Houston solves ‘problem’ with thermal imaging and thermography

01 Aug 2024

New approach cuts wavelength and temperature dependence, yielding applications for police, military, and medicine.

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, could improve thermal imaging and infrared thermography, techniques used to measure and visualize temperature distributions without direct contact with the subject being photographed.

Thermal cameras and infrared thermometers measure temperature accurately from a distance, giving them applications in many fields from the military to medical diagnostics. They detect infrared radiation, invisible to the human eye, and convert it into visible images.

Applications

• Medical diagnostics: identifying inflammation and poor blood flow
• Building inspection: 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

But with many conventional thermal imagers there is a problem: thermal cameras and infrared thermometers cannot provide accurate readings because they rely on emissivity, a measure of how effectively a real object emits thermal radiation, and that varies with temperature — to determine temperature. Multi-spectral techniques address this by measuring infrared intensity at multiple wavelengths, but their accuracy depends on their emissivity models.

Houston’s solution

Houston has a solution to this problem: Prof. Jiming Bao is reporting a new method set to improve thermal imaging and infrared thermography. The work is described in the journal Device.

He said, “We designed a technique using a near-infrared spectrometer to measure the continuous spectrum and fit it using the ideal blackbody radiation formula,” commented Prof. Bao. “This technique includes a simple calibration step to eliminate temperature- and wavelength-dependent emissivity.”

Prof. Bao has 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.

Prof. Bao added, “This technique overcomes challenges faced by conventional thermal cameras and infrared thermometers due to the unknown emissivity of targets and reveals much higher surface temperatures of photothermal catalysts than those measured by a buried thermocouple under strong light illumination.”

New technique features

• Overcoming limitations of single-wavelength and multi-spectral thermometry
• Simple calibration to eliminate wavelength- and temperature-dependent emissivity
• Accurate temperature determination over a wide temperature range
• Revealed a huge temperature gradient in a catalyst powder under laser heating