The beam pattern shows the relative amplitude of the acoustic pressure as a function of direction relative to the transducer. Beam patterns are three-dimensional. The transmit and receive beam patterns are basically the same.

The near field (also called Fresnel zone) is the proximal part of an ultrasound beam. The Fresnel zone is adjacent to the transducer surface and has a converging sound beam profile. A narrow beam shape is maintained in the near field owing to constructive and destructive interference patterns of sound wavelets emitted from the transducer crystal.
The length of the near field is equal to
r²/l = d²/4l
where r is the radius, l is the ultrasound wavelength in the medium of propagation and d the diameter of the piezoelectric crystal.

See also Beam Pattern, and Sonographic Features.

Anatomic structures respond with characteristic features on ultrasound scanning.
There are some ultrasound terms, referring to the echo appearance, that describes tissue appearance in a uniform manner:

Tendons characteristically are hyperechoic on ultrasound because of the fibrillar pattern. Ligaments appear hyperechoic when the beam is perpendicular to the tissue. Peripheral nerves are hyperechoic relative to muscle.
Muscle appears relatively hypoechoic to tendon fibers. Close observation reveals hypoechoic muscle fibers separated by hyperechoic septae that converge on a hyperechoic aponeurosis. Articular hyaline cartilage appears hypoechoic. The presence of fluid within the joint outlining the cartilage produces a thin bright echo at this interface.
Sound beams do not penetrate the bone cortex. The very bright echo produced at the interface allows both recognition of the bone cortex but also can demonstrate fracture, spurring and bone callus bridging. Abnormal soft tissue calcification and ossification also produces bright reflective echoes.
Cysts or fluid filled areas are without internal echoes and are called echo free or anechoic and may demonstrate enhanced soft tissue echoes posterior to the fluid collection. Inflamed metatarsal bursae and calcaneal bursae clearly depict fluid swelling.

See also Beam Pattern and Zero Offset.

The elements of a rectangular array transducer (also called matrix transducer) are arranged in a rectangular pattern. Rectangular arrays with unequal rows (e.g. 3, 5, 7) of transducer elements are in real 2D (two-dimensional), but they are termed 1.5D, because the number of rows is much less than the number of columns. Their main advantage is electronic focusing even in the elevation plane (z-plane).
The transducers that are termed 2D have an equal number of rows and columns. 2D transducers have the potential to provide real-time 3D ultrasound imaging without moving the transducer.
Active matrix array transducers have several elements in the short axis and in addition multiple elements along the long axis. This allows electronic focusing in both axes, resulting in a narrower elevation axis beam width in the near field and far field.

The term hyperechogenic or hyperechoic is used if there are many internal echoes. Hyperechoic tissues appear bright in ultrasound imaging. Tendons are hyperechoic because of the fibrillar pattern. Ligaments appear hyperechoic when the beam is perpendicular to the tissue. Peripheral nerves are hyperechoic relative to muscle. Liver angiomas, tumor cells, blood vessels, fibrosis, and liver steatosis appear diffuse hyperechoic.