Rectification control changes how the received signal is shown on the display by converting negative portions of the waveform to positive (a display polarity adjustment). This makes echo amplitudes easier to read and compare, since everything appears with the same polarity. It does not change the actual ultrasonic energy sent into the material, the material properties, or the transducer frequency; it’s purely a display adjustment for the waveform.

High attenuation means the material absorbs and scatters ultrasonic energy as it travels, so the wave loses more energy before returning. When a reflector is hit, the echo that comes back is smaller in amplitude, making it harder to distinguish from noise and reducing the overall signal quality. While frequency can influence attenuation (higher frequencies attenuate more), the main effect described here is the reduction in echo strength, not a change in frequency. Saying there’s no effect contradicts the energy loss, and claiming echoes grow stronger is the opposite of what happens in a highly attenuating material. In practice, using a lower frequency can help penetrate such materials because it experiences less attenuation, improving penetration and visibility of echoes.

Rayleigh waves produce particle motion that is elliptical in the vertical plane of propagation right at the surface. This comes from how these surface waves combine vertical and horizontal ground motions as the wave travels, so a particle traces an ellipse rather than moving in a straight line or purely along one direction. The motion is strongest near the surface and decays with depth, so you don’t get circular motion deeper down. That’s why the characteristic description is elliptical motion near the surface. The other descriptions—straight-line motion parallel to the surface, purely longitudinal motion, or circular motion at depth—don’t match how Rayleigh waves actually move the ground.

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.