Beam Spread
Beam spread is the angular divergence of an ultrasonic beam beyond the near-field distance, governed by transducer diameter and frequency; it sets the lateral resolution of the inspection.
Definition
Beam spread is the half-angle θ of divergence of the ultrasonic beam in the far field. For a circular piston transducer, sin θ ≈ 1.22 λ/D, where λ is the wavelength and D the element diameter.
Technical Context
Higher frequencies and larger diameters give narrower beams (better lateral resolution). Beam spread directly influences DAC and DGS curves and the minimum resolvable flaw spacing.
Related terms
- Near-Field — The near-field is the region close to an ultrasonic transducer where the beam has complex pressure variations and a converging shape; precise amplitude measurements are unreliable until beyond the near-field length N.
- Far-Field — The far-field is the region beyond the near-field distance N where the ultrasonic beam diverges in a predictable manner and amplitude decays inversely with distance, suitable for quantitative sizing.
- Transducer (Ultrasonic) — An ultrasonic transducer is a device — typically containing a piezoelectric element — that converts electrical pulses to mechanical vibrations and vice versa, used to launch and receive ultrasonic waves in the test piece.
More physics terms
Back-Wall Echo · Dead Zone · Shear Wave · Longitudinal Wave · Surface Wave · Lamb Wave · Mode Conversion · Attenuation · Geometric Unsharpness · Radiographic Density
Where this comes up in practice
Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.
Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.