Infrared thermotransmittance-based temperature field measurements in semitransparent media

TL;DR

This paper introduces a novel infrared thermotransmittance method with lock-in detection and demodulation for contactless temperature measurement in semitransparent media, enabling estimation of thermal properties with high accuracy.

Contribution

It presents an innovative approach combining infrared thermotransmittance, lock-in acquisition, and demodulation to measure temperature fields and thermal properties in semitransparent materials.

Findings

Achieved temperature measurement accuracy within ±2°C.

Successfully estimated thermal diffusivity and conductivity of borofloat 33 glass.

Validated measurements with analytical model showing good agreement.

Abstract

Temperature field contactless measurements in or at the surfaces of semitransparent media are a scientific challenge, as classical thermography techniques based on proper material emission cannot be used. In this work, an alternative method using infrared thermotransmittance for contactless imaging temperatures is proposed. To overcome the weakness of the measured signal, a lock-in acquisition chain is developed, and an imaging demodulation technique is used to retrieve the phase and amplitude of the thermotransmitted signal. These measurements, combined with an analytical model, enable the estimation of the thermal diffusivity and conductivity of an infrared semitransparent insulator (wafer of borofloat 33 glass) as well as the monochromatic thermotransmittance coefficient at 3.3 um. The obtained temperature fields are in good agreement with the model, and a detection limit of $\pm 2^{\circ}$ C is estimated with this method. The results of this work open new opportunities in the development of advanced thermal metrology for semitransparent media.