New UH method enhances accuracy in thermal imaging for diverse applications

A new method to measure the continuous spectrum of light, developed in the lab of University of Houston professor of electrical and computer engineering Jiming Bao, is set to improve thermal imaging and infrared thermography. These techniques are used to measure and visualize temperature distributions without direct contact with the subject being photographed.

Thermal cameras and infrared thermometers, which are highly sensitive, measure temperature accurately from a distance. This makes them versatile tools in fields ranging from the military to medical diagnostics. They detect infrared radiation, invisible to the human eye, and convert it into visible images. Different colors on the image represent varying temperatures, allowing users to see heat patterns and differences.

Applications include:

- Medical Diagnostics: Identifying inflammation and poor blood flow

- Building Inspections: Detecting heat loss, insulation issues, and water leaks

- Military, Security, and Surveillance: Spotting people or animals in low visibility conditions

- Mechanical Inspections: Finding overheating machinery or electrical faults

Both techniques rely on the principle of blackbody radiation — a theoretical perfect emitter — where objects emit infrared radiation based on their temperature. By capturing this radiation, these tools provide valuable insights into the thermal properties and behaviors of various objects and environments.

However, thermal cameras and infrared thermometers face challenges because they rely on emissivity — a measure of how effectively an object emits thermal radiation — which varies with temperature. Multi-spectral techniques address this by measuring infrared intensity at multiple wavelengths but depend heavily on their emissivity models.

At the University of Houston, Professor Jiming Bao has reported a new method set to improve these technologies. "We designed a technique using a near-infrared spectrometer to measure the continuous spectrum and fit it using the ideal blackbody radiation formula," reports Bao in the journal Device. "This technique includes a simple calibration step to eliminate temperature- and wavelength-dependent emissivity."

Bao demonstrated his technique by measuring the temperature of a heating stage with errors less than 2°C and measuring the surface temperature gradient of a catalyst powder under laser heating. Using the near-infrared spectrometer, thermal radiation from a hot target is collected with an optical fiber and recorded by a computer. The collected spectrum is normalized using a system calibration response and fitted to determine the temperature.

"This technique overcomes challenges faced by conventional thermal cameras and infrared thermometers due to the unknown emissivity of targets," said Bao.

Highlights include:

- Overcoming limitations of single-wavelength and multi-spectral thermometry

- Simple calibration to eliminate wavelength- and temperature-dependent emissivity

- Accurate temperature determination over a wide range

- Revealed significant temperature gradients in catalyst powder under laser heating

"This technique overcomes challenges faced by conventional thermal cameras due to unknown emissivity," reiterated Bao.

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