Doppler effect and Ultrasound waves

In summary, the expected beat frequency when blood is flowing normally in large leg arteries at 3.0 cm/s directly away from the sound source is approximately 2.2 Hz.
  • #1
mathcrzy
47
0

Homework Statement



Ultrasound waves are used to measure blood-flow speeds. Suppose a device emits sound at 450 kHz, and the speed of sound in human tissue is taken to be 1540 m/s. What is the expected beat frequency if blood is flowing normally in large leg arteries at 3.0 cm/s directly away from the sound source?
_____Hz

Homework Equations



F2 = F1 / ( 1 + ( Vs / V ) )

The Attempt at a Solution



F2 = 450000 / (1 + ( 1540 / 343 ) )
F2 = 81970.26 Hz
 
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  • #2
F2 = F1 / ( 1 + ( Vs / V ) )
Your formula is wrongIt should be F2 = F1/[1 + v/vs] and what is 343?
 
  • #3
rl.bhat said:
F2 = F1 / ( 1 + ( Vs / V ) )
Your formula is wrongIt should be F2 = F1/[1 + v/vs] and what is 343?

I am a bit confused. The OP has used the correct formula for the Doppler Effect for moving source. However, the formula given by you is the correct formula for the beat frequency.

To help the OP, I'll just give a short deduction.

f1 = f/(1 + vs/v) = fv/(v+vs), where v = speed of sound = 1540 m/s, f = 450 kHz, vs = 0.03 m/s.

Frequency of beats = f –f1 = f(1 – v/(v+vs) = f*vs/(v+vs) ~ f*vs/v, since v>>vs.

Now plug in the values.
 

Related to Doppler effect and Ultrasound waves

What is the Doppler effect?

The Doppler effect is the perceived change in frequency of a wave when there is relative motion between the source of the wave and the observer. This can be observed in sound waves, light waves, and other types of waves.

How does the Doppler effect apply to ultrasound waves?

In ultrasound imaging, the Doppler effect is used to measure the velocity of blood flow. The ultrasound waves are emitted from a transducer and reflect off of moving blood cells, causing a change in frequency. By measuring this change, the speed and direction of blood flow can be determined.

What is the difference between the Doppler effect and Doppler shift?

The terms "Doppler effect" and "Doppler shift" are often used interchangeably, but technically, the Doppler effect refers to the perceived change in frequency, while the Doppler shift refers to the actual change in frequency that occurs due to the relative motion between the source and observer.

How is the Doppler effect used in medical diagnostics?

In addition to measuring blood flow, the Doppler effect is also used in medical diagnostics to determine the location and movement of organs and tissues. It can also be used to detect abnormalities such as tumors or blockages in blood vessels.

What are some real-world applications of the Doppler effect and ultrasound waves?

The Doppler effect and ultrasound waves have many practical applications in various industries. In addition to medical diagnostics, they are used in weather forecasting, speed detection for law enforcement, and in navigation systems for ships and aircraft. They are also utilized in non-destructive testing for materials and structures, and in oceanography to measure currents and tides.

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