Device for determining material parameters by means of microwave measurements

A device for determining, by means of microwave measurements, a physical characteristic of a product in a dielectric medium, in combination with a pipeline through which the medium is flowing, said pipeline having a pipeline longitudinal axis and comprising a section composed at least partially of dielectric material located in a measurement area, said section having a wall, an outer diameter and an interior cross section and the dielectric material having low dielectric losses, said device comprising:

• a microwave transmitting/receiving system for interacting with the medium, said system including a waveguide at least partly enclosing the pipeline section to define the measuring region, said waveguide having a side wall provided with two opposed openings through which said pipeline section passes, a waveguide longitudinal axis, an internal width dimension perpendicular to said waveguide longitudinal axis, a microwave radiation input and a microwave radiation output, said measuring region being interposed between said input and said output so that radiation guided in said waveguide traverses said measuring region and has a transverse electric field which extends perpendicular to said waveguide longitudinal axis and to said width dimension, and
• means connected to said output for evaluating microwave radiation which has traversed said measuring region by measuring at least one of the damping and phase shift induced in the microwave radiation by product in the medium flowing through said waveguide, and wherein
• said pipeline section extends through said openings in said waveguide side wall in such a way that said pipeline longitudinal axis coincides with the direction of said transverse electric field formed inside said waveguide,
• the outer diameter of said pipeline section is not larger than said internal width dimension of said waveguide perpendicular to said pipeline longitudinal axis and perpendicular to said waveguide longitudinal axis so that said pipeline section substantially completely fills the cross-section of said waveguide and the microwave radiation acts on substantially all of the medium flowing through said pipeline, and
• the interior cross section of said pipeline section has a dimension in the direction of said waveguide longitudinal axis which decreases from said waveguide longitudinal axis in the direction of said internal width dimension, and the mode of the transverse electric field is selected such that the intensity of the transverse electric field decreases from said waveguide longitudinal axis in the direction of said width dimension to approximately the same degree as said dimension of said pipeline section.