The far field (Fraunhofer zone) is the region of the ultrasound beam beyond the focal zone, where the beam diverges progressively. As the beam widens, lateral resolution decreases and the ability to distinguish closely spaced structures side by side diminishes. Attenuation also increases with depth in the far field. Lower frequency transducers have better far-field penetration, making them preferable for imaging deep structures such as the liver, kidneys, and aorta.