The Optimization of Multilayer Spacing for Miniaturization of Mechanical Antenna Based on Unipolar Electrets

The low-frequency mechanical antenna (MA) shows promise in various applications such as underwater communication and navigation. Meanwhile, the design of stacked structure with multilayer unipolar electrets has significantly improved the communication distance. However, because it increases the risk of interlayer electric field breakdown caused by the unipolar electret, reducing the size of the MA becomes necessary but challenging. In this work, an optimization method of stack spacing that can enhance the space utilization efficiency and radiation capability of MA based on unipolar electret is presented. By analyzing the difference between unipolar and bipolar electrets in the stacked layers, a non-equal spacing strategy for antenna structure design is implemented. This strategy takes advantage of the symmetric electric field between the layers of the stacked unipolar electret. In a verification scenario with four layers of unipolar electret, the size of the stack can be reduced by 22.3% compared with the equally spaced arrangement, and a theoretical communication distance of 30.2 m can be achieved. The optimization method can be applied to stacked structures with any number of layers. It provides additional design guidance, especially when increasing the number of layers to achieve a greater communication distance.