A transducer for non-invasive measurement includes: a shear-type piezoelectric element; and a host material. The shear-type piezoelectric element is mounted to a first face of the host material. A second face of the host material is mountable to a wall of a vessel that holds a liquid. When the second face of the host material is mounted to the wall of the vessel, the transducer when activated at an activation frequency launches a Lamb wave into the wall of the vessel. The transducer is designed such that a phase velocity of the Lamb wave in the wall of the vessel is greater than a speed of sound in the liquid held by the vessel.