Topic: Electromagnetics
Consider a lossy dielectric with complex permittivity $\epsilon=\epsilon^{\prime}-j\epsilon^{\prime\prime}$. The loss tangent is defined as $\tan~\delta=\epsilon^{\prime\prime}/\epsilon^{\prime}$. What does $\tan~\delta\rightarrow\infty$ physically imply?
- A. The medium behaves like a perfect conductor
- B. The medium behaves like a lossless dielectric
- C. The medium behaves like a perfect insulator
- D. The displacement current dominates conduction current
Answer: A. The medium behaves like a perfect conductor
Explanation: The loss tangent $\tan \delta = \frac{\sigma}{\omega \epsilon'} = \frac{\epsilon''}{\epsilon'}$. It represents the ratio of the conduction current density to the displacement current density. As $\tan \delta \to \infty$, the conduction current heavily dominates over the displacement current, which is the defining characteristic of a good conductor. Thus, the medium behaves like a perfect conductor.