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As sound enters the inspection material from the transducer, the sound energy propagates directly through the material but also dissapates at 90° to the beam central beam axis. This dissapation (which in the far zone increases with distance) is known as beam spread and is an important factor when defect sizing, interpreting echo amplitude or when choosing the right transducer for the particular material or discontinuity expected

This online tool calculates the beam spread of a given diameter ultrasonic element of a given frequency in a particular velocity material.

Material velocity:
Transducer diameter:
Transducer frequency:

6dB or 12dB beam spreads should always be plotted using the appropriate industry standard, however, knowing the effect of frequency, velocity and element diameter on beamspread will always benefit an NDT technician when choosing the right probe for the job

the above calculator uses the following equation:

$sin\theta=q\frac{V}{DF}$

Where:

θ = The full beam spread

q = The constant beam divergance factor (0.51 for 6dB and 1.02 for 12dB)

V = The material velocity (m/µs)

D = The transducer crystal diameter (mm)

F = The transducer frequency (mHz)

Example 1:

Suppose you wish to calculate the 6dB beam spread of a 10mm diameter, 5mHz transducer in carbon steel specimen whose velocity is 5900m/s

θ = we dont know!

q = 0.51

V = 5900000

D = 10

F = 5000000

Subsituting these figures into the equation above gives us:

$sin\theta=0.51\frac{5.9}{10*5}$

$sin\theta=0.51\frac{5.9}{50}$

$sin\theta=0.51*0.118$

$sin\theta=0.6018$

$\theta=\sin^{-1}(0.6018)$

$\theta=3.45\deg$