Near-field length
Near field length is the area in front of the ultrasonic transducer where sound pressure fluctuates strongly and defects are hard to detect. Therefore, delay lines are used.
Physical-Chemical Mechanism of Action
The near-field length is the region directly in front of the ultrasonic probe where the sound pressure varies strongly and is no longer uniform. This leads to inaccurate measurements and makes it hard to pinpoint defects.
Metallurgical Relevance & Welding Risks
Uneven sound pressure in the near-field can cause missed or false defect indications. This raises the risk of overlooking critical defects and compromising part safety.
Shop Practice & Action Instructions
To minimize the near-field and ensure accurate readings, use delay lines. These provide a uniform sound path and improve ultrasonic testing accuracy. A typical delay line is at least 10 cm long. Make sure the probe is properly aligned and the test material is homogeneous.