Abstract: An ultrasonic flow meter has two ring-shaped piezoelectric transducers (1, 2) comprising ring-shaped piezoelectric elements or being composed of piezoelectric sections. Both the transducers (1, 2) are arranged in axial symmetry in a distance to each other. One of them is operated as the ultrasonic transmitter and the other one as ultrasonic receiver. The medium, the flow rate of which is to be measured, flows through both the transducers (1, 2) essentially parallel to the axis (L--L).

Abstract: An apparatus and a method for the measurement of the complex dielectric constant of a material by evaluating the amount of detuning introduced by the presence of the material. In order to simplify the circuitry required for measurement and evaluation according to the invention there are provided two rf resonators (8, 8') of the same construction, each of them comprising a dielectric solid state resonator (1, 1') in a case having a first conductive section (2, 2') and a second section (3, 3'), which is permeable for alternating fields. Both the rf resonators are positioned to each other in such a way as to provide a shielding effect by their conductive case sections (2, 2') against mutual interference and to have their sections permeable for electromagnetic fields (3, 3') facing towards the material to be measured.