Doppler Pulse Detection The Doppler effect in an ultrasonic pulse probe detects the reflected sound from moving blood. The frequency of the reflected sound is different, and the beat frequency between the direct and reflected sounds can be amplified and used in earphones to hear the pulse sound. Further discussion	Index Traveling wave concepts
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Doppler Pulse Probe The pulse of a premature infant may be very difficult to detect with a stethoscope since the sound produced is extremely faint. A sensitive Doppler pulse probe can be used to advantage because it detects the movement of the blood through an artery. The ultrasonic echo from the moving blood can be mixed with the source frequency to produce a beat frequency. As the blood surges with the pumping action of the heart, the beat frequency signal changes in frequency and amplitude. Remarkably, in clinical Doppler pulse detectors the sound output is similar in nature to what you hear with a stethoscope; you immediately recognize it as a pulse sound.

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