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Introduction to Ultrasonic Testing

Introduction
Basic Principles
History
Present State
Future Direction

Physics of Ultrasound
Wave Propagation
Modes of Sound Waves
Properties of Plane Waves
Wavelength/Flaw Detection
Elastic Properties of Solids

Attenuation
Acoustic Impedance
Reflection/Transmission
Refraction & Snell's Law
Mode Conversion
Signal-to-noise Ratio
Wave Interference

Equipment & Transducers
Piezoelectric Transducers
Characteristics of PT
Radiated Fields
Transducer Beam Spread
Transducer Types
Transducer Testing I
Transducer Testing II
Transducer Modeling
Couplant
EMATs
Pulser-Receivers
Tone Burst Generators
Function Generators
Impedance Matching
Data Presentation
Error Analysis

Measurement Techniques
Normal Beam Inspection
Angle Beams I
Angle Beams II
Crack Tip Diffraction
Automated Scanning
Velocity Measurements
Measuring Attenuation
Spread Spectrum
Signal Processing
Flaw Reconstruction

Calibration Methods
Calibration Methods
DAC Curves
Curvature Correction
Thompson-Gray Model
UTSIM
Grain Noise Modeling
References/Standards

Selected Applications
Rail Inspection
Weldments

Reference Material
UT Material Properties
References

Quizzes

Lamb Wave Generation

Lamb waves are similar to longitudinal waves, with compression and rarefaction, but they are bounded by the sheet or plate surface causing a wave-guide effect.

Electromagnetic-acoustic transducers (EMAT) designed to generate Lamb waves vibrate the atoms within the material being investigated. When a wire is placed near to the surface of an electrically conducting object and is driven by a current at the desired ultrasonic frequency, eddy currents will be induced in a near surface region. If a static magnetic field is also present, these currents will experience Lorentz forces of the form

F = J x B

F is the body force per unit volume, J is the induced dynamic current density, and B is the static magnetic induction.

Pictured above is a cross-sectional view of a meander coil EMAT for exciting Lamb waves in plates.