Abstract
Understanding the dynamics of thermoelectric (TE) phenomena is important for the detailed knowledge of the operation of TE materials and devices. By analyzing the impedance response of both a single TE element and a TE device under suspended conditions, we provide new insights into the thermal dynamics of these systems. The analysis is performed employing parameters such as the thermal penetration depth, the characteristic thermal diffusion frequency and the thermal diffusion time. It is shown that in both systems the dynamics of the thermoelectric response is governed by how the Peltier heat production/absorption at the junctions evolves. In a single thermoelement, at high frequencies the thermal waves diffuse semi-infinitely from the junctions towards the half-length. When the frequency is reduced, the thermal waves can penetrate further and eventually reach the half-length where they start to cancel each other and further penetration is blocked. In the case of a TE module, semi-infinite thermal diffusion along the thickness of the ceramic layers occurs at the highest frequencies. As the frequency is decreased, heat storage in the ceramics becomes dominant and starts to compete with the diffusion of the thermal waves towards the half-length of the thermoelements. Finally, the cancellation of the waves occurs at the lowest frequencies. It is demonstrated that the analysis is able to identify and separate the different physical processes and to provide a detailed understanding of the dynamics of different thermoelectric effects.
Highlights
Frequency resolved methods such as impedance spectroscopy has been proved very successful for the characterization of a variety of systems of great technological interest.[1,2,3,4,5] The potential of these methods, unlike experiments performed in the time domain, typically difficult to analyze and with responses commonly governed by overlapping processes, resides in their high sensitivity and their ability to separate the different physical processes occurring in the devices.[6]
By analyzing the impedance response of both a single TE element and a TE device under suspended conditions, we provide new insights into the thermal dynamics of these systems
The thermal dynamics of both a single TE element and a TE device has been analyzed by impedance spectroscopy
Summary
Frequency resolved methods such as impedance spectroscopy has been proved very successful for the characterization of a variety of systems of great technological interest.[1,2,3,4,5] The potential of these methods, unlike experiments performed in the time domain, typically difficult to analyze and with responses commonly governed by overlapping processes, resides in their high sensitivity and their ability to separate the different physical processes occurring in the devices.[6]. By using impedance spectroscopy, which employs ac current excitation waves, we can extract very useful information about the dynamics of these fundamental TE processes, which provides a unique detailed knowledge of the system operation This detailed analysis, in despite of the fact that previous work has been reported in the application of frequency resolved methods in the TE field,[7,8,9] has not been developed so far. The different regimes of behavior previously observed are analyzed in detail, which allows the identification of semi-infinite diffusion and interacting regimes Through this more extended analysis the identification and separation of the different physical processes occurring in the device is achieved, which provides a unique detailed understanding of the system dynamics
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