Lecture 1 Notes

Tissue zl zl fresnel zt 1 3 zl 2 z t 4 z l 4 beam

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Unformatted text preview: (resonate) –  Resonant frequency f=c/2d (d=thickness) –  The damping material damps the vibration after 3-5 cycles When the diameter D of the surface is much larger than d, longitudinal waves are transmitted into the body The crystal is shaped into a disk or rectangle, with either flat or concave surface Matching Layer(s)   Zl ,1 = Z T3 / 4 Z 1/ 4 ; L Transducer Fraunhofer Load (tissue) ZL Zl Fresnel ZT 1/ 3/ Zl ,2 = Z T 4 Z L 4 Beam Properties of a Piston Transducer           Focused Transducer At border of the beam width, the signal strength drops by a factor of 2, compared to the strength on the z-axis Beam width determines the imaging resolution (lateral resolution). Smaller D is good only before far field D=1~5 cm in practice, very poor lateral resolution Focused plate is used to produce narrow beam   Single Element Transducer Beam focusing can be accomplished by –  Using a crystal with a curved surface –  Placing a concave lens in front of the crystal Transducer Array HUNT et al.: ULTRASOUND TRANSDUCERS 455 With a single crystal, manual or Transducer compromises mechanical steering of the beam is needed to produce a two-dimensional Maximum frequency namic Attenuation image Maximize range (frequency shifts) Enough lateral resolution f penetration ? Strong   Practical systems today use an array of \ ~~~~focussing ? LoseI sensitivity? Solve depth of small piezoelectric crystals field limi...
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This document was uploaded on 03/12/2014 for the course EL 5823 at NYU Poly.

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