Whispering gallery mode resonators in microwave physics and technologies

Abstract

We review the main results of the development of whispering gallery mode (WGM) resonators and their unique applications due to their quasi-optical functionality. Several types of advanced WGM resonators are proposed by the authors. The theoretical results are described for the resonators with an analytical solution of the electromagnetic problems. Special emphasis is given to the interaction of moving charged particles and waves of cylindrical resonators. Important aspects are described concerning the developed sapphire resonators, for which an exact solution can only be found by using specially designed computer program products. A separate section of the paper is devoted to application aspects of the WGM resonators. In particular, it describes advanced solutions for overcoming the problems of measuring the small microwave (MW) surface impedance of unconventional superconductors in the form of large-area thin films and small samples under study. In addition, a demonstration of accurate complex permittivity measurements of small volumes of lossy liquids is provided. Special emphasis is given to highly stable MW signal sources, namely Ka-band transistor-based feedback oscillator and solid-state maser WGM oscillators. Recently obtained results are presented of experimental studies of the auto-oscillatory system developed on the basis of the WGM resonator with relativistic electron beam.

Accurate Characterization of High-$Q$ Microwave Resonances for Metrology Applications

“…Nevertheless, microwave and millimetre-wave WGMRs, made of lowloss single crystalline materials (quartz, sapphire, ruby, ect. ), do also show remarkable quality factors finding applications both in high-performance microwave components and as high sensitivity sensors for thermometry [11], spectroscopy [40] and accurate complex permittivity measurements [41].…”

Contactless exploration of graphene properties using millimeter wave response of WGM resonator

“…It should be emphasized that in a Ka-band, a sapphire WGM resonator has relatively high intrinsic Q-factor of up to 4 Â 10 4 (frequency f ffi 40 GHz and T ¼ 300 K). 10 This manuscript was preceded by other publications 11,12 on the investigation of a WGM sapphire resonator with ultrathin copper films, demonstrating peculiarities at small copper thicknesses.…”

“…1(a) and Ref. 10 for experimental setup details as well as advantages of WGM resonator technique]. The optical axis of the sapphire is parallel to the geometric axis of the disk.…”

“…For this mode, the longitudinal component of the electric field exceeds the azimuthal, at least inside the dielectric disk. 10 For the microwave measurements, a vector network analyzer N5230A was used. The response was measured for the following cases: (i) a bare sapphire-based disk resonator without a substrate [ Fig.…”

Спектры Собственных Волн Анизотропного Цилиндрического Твердотельного Волновода

“…Отметим, что на практике, когда материал цилиндра обладает потерями, в волноводе, как правило, проявляются собственные моды с радиальными индексами s = 1, 2, а остальные затухают [10,22]. В действительности слабое затухание собственных мод волновода обеспечивается сосредоточением их полей вблизи цилиндрической поверхности волновода.…”