Abstract

This presentation explains a major reason for this performance improvement. A mathematical model is used to predict the received waveform for both a monolithic PZT transducer and a piezocomposite design. Frequency spectra are recorded for each model transdueer and used as input to the model. We then increase the test material attenuation to determine the effeet on the eeho responses. The results demonstrate that the broader bandwidth of the piezoeomposite transdueer aecounts for the improved penetration. Are piezocomposite transducers necessary to achieve broad bandwidth? No, but most monolithic designs rely on heavy backing to increase bandwidth. This causes signifieant reduction in signal amplitude. Piezoeomposite designs provide both broad bandwidth and high signal amplitudes making them more suitable for use on lossy test materials.

Outline

• Desirable Characteristics of UT Transducers
• Earlier Experimental Results Demonstrated Better than Expected Improvements in Signal-to-Noise
• This Presentation Shows That Improved Bandwidth Accounts for This Effect

Desirable Characteristics of UT Transducers

• High Pulse Amplitude (and Low Noise)
• Short Pulse Duration

Piezocomposite Material

• Combination of a Piezoelectric Material and Some Other Material
• Improved Piezoelectric Performance

Fig.1: Rods Ceramic in a PolymerMatrix

Fig.2: Acoustic Impedance as a Function of Ceramic Volume Fraction

Fig.3: Thickness Coupling Factor as a Function of Ceramic Volume Fraction

3.5 MHz 3/8 inch Diameter 45 Degree Angle Beam Transducer Results

Fig.4: 3.5 MHz 3/8 inch Diameter PZT Angle Beam Transducer on the 4 Inch Radius of an IIW Block

Fig.5: 3.5 MHz 3/8 inch Diameter Composite Angle Beam Transducer on the 4 Inch Radius of an IIW Block

5.0 MHz 1/2 Inch Diameter 45 Degree Angle Beam Transducer Results

Fig.6: 5.0 MHz 1/2 Inch Diameter 45 Degree PZT Angle Beam Transducer (Type-A) on on a full Node Corner of a 1 Inch Thick Cast Iron Block Fig.7: 5.0 MHz 1/2 Inch Diameter 45 Degree PZT Angle Beam Transducer (Type-B) on on a full Node Corner of a 1 Inch Thick Cast Iron Block

Fig.8: 5.0 MHz 1/2 Inch Diameter 45 Degree Composite Angle Beam Transducer (Type-A) on on a full Node Corner of a 1 Inch Thick Cast Iron Block

Why is the Performance Better than Expected?

• Decreased Piezoelectric Noise
• Increased Bandwidth

We will use a Mathematical Model to Simulate the Effect of Material Attenuation on the Transducer Pulse Amplitude




Fig.10: Loss as a Function of Frequency for Three Attenuation Levels	Fig.11: Comparison of Absolute Spectra Before and After Attenuation	Fig.12: Comparison of Absolute Spectra Before and After Attenuation	Fig.13: Comparison of Normalized Spectra Before and After Attenuation
The Transmitted Spectrum is also an Indication of the Receive Capability as a Function of Frequency
Fig.14: Comparison of Transmitted and Attenuated Spectra for a Non- Attenuating Material	Fig.15: Comparison of Transmitted and Attenuated Spectra of a Material with Moderate Attenuation	Fig.16: Comparison of Transmitted and Attenuated Spectra for a Material Having High Attenuation
Fig.17: Received RF Waveform With No Attenuation	Fig.18: Received RF Waveform With Moderate Attenuation

However

• Nothing I Have Said Mandates the Use of Piezocomposites
• It is the BANDWIDTH of the Transducer that Accounts for the Performance
• Why Not Use a Broadband Monolithic Transducer?

Broadband Monolithic Transducers:

• Rely on a Heavy Damping Material to Achieve the Bandwidth
• This Significantly Reduces the Sensitivity of the Transducer

Piezocomposite Transducers Yield:

• Broad Bandwidth and High Sensitivity Because of Lower Acoustic Impedance and Higher Coupling Factor
• This is the Advantage in Attenuative Materials!

Summary

• Broadband Transducers Yield Better Penetration in Attenuative Materials
• Piezocomposite Transducers Have Broad Bandwidth as Well as Higher Sensitivity Resulting in Superior Performance.

Author:

Paul A. Meyer, Ph.D.