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

  • Thread starter Thread starter baby_1
  • Start date Start date
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.
baby_1
Messages
159
Reaction score
16
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?
 
Physics news on Phys.org
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!
 
Thread 'Minimum mass of a block'
Here we know that if block B is going to move up or just be at the verge of moving up ##Mg \sin \theta ## will act downwards and maximum static friction will act downwards ## \mu Mg \cos \theta ## Now what im confused by is how will we know " how quickly" block B reaches its maximum static friction value without any numbers, the suggested solution says that when block A is at its maximum extension, then block B will start to move up but with a certain set of values couldn't block A reach...
TL;DR Summary: Find Electric field due to charges between 2 parallel infinite planes using Gauss law at any point Here's the diagram. We have a uniform p (rho) density of charges between 2 infinite planes in the cartesian coordinates system. I used a cube of thickness a that spans from z=-a/2 to z=a/2 as a Gaussian surface, each side of the cube has area A. I know that the field depends only on z since there is translational invariance in x and y directions because the planes are...
Thread 'Calculation of Tensile Forces in Piston-Type Water-Lifting Devices at Elevated Locations'
Figure 1 Overall Structure Diagram Figure 2: Top view of the piston when it is cylindrical A circular opening is created at a height of 5 meters above the water surface. Inside this opening is a sleeve-type piston with a cross-sectional area of 1 square meter. The piston is pulled to the right at a constant speed. The pulling force is(Figure 2): F = ρshg = 1000 × 1 × 5 × 10 = 50,000 N. Figure 3: Modifying the structure to incorporate a fixed internal piston When I modify the piston...
Back
Top