Session: 11-45-01: Technique development for thermophysical characterization

Paper Number: 119791

119791 - Structured Illumination With Infrared Thermometry for Thermal Property Characterization 

With developments in advanced manufacturing and materials by design comes the need for high-throughput thermal characterization and inspection. Towards this end, Structured Illumination with Thermal Imaging (SITI) is an all-optical pump-probe thermal characterization technique recently developed by our group.  In the first generation [Zheng et al., Appl. Phys. Rev. 9, 021411 (2022)] SITI uses an LED with a digital micromirror device (DMD) [Mightex Polygon400, adapted from biological applications] to “structurally illuminate” and heat the sample with dynamic patterns, a visible light camera for thermoreflectance based “thermal imaging” [leveraging a Microsanj MTIR120], and the resultant temperature response was fit with a thermal model to characterize the sample’s thermal properties. This represents a novel approach to dynamic and flexible spatial mapping of thermal properties by virtue of being a non-contact technique and having a simpler scanning means (computer control only) than conventional pump-probe laser methods.  SITI also can tolerate rough samples with diffuse reflections.  The system’s adaptability to anisotropy and spatial heterogeneity in the sample was also demonstrated through its software-controlled patterns.
 
This talk presents the second generation of SITI.  The pumping is now based on a lower cost off-the-shelf digital projector.  The thermometry is now performed using an infrared (IR) camera, which we find is a more flexible and accessible hardware approach compared to the thermoreflectance microscopy used previously. With these updates the setup can deliver higher heating power and a broader range of frequencies up to the order of kHz, allowing an extended range of samples that can be studied.  We have demonstrated SITI’s ability to measure the thermal conductivity of a range of materials from insulating polymers to metals.  We also show how SITI can visualize and locate buried interfaces by varying the heating frequency to control the penetration depths. Further, as each pixel of the projector can be controlled independently, SITI’s theoretical degrees of freedom in heating of the order of millions - and we show how this can be used for spatial and frequency domain multiplexing by superposing multiple frequencies and colors (the three RGB channels) for higher throughput.  Software control of the heating patterns allows us to drive the heat flow in certain directions to extract anisotropic sample properties, and also ‘virtually’ replicate other methods such as mimicking the 3-omega method by creating a time-periodic optical heating line.  These examples help demonstrate some of the unique capabilities of the SITI approach towards 3D thermal mapping with its megapixel level degrees of freedom in both heating and thermometry.

Presenting Author: Ashwath Bhat University of California, Berkeley

Presenting Author Biography: Ashwath Bhat is a PhD student in the Department of Mechanical Engineering at University of California, Berkeley. His research concerns with measurement techniques related to thermal transport.

Authors:

Ashwath Bhat University of California, Berkeley
Chris Dames University of California, Berkeley