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Ultrasonic field
Transducer Parameters: D = Diameter, f = frequency V = velocity, λ=wavelength |
Near field z<No (Circular Transducer) |
The field intensity is irregular and the beam width is smaller than the transducer diameter.
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Near field z<No (Rectangular Transducer) |
where “a” is the shorter size of the transducer and “b” the largest size of the transducer |
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Beam spread The beam spread can be reduced by selecting a transducer with a higher frequency, a larger element diameter or both
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For flat transducers, the pulse-echo beam spread angle is given by:
where: α/2 = Half angle spread. ”k” = constant value which depends on where the beam edge is defined |
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“k” = 0.51 gives the half beam width at -6dB drop in pulse-echo mode. |
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“k” for Transmission mode |
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Drop % dB |
Circular transducer |
Rectangular transducer |
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10% (20 dB) |
1.08 |
0.60 |
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50% (6 dB) |
0.54 |
0.91 |
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“k” value for Pulse-echo |
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10% (20 dB) |
0.87 |
0.74 |
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50% (6 dB) |
0.51 |
0.44 |
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Focused sound fields |
The beam width can be reduced by focusing in the near-field zone using a lens
The focus position (zfoco) for a given lens radio is:
=> VM: means de sound velocity in the specimen => VL: sound velocity in the lens material => R: lens curvature radius |
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Focusing factor |
A focused beam is characterized by:
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A focused beam can be classified by Sac as:
0.1 ≤ Sac ≤ 0.33 => strong focusing. 0.33 ≤ Sac ≤ 0.67 => medium focusing. 0.67 ≤ Sac ≤ 1.0 => weak focusing.
Most of the industrial applications use: Sac < 0.6 |
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Focusing Depth |
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The formula is only valid for Sac < 0.6 |
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Focused beam diameter |
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The beam diameter in mm at -6dB drop |
