Why does the propagation constant in the Helmholtz equation include j?

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AI Thread Summary
The discussion centers on the presence of the imaginary unit "j" in the propagation constant γ of the Helmholtz equation. It highlights confusion regarding the equation γ = j √(ω²μ(1 - jσ/ω)), where the factor of j appears to be a mistake. Participants clarify that the correct representation should reflect a negative sign for the propagation constant. The conversation emphasizes the importance of understanding the mathematical representation of electromagnetic wave propagation. Overall, the inclusion of j is linked to the complex nature of wave behavior in lossy media.
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Homework Statement
This is my own question: Why do we intentionally include the imaginary unit jj in the propagation constant after taking its square root?
Relevant Equations
Helmholtz equation
Here is my question:
$$
\nabla^2 \bar{E} + \omega^2 \mu \left( 1 - j \frac{\sigma}{\omega} \right) \bar{E} = 0
$$

where

$$
\gamma = \alpha + j \beta
$$

$$
\gamma^2 = \omega^2 \mu \left( 1 - j \frac{\sigma}{\omega} \right)
$$

$$
\gamma = j \sqrt{ \omega^2 \mu \left( 1 - j \frac{\sigma}{\omega} \right) }
$$

why is there a factor of j in the expression for γ?
 
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baby_1 said:
$$
\gamma^2 = \omega^2 \mu \left( 1 - j \frac{\sigma}{\omega} \right)
$$

$$
\gamma = j \sqrt{ \omega^2 \mu \left( 1 - j \frac{\sigma}{\omega} \right) }
$$

why is there a factor of j in the expression for γ?
Yes, the ##j## outside the square root in the second equation above looks like a mistake. If you square this equation, you do not get the first equation.

Where did you see the second equation?
 
Dear TSny,

Thank you for your help.
In many electromagnetics resources, I have noticed that the propagation constant is often represented with a "j," but I am having trouble understanding why this is the case. I have attached one of the references for your review.
 

Attachments

I realized my mistake: in the main equation, the sign of the propagation constant should be negative. Thank you once again for your help!
 
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