Microwave field of temperature measurement
 Microwave heating of the sample is inside , but without heating the surrounding environment or heating level is not the same . To get the true temperature , the temperature must be measured within the sample , rather than the temperature near the sample .
Conventional temperature measuring device such as a conventional thermocouple , which are not suitable for applications in the microwave field , because the thermocouples in the microwave field are also subject to effects of electromagnetic fields , the same will be microwave heated , so if using the conventional microwave field thermocouple the temperature of the sample , the measured temperature with a large error , that the thermocouple itself is sometimes microwave heating temperature , rather than the true temperature of the sample itself , therefore , must be used in the microwave field of special temperature measurement system . Currently, for the microwave field in the temperature measurement system has three categories.
The first category, normally used in household microwave oven shielded thermistor thermistor probe type of the maximum temperature is only slightly higher than 100 degrees. The thermistor insertion conductive stainless steel tube, stainless steel pipe and then connected to the furnace wall copper ground line , shielding can be achieved thermistor . Temperature measurements to be successful , you must place the probe in the sample absorb microwaves among the probe largely unaffected by the impact of the microwave field . Organizations such as water and hydrates strong absorption of microwave materials, available in a distance of about 2.5cm to 2.45GHz microwave energy is completely absorbed. This shielding method has been proven not suitable for most laboratory applications , because the probe is not exposed to the full protection of the dielectric microwave absorber field will accumulate sufficient charge and arcing .
The second category , shielded thermocouple sheath . The researchers used a shielded thermocouple sets the temperature in the microwave field measurements have been successful . M.A.Janney such as the use of a thermocouple with a metallic shield during sintering A1203 measured sample temperature . With the microwave field intensity on the off and thermocouple along with the received signal decreases and increases , but when the microwave is off, the thermocouple receiving process does not appear discontinuous phenomenon was observed only with the conventional heating and cooling in a similar phenomenon . This indicates that the microwave field does not affect shielded sleeve C -type thermocouple temperature measurements. J.W.Walkiecz other sets with shielded K-type thermocouple measured the microwave field minerals heating temperature . After boiling point of water measurement comparison experiments that shielded sleeve type K thermocouple temperature error range at 12 ℃ range. H.M.Kingston other sets with shielded copper -constantan thermocouple measured the microwave field in the acid decomposition temperature .
The third category , fiber optic devices . Optical devices have been used for the microwave field temperature measurements. With shielded thermistor and thermocouple compared to optical devices in the microwave field is transparent waves , not interacting with the microwave . Although this fiber is relatively expensive device , but it ' reliable and accurate temperature measurements .