Nondestructive Testing Encyclopedia- Ultrasonic Testing - MainUT A-Z

#### 1. Wavelength

where:
f = frequency
c = acoustic velocity
= wavelength
|wave length|
|frequency|
|velocity|

#### 2. Acoustic Impedance

where:
Z = acoustic impedance
c = acoustic velocity
= density of transmitting medium
acoustic impedance

|acoustic impedance|

#### 3. Transmission Coefficient for Normal Incidence

where:
Z1 = acoustic impedance in medium 1
Z2= acoustic impedance in medium 2
D = transmission coefficient
|transmission factor (coefficient) |

#### 4. Reflection Coefficient for Normal Incidence

where:
Z1 = acoustic impedance in medium 1
Z2 = acoustic impedance in medium 2
R = reflection coeffcient
|reflection coefficient

#### 5. Snell's Law

where:
c1 = acoustic velocity in medium 1
c2 = acoustic velocity in medium 2
1 = beam angle in medium 1
2 = beam angle in medium 2
Example
|Snell's law|

#### 6. Near Zone

where:
D = the diameter of a flat circular oscillator
= wavelength of the ultrasound
N = length of near zone
|near field|

#### 7. Half Angle of Divergence (for flat circular oscillators)

where:
= half angle of divergence
k dB = constant based on stated dB drop from center maximum
= wavelength
D = the diameter of a net circular oscillator
Values of k dB vary for the dB drop that is to be determined.
-1.5dB k=0.37
-3dB k=0.51
-6dB k=0.7
-10dB k=0.87
-12dB k=0.93

#### 8. Convergence Point

For determining the focal distance of a focused beam in a 2 media geometry.

where:
fx = new focal distance
f1 = focal distance in coupling medium
c1 = acoustic velocity in coupling medium
c2 = acoustic velocity in second medium
P1 = pathlength in the coupling medium
|convergence point|

#### 9. Sound Pressure

where:
= density
c = velocity of sound
= angular frequency
= particle displacement
Z = c = acoustic impedance
normally in units of N/m2
|acoustic power density|

#### 10. Intensity of Acoustic Power

where:
p = pressure
= angular frequency
= particle displacement
Z = c = acoustic impedance
normally in units of W/m2

## B = 10 log (J/Jo)

where:
Jo is the arbitrary (10-12 W/m2) reference level corresponding to the faintest sound detectable by the ear.

Since J is proportional to the sound pressure squared, the difference between two intensity levels can be determined by;

normally units are in deciBells (abbr.dB)

#### 12. Attenuation

where:
po and p are sound pressures at the start and end of a length d.
alpha is the coeffcient of attenuation for a given material

alternatively;

normally units of attenuation are in dB and the attenuation coeffcient is in dB per unit length
|attenuation coefficient|

Reference:
Ultrasonic Inspection 2 - Training for Nondestructive Testing