Applications of the Doppler Effect with ultrasound waves

1. What is Ultrasound?

• Ultrasound is a longitudinal wave with a very high frequency (above 20 kHz) that humans cannot hear.
• Used in medical diagnostics to measure blood flow in arteries and veins.

2. How the Doppler Flow Meter Works

a) Transmission of Ultrasound Waves

• A catheter with a Doppler flow meter is inserted into a blood vessel.
• The meter emits ultrasound waves into the blood.

b) Doppler Shift and Frequency Change

• Blood flow through the heart causes a Doppler shift (change in frequency) in the reflected ultrasound waves.
• The meter compares the original and reflected frequencies.

c) Detection and Analysis

• A receiver detects the reflected sound.
• An electronic counter measures the change in frequency.
• From this, the speed of blood flow is determined.

3. Importance in Medical Diagnosis

✔ Detects blood clots and blockages in arteries.

✔ Measures the speed of blood flow in different parts of the body.

✔ Helps identify narrowing of blood vessels (useful in diagnosing heart disease).

Exam Tip

💡 Remember that a higher detected frequency means blood is flowing towards the detector, while a lower frequency means blood is moving away.