ICMAB researchers have developed a method to obtain thermal properties of materials, i.e. how heat propagates in these materials in different directions.
28 November 2022
The CSIC Technlogy Transfer has created now some videos to promote the new technologies invented by our researchers. In this video you will see Sebastián Reparaz, ICMAB researcher at the NANOPTO group, explaining the basics of this new technology.
The method developed has many advantages over current available methods. In particular, it is worth highlighting that it is a method that operates without contact with the sample, and that the analysis of the results obtained does not require the effort of calculations or numerical analysis, as the thermal conductivity of the materials under study is obtained directly from the results themselves without the need for numerical processing.
On the other hand, the method makes it possible to study the propagation of heat in different directions in space. The method is of particular interest for the study of materials with thermal properties that depend on orientation (anisotropic materials), both in thin layers and substrates. This type of study is relevant in microelectronics (heat dissipation), thermoelectricity (utilisation of waste heat), thermal insulation, etc.
The inventors of this technology are currently developing a prototype that will aim to commercialise the device. In particular, the current development is within the framework of a "Proof of Concept" project of the AEI (call 2021), and aims to achieve an inexpensive, small, fully automated device. In the near future, researchers would like to collaborate with experts to help them develop an exploitation plan for the technology.
Why do we need to measure thermal conductivity?
Thermal conductivity is the most essential thermal parameter of a material, which determines how heat propagates through or is dissipated within a material. It constitutes a key characterization of materials for a large range of energy applications, including thermoelectrics, thermosolar, concentration photovoltaics, heat insulation, radiative generators, phase change materials, etc.
It also plays an indirect, but crucial, role in other applications for which performance is strongly linked with temperature, and thus heat management is a must. These include insulating capping in electric wires, heat management in batteries, heat release in electronics, smart windows for efficient thermal management, etc.
Materials in which heat propagates at different rates in different directions are in the forefront of research and development, as these thermal anisotropic properties can be used to enhance performance, and enable new heat management strategies.
How does the method work and how does it compare to others?
The patented technology is a contactless approach based on frequency-domain thermoreflectance thermometry with a line-shaped (1D) heater geometry, obtained through a focused laser beam, whose intensity distribution is modified using special diffractive optical elements. Researchers can obtain thermal conductivity of bulk materials and films in different directions by simply rotating the sample with respect to the line-shaped heater defined by the focused laser.
Current methods to study thermal transport based on linear heat sources offer important advantages to study anisotropic materials, where thermal conductivity is dependent on the direction. Electrical methodologies typically require the deposition of electrical contacts as well as electrical insulation from the underlying samples, and do not allow the arbitrary rotation of the sample. On the other hand, contactless methods based on focused laser beams, such as Gaussian heater spots, suffer from complicated analysis of data and, in most configurations, anisotropic information is not accessible.
This new approach provides all advantages offered by a line-shaped heater geometry, keeping at the same time the advantages offered by contactless methodologies.
Advantages of our contactless laser-based thermal conductivity measurement method
Using a focused laser beam as linear heat source benefits from the geometry of the heat source to determine thermal conductivity, and thermal anisotropy.
Simple data analysis procedures to obtain the thermal conductivity tensor.
The method can be applied in isotropic and anisotropic materials. It can also be used to determine the thermal properties of thin films.
Suitable for electrically insulating and conductive samples.
Possibility to automatize and to operate in transducer-free mode.
Significant cost reduction in the restricted frequency operational range.
For more information, take a look at this related article:
Anisotropic thermoreflectance thermometry: A contactless frequency-domain thermoreflectance approach to study anisotropic thermal transport Luis A. Pérez, Kai Xu, Markus R. Wagner, Bernhard Dörling, Aleksandr Perevedentsev, Alejandro R. Goñi, Mariano Campoy-Quiles, M. Isabel Alonso, and Juan Sebastián Reparaz Review of Scientific Instruments 93, 034902 (2022) https://doi.org/10.1063/5.0066166
Patent application: PCT1641.1660 International patent application: PCT/ES2022/070534