Objective The Micro Miniature Refrigerator（MMR） is a novel Joule-Thomson cryocooler manufactured by micro-machining technologies, its axial length is significantly shorter than traditional Joule-Thomson cryocoolers commonly employed in infrared detectors. MMRs can greatly reduce the size of infrared detectors upon successful implementation. However, contemporary MMR products encounter challenges such as relatively low cool-down rates, cooling power, and structural strength. To address these issues and enhance the cool-down performance of the MMR for effective application in infrared detectors, a calculation model describing flow and heat transfer besides working characteristics of the MMR is proposed and verified. MMR prototypes are fabricated and experimentally studied. Building upon theoretical analysis and experimental findings optimization methods including transitioning the MMR material from glass to metal and modifying the structure and channel patterns of the MMR are introduced, the cooling performance of the MMR is thus greatly improved. Furthermore, an integrated design incorporating an MMR into an infrared detector is also proposed.

Methods A novel calculation model implemented through C language programming is proposed and verified by experiments, based on the calculation model the flow and heat transfer characteristics in micro-channels of MMR is obtained. The theoretical insights derived from the calculation model guide the fabrication of a glass MMR prototype. This prototype becomes the focal point of experimental studies, providing a tangible platform for validating the theoretical model. The liquefaction of the working fluid during experimentation serves as a crucial validation step, affirming the accuracy and applicability of the theoretical framework. Building upon theoretical analysis and experimental findings, optimization methods are introduced to address the identified challenges. Notably, significant improvements are achieved by transitioning the MMR material from glass to metal and incorporating adiabatic slots. These optimization measures result in a remarkable enhancement of the MMR's cooling performance

Results and Discussions The optimization methods, particularly the transition from glass to stainless steel and the incorporation of adiabatic slots, prove to be highly successful. The resulting stainless steel MMR prototype demonstrates a rapid 68-second cool-down time (cool down to 123 K) and a substantial cooling power of 1 102 mW. The research extends beyond the standalone MMR improvements to propose an integrated design incorporating the MMR into an infrared detector. This innovative integration results in a remarkable reduction of the detector's axial length by 65.3% compared to conventional infrared detectors. The integration holds promise for enhancing the miniaturization and integration of infrared detectors. The exploration of materials extends to the development of a Kovar alloy MMR, building upon the successes achieved with the stainless steel counterpart. The Kovar alloy MMR not only facilitates integration into infrared detectors but also exhibits an ability to withstand a high working pressure of 60.9 MPa and achieve a rapid 38-second cool-down time (cool down to 126 K) under 60 ℃ temperature conditions. These advancements showcase the adaptability and versatility of the MMR in varying working conditions.

Conclusions The MMR, as an innovative Joule-Thomson cryocooler, holds a distinctive advantage in significantly reducing the axial length of infrared detectors. This characteristic is identified as a key driver in advancing the miniaturization and integration of infrared detectors. The theoretical insights obtained from the calculation model guide the fabrication of a glass MMR prototype, allowing for the liquefaction of the working fluid and validation of the theoretical model through experimental research. The success of optimization strategies, particularly the transition to stainless steel and the introduction of adiabatic slots, stands out as a pivotal achievement. The resulting improvements in cooling performance demonstrate the efficacy of informed optimization measures in overcoming the challenges faced by contemporary MMRs. The integration of the MMR into an infrared detector and the subsequent advancements with the Kovar alloy MMR underscore the practical applications of this research. The proposed integrated design showcases a substantial reduction in axial length. The Kovar alloy MMR and the integrated infrared detector design exhibit several advantages over similar products reported in the literature. These include higher reliability, reduced structural complexity, and ease of fabrication. The cumulative technical advantages position the proposed MMR and infrared detector design as promising contributors to the broader field of cryocooler technology.