Transducers

• what is a ultrasound transducer 


  converts electric energy into ultrasound energy
• what is transmission 


  electrical energy from the system is converted into sound
• what is reception 


  reflected sound pulse is converted into electrical energy
• what is piezoelectric effect 


  property of certain materials to create a voltage when they are mechanically deformed or when pressure is applied
• what are the different piezoelectric elements

  PZT

  quartz and tourmaline

  ceramic
• what is polarization 


  piezoelectric properties of PZT are created by exposing the materials to be strong electrical field while being heated to a substantial temp
• what is curie temperature 


  temp at which polarization occurs
• what happens if PZT is heated above curie temp 


  crystals piezoelectric properties are destroyed-depolarization
• capacitive micromachined ultrasonic transducers 


  contains miniature elements with 2 electrically conducting layers facing each other
• what are the 2 conducting layers of CMUTs 


  fixed layer

  flexible membrane
• what are the advantages of CMUT over PZT elements 


  broad bandwidth

  improved detail resolution
• what determines operating frequency 


  propagation speed of element material

  thickness of transducer element

  thinner elements operate at higher frequencies
• what is damping material 


  mix of plastic or epoxy resin attached to the rear face of the transducer element
• what does damping material reduce

  number of cycles in a pulse

  pulse duration and spatial pulse length

  amplitude

  decreases efficiency and sensitivity
• what is the matching layer 


  material placed on the transducer face to improve sound transmission across the element-tissue boundary
• what is the impedance element of the matching layer 


  20 times that of tissue
• coupling medium 


  eliminates air layer between transducer and skin
• what is the order of impedance from highest to lowest

  PZT, matching layer, gel, skin