Which unit is typically used to express Doppler frequency shifts?

Which unit is typically used to express Doppler frequency shifts?

• A. Meters per second (m/s)
• B. Hertz (Hz)
• C. Kilohertz (kHz)
• D. Decibels (dB)

Answer: (B)

Doppler frequency shifts are about the change in the rate of acoustic cycles per second, so the natural unit is hertz. In ultrasound Doppler, the difference between transmitted and received frequencies, Δf, is measured in Hz, since it directly represents cycles per second altered by motion. The Doppler relationship Δf = 2 f0 v cosθ / c shows that the shift comes from a frequency term and is expressed in Hz; velocity is what you’d compute from it, not the unit of the shift itself. Meters per second would describe speed, not a frequency difference. Decibels quantify amplitude or power, not frequency. Kilohertz is also a frequency unit, but Doppler shifts are conventionally expressed in hertz for the precise, base-unit representation, with kilohertz used only as a larger-scale display sometimes.

Doppler frequency shifts are about the change in the rate of acoustic cycles per second, so the natural unit is hertz. In ultrasound Doppler, the difference between transmitted and received frequencies, Δf, is measured in Hz, since it directly represents cycles per second altered by motion. The Doppler relationship Δf = 2 f0 v cosθ / c shows that the shift comes from a frequency term and is expressed in Hz; velocity is what you’d compute from it, not the unit of the shift itself.

Meters per second would describe speed, not a frequency difference. Decibels quantify amplitude or power, not frequency. Kilohertz is also a frequency unit, but Doppler shifts are conventionally expressed in hertz for the precise, base-unit representation, with kilohertz used only as a larger-scale display sometimes.