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Study of Unidirectional Surface Waves Propagation in Magnetic Layers and their Behavior Near Different Barriers

Emad Marvasti, Mohammad Fater | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50153 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Rejaei Salmasi, Behzad
  7. Abstract:
  8. Lorentz reciprocity theorem is one of the most fundamental concepts in electromagnetism. Although, in specific conditions, for example in nonlinear systems or systems with broken time-reversal symmetry it can be violated. In recent years, many interests have been attracted towards such systems. With a proper design, they can support nonreciprocal or at specific conditions unidirectional propagation behavior. For example, despite ordinary dielectrics, in ferrite layers, the propagation constant of surface waves on ferrite edge, depends on the direction of propagation with respect to magnetization direction. Furthermore, in the specific interval of frequencies, ferrite structures allow propagation to be taken place only in specific directions. This is because of nonsymmetrical permeability tensor of the ferrite which leads to broken time-reversal symmetry and nonreciprocity of ferrite systems. With this in mind, a waveguide, which is partially loaded with YIG, can be properly designed to be a one-way channel of waves. Considering such waves can propagate only in one direction and no reflection is permitted, we’re going to investigate the behavior of them in the collision with a barrier. furthermore we’ll investigate the distribution of fields (amplitude and phase) near a barrier, the effect of barrier width or barrier type, the effect of frequency and direction of incident wave (with respect to magnetization direction), the different methods of creating a barrier and the effect of the magnetic bias on the propagation parameters of the waves. Finally using obtained results we’ll try to present ideas for making magnetic devices such as memories or switches. However, a brief explanation of the results that we’ll obtain in this thesis are presented here:
    • General result of investigation of behavior of collision of the unidirectional waves with the barrier would be that: waves will accumulate behind impenetrable barriers or tunnel through penetrable ones
    • Form studying field amplitude and phase we’ll conclude that: fields amplitude inversely dependent on the distance from barrier edges to the power of a number which is slightly less than 1, although the dependence of phase can be expressed by a logarithmic function.
    • There are two types of barrier that we’ll study during this thesis, the result of this study would be: penetrable PEC barrier has maximum dissipation while barrier which is created by cutting off a piece of the ferrite layer has less attenuation. In both cases, however, attenuation increases with the increase of barrier width.
    • The investigation of the effect of the frequency and direction of the incident wave would result in: changes in frequency lead to changes in propagation constant which are lead to various effects on barrier delay and attenuation. The increase of the angle of incident wave leads to increase of propagation constant and decrease of barrier attenuation.
    • From various simulations, we’ll achieve a general definition for the barrier which can be summarized as If in an area, no answer can be found for the propagation constant, then it would be known as a barrier. So a barrier can be created in various ways such as putting thin PEC layer in ferrite/dielectric interface, cutting off a piece of ferrite layer or increase/decrease of the magnetic bias.
    • Finally, the results of the investigation of magnetic bias change can be summarized as: changes in the magnetic bias also lead to changes in propagation constant. Huge changes, however, might cause the area no longer supports waves propagation and thus no answer for propagation constant would be found. Switching the magnetic bias between two specific values can be used to block wave propagation for the arbitrary amount of time and then again to provide permission of propagation after this period of time. The idea can be used to realize a switch or memory
  9. Keywords:
  10. Waveguides ; Dispersion Equation ; Sloshing ; Nonreciprocal Magnetic Devices ; Magnetostatic Approximation ; Unidirectional Surface Wave

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