Optimization and Minimization of Dimensions of Direct Charging Nuclear Battery Based on 90Sr Radioactive Source for Use in MEMS

Today, microelectromechanical system (MEMS) technology plays an important role in human daily life. One of the main items in MEMS design is the use of a small battery with a long life. In this work, the ۹۰Sr radioisotope with a half-life of ۲۸.۸ years and an activity of ۱۶.۳۲۸ mCi was considered as a radioactive source. First, the ۹۰Sr cylindrical source was designed with a gold substrate and antimony side surface coating. Then, the optimum radius and thickness of the source were investigated. Next, the optimized ۹۰Sr cylindrical source was considered as the direct charge nuclear battery source. In the next step, the effect of collector coating on collector efficiency was investigated. Then, different positions were considered for collector placement, substrate and side surface coating and the best mode was selected. The purpose is to determine the smallest size possible for a direct charge nuclear battery with the maximum amount of short circuit current. Finally, by comparing the results of simulations performed with Monte Carlo N–Particule Transport (MCNPX) code, the present work concluded that the best parameters for direct charge nuclear battery are the use of beryllium and the ۹۰Sr radioisotope as collector coating and source, respectively, source thickness of ۰.۰۱ µm, source  radius of ۳۷.۵ µm, collector thickness ۰.۰۱ µm and collector distance from source about ۳.۷۵ µm. Under these parameters, the short circuit current is ۰.۰۹۲ fA. In this case, the designed direct charge nuclear battery has the highest short circuit current and the smallest dimension possible. If the dimensions of the optimized nuclear battery are ۱۰۰ times, i.e., the thickness of the source increases from ۰.۰۱ to ۱ µm and the radius of the source increases from ۳۷.۵ to ۳۷۵۰ µm, only about ۲.۹۲% of the source efficiency decreases, but the activity is ۱۰۶ times more. In other words, the activity increases from ۰.۰۱۶۳۲۸ µCi to ۱۶.۳۲۸ mCi; therefore, the short circuit current of this direct charge nuclear battery reached ۰.۰۷۸ nA, which is suitable for use in MEMS. Also, the collector height of this battery is ۱۹۶۰ µm, its radius is ۳۸۵۰ µm, and its thickness ۱ µm.

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