Which describes the natural frequency of the transducer; determined by propagation speed and thickness in pulsed ultrasound and by the electrical frequency in continuous wave?

Which describes the natural frequency of the transducer; determined by propagation speed and thickness in pulsed ultrasound and by the electrical frequency in continuous wave?

• A. Operating frequency
• B. Center frequency
• C. Bandwidth
• D. Wavelength

Answer: (A)

The transducer’s natural, or resonant, frequency is set by its physical make-up: the thickness of the piezoelectric element and how fast sound travels through that material. For a thickness-mode transducer, the fundamental resonance occurs roughly when half a wavelength fits into the crystal thickness, so the resonance frequency is about f ≈ v/(2t), where v is the propagation speed in the crystal and t is its thickness. In pulsed ultrasound, this resonance defines the frequency around which the emitted pulse is centered. In continuous-wave operation, you drive the crystal with a constant electrical frequency, and the transducer naturally oscillates at that same frequency because that’s the frequency at which it resonates. So the frequency you drive at determines the transducer’s natural frequency in CW mode. Center frequency, bandwidth, and wavelength relate to the emitted signal differently. The center frequency is the spectral midpoint of the pulse’s frequencies, bandwidth is the range of frequencies present due to pulse duration and damping, and wavelength is derived from the speed of sound and the frequency.

The transducer’s natural, or resonant, frequency is set by its physical make-up: the thickness of the piezoelectric element and how fast sound travels through that material. For a thickness-mode transducer, the fundamental resonance occurs roughly when half a wavelength fits into the crystal thickness, so the resonance frequency is about f ≈ v/(2t), where v is the propagation speed in the crystal and t is its thickness. In pulsed ultrasound, this resonance defines the frequency around which the emitted pulse is centered.

In continuous-wave operation, you drive the crystal with a constant electrical frequency, and the transducer naturally oscillates at that same frequency because that’s the frequency at which it resonates. So the frequency you drive at determines the transducer’s natural frequency in CW mode.

Center frequency, bandwidth, and wavelength relate to the emitted signal differently. The center frequency is the spectral midpoint of the pulse’s frequencies, bandwidth is the range of frequencies present due to pulse duration and damping, and wavelength is derived from the speed of sound and the frequency.