Topology Design of Reconfigurable Intelligent Surfaces Based on Current Distribution and Otsu Image Segmentation

Miniaturization of reconfigurable intelligent surface (RIS) elements is a crucial trend in the development of RISs. It not only facilitates the attainment of multifunctional integration but also promotes seamless amalgamation with other elements. The current on the RIS element plays a crucial role in determining the characteristics of the induced electromagnetic field components. Segments with high current intensity determine the performance of RIS elements. Carving the parts with strong current distribution density into the metal patch of RIS element structure can achieve miniaturization. Based on this insight, this work proposes a topology design method that leverages current distribution and image processing techniques to achieve efficient miniaturization of the RIS elements. In this proposed method, we first obtain the current distribution across different operational states and the period of the working frequency. Next, we employ the Otsu image segmentation method to extract relevant image information from the current distribution images of the RIS elements. Subsequently, we utilize linear mapping techniques to convert this image information into the structure of RIS elements. Then, based on the structure of the RIS elements, the Quasi-Newton optimization algorithm is utilized to obtain the parameters of the tunable device that correspond to various operational states. As a result, we successfully construct the structural topology of the RIS elements based on their current distribution, designing areas with strong current distribution as metal patches. To validate the performance of the proposed method, a 16 × 16 3-bit RIS was developed, fabricated and measured. Compared with existing RIS designs, the proportion of the top-layer metal patches is smaller, which provides the possibility for integrating other functions and devices.