The new technique that is called "Depth Thermography", can derive the temperature of an object as a function of depth by utilizing "thermal-emission spectrum in the semitransparent spectral region of the target object".
Depth Thermography can be used in items where current sensors are inapplicable. Those sensors usually measure the infrared spectrum from an object to derive their actual temperature.
Every object that has a temperature greater than absolute zero emits energy. The amount of the emitted energy increases with temperature. Based on this principle, infrared thermography detects the infrared energy emitted from an object and then converts it to temperature.
Nevertheless, Depth Thermography utilizes another approach to measure the temperature of materials that are "transparent" to infrared radiation such as semiconductors and future nuclear reactors that will use a fluid fuel in the form of very hot fluoride or chloride salt (Molten Salt Reactors)."...we anticipate relevance to molten-salt nuclear reactors, where you want to know what’s going on in terms of temperature of the salt throughout the volume. You want to do it without sticking in temperature probes that may not survive at 700 degrees Celsius for very long,” Mikhail Kats, co-author of the study and a Professor of Electrical and Computer Engineering at the University of Wisconsin–Madison, stated.
Researchers examined their method by heating fused quartz, a type of glass that consists of non-crystalline silica. Having already conducted experimental tests on the material, they utilized computational tools developed by Yuzhe Xiao, lead author of the study and a Postdoc researcher at the University of Wisconsin-Madison, to derive the thermal radiation of the item and back-calculate the temperature gradient within the object in order to fit the experimental data. This endeavor was useful to prove that the method is reliable and accurate.
The new technique is completely remote and does not necessitate the utilization of sensors to detect the temperature of an object. The method may also be utilized in deriving the temperature of heated gases and liquids. "Depth thermography may enable non-contact volumetric temperature measurements of microscopic objects such as multilayer electronic devices or macroscopic volumes of liquids and gases, as well as simultaneous all-optical measurements of optical and thermal properties of materials," the study, mentions.
The scientific team plans to apply the new method to more complex materials and utilize machine learning to optimize their technique in the future.
Details on the mathematical techniques utilized to make the method function can be found here.
Source: University of Wisconsin-Madison