Near-Field (Fresnel Zone)

The region immediately in front of an ultrasonic transducer where the sound beam is compressed and interference effects dominate. In the near-field, the beam does not diverge uniformly and sound pressure is non-uniform. The near-field length is calculated as: L = D²/(4λ) where D is transducer diameter and λ is wavelength. Operating within the near-field affects defect detection, so proper transducer selection and inspection geometry are critical.

Physical Foundation

Understanding near-field (fresnel zone) is fundamental to effectively applying NDT methods. Many NDT techniques rely directly on these physical principles.

Practical Impact on Inspections

This principle affects equipment selection, test parameters, inspection procedures, and data interpretation. Proper application requires understanding these physics fundamentals.

Best Practices

• Always follow applicable NDT standards and procedures
• Use properly calibrated and maintained equipment
• Ensure personnel are properly trained and certified
• Document inspection procedures and results completely
• Keep current with industry standards and best practices