NDTnet - March 1997, Vol.2 No.03

Guided Wave Applications of Piezocomposite Transducers

Authors: Paul A. Meyer, Ph.D.and Joseph L. Rose


Abstract

The majority of ultrasonic nondestructive testing applications in use today utilize longitudinal wave techniques. These are very effective for flaw detection and thickness measurement in scanning applications. In sheet and tube type materials, however, a more rapid technique has been developed utilizing Guided Wave Inspection. This method is capable of interrogating large areas of the material without extensive transducer scanning. An important requirement in this method is the ability to utilize relatively broad bandwidth transducers in the test. This paper presents the concepts on which Guided Wave Inspection is based as well as piezocomposite transducer design considerations which increase the usefulness of the inspection method. Piezocomposite transducers incorporate a combination of piezoelectric ceramics and polymers to enhance the ultrasonic performance of the device. Additionally, the transducer can be designed to match to non-planar surfaces increasing its versatility when a difficult shape is involved.

Start
Mr Meyers's speech in Seattle about this chapter.
(7 min, 818k, a streaming Real Audio file. Download the Player)
ASNT prohibits the further distribution of the audio record.
Since we don't want to escalate the matter into the legal arena, we have decided to delete it - Sorry.
See also ASNT Policies taken to Extemes.

Conventional UT Techniques

  • Longitudinal or Mode Converted Shear Wave Inspection
  • Interrogation Along a Line Through the Part
  • Limitation: Mechanical Scanning is Necessary to Inspect the Entire Part

"New" Concept

  • Applications Involving Sheet or Tubular Geometries
  • Guided Waves Can Interrogate Large Areas (perhaps the entire part) from a Single Location

Guided Waves

  • What Are They?
  • How Are They Generated?
  • What Are the Defining Variables?
  • What Are the Limitations?

    Guided Waves Are:
    Waves whose propagation characteristics depend on a structural boundary (Lots of reflections, mode conversion, hence wave superposition to form packets of energy, or modes, that depend on wave input angle and frequency) i.e. rods, tubes, and embedded layers, etc.

    Wave Structure:

    • Describes the Distribution of Particle Motion Through the Thickness of the Plate
    • When Multiple Layers Exist, the Wave Structure Can Become More Complex


    Fig.5:
    Possible Wave Structures
    (depends on the location on the dispersion curve)


    Fig.6:
    Other Possible Wave Structures


    Fig.7:
    Guided Wave Dispersion Curve

    • Different Modes Have Different Regions of Sensitivity Through the Thickness of the Material
    • Selection of the Appropriate Mode is Very Important to Inspection Optimization

    Limitations

    • Not Practical for Materials Thicker Than 0.25 inch
    • Requires a Basic Understanding of the Flaw Geometry

    Multiple Modes

    • Broad Bandwidth Transducers Permit the Generation of More Modes
    • More Available Modes Improve Probability of Detection, Classification, and Sizing
<-- Speech end

Piezocomposite Transducer Technology

What Can We Do With This "New" Technique?

Summary

This paper was presented at the ASNT Fall Conference Seattle, Washington October 17, 1996. See our Report.

Refer to another article:
Improved Sound Field Penetration Using Piezocomposite Transducers Paul A. Meyer, Ph.D.

Authors:

Paul A. Meyer, Ph.D. Krautkramer Branson, Email: Meyer@KB-Ltn.MHS.compuserve.com
and Joseph L. Rose Joseph L. Rose Penn State University, Email: JLR9@PSUVM.PSU.EDU |Top |
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