Control of resonances in a one-dimensional bragg structure of the microwave range using a distilled water layer as an interface

Background and Objectives: The methods to control the characteristics of microwave devices on photonic crystals are based on the high sensitivity of resonance states in the forbidden band to the creation of volume defect in the periodic structure and the features of its interface. The appearance of surface photonic Tamm states in microwave photonic crystals adjacent to the electromagnetic radiation absorber layer can be considered as interface states. Currently, there is an increasing interest in the possibility of using structures containing polar liquids, such as water, both in the form of continuous layers and in the form of individual periodically located drops as an absorber of electromagnetic energy in microwave technology, since water in the microwave range is characterized by both a significant value of the real part of the complex permittivity and an imaginary part of the complex permittivity. At the same time, microwave absorbers based on water-containing structures, compared to more traditional materials based on layers with high electrical conductivity, have a number of advantages, such as biocompatibility, availability, ease of adjustment, optical transparency. The appearance of analogs of photonic Tamm states is also possible in the presence of an interface in the form of a polar liquid layer characterized by a positive value of the real part of the complex permittivity and a significant value of the imaginary part of the complex permittivity. When choosing a polar liquid as an absorber, it is necessary to take into account that both the real and imaginary parts of the permittivity significantly depend on the frequency of the probing microwave signal. For the appearance of photonic Tamm states in a photonic crystal with an interface in the form of a polar liquid layer, the imaginary part of the complex permittivity of which is several orders of magnitude smaller than this value for metal nanolayers, the thickness of the liquid layer should be of the same order of the wavelength of electromagnetic radiation, unlike conducting nanolayers. In this case, the electric field of the electromagnetic wave turns out to be partially localized in the liquid layer. In this regard, it is of interest to carry out theoretical and experimental research of the resonance characteristics of microwave photonic crystals associated with the effect of the appearance of photonic Tamm states in the forbidden band, depending on the parameters of the interface based on a structure containing water in the form of a continuous layer. Materials and Methods: To carry out the research of Tamm states, a photonic crystal consisting of alternating layers of two types of dielectrics was created. Its last layer was separated from the distilled water layer by a thin dielectric film. The distance between the film and the last layer of the photonic crystal could be adjusted. A vector network analyzer was used to measure frequency characteristics in the frequency range of 7–13 GHz. Results: It has been established that with an increase of thickness of the distilled water layer, oscillations of the frequency and amplitude of the Tamm resonance are observed both in the first and in the second forbidden bands of the one-dimensional microwave Bragg structure, damping at a large thickness of the water layer. In this case, the greatest amplitude of the Tamm resonance is achieved for each thickness of the water layer at a certain value of the air gap. Conclusion: Based on the results of computer modeling using the transfer matrix method and experiment, the possibility to control photonic Tamm resonances by changing both the thickness of the distilled water layer and the size of the air gap between the photonic crystal and the water layer has been established.