| 摘要 |
An apparatus for monitoring movement of a blood vessel in an animal body. A pair of transducers are disposed adjacent the skin of an animal body in the general region of the blood vessel. One of the transducers has the output of a voltage-controlled oscillator connected thereto and directs an ultrasonic signal at the vessel. Because of Doppler effect, the portions of this ultrasonic signal which are reflected to the other transducer have a different frequency, and thus phase, than the transmitted signal. The magnitude and sign of this phase difference is detected by feeding both the received signal and the transmitted signal to a balanced mixer. The output signal from the balanced mixer is supplied to a monitor and display device and additionally through a delay circuit to the voltage-controlled oscillator to adjust its frequency so that the phase thereof is always locked to further movements of the blood vessel.
|
