Key Takeaways & Executive Findings
- •• A novel method for achieving calibrated and stable emissivity using a blackbody, a perforated screen, and a novel IR thermal sensor (TMOS) is presented. • The methodology employs two-color measurements with optical filters to conform to the grey body definition, enabling accurate emissivity determination. • The effective emissivity of a photochemically etched perforated screen is directly related to the hole density area, simplifying calibration. • Ray tracing simulations and experimental results validate the approach, demonstrating its practical applicability in IR radiometry.
Abstract
The concept of emissivity has been with the scientific and engineering world since Planck formulated his blackbody radiation law more than a century ago. Nevertheless, emissivity is an elusive concept even for experts. It is a vague and fuzzy concept for the wider community of engineers. The importance of remote sensing of temperature by measuring IR radiation has been recognized in a wide range of industrial, medical, and environmental uses. One of the major sources of errors in IR radiometry is the emissivity of the surface being measured. In real experiments, emissivity may be influenced by many factors: surface texture, spectral properties, oxidation, and aging of surfaces. While commercial blackbodies are prevalent, the much-needed grey bodies with a known emissivity, are unavailable. This study describes how to achieve a calibrated and stable emissivity with a blackbody, a perforated screen, and a reliable and linear novel IR thermal sensor, dubbed TMOS. The Digital TMOS is now a low-cost commercial product, it requires low power, and it has a small form factor. The methodology is based on two-color measurements, with two different optical filters, with selected wavelengths conforming to the grey body definition of the use case under study. With a photochemically etched perforated screen, the effective emissivity of the screen is simply the hole density area of the surface area that emits according to the blackbody temperature radiation. The concept is illustrated with ray tracing simulations, which demonstrate the approach. Measured results are reported.
1. Introduction
What is emissivity and who needs measurements of emissivity? As a fundamental principle of physics, all materials emit electromagnetic radiation. The intensity of this radiation, measured in terms of power, is directly influenced by the material's temperature and its emissivity. Emissivity is a property that quantifies a material's ability to emit thermal radiation relative to a perfect black body.
More than a century ago, Planck formulated his radiation law, expressing the power emitted by a model body named 'blackbody', as a function of temperature and wavelength. Planck's radiation law is a mathematical model describing the amount of radiation from a closed metallic furnace held at a well-controlled temperature. The model body has become known as a blackbody.
Every material radiates power, but real materials are not perfect blackbodies. Emissivity is a material's ability to radiate a fraction of the power that a perfect blackbody would radiate at a given temperature. Thus, the amount of radiated power is dependent on the material's temperature and the material's emissivity. IR thermometers take advantage of this. They measure the amount of power exiting an object in an infrared band. They calculate the temperature based on this measured power and the material's emissivity. Accordingly, accurate temperature measurements cannot be obtained without measuring simultaneously the emissivity. The errors introduced by non-accurate emissivity value are significant and increase with object temperature.
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Moshe Avraham, Shlomi Bouscher, Jonathan Nemirovsky, Yael Nemirovsky (2025). Measurement of emissivity with a new grey body and novel IR thermal sensor dubbed TMOS. SinoTechIntel Verified Research. https://doi.org/10.11972/j.issn.1001-9014.2025.01.2024212
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Frequently Asked Questions
What is emissivity and why is it important in IR thermometry?
Emissivity is a measure of a material's ability to emit thermal radiation compared to a perfect blackbody. It is crucial in IR thermometry because accurate temperature measurements require knowing the emissivity of the object's surface; errors in emissivity can lead to significant temperature measurement errors.
How does the new grey body method work?
The method uses a blackbody, a perforated screen, and a novel IR thermal sensor (TMOS). By using two-color measurements with optical filters, the effective emissivity of the screen is determined by the hole density area, which emits according to blackbody radiation. This provides a calibrated and stable emissivity source.
What is TMOS and what are its advantages?
TMOS is a novel IR thermal sensor that is low-cost, low-power, and has a small form factor. It is reliable and linear, making it suitable for precise emissivity measurements in the proposed method.
How is the effective emissivity of the perforated screen calculated?
The effective emissivity of the photochemically etched perforated screen is simply the hole density area (the fraction of the surface area that is holes) that emits according to blackbody temperature radiation. This simplifies the calibration process.
What are the potential applications of this emissivity measurement technique?
This technique can be applied in industrial, medical, and environmental fields where remote temperature sensing is important. It provides a reliable method for calibrating IR thermometers and improving accuracy in various applications.
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