PCS => Probe center separation.

TLat.Wave => Time-of-flight lateral wave.

S => Distance from the probe index point to the weld center.

d => Upper ligament.

h => Defect height.

VL => Ultrasound longitudinal velocity.

TPP => Time-of-flight to the backwall.

TM => Material thickness.

Time-of-flight difraction technique

PCS => Probe center separation.

TM => Material thickness.

VL => Velocity of propagation of longitudinal waves in test material.

VT => Velocity of propagation of shear waves in test material.

* The time-of-flight of the lateral shear wave must be greater than the backwall time-of-flight.

The beam is incident at the selected input angle – θ - , in two-thirds of the material thickness - TM  -

VL => Velocity of propagation of longitudinal waves in test material.

tB=> Time-of-flight echo coming from point B.

tC => Time-of-flight echo coming from point C.

tD => Time-of-flight echo coming from the backwall - point D.

dTOFB => Distance from B to the receiver transducer.

dTOFC => Distance from C to the receiver transducer.

dTOFD => Distance from the backwall  to the receiver transducer.

d1=> Depth of point B.

d2=> Depth of point C.

dBW=> Depth of point D.

f => Emitting frequency of wide band transducers with a duration pulse of ΔTLW = 1.5/f.

TM => Material thickness.

VL => Velocity of propagation of longitudinal waves in test material.

DZLW => Dead zone of the lateral wave INCREASES when  frequency (f ) DECREASES.

DZBW => Dead zone of the backwall echo INCREASES when  frequency (f ) DECREASES.

The spatial resolution (Δd) is the ability of the ultrasonic signal to distinguish two separate reflectors along the depth of the test material. The spatial resolution (Δd) is a function of pulse duration (ΔT) that INCREASES as the depth (d) INCREASE.