Ch 9 unfocused beam

Focus

(focal point) the location where the beam is the narrowest.

Near Zone

(near field, Fresnel Zone) region from the trx to the focus. beam gradually narrows (converges), located at the end of the near zone.

Focal Length

(focal depth, NZL) focal length is the distance from the trx to the focus

Far Zone

(far field, Fraunhofer zone) region that starts at the focus and extends deeper. beam diverges

Focal Zone

Region around the focus where the beam is relatively narrow

focus can also be described as:

focal point, end of near zone, beginning of the far zone, or middle of the focal zone

beam diameter at the transducer

equal to the diameter of the trx

beam diameter at the focus

one-half trx diameter

beam diameter at 2 NZL’s

equal to the trx diameter

beam diameter deeper than 2 NZL’s

wider than trx diameter

equation for relationship b/w diameter, freq., and focal depth

focal depth (mm)= diameter (mm)² x frequency / (heart)

diameter has a greater impact b/c it is to the second power

beam divergence formula

Div = (heart) / Diameter X Frequency

Huygen’s principle

v shaped waves that make an hour glass shaped beam; constructive and destructive; converge and diverge