Resonator method

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The microwave resonator method is a measuring method for determining the humidity and / or the mass or the density of a product that works with electromagnetic fields .

It is suitable for laboratory or process applications. Either cavity resonators or stray field resonators are used as sensors . The respective resonance used for the measurement is characterized by two parameters: the resonance frequency and the half-width of the resonance curve. If a material to be measured is introduced into the resonator or, in the case of stray field resonators, brought into contact with the resonator, the resonance frequency drops and at the same time the half-width of the resonance curve increases. In each measurement, the change in these two resonance parameters when the resonator is loaded with material to be measured is measured. The change in both measured parameters depends in the same way on the mass of the material to be measured, but in different ways on the moisture of the material to be measured. The quotient of the two measured variables is therefore only dependent on the moisture content of the material to be measured. This quotient is therefore a suitable value for density and mass-independent moisture measurement.

Since the changes in the two resonance parameters (resonance frequency and half-width) are dependent on the mass of the material to be measured that is located in the measuring field, a density measurement can be carried out using one of the two parameters for objects to be measured that fill the entire measuring field area homogeneously with regard to their density. Fluctuating product moisture levels can be compensated for using the other resonance parameter. The density measurement is therefore independent of moisture.

A mass measurement can then be carried out on objects to be measured if these objects are in a homogeneous electric field area during the measurement. Such a homogeneous measuring field can only be generated in a limited spatial area. In the case of pharmaceutical products such as capsules or tablets, a mass measurement is possible. Fluctuating product moisture levels can be compensated for using the other resonance parameter. The mass measurement is therefore independent of moisture.

literature

  1. T. Hauschild: Density and Moisture Measurements Using Microwave Resonators , in: K. Kupfer (Ed.): Electromagnetic Aquametry , Springer-Verlag, Berlin Heidelberg, 2005, p. 193 ff.
  2. Patent EP0468023 : Method for measuring the humidity of a material to be measured with the aid of microwaves and a device for carrying out the method. Applicant: TEWS Electronics. ‌