Non-linear ultrasound method and apparatus for quantitative detection of materials

A system for determining a fill level of a fluid within a fluid vessel comprising:

• a vessel containing the fluid;
• at least two acoustic sensors positioned substantially on an exterior sidewall of the vessel, the at least two acoustic sensors positioned at different heights on the exterior sidewall, wherein each of the at least two acoustic sensors transmits a longitudinal signal through the exterior sidewall of the vessel, at a location on the vessel where the at least two acoustic sensors are positioned, and to an interface between an inner surface of the exterior sidewall of the vessel and the fluid contained within the vessel, wherein the transmitted signal generates a detection signal reflected from the interface between the inner surface of the exterior sidewall and the fluid contained within the vessel, the detection signal based on at least one fluid property of the fluid at the interface between the inner surface of the exterior sidewall and the fluid contained within the vessel, wherein the detection signal is received at the acoustic sensor from which the transmitted signal was transmitted;
• and
• a computerized device in communication with the at least two acoustic sensors, wherein a processor of the computerized device receives the detection signal from at least one of the at least two acoustic sensors and communicates an alert of the detection signal.