Systems and techniques are described making use of a vibratory transducer and a reflector spaced from the vibratory transducer to form a cavity for receiving a fluid between the vibratory transducer and the reflector, wherein the vibratory transducer is vibrated to generate a wave in the cavity, which propagates through fluid in the cavity from a surface of the vibratory transducer and is being reflected by the reflector to generate a counter-propagating wave in the cavity. Based on the wave generated at the vibratory transducer and the counter-propagating wave generated at the reflector in combination, an indication of the energy returned to the vibratory transducer by the reflector is determined. One or more material properties of the fluid are determined based on the determined indication of the energy returned to the vibratory transducer.