Which transducers produce side lobes or grating lobes?

• A. Mechanical sector
• B. Linear sequential array
• C. Phased array
• D. All listed transducers produce side lobes

Answer: (D)

Side lobes come from the way ultrasound energy is emitted from a finite aperture. Any transducer with a non-infinite, finite emitting area sends not only a main beam but also smaller off-axis energy, known as side lobes. This is true for a mechanical sector, which uses a single rotating element, because its aperture is finite and generates off-axis energy. It is also true for linear sequential arrays and phased arrays, which form the beam from multiple elements arranged along a line; their finite, discrete structure naturally produces side lobes. In array types, when the element spacing is large relative to the wavelength, these off-axis energies can become grating lobes, which are a specific kind of additional beam away from the main lobe. Since every listed transducer has a finite emitting aperture, they all produce side lobes, and the array types can exhibit grating lobes under certain spacing conditions.