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Technical Discussions
Igor
Igor
10:03 Nov-26-2018
Length of the near field

Hello everyone,

I know that for calculate the near field distance for a single element transducer we can use the formula bellow

d = D^2*c/4*c

However, I can not find the formula to calculte the near field distance for a linear array or phased array. The formula is aways th same ? Someone could explain me that ?

Siva Degala
NDT Inspector,
Oceaneering, India, Joined Oct 2017, 1

Siva Degala

NDT Inspector,
Oceaneering,
India,
Joined Oct 2017
1
11:11 Nov-26-2018
Re: Length of the near field
In Reply to Igor at 10:03 Nov-26-2018 (Opening).

Asquare*F/4V
Where A-Apperture
F-Frequency
V-Velocity
This is the formula for calculating Near field.

Igor
Igor
11:14 Nov-26-2018
Re: Length of the near field
In Reply to Siva Degala at 11:11 Nov-26-2018 .

I wrote wrong the formular is :
d = D^2*f/4*c

But the question is still here....

I can not find the formula to calculte the near field distance for a linear array or phased array. The formula is aways th same ? Someone could explain me that ?

William A Jensen
Other,
IHI Southwest Technologies, Inc., USA, Joined May 2017, 67

William A Jensen

Other,
IHI Southwest Technologies, Inc.,
USA,
Joined May 2017
67
14:06 Nov-26-2018
Re: Length of the near field
In Reply to Igor at 11:14 Nov-26-2018 .

The near field length and hence the natural divergence of an ultrasonic beam are determined by aperture (equal to element diameter in the case of conventional monolithic transducers) and wavelength (wave velocity divided by frequency). For an unfocused transducer, the near field length, beam spread angle, and beam diameter can be calculated as follows:
NF = D2f / 4/c
D = element diameter or aperture
f = frequency
c = sound velocity in test medium

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