Berlin 2012 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 23: Magnetization / Demagnetization Dynamics II
MA 23.8: Vortrag
Mittwoch, 28. März 2012, 11:45–12:00, H 1012
Rotational Doppler Effect in Magnetic Resonance — •Sergi Lendínez1, Eugene Chudnovsky2, and Javier Tejada1 — 1Departament de Física Fonamental, Facultat de Física, Universitat de Barcelona, Barcelona, Spain — 2Physics Department, Lehman College, The City University of New York, New York, U.S.A.
The Doppler Effect consists of a shift on the frequency received by an observer which is moving with respect to the source of the radiation. Commonly, linear Doppler is observed. In this case, an observer moving at relative velocity v will perceive a frequency shifted by v/c: f′= f(1 ± v/c), where the plus (minus) sign is for an observer moving towards (backwards) the source. However, the Doppler Effect can also be observed at rotations of the body. In particular, if a solid rotates with an angular velocity Ω in the field of a circularly polarized electromagnetic wave, in its rotating frame the frequency of the wave will be shifted by ω′ = ω ± Ω, where the plus (minus) sign is for a rotation in the opposite (same) direction of the circular polarization.
In the case of a rotating object with a resonant frequency, one would firstly think that the frequency will be shifted by Ω. However, a mechanical rotation of a system of charges is equivalent to a magnetic field, hence it must be checked whether the resonant frequency is affected by this magnetic field. Resonant frequencies of LC circuits are insensitive to magnetic fields, and the frequency will by shifted by Ω as expected. On the contrary, frequencies based upon magnetic resonance will be sensitive to this magnetic field, so the frequency shift may not be Ω.