Microwave measuring device

A microwave measuring device for a flowable medium, comprising:

• a measuring tube for conducting the medium;
• a first microwave antenna designed to generate a variable microwave signal and emit said signal into the medium;
• a first magnetic-field-sensitive measuring device for determining a magnetic field, the first magnetic-field-sensitive measuring device including:
• a measuring device component having an optically excitable material, wherein the microwave signal acts on the optically excitable material;
• an optical excitation device designed to optically excite the optically excitable material;
• and
• an optical detection device designed to provide a detection signal correlating with light emitted by the optically excitable material;
• and
• an evaluation circuit designed to determine a magnetic field and/or a change in the magnetic field on the basis of the detection signal.