A new detection method of ultrasonic flowmeter beam incident angle.

We have developed a new method of continuously measuring the angle between a pulsed Doppler blood flowmeter ultrasonic beam and the flow axis for precise blood flow velocity measurements. The transducer employed in the flowmeter system design is formed by two LZT 10 MHz crystals held in a lightweight polystyrene shell. Recessed internal cavities in the shell hold one 10 MHz crystal at a 45 degree angle for blood flow velocity measurement and the other crystal at a 90 degree angle for beam angle detection. The angle and Doppler frequency are supplied to a digital signal processor to precisely calculate instantaneous flow velocity. This automatic angle correction system is designed for applications where the transducer-flow angle is subject to change. Typical use examples are half-cylinder flow transducers that do not encircle the artery and external, hand-held, transcutaneous transducers.