Why Do We Use the Complex Conjugate of Velocity to Calculate Acoustic Intensity?

[Radel]

Hello All,

I would like to know why do we multiply the complex conjugate of velocity (not just the velocity) with the complex pressure to obtain the complex acoustic intensity. Could someone please help me with this?

Regards,
Radel...

 

[zoki85]

I guess for the same reason the apparent electrical power in complex form is given by S = VI*. Correct phase angle between voltage phasor V=V⋅e^jφ_v and current phasor I=I⋅e^jφ_i is φ=φ_v-φ_i. Without conjugate you would get in the product φ=φ_v+φ_i. Conjugate of the current I*=Ie^-jφ_i solves this problem since S=VI*=V⋅e^jφ_v⋅I⋅e^-jφ_i=V⋅I⋅e^j(φ_v-φ_i).