On the Parametric Thermal Analysis of Emissive Heat Loss in Multi-Layer Vacuum-Enclosed Timing Systems

Kyle Miskell, Andrew N. Lemmon, H. Bryan Owings

Abstract:	In the design of contemporary frequency standards, significant effort is expended in the implementation of thermal and magnetic shielding to abate the impact of external environmental factors on frequency stability. Typically, this isolation is accomplished through the implementation of multiple concentric layers of thermal and magnetic shielding material. The implementation of a vacuum enclosure in these systems provides an additional benefit in this regard by restricting convective heat flow. Moreover, attempts to mechanically restrict the effects of thermal conduction—and to a lesser extent emissive heat transfer through thermal shields—are also made to further improve thermal regulation. However, in attempting to thermally isolate frequency standards through the elimination of convective and conductive heat loss, a sensitive dependence of operating temperature on emissive heating mechanisms is revealed. Furthermore, given the tendency of frequency standards to employ a wide variety of materials in their construction, it often proves laborious to obtain accurate emissivity data for each component. Additionally, each concentric layer in the shielding stack-up provides a reflective and emissive contribution to its neighboring layers. This adds complexity to the emissive heat propagation within the system, effectively coupling the emissive heating behaviors of all layers. The combination of systemic thermal sensitivity to emissivity and lack of widely-available emissivity properties makes the theoretical prediction of the thermal characteristics of frequency standards difficult. In this study, a simple, cheap, and reasonably accurate methodology for the experimental extraction of material emissivity values through infrared thermography is presented. This study considers a range of materials and material finishes used in the fabrication of microwave frequency standards. Finally, a finiteelement analysis (FEA) study is presented to highlight the importance of accurate emissivity estimation for predicting the thermal behavior of a microwave frequency standard.
Published in:	Proceedings of the 47th Annual Precise Time and Time Interval Systems and Applications Meeting January 25 - 28, 2016 Hyatt Regency Monterey Monterey, California
Pages:	161 - 166
Cite this article:	Miskell, Kyle, Lemmon, Andrew N., Owings, H. Bryan, "On the Parametric Thermal Analysis of Emissive Heat Loss in Multi-Layer Vacuum-Enclosed Timing Systems," Proceedings of the 47th Annual Precise Time and Time Interval Systems and Applications Meeting, Monterey, California, January 2016, pp. 161-166. https://doi.org/10.33012/2016.13159
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