Temperature Correction Using Degenerate Modes for Cylindrical Cavity Perturbation Measurements

Abstract

Microwave cavity perturbation measurements are a useful way to analyze material properties. Temperature changes can be introduced during these measurements either intentionally or as a result of some other process. The microwave cavity itself also has a temperature-dependent response, which can affect the results. A common method to correct is to use another resonant mode separately to the measurement mode, which is not affected by the sample. Instead of using independent modes, this paper describes a method to use split degenerate TM m10 modes of cylindrical cavities. TM m10 consists of two modes with identical field patterns with a relative rotation between them and identical resonant frequencies. A strategically placed perturbation reduces the frequency of one of the TM m10 modes and affects the coupling of both modes by reconfiguring the fields. This can be used for temperature correction by placing a sample such that both modes are equally coupled. The lower frequency, the perturbed mode is used as a measurement mode. The higher mode is used as a reference for temperature correction as it is unaffected by the sample. This technique was verified by measuring the permittivity of pure water using an aluminum microwave cavity resonator at 3.96 GHz. The temperature was swept between 20 • C and 60 • C, and the results was verified against the literature.

Microwaves in Chemistry

“…Some examples now follow on the application of microwave resonators, together with resonator (cavity) perturbation theory [63]- [66], to measure the dielectric properties of samples. The polarization is found from the shift downwards in resonant frequency, whereas the loss is found from the decrease in resonator quality factor (Q).…”

“…We can stabilize the ambient temperature to ±0.1°C by inserting the resonator equipment into a temperature-controlled oven, which is the best we can hope to achieve, yielding changes in the fractional change in complex permittivity values for typical polar solvents of around ±0.5%. We make great efforts to correct for long term temperature drifts by using reference resonant modes which do not couple the sample [66], [70], which have been shown to be very effective for calculating relative permittivities of standard materials that compare favorably with accepted, precision values (e.g. quartz).…”

A dual-material strategy for enhancing the temperature robustness of microwave resonant cavity

“…A split degenerate TM m10 mode of the cylindrical cavity was innovatively designed by Barter et al . to enhance the temperature robustness [22].…”

“…By monitoring two working modes of a specific resonant cavity, Cuenca et al proposed a method to correct the influence of temperature on the system during the perturbation measurement of the resonant cavity [21]. A split degenerate TM m10 mode of the cylindrical cavity was innovatively designed by Barter et al to enhance the temperature robustness [22].…”

Complex Permittivity Characterization of Liquid Samples Based on a Split Ring Resonator (SRR)

“…Meanwhile, the permittivity characterization methods based on resonance structure provide a quite convenient measurement progress of the resonant frequency, peak attenuation and quality factor which can be directly read out from the S-parameters. Therefore, researchers have proposed a variety of resonant structures for the characterization of complex permittivity, such as cavity device [ 11 , 12 ] and substrate integrated waveguide (SIW) device [ 13 , 14 ]. A rectangular cavity device based on improved cavity perturbation method at the range of 26.5–40 GHz has been proposed in our previous work [ 15 ].…”