The cut off frequency of TEM wave is

Cut-off Frequency of TEM Wave

Definition: The cut-off frequency of a wave refers to the minimum frequency below which the propagation of a particular wave mode ceases in a specific medium or waveguide. For a Transverse Electromagnetic (TEM) wave, the cut-off frequency is a critical parameter that determines the conditions under which the wave can propagate through a waveguide or transmission line.

Correct Option Analysis:

The correct answer is Option 2: DC. This implies that the cut-off frequency for a TEM wave is zero, meaning that TEM waves can propagate even at very low frequencies (including DC). This unique property arises due to the nature of TEM waves, where both the electric and magnetic fields are perpendicular to each other and to the direction of wave propagation.

Why is the Cut-off Frequency for TEM Waves Zero?

• Structure of TEM Waves: TEM waves consist of electric and magnetic fields that are transverse to the direction of propagation. Unlike other wave modes (such as TE or TM modes), TEM waves do not have any longitudinal field components.
• Propagation Conditions: TEM waves do not require a minimum frequency to propagate. As a result, they can exist even at a frequency of zero, which corresponds to DC (Direct Current).
• Waveguide Design: In structures such as coaxial cables or two-wire transmission lines, the geometry allows TEM waves to propagate without requiring a specific minimum frequency.

Applications of TEM Waves:

• Used in coaxial cables for transmitting signals over a wide range of frequencies, including DC.
• Ideal for low-frequency applications due to their zero cut-off frequency.
• Widely used in RF and microwave engineering for signal transmission.

Conclusion:

The zero cut-off frequency of TEM waves makes them highly versatile and suitable for applications across a broad spectrum of frequencies, including DC. This property distinguishes TEM waves from other modes, such as TE and TM modes, which have non-zero cut-off frequencies.