US TRANSDUCER

• Attenuation can happen via 

  • Energy transfer into heat.

  • Scattering of wave.

• Piezoelectric material (PM) at front of transducer is responsible for creating US waves, receiving returning echoes, and converting that energy into an electrical signal that can be converted into a digital image on US machine.

  • Made up of PZT crystal that has unique characteristics. PZT crystal is sandwiched between 2 electrodes which can compress the PC and induce a current.

  • Region of compression comes towards PZT material and compresses it to induce a current within the material. An electronic signal will head back up to the wiring towards the US machine. This compression changes the orientation/shape of the PZT material and causes an electronic signal to be induced.

  • Compression of PZT material will induce a current around the material which will induce movement.

Sound waves comes towards PZT material -> current will be induced around material -> induce movement in material -> electronic signal will head back into US machine.

We can either run an alternating current and cause the shape to change continuously and propagate the wave at a set f through tissue or we can apply a large electric current over a short period of time over this PZT material which will then resonate at a set frequency. This resonance will cause the soundwave to propagate throughout the tissues.

Think about PZT crystals in 2 ways:

• One PZT crystal unit is a drum set. When u hit it that symbol will resonate at a set frequency. The wider / bigger the radius of the symbol, the lower the frequency of that sound when we hit it. The smaller the symbol gets, the higher the pitch, the higher the frequency will be when we hit that symbol. 

• Second way is to think of PZT material as a guitar string that is held b/n 2 fixed points. When it is strummed a certain note is played. No matter how hard you strum the guitar string, the same note will be played. The same frequency will come from strumming that guitar string. 

• Frequency of transducer is controlled by 2 things

  • Speed of sound through PM

  • Thickness of PM

    • Thinner material -> higher the f

      • Attenuate quicker

    • Thicker material -> lower the f