| Two diffraction-grating transducers on either side of a conventional transducer form a configuration with useful properties: when placed in or on the wall of a blood vessel, the blood velocity along the axis of the vessel, i.e. the component of velocity that produces net flow, equals the Doppler shift multiplied by the spatial period of the diffraction-grating transducers, independently of the frequency used to drive the transducers. That and other properties leading to better blood flow measurement are described and experimentally validated. |