8 Sound Beams Flashcards
What is the rule for beam width?
Narrow beams create better images
Describe the beam width as sound travels.
Starts out at the same size as the transducer diameter
Gets progressively narrower until it reaches its smallest diameter
Then it diverges
What is the focus or focal point?
Location where the beam reaches its minimum diameter
What is the focal depth?
The distance from the transducer face to the focus
What is the near zone?
Fresnel Zone
Region/zone in between transducer and focus
What is the far zone?
Fraunhofer Zone
Region or zone deeper than the focus, beyond the near field
What is the focal zone?
Region surrounding the focus where the beam is “sort of narrow” and the pic is relatively good
Determine the beam diameter of an unfocused CW disc transducer.
At end of near zone - 1/2 transducer diameter or aperture
At 2 near zone lengths - equal to transducer diameter
What determines the focal depth?
Transducer diameter or aperture
Frequency of the US
Compare shallow focus to deep focus.
Shallow - small diameter, low frequency
Deep - large diameter, high frequency
What is sound beam divergence?
Describes the spread of the sound beam in the deep far zone
What determines sound beam divergence?
Transducer diameter or aperture
Frequency of the ultrasound
What is associated with less divergence?
Narrower beam in far field
Larger aperture or diameter of active element
High frequency
Improved lateral resolution in far field
What is associated with more divergence?
Wider beam in far field
Smaller aperture or diameter of active element
Low frequency
Degraded lateral resolution in far field
What are the characteristics of sound beam anatomy?
Frequency (CW) - electronic frequency
Frequency (Pulsed) - thickness of ceramic & speed of sound in ceramic
Focal length - aperture & frequency of sound
Divergence - aperture & frequency of sound
