Mark Clulow

Fighter Jet flying over snowy mountains

10 Biggest Factors Related to Ultrasonic NDT with Focus on Phased Array and Matrix Array

CAVEAT: NDT is such a critical science that I see most respected sources for information preface ANYTHING they say with "Do Your Own Research, Follow Your Manual, Be Guided By Your Level 3". So there.

1. Material Properties

  • Acoustic impedance: The difference in acoustic impedance between the material being tested and the defect will determine the amount of sound reflected back to the transducer.

  • Grain size: Smaller grain sizes tend to scatter ultrasonic waves more than larger grain sizes, which can affect the resolution of the inspection.

  • Anisotropy: Some materials, such as composites, have different properties in different directions. This can make it difficult to inspect these materials with ultrasonic waves.

2. Transducer selection Brought to you by

  • Frequency: Higher frequencies provide better resolution but less penetration depth. Lower frequencies provide less resolution but greater penetration depth.

  • Transducer size and shape: The size and shape of the transducer will determine the size and shape of the area that can be inspected.

  • Beam angle: The beam angle of the transducer will determine the angle at which the ultrasonic waves are directed into the material. This may come from a wedge, the material itself, or operator technique.

3. Inspection technique

  • Pulse-echo: The most common technique, where the transducer transmits and receives the returning sound waves.

  • Pitch-catch: Uses two transducers, one to transmit and one to receive.
    An example of this is MxTTU™ (Matrix Through-Transmission Ultrasound) system from

  • TOFD (Time-of-Flight Diffraction): Measures the time it takes for sound waves to diffract around a defect. This is particularly useful for detecting cracks.

4. Data acquisition and analysis

  • Phased array and matrix array technology: Allows for the electronic steering and focusing of the ultrasonic beam, providing better coverage and resolution.

  • Signal processing: Techniques such as filtering and gating can be used to improve the signal-to-noise ratio and extract useful information from the data.

  • Image reconstruction: The acquired data can be used to create images of the internal structure of the material, which can be used to identify defects.

5. Inspection environment

  • Temperature: Temperature can affect the velocity of sound in the material, which need to be considered and compensated for, to avoid inaccurate measurements.

  • Surface condition: The surface of the material must be clean and smooth for good contact with the transducer.

  • Accessibility: The inspection area must be accessible to the transducer and operator.

6. Operator skill and experience

  • Skilled and experienced operators are required to properly interpret the results of the inspection.

  • Training and certification programs are available to help operators develop their skills.

7. Code and standards

  • There are many codes and standards that apply to ultrasonic NDT, such as ASME, ASTM, and AWS. There are also differences with ISO.

  • These codes and standards specify the requirements for the equipment, procedures, and personnel.

8. Safety

  • Ultrasonic NDT is a safe method of inspection, but there are some potential risks, such as electrical shock and exposure to ultrasonic waves.

  • Proper safety procedures must be followed to minimize these risks.

9. Cost

  • The cost of ultrasonic NDT can vary depending on the size and complexity of the inspection.

  • Factors such as the equipment, personnel, and data analysis must be considered.

10. Future trends

  • Phased array and matrix array technology is becoming increasingly popular due to its advantages in coverage, resolution, and data acquisition.

  • Other new technologies, such as laser ultrasonics and guided waves, are also being developed.

This list is not exhaustive, but it covers some of the most important factors related to ultrasonic NDT, with a focus on phased array and matrix array technology.

Last Updated: 2023-12-07


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