UT Useful Formulas
Main ultrasonic parameters and their definition or relationship:
Feature
Remarks
Formula
Where:
= Modulus of elasticity (Young’s modul
2
us) [N/m ]
Longitudinal
(Compression)
velocity
; [ m/s ]
3
=
Mass density [kg/m ]
=
Poisson’s ratio
Where:
Transverse
(shear)
velocity
=
2
Shear modulus [N/m ]
; [m/s ]
Where:
=
Frequency
; [Hz]
Acoustic
impedance
; [kg/m2s]
=
Velocity [m/s]
Where:
=
Velocity [m/s]
=
Near‐field
(circular)
Wave Length [m]
3
Density [kg/m ]
Where:
=
Transduser diameter [mm]
=
Transduser frequency [Hz]
=
Sound velocity [mm/s]
; [mm]
Beam
divergenceangle (circular)
Where:
=
Reflection
coefficient
Where:
=
Acoustic impedance of Medium 1
=
Acoustic impedance of Medium 2
Where:
=
Transmission
coefficient
UT Useful Formulas
Page 1 of 2
Beam divergence angle from
centerline to point where signal
is at half strength
Reflection coefficient
Where:
Snell’s law
=
=
Where:
=
Amplitude
attenuation
Sound amplitude
gain (or loss) in
Decibel
=
the angles of incident and
refracted longitudinal waves,
respectively
=
the angles of the converted
reflected and refracted shear
waves, respectively
Initial (unattenuated) amplitude
=
Attenuation coefficient [dB/m]
=
Traveled distance [m]
Where:
= Amblitude of the first pulse
; [dB]
= Amblitude of the second pulse
Where:
=
Distance to
reflector or
discontinuity
(normal or angle
beam)
=
Surface Distance
& Depth (1st
Leg)
Surface Distance
& Depth (2nd
Leg)
Skip Distance for
weld inspection
UT Useful Formulas
the longitudinal wave velocities
in the first and second materials,
respectively
the shear wave velocities in the
first and second materials,
respectively
Page 2 of 2
Sound velocity (longitudinal or
shear) [m/s]
Time difference [s]