Investigating the Reliability of Machine Learning Algorithms for Inverse Design: Polarization Rotator Unit-Cell Model

In this article, we implement three types of data-driven algorithms for the inverse design of the polarization rotator (PR) unit cell. Toward this end, a novel configuration pattern of the PR unit cell is proposed, which is reshapable to different geometries with a large number of design variables and recasts as a regression problem. The state-of-the-art algorithms including the neural network (NN), the deep neural networks (DNNs) with multiple hidden layers, and the support vector regression (SVR) are experimented with cross validations for ensuring the prediction generalizability. Averaged over all the experiments with competitive performances, the highest prediction accuracy about 95.23% was achieved for the SVR algorithm. This demonstrates the enormous capability of the data-driven algorithms in the geometrical dimension prediction of the unit cells for any given frequency band designated in the radar range (X, Ku, K, and Ka). The proposed inverse design procedure can expedite, facilitate, and to some extent replace the conventional and time-consuming manual design approaches with electromagnetic (EM) simulation software. Although these models can be very efficient in practice, they might be vulnerable against adversarial attacks that craft fake inputs to purposely fool the victim regressors toward adversary's wishes. This poses security concerns for the learning-based algorithms and might negatively affect their prediction reliabilities in runtime. In this article, we only characterize the existence of the adversarial attacks for the regression models using the fast gradient sign method. Our conducted experiments uncover that the fooling rate of all the aforementioned cutting-edge NN and DNN-based regressors is above 98% and this rate for the SVR model is about 11% better than other models.