A sapphire sphere resonator for the measurement of low dielectric losses in the millimetre-wave range in liquids

Abstract

A measuring resonator in the form of a dielectric sphere is proposed for the measurement of low dielectric losses in the millimetre-wave range in liquids. The dielectric sphere resonator (DSR) was made from sapphire crystal with extremely low dielectric losses in the millimetre-wave range. Owing to this super-high-quality oscillations of 'whispering gallery' type are excited in a DSR. The spatial distributions of the electric and magnetic field strengths of E -and H -type oscillations both inside the sphere and in the surrounding liquid are considered. The expression connecting the measured quality of the DSR and the dielectric loss angle of the liquid is found. The condition for the choice of optimal parameters of the resonator for the measurement of the dielectric losses in various liquids is obtained also. The DSR method for the measurement of low dielectric losses in the millimetre-wave range in liquids is described.

9 Dielectric relaxation in solutions

“…A promising new development which may circumvent this problem is whispering gallery dielectric resonators. 70,71 Such systems work on a similar principle as the well-known ATR technique in infrared spectroscopy and consist of a low-loss dielectric waveguide of permittivity eA res (n) (made, e.g., from alumina) immersed in the sample. It is required that, for the sample, eA(n) < eA res (n), but in principle such systems should allow broad-band experiments up to the THz region.…”

Broadband dielectric spectrometry of liquids and biosystems

“…Aiming at a broadband utilization of the sensitivity of resonator techniques, whispering gallery mode resonators have been employed for complex permittivity measurements [128,129]. Dielectric spheres [128] or discs [129] from materials with extremely low dielectric losses are used to generate, due to the rephasing after a complete turn of the electromagnetic field, resonances with high quality factor. Owing to total reflections at the resonator surface the electromagnetic energy is confined inside the resonator.…”

Electromagnetic moisture measurement

“…Resonator techniques often enable measurements at one fundamental frequency only and are thus notoriously smallband. To a certain extent this disadvantage is overcome by whispering-gallery-mode resonators which, due to their rich resonance frequency spectrum, offer a broader frequency range of measurement [281][282][283][284][285]. Dielectric spheres or discs made from materials with extremely small dielectric loss, such as sapphire, are utilized as resonant device (1, Fig.…”

“…Whispering gallery mode resonator combined with a sample-filled microchannel[281]: 1, spherical resonator made of sapphire; 2, dielectric waveguide; 3, substrate containing the microchannel (4) that is filled with the sample (ε).…”