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Transducer array types

Created: 23/11/2004
 
- Single crystal design
- Multi-element arrays


Mechanically swept, single crystal design

This is the simplest type of real-time imaging scanhead.

If the transmitting / receiving face of the transducer is made slightly concave, it can generate a concave wavefront, producing a degree of focusing in the ultrasonic beam. This will give improved lateral spatial resolution and energy concentration, increasing the reflected signal.

Disadvantages of this design are:

    • limited focal control
    • unreliability due to moving mechanical components
    • limited frame rate

Focus


Multi-element arrays

It is now common to use "linear array" multi-element ultrasound transducers.

  • Each element carefully manufactured to resonate at the same frequency
  • Each element has its own pulsing circuit, transmit-receive switch, and signal amplifier-detector
  • All elements are concave in the plane perpendicular to the array axis to give some beam focusing in this plane

    Elements may be excited using different timing schemes to create specific steering/focusing effects:

  • All elements excited simultaneously
    Linear Array
  • Successive delays along the array to produce 'electronic beam steering'
    Beam Steering
  • Excitation of the elements towards the centre of the array further delayed relative to the ends for concave beam focusing. Simultaneous steering and focusing is possible.
    Steering and Focus
    To provide the same spatial response when receiving echo signals, the same delay and amplitude control must be applied to the signal from each array element as for transmission (Reciprocity Principle). This is now done by analog to digital conversion of each signal, and then numerically processing and combining the signals in the digital domain before generating the image display.
  • Curved Linear array transducers rely on a geometric curved design to achieve the combined advantage of a wide field of view at depth and a relatively large aperture for visualising more superficial structures in their entirety.

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ArticleDate:20041123
SiteSection: Article
 
   
    
                                            
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