Ultrasound physics ch 9

shape of a sound beam is based on

-single disc-shaped
-unfocused PZT crystal
-operating in a CW mode

sound beam width changes as

it travels
-progressively narrows until it reaches its smallest diameter, then begins to diverge

beam diameter initially=

PZT diameter

focus also called

focus point

Focus/point

location where sound beam reaches its minimum diameter
-beam most narrow

Focus=

1/2 width of beam at origin

near zone also called

fresnel zone

near zone

space or region between transducer and focus

focal length also called

-focal depth
-near zone length
-fresnel zone

focal length

distance from transducer face to focus

far zone also called

far field or Fraunhofer zone

far zone

region beyond near field

focal zone

area around focus
-1/2 in near field, 1/2 in far field
-best image quality

beam diameter is 1/2 transducer diameter at ________

focus

at 2 near zone lengths, beam diameter is equal to

transducer diameter

Focal depth, or near zone length in a fixed focus transducer is determined by:

transducer diameter
F of US

adjustable focus systems

phased array

larger diameter=

longer focal length

Higher F=

longer focal depth or near zone length

F and depth have a ___________ relationship

direct

focus determined by

diameter and F

high F sound wave with a shallow focus can be achieved with

a small diameter

what probed would create a beam with the shallowest focus

smallest diameter and lowest F

F and focal depth relationship

direct

crystal diameter and focal depth relationship

direct

divergence

spread of sound wave in far field

divergence affected by

F and crystal diameter

larger diameter crystal improves

lateral resolution

smaller diameter crystals _________ more readily than large

diverge

relationship between diameter and divergence

inverse

F and divergence relationship

inverse

lesser divergence=

greater diameter, higher F

greater divergence=

smaller diameter, lower F

crystal diameter and divergence relationship

inverse

spherical waves each created a wallet with V-shape, also known as

-spherical waves
-diffraction patterns
-huygen's wavelets

Huygen's principal

Constructive and destructive interference of sound wavelets. Cumulative sound wave is shaped like an hourglass.

Which transducer will provide the longest near zone length?

greater diameter and higher F

Name the properties of a pulsed wave transducer that will provide the highest emitted sound wave frequency.

thin, fast prop speed of crystal

What happens when pressure is applied to a piezoelectric crystal?

emits electrical signal

Why does a coin shaped crystal create an hour glass sound beam?

Constructive and deconstructive interference (Huygen's)

A shorter focal length is associated with a _______f transducer and a _______crystal diameter.

Low, small

Active element diameter and beam divergence have this relationship:

inverse

The ceramic has a diameter of 9 mm. What is the beam diameter at the focus?

4.5mm

T/F The Fraunhofer zone is the only region of the sound beam where the beam diameter is greater than the PZT diameter.

true

relationship between wavelength and near zone length

inverse

Two transducers are identical except for their frequencies. One TRX is operating at 8MHz and the other 4 MHz. The focal zone will be longer for TRX :

8MHz

Focus/focal point

Near zone/nearfield/frensel zone

focal length/focal depth/near length

(distance)

Far zone/far field/fraunhofer zone

Focal zone

10mm
5mm

What is the diameter of sound beam at 16 cm? 8 cm?

8cm

depth at focus?

5mm

at 8cm the beam's width is

3cm, 3cm

focal zone is ______ and ______ in the Fraunhofers zone

16cm
(8+8)

How deep is the beam when its diameter matches the PZT diameter?

focal depth/near zone length

12mm

beam diameter at point C

at 2 near zone lengths

beam diameter equals transducer diameter

deeper than 2 near zone lengths

beam diameter is wider than transducer diameter