Operating frequency is determined by which factors?

Operating frequency in ultrasound is primarily influenced by the propagation speed of the sound wave in the material of the active element (usually a piezoelectric crystal) and the thickness of the crystal itself. The relationship can be understood through the principles of ultrasound transducer design.

The frequency at which the transducer will operate is inversely proportional to the thickness of the piezoelectric element. Thinner crystals vibrate at higher frequencies, while thicker crystals vibrate at lower frequencies. Additionally, the propagation speed of sound in the crystal material plays a crucial role; different materials have varying propagation speeds, which also affect the frequency of the sound waves generated.

Thus, the correct answer correctly identifies that both the propagation speed and the thickness of the element are key determinants of the transducer's operating frequency. This understanding is foundational for optimizing the performance of ultrasound systems and achieving desired imaging characteristics. Other options may touch on related concepts but do not provide the complete picture as effectively as this one does.