Sound Beams and Beam Profile Vocabulary

Vocabulary flashcards covering the key components, parameters, and physical principles of a single disc PZT sound beam.

Focus (Focal Point)

The location where the sound beam reaches its minimum diameter, which is equal to $\frac{1}{2}$ the diameter of the aperture.

Near Zone (Fresnel Zone)

The region from the transducer to the focus where the sound beam converges and progressively narrows.

Focal Length (NZL)

The distance from the transducer to the focus, also known as focal depth or Near Zone Length.

Far Zone (Fraunhofer Zone)

The region deeper than the focus where the sound beam expands and diverges.

Focal Zone

The region surrounding the focus where the sound beam is relatively narrow, with the focus located at its center.

Anatomy of a Sound Beam

The structural profile of a sound beam originating from a single disc transducer, showing the near zone, focus, far zone, focal length, and focal zone.

Convergence

The process where the sound beam comes together and gets narrower as it moves forward toward the focus.

Divergence

The process where the sound beam spreads out and expands as it travels beyond the focus.

Focal Depth

The distance from the transducer face to the focal point, determined by the transducer diameter and sound frequency.

Shallow Focus

A focal depth located closer to the transducer face, produced by a small transducer diameter and low sound frequency.

Deep Focus

A focal depth located deeper from the transducer face, produced by a large transducer diameter and high sound frequency.

Sound Beam Divergence

The spread of the sound beam in the deep far zone, determined by active element diameter and sound frequency.

Less Divergence

A narrower sound beam in the far field, produced by a large diameter/aperture element and high frequency.

More Divergence

A wider sound beam in the far field, produced by a small diameter/aperture element and low frequency.

Diffraction

The propagation of V-shaped waves (Huygens' wavelets) produced by a tiny source with a size near the wavelength of the sound waves.

Huygens' Principle

The principle explaining that the hourglass shape of an imaging transducer's sound beam results from the constructive and destructive interference of diffracted wavelets.

Beam Width at $2\,\text{NZL}$

The depth at which the diverging sound beam in the far zone expands back to the exact diameter/width of the transducer aperture.