Methods of temperature measurement in microwave heating technologies

In industrial technological processes associated with the heating of the processed material by microwave radiation, it is necessary to measure the temperatures of objects. Methods for measuring temperatures in the fields of technology using microwave heating systems are considered. The main possibilities, disadvantages and limitations of the used contact and non-contact (optical) measurement methods are determined. The requirements for temperature measurement systems under conditions of exposure to strong electromagnetic fields are listed. The possibilities of the spectral pyrometry method are especially noted.

Determination of the profile of the temperature field of material heated by continuous laser radiation

Spectral pyrometry was used to determine the surface temperature distribution of Si, Nb, Cu, and graphite samples when they were locally heated by continuous radiation of an Nd:YAG laser (λ = 1.064 μm). With prolonged exposure to radiation, a stationary temperature field was established in the samples. The thermal spectra were recorded with a small spectrometer in the visible range in the temperature range above 850 K. The optical fiber used to transmit the radiation spectrum to the spectrometer had an additional diaphragm with a diameter of 1 mm located at a certain distance from the fiber end, which ensured the locality of the recorded spectra. The optical fiber moved continuously along the sample, and the spectrometer recorded up to 100 spectra with a frequency of 5-10 Hz. The temperature profile of the samples was calculated based on the results of processing the spectra using the Spectral Pyrometry program.

High-temperature spectral thermometry in conditions of intense microwave electromagnetic fields

In this paper, a practical application variant of the high-temperature spectral thermometry method for controlling the temperature of a dielectric object heated in a high-intensity microwave electromagnetic field is proposed. The advantages of using the spectral pyrometry method over the methods of color and brightness pyrometry when registering high temperatures (from 500 °C and above) are described. The optical fiber cable used in this method, which receives thermal radiation from an object heated in the microwave field, is subject to the negative influence of the electromagnetic field, which leads to its unacceptable heating and failure. To eliminate this phenomenon, a non-standard use of an cutoff waveguide placed not outside, but inside the microwave heating chamber is proposed. It is shown that this solution completely eliminates the negative influence of the electromagnetic field on the fiber optic cable and allows placing the receiving end of the cable in close proximity to the object being heated. The calculation of geometric parameters of the cutoff waveguide for the operating frequency of the electromagnetic field of 2450 MHz is given.