JPS6432846A - Ultrasonic doppler meter - Google Patents

Abstract

PURPOSE:To accurately measure a speed subjected to high speed aliasing, by calculating the phase difference of a receiving signal within the transmitting pulse interval of an ultrasonic wave and further measuring the difference between two continuous phase differences, that is, the acceleration of a body and correcting a speed using said acceleration. CONSTITUTION:The receiving signal inputted from a terminal D is decomposed into a real number part and an imaginary number part by a demodulator 10 and a low-pass filter 11 to be inputted to a phase angle detector 12. A phase angle theta is calculated in the phase angle detector 12. The difference DELTAtheta (corresponding to the first speed) between the phase angles of the receiving signal is calculated at a point A by the first delay circuit 13-1 and the first subtraction circuit 14-1. In the same way, the difference DELTADELTAtheta between the differences of the phase angles is calculated at a point B by the second delay circuit 13-2 and the second subtruction circuit 14-2. This difference DELTADELTAtheta between the differences of the phase angles is converted to the difference DELTAtheta(corresponding to the second speed) between the phase angles by an integrator 15. Subsequently, judgement is performed by an aliasing judge device 16 and an accurate speed (second speed) is calculated. By this method, a high blood flow speed of a limit or more determined by a transmitting pulse interval can be measured accurately.