Emissivity Measurement Techniques in Thermal Analysis

Emissivity lies at the heart of non-contact thermal analysis, governing the radiative properties of surfaces across industry and scientific research. It quantifies the ratio of energy emitted by a body to that of an ideal blackbody at the same temperature. Accurate determination of emissivity is vital for applications ranging from furnace monitoring and aerospace component testing to solar receiver design and advanced materials development. A suite of direct and indirect approaches has evolved to address challenges such as surface roughness, temperature dependence and spectral variation. Direct methods commonly employ reference blackbody cavities or Vantablack-coated enclosures to calibrate radiometric instruments under controlled conditions, yielding directional or hemispherical emissivity values with well-characterised uncertainty. Indirect techniques leverage spectrometric data, extracting spectral emissivity via combined reflectance and transmittance measurements using integration spheres and Fourier transform infrared spectrometry. Concurrently, multi-wavelength pyrometry has become indispensable for high-temperature applications, coupling constraint-based inversion algorithms with optimisation or machine-learning frameworks to resolve temperature and emissivity simultaneously. Surface engineering considerations, such as coating thickness and morphology, further complicate emissivity measurement, prompting tailored methodologies for semitransparent layers or rough microtopographies. Recent advances continue to refine measurement fidelity, enhance processing speed and extend operational bandwidth, underlining the global importance of emissivity characterisation in energy conversion, materials science and thermal management.

Research from Nature Portfolio

Recent work has introduced a non-invasive technique for measuring spectral emissivity of thin semitransparent coatings at ambient temperature. By employing an integration sphere and Fourier transform infrared spectrometry on specimens with varying layer thicknesses deposited on transparent substrates, researchers have extracted transmittance and reflectance spectra to derive emissivity profiles across 2–20 µm. This approach isolates coating-specific emissivity from substrate contributions, facilitating the characterisation of biomedical and nanocoatings without thermal loading.

Emissivity Measurement Techniques in Thermal Analysis publication trend

The graph below shows the total number of articles in emissivity measurement techniques in thermal analysis across all publications each year (not limited to Nature Index journals).

Technical terms

Emissivity: A measure of a surface’s ability to emit thermal radiation relative to an ideal blackbody at the same temperature.

Spectral emissivity: The emissivity value as a function of wavelength, reflecting how emission varies across the spectrum.

Multi-wavelength pyrometry: A temperature measurement technique that records thermal radiation at several wavelengths and uses inversion algorithms to determine temperature and emissivity.

Integration sphere: A hollow spherical chamber coated internally with highly diffuse reflector used to capture and measure total reflectance and transmittance.

Fourier transform infrared (FTIR) spectrometry: A spectroscopic method that collects spectral data by measuring an interferogram and applying a Fourier transform to obtain the absorption or emission spectrum.

Blackbody: An idealised object that absorbs all incident radiation and emits the maximum possible thermal radiation at each wavelength for a given temperature.

References

1. A straightforward spectral emissivity estimating method based on constructing random rough surfaces. Light: Science & Applications (2023).
2. Generalized inverse matrix - long short-term memory neural network data processing algorithm for multi-wavelength pyrometry.. Optics Express (2022).
3. Multispectral radiometric temperature measurement algorithm for turbine blades based on moving narrow-band spectral windows.. Optics Express (2021).
4. Method for emissivity measurement of semitransparent coatings at ambient temperature. Scientific Reports (2017).
5. An accurate instrument for emissivity measurements by direct and indirect methods. Measurement Science and Technology (2020).