Apodization is a method for reducing side lobes (lateral array elements) in some arrays. It gradually decreases the vibration of the transducer surface with distance from its center by improving the directivity. It is usually accomplished by using more power to excite the innermost elements.

The wider the ultrasound beam, the more severe the problem with volume averaging and the beam-width artifact, to avoid this, the ultrasound beam can be shaped with lenses.
Different possibilities to focus the beam:

Conventional multi-element transducers are electronically focused in order to minimize beam width. This transducer type can be focused electronically only along the long axis of the probe where there are multiple elements, along the short axis (elevation axis) are conventional transducers only one element wide. Electronic focusing in any axis requires multiple transducer elements arrayed along that axis. Short axis focusing of conventional multi-element transducers requires an acoustic lens which has a fixed focal length.
For operation at frequencies at or even above 10 MHz, quantization noise reduces contrast resolution. Digital beamforming gives better control over time delay quantization errors. In digital beamformers the delay accuracy is improved, thus allowing higher frequency operation. In analog beamformers, delay accuracy is in the order of 20 ns.
Phased beamformers are suitable to handle linear phased arrays and are used for sector formats such as required in cardiography to improve image quality. Beamforming in ultrasound instruments for medical imaging uses analog delay lines. The signal from each individual element is delayed in order to steer the beam in the desired direction and focuses the beam.
The receive beamformer tracks the depth and focuses the receive beam as the depth increases for each transmitted pulse. The receive aperture increase with depth. The lateral resolution is constant with depth, and decreases the sensitivity to aberrations in the imaged tissue. A requirement for dynamic control of the used elements is given. Since often a weighting function (apodization) is used for side lobe reduction, the element weights also have to be dynamically updated with depth.

See also Huygens Principle.

The dimension of the ultrasound beam and the transducer array are the origin of grating-lobe artifacts (also called side lobe artifact). Grating lobes as side lobes are off-axis secondary ultrasound beams projecting at predictable angles to the main lobe. Side lobes are too small to produce important artifacts.

See also Apodization, and Subdicing.

Side lobes are secondary and smaller acoustic beams falling outside at predictable angles located around the main lobe.

See also Grating-lobe Artifact, Amplitude Shading, and Apodization.