A low temperature study of electromagnetic energy loss in low-loss materials in the 110…140 MHz frequency range

Abstract

Subject and Purpose. The subject of the study is spectral and energy characteristics of whispering-gallery disk resonators made up of low-loss microwave dielectric and semiconductor materials, namely, gold-doped silicon Si:Au, Chemical Vapor Deposition (CVD) diamond, Arc Plasma Jet (APJ) diamond, and alumina ceramics Al2O3. On the basis of the temperature dependences of the microwave energy loss in the materials mentioned, we seek to classify the loss contributions among the electromagnetic energy absorption mechanisms and find physical parameters responsible for these mechanisms. Methods and Methodology. The loss values were experimentally obtained by the whispering-gallery disk resonator technique with the usage of a cryodielectrometer. A phenomenological simulation was performed to classify the loss contributions to the temperature dependence of electromagnetic energy absorption among the major loss mechanisms in the examined materials. Results. The experimental study results on the dielectric loss temperature dependence within 4.2...300 K have been presented and discussed for low-loss semiconductor and dielectric materials, including gold-doped silicon Si:Au, CVD-diamond, APJ-diamond, and alumina ceramics Al2O3 with reference to the frequency band 110...140 GHz. Certain design features have been suggested to use in the authors’ software-controlled measuring unit to provide the interchangeability of backward wave tubes (BWT) inside the cryodielectrometer and extend the merasuring bandwidth up to 34...144 GHz. The unit offers software-controlled frequency tuning with a spectral resolution of about 0.1 MHz. The loss contributions have been classified among the major loss mechanisms, and physical constitutive parameters responsible for these mechanisms have been determined. Conclusion. The temperature dependences of dielectric loss in low-absorption materials have been registered and analysed. The developed measuring unit has advantageous design features and provides, in addition, an independent controllable radiation source which can be included in a frequency synthesis system with phase-locked loop.

Keywords

• cryogenic temperatures
• disk dielectric resonator
• high-resistance semiconductor
• low-loss dielectric
• low-temperature dielectrometry
• millimeter waves
• whispering gallery modes