Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

In more practical terms, for water with longitudinal wave of 500KHz this would
mean an attenuation of about 5 dB per meter.
Example:
Attenuation factor for water = 25.3x 10 -15 Neper
Frequency= 0.5MHz
The attenuation = Attenuation Coefficient x f 2
The attenuation = 25.3 x 10 -15 x (0.5x10 6 ) 2 Neper/ cm
The attenuation = 25.3 x 10 -15 x (0.5x10 6 ) 2 x 8.686 = 0.055 dB/cm or 5.5 dB/m
Since such long water path lengths are not normally used the 0.005 dB/mm
attenuation is considered negligible. But for the heavier oils attenuations 200
to 500 times greater can have significant effects on signal amplitude and
frequency content.
For the fixed delay-lines or wedge materials used in contact testing
attenuation variations can be far more pronounced and variation between
manufacturers can cause considerable response differences.