A Phase-Shift Ultrasonic Flowmeter

An ultrasonic flowmeter using phase-shift techniques has been developed to measure phasic blood flow in animals. Lead zirconate titanate transducers are located diagonally opposed over the vessel so that 1-Mc ultrasound may be transmitted alternately upstream and downstream. The upstream and downstream transit times are measured by heterodyning the 1-Mc receiver crystal output to 10 kc, and then feeding this signal to an audio phasemeter. The phasemeter output is an ac signal whose magnitude represents flow velocity, and phase (relative to the chopper drive) indicates flow direction. The phasemeter output is amplified and synchronously detected to drive a recorder