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 		beam spread

|divergence|

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|

|focused beam|

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
11. Intensity Level

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|

|decibel (dB)|

Reference:
Ultrasonic Inspection 2 - Training for Nondestructive Testing
E.A. Ginzel; Prometheus Press Canada.