may vary depending on changing densities due to different product heights on top of the probe or due to compression of the product.
These variations in density lead to a change in the propagation speed of the electromagnetic waves. This change in propagation speed is detected and compensated for. This measuring technique allows for the determination of the moisture content of a given material independent of its density.
A new, patent-pending probe structure developed by Döscher & Döscher now allows to eliminate environmental influences, such as temperature, completely. For this new development, the well-known method of a reference measuring section was for the first time applied to microwave measurement technology. Maximal precision, reproducibility and long-term stability have thus become possible, even under extreme temperature conditions.