Uneven speeds of the sound wave through compressions (faster) and rarefactions (slower) create which energy?

• A. Harmonic
• B. Fundamental
• C. Doppler
• D. Thermal

Answer: (A)

Nonlinear propagation is at work here: when the wave moves through tissue, compressions travel faster than rarefactions. That speed difference distorts the waveform, causing it to steepen and develop sharp corners. That distortion adds energy at new frequencies that are whole-number multiples of the original pulse—the harmonics. So the energy described is harmonic energy, the higher-frequency content produced by the wave’s nonlinear propagation.

Doppler energy would come from motion-related frequency shifts, not waveform distortion. Thermal energy refers to heat from absorption, not new frequency components. The fundamental energy is just the original frequency, while the question points to energy in those additional frequencies created by distortion.