Abstract: A resonator device for testing a material quantity in the tobacco-processing industry for existence of at least one foreign substance and/or for detecting at least one of weight, density and humidity level of the material includes a resonator housing having a through opening for the material to pass through and a testing region located inside the resonator housing to which the material can be moved at least in part. The device has at least one element that increases energy density of electromagnetic waves for increasing the energy density in at least a portion of the testing region.

Abstract: A method of detecting impurities in a mass, such as detecting metallic and/or plastic particles in a stream of tobacco particles or filter material for tobacco smoke, includes the steps of moving the mass relative to a microwave field and/or vice versa, and analyzing the influence of the mass upon the microwave field. The analyzing step involves simultaneously measur- the actual values of a first and a second parameter of the microwave field, ascertaining the presence or absence of those changes of the parameters which are attributable to the presence of impurities in the mass, determining whether or not the changes are within an acceptable range, and generating signals for segregation of impurities-containing portions of the mass from the other portions when the changes are outside of the acceptable range.

Abstract: A resonator device for testing a material quantity in the tobacco-processing industry for existence of at least one foreign substance and/or for detecting at least one of weight, density and humidity level of the material includes a resonator housing having a through opening for the material to pass through and a testing region located inside the resonator housing to which the material can be moved at least in part. The device has at least one element that increases energy density of electromagnetic waves for increasing the energy density in at least a portion of the testing region.