UNIT 9

Focus

Aka focal point, end of near zone, beginning of far zone

Location where beam is narrowest

Near zone

Location between transducer and focus

Aperture

Diameter of the crystal

Focal length

Aka focal depth, near zone length

Distance from the transducer to the focus

Frequency and NZL relationship

Frequency and NZL are directly related

Near zone length formula

NZL = (D² x F) / (4 x λ)

Far zone

Starts at focus and extend deeper

What is far field's NZL?

2 NZL

What is near fields NZL?

1 NZL

Focal zone

Region around the focus where beam is narrow

What is the beam diameter at the focus?

Beam diameter is ½ of transducer diameter

What is the beam diameter at the transducer?

Beam diameter = transducer diameter

What is the beam diameter at 2 near zone lengths?

Beam diameter = transducer diameter

What is the beam diameter deeper than 2 zone lengths?

Beam diameter is wider than transducer diameter

Sound beam divergence

Deeper than the focus

A gradual spread of the beam in the far field

divergence and frequency relationship

divergence and frequency are inversely related

if frequency is high then there is ____ divergence…?

if frequency is high then there is less divergence

if there is a larger diameter in the far field, what happens to divergence and the lateral resolution?

less divergence, improves lateral resolution

if there is a higher frequency in the far field, what happens to divergence and the lateral resolution?

less divergence, improves lateral resolution

diameter and beam divergence relationship

diameter and beam divergence are inversely related

beam divergence formula

sin divergence angle = 1.85 / (d x f)

sin divergence angle = (1.2 x λ) / d

huygens principle

V shape wave is created when source is about the same size of sound wavelengths

• sound beam is shaped as a hourglass due to multiple, individual, in-phase and out-phase huygen wavelets interfering with each other

what is another word for near field?

fresnel zone

what is another word for far field?

fraunhofer zone

if frequency is high, then NZL will be..?

if frequency is high, then NZL will be deeper..?

if diameter is narrow, then NZL will be..?

if diameter is narrow, then NZL will be shallow

if diameter doubles, what happens to NZL?

NZL quadruples

if frequency doubles, what happens to NZL?

NZL doubles