Secondary sound beams produced by an array transducer that can duplicate structures lateral to the real structure are called what?

• A. Grating lobes
• B. Side lobes
• C. Mirror image
• D. Aliasing

Answer: (A)

When an array transducer emits, the energy is not confined to a single narrow beam but can form additional secondary beams due to the way the elements interact. The strongest of these secondary beams that can illuminate tissues to the side of the main focus are called grating lobes. They occur when the element spacing is large relative to the wavelength, causing constructive interference in directions away from the main beam. These grating lobes can create duplicate-looking structures laterally because they produce separate beams that sample structures off-axis, essentially mimicking real objects in those side locations. To minimize them, designers keep element spacing at or below about half a wavelength and use techniques like apodization to suppress the outer elements. Side lobes are weaker surrounding the main beam and don’t typically replicate full structures, mirror images are artifacts from strong reflectors causing a ghost image across a reflector, and aliasing relates to sampling limitations rather than lateral beam duplication.