A transducer for non-invasive measurement includes: at least one first piezoelectric element; a second piezoelectric element; and a base material mountable to a wall of a vessel that contains a liquid. The base material has a planar portion and an angular shaped portion. The angular shaped portion has a plurality of outer faces, a first face of the plurality of outer faces of the angular shaped portion being connected to (or part of) a first face of the planar portion, a second face of the planar portion opposite to the first face of the planar portion being mountable to the wall of the vessel, at least one second face of the plurality of outer faces of the angular shaped portion being angled to the first face of the angular shaped portion at an angle less than an angle of 90 degrees internal to the base material.