Non-Hermitian degeneracies, also known as exceptional points (EPs), have been the focus of much attention due to their singular eigenvalue surface structure. Nevertheless, as pertaining to a non-Hermitian metasurface platform, the reduction of an eigenspace dimensionality at the EP has been investigated mostly in a passive repetitive manner. Here, we propose an electrical and spectral way of resolving chiral EPs and clarifying the consequences of chiral mode collapsing of a non-Hermitian gated graphene metasurface. More specifically, the measured non-Hermitian Jones matrix in parameter space enables the quantification of nonorthogonality of polarisation eigenstates and half-integer topological charges associated with a chiral EP. Interestingly, the output polarisation state can be made orthogonal to the coalesced polarisation eigenstate of the metasurface, revealing the missing dimension at the chiral EP. In addition, the maximal nonorthogonality at the chiral EP leads to a blocking of one of the cross-polarised transmission pathways and, consequently, the observation of enhanced asymmetric polarisation conversion. We anticipate that electrically controllable non-Hermitian metasurface platforms can serve as an interesting framework for the investigation of rich non-Hermitian polarisation dynamics around chiral EPs.

This work presents an operating frequency and sensitivity evaluation methodology for an ultrasonic fingerprint on display (FoD). Understanding the underlying physics of the complicated, highly coupled behavior of electromechanical sensors is indispensable for predicting the responses of ultrasonic waves in the multi‐layered system. And predicting the behavior of the ultrasonic waves in a multi‐layered display panel structure is critical for evaluating and optimizing its performance. In this work, we evaluated the optimal operating frequencies from Fabry‐erot resonance and represented acoustic pressure imaging at an operating frequency by developing the Finite Element Method (FEM) based numerical analysis models. This work allows engineers to predict behavior of devices, modify and optimize the designs efficiently

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In this work, we proposed the modified phase correction approach to enhance the fingerprint image quality of the ultrasonic fingerprint sensor on display (FoD). The mechanical wave is diffracted at the boundary between the finger and display panel so that the interference pressure is captured by the sensor. Diffracted waves play a critical role in enhancing sensing images. To correct the diffracted patterns, the corresponding point spread function (PSF) based convolution has been generally required in the conventional approach. In this study, we proposed a modified phase correction method using the sinusoidal implicit typed function, which is derived from the desired magnitude and phase spectrum based on the analyzed pressure distribution. The proposed approach is available for the multi‐physical structure such as acoustic, elastic and viscoelastic mediums in the multi‐layered structure. We verified the proposed approach to be a useful process for diffraction correction in comparison with the numerical and experimental results.

In this study, we proposed a numerical approach to predict a sound quality of the large‐sized OLED panel speaker. In order to perform accurate numerical analysis of the panel speaker, it is necessary to build the entire display module and the multiphysic simulation of elastic and acoustics must be analyzed. In this study, we totally constructed a three‐dimensional (3D) finite element model of the OLED panel to analysis the multi‐physics and it is sequentially simplified to reduce the computational cost. The modified incident condition is applied as an external pressure boundary condition to correct the total energy decrease by increasing the operation frequency. The results of the proposed method was verified by numerical simulations and experimental measurements.