Near-field Distance Calculation

If using a transducer with frequency f=120 kHz, with half power beam angle of θ3dB = 7^o and speed of sound c=1450 m•s^-1, then we may compute first the wavelength λ:

,
 

second the wave number k:

third the active radius a (here given in cm):

and finally, near-field distance:

 

Data from within 1.7 m (2•R_nf) of the transducer face should not be included in the analysis.