Ultrasonic Testing Level 1 Practice Test

Beam divergence is governed by diffraction from the transducer’s aperture and the wavelength of the emitted ultrasound. A circular transducer acts like an aperture, and the beam spreads in the far field with an angle that is roughly proportional to lambda over the aperture diameter (lambda/D). Because frequency and wavelength are inversely related (lambda = c/f), increasing frequency shortens the wavelength, which tightens the beam. Likewise, increasing the transducer diameter while keeping frequency the same also narrows the beam. The other factors don’t set the angular spread: the coupling medium and crystal material affect how efficiently sound is transmitted and reflected (impedance matching), not the geometric spread of the beam. Pulse duration and gain influence axial resolution and amplitude, not the beam’s divergence. Temperature and pressure may slightly affect the speed of sound, but they don’t determine the main diffraction-limited divergence. So the factors that primarily determine beam divergence are the transducer diameter and frequency.