The width of each crystal in a convex array is approximately equal to:

• A. Half a wavelength
• B. One wavelength
• C. Two wavelengths
• D. Three wavelengths

Answer: (B)

In ultrasound transducers, the element width is tied to the wavelength of the sound in tissue. The width of each crystal in a convex array is chosen to be about one wavelength so the element acts as a practical aperture: large enough to form a reasonably narrow beam for good lateral resolution, yet small enough to keep manufacturing feasible and the beam pattern well behaved. If the width were much smaller than a wavelength, the aperture would be too small, broadening the beam and reducing lateral resolution. If it were much larger, the beam would become overly directive and could introduce unwanted side lobes when steering. So, roughly one wavelength is the typical, effective choice.