Filling level monitoring device for monitoring the filling level of a fluid container, hydrogen tank, and aircraft comprising such hydrogen tank

A filling level monitoring device configured to monitor a filling level of a fluid container, the filling level monitoring device comprising:

• at least one exciting element;
• at least one sensing element;
• a signal source;
• at least one suspension element having a suspension stiffness;
• and
• a processing unit;
• wherein the at least one exciting element is configured to be mounted to at least one of the fluid container or the at least one suspension element such that the at least one exciting element is operable to excite at least one suspension mode of vibration, wherein the suspension mode of vibration is a distinct mode of vibration of the at least one suspension element;
• wherein the at least one suspension element is configured to be fixedly connected to the fluid container such that, when excited by the at least one exciting element, the fluid container and the at least one suspension element together vibrate in unison;
• wherein the at least one sensing element is configured to be mounted to at least one of the fluid container or the at least one suspension element, and to sense vibrations corresponding to the at least one suspension mode of vibration;
• wherein the signal source is connected to the at least one exciting element and is configured to generate an input signal comprising a multitude of frequency components;
• wherein each of the at least one sensing element is connected to the processing unit and is configured to sense vibrations within the fluid container and to generate and send a corresponding vibration signal to the processing unit;
• and
• wherein the processing unit is configured:
• to identify the at least one suspension mode of vibration from the vibration signals of the at least one sensing element and the input signal;
• to determine a modal frequency of the at least one suspension mode of vibration;
• and
• to determine a current filling level of the fluid container based on the modal frequency of the at least one suspension mode of vibration.