Magnetic-dipolar-mode Fano resonances for microwave spectroscopy of high absorption matter

Abstract

The interaction between high absorption matter and microwave radiated energy is a subject of great importance. In particular, this concerns the microwave spectroscopic characterization of biological liquids. The use of effective testing methods to obtain information about physical properties of different liquids on the molecular level is one of the most important problems in biophysics. However, the standard methods based on microwave resonant techniques are not sufficiently suitable for biological liquids because the resonance peak in a resonator with high-loss liquids is so broad that the material parameters cannot be measured correctly. Although molecular vibrations of biomolecules may have microwave frequencies, it is not thought that such resonant coupling is significant due to their low energy compared with thermal energy and the strongly dampening aqueous environment. This paper presents an innovative microwave sensing technique for different types of lossy materials, including biological liquids. The technique is based on the combination of the microwave perturbation method and the Fano resonance effects observed recently in microwave structures with embedded magnetic-dipolar quantum dots. When the frequency of the magnetic dipolar mode (MDM) resonance is not equal to the cavity resonance frequency, one gets Fano transmission intensity. When the MDM resonance frequency is tuned to the cavity resonance frequency, by a bias magnetic field, one observes a Lorentzian line shape. Use of an extremely narrow Lorentzian peak allows exact probing of the resonant frequency of a cavity loaded by a highly lossy material sample. For different kinds of samples, one has different frequencies of Lorentzian peaks. This presents a picture of precise spectroscopic characterization of high absorption matter in microwaves.