Ultrasonic Imaging Using Trapped Energy Mode Fresnel Lens Transducers

  • P. Das
  • S. Talley
  • R. Kraft
  • H. F. Tiersten
  • J. F. McDonald
Part of the Acoustical Imaging book series (ACIM, volume 9)


A focusing transducer utilizing trapped energy modes can be easily fabricated by plating a number of concentric rings of electrodes on a suitable piezoelectric plate of uniform thickness. The concentric ring structure acts as a Fresnel lens and can be used to obtain excellent lateral focusing of ultrasonic waves. Several transducers operating in the 2–5 MHz range have been produced using PZT-7A as the piezoelectric material. The near field radiation pattern has been observed directly in front of the plate using the first order diffraction peak from a laser probe. It is confirmed that there is good acoustic isolation between the rings and that they radiate in the trapped energy mode. The ultrasonic radiation pattern of the Fresnel lens has been observed at various distances from the plate and compared with computed results which show excellent agreement. Furthermore, the axial diffraction pattern of the lens can be optimized by adjusting ring spacings. During the course of this study a new, previously unreported mode of energy trapping has been discovered. The explanation for this method of trapping is briefly discussed. Finally an acoustic through-transmission imaging system incorporating one focusing transducer is used for imaging of flaws in composite materials.


Dispersion Curve Zone Plate Ultrasonic Image Fresnel Lens Ring Spacing 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Plenum Press, New York 1980

Authors and Affiliations

  • P. Das
    • 1
  • S. Talley
    • 1
  • R. Kraft
    • 1
  • H. F. Tiersten
    • 1
  • J. F. McDonald
    • 1
  1. 1.Electrical and Systems Engineering DepartmentRensselaer Polytechnic InstituteTroyUSA

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