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What is Faraday rotation in Ferrite? Explain working of the isolator using Faraday rotation.
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When an electromagnetic wave passes through ferrites, plane of polarization continuous to rotate to angle θ in one particular direction (either clockwise or anticlockwise). This plane of polarization changes in the same direction whatever may be the direction of propagation of wave. This is called as Faraday rotation. Isolator comprises of four components i) rectangular waveguide with planar resistive card, ii)Mechanical bend of 450 in anticlockwise direction. It is reciprocal device iii) circular waveguide with ferrite rod to give a polarization rotation of 450 in clockwise direction. It is nonreciprocal device, iv) rectangular waveguide with resistive card.

Working of Isolator:

Case1) A TE10 mode is applied to the rectangular waveguide so the field is oriented in vertical direction as shown in figure. When the wave passes through mechanical twist (bend) the field polarization rotates by 450 in anticlockwise direction. This field now passed through the Ferrite material and the field polarization now is rotated in clockwise direction by 450. Due to anticlockwise and clockwise rotation of 450 the overall rotation in polarization is nullified and the field becomes vertical as it was at the input. This vertical polarized field when passes through the last component of rectangular waveguide, it does not interact with the resistive card since card is horizontally placed.

Case2) When a vertically polarized wave is reflected from the second port, it travels with same orientation of the field till the ferrite rod. When it passes through ferrite material it under goes a rotation of 450 in clockwise direction and this rotated filed when passes through the mechanical twist, field is further rotated by the 450 in clockwise as the mechanical twist is reciprocal in nature. Now the total filed rotation is of 900 in clockwise and due to this field becomes parallel with the resistive card at the input of isolator and is absorbed by the card. Thus the isolator gives different response in different direction of propagation.

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