A PULSED ULTRASONIC FLOWMETER EMPLOYING TIME DOMAIN METHODS

In this thesis the flow velocity profile across a vessel is determined. Knowledge of the velocity profile is valuable in determining the condition of the vessel and the heart. The time domain method (TDM) being described is an ultrasonic approach for determining flow velocity profiles. Currently available ultrasonic methods transmit more energy into the body than the TDM for the same degree of accuracy and they cannot correct for vessel motion.;In this work, the TDM is first studied by computer simulation. In the simulation a variety of parameters are used: vessel diameter, beam width of the transducer, the amount of damping of the transducer, and the type of velocity profile. Next, the TDM is applied to determine the velocity profile of buttermilk (substitute for blood) pumped through tubing. The application of the TDM on the buttermilk is in agreement with the simulation. Included is a discussion of the sources of errors resulting from each system parameter.;The motion of the tubing can be eliminated by first lining up the second echo with the first at the tube wall where there is a large echo, then applying the TDM. With two ultrasonic pulses, the TDM achieves a precision of 3% in estimating midstream flow. Other available ultrasonic means must use many more pulses (hundreds) to achieve the same precision.;The TDM measures the velocity profile by transmitting two short ultrasonic pulses separated by a known amount of time. Two echoes from the two pulses scattered from the medium are amplified, digitalized, and then stored in a high speed memory in which the digitalized data can be read by the computer used for digital signal processing. The TDM then cuts out a portion of the first echo at a desired range and overlays and moves it across the second echo. The point at which the cut-out portion of the first echo is maximally correlated with the second echo is the change in range which the scatterers of the second echo have moved with respect to the first echo in the intervening time between the transmission of the two pulses. From the change in range information and the time interval between the two pulses, the radial velocity of the scatterers can be determined.