This paper presents a method of mood transition design of a robot for autonomous emotional interaction with humans. A 2-D emotional model is proposed to combine robot emotion, mood, and personality in order to generate emotional expressions. In this design, the robot personality is programmed by adjusting the factors of the five factor model proposed by psychologists. From Big Five personality traits, the influence factors of robot mood transition are determined. Furthermore, a method to fuse basic robotic emotional behaviors is proposed in order to manifest robotic emotional states via continuous facial expressions. An artificial face on a screen is a way to provide a robot with a humanlike appearance, which might be useful for human-robot interaction. An artificial face simulator has been implemented to show the effectiveness of the proposed methods. Questionnaire surveys have been carried out to evaluate the effectiveness of the proposed method by observing robotic responses to a user's emotional expressions. Preliminary experimental results on a robotic head show that the proposed mood state transition scheme appropriately responds to a user's emotional changes in a continuous manner.

Metamaterial of dual-square array is proposed to design a dual-band circular polarizer. The novel design of asymmetric unit cell and layout of duplicate arrays significantly enhances the coupling between electric and magnetic fields. Simulation and measurement results show that the polarizer presents wide angle circular dichroism and circular birefringence. Moreover, the polarization conversion of the proposed metamaterial changes with frequency, incident angle, and polarization of incident waves. The fundamental mechanism behind is concluded to be the angle-dependent chirality and dispersion of our novel design.In recent years, metamaterials have been studied intensively for their special electromagnetic properties which are inexistent in natural materials. Application-oriented metamaterials' effective permittivity and permeability 1,2 can be designed for some amazing functions such as invisible cloaking 3 , diffraction-limit breaking imaging 4,5 and perfect lens 6 .Recently, metamaterials have been used to manipulate polarization of electromagnetic waves 7-11 , for example, circular dichroism (CD) and circular birefringence (CB). One of the critical points behind polarization manipulation by using metamaterials is thought to be the artificial chirality. Chirality in metamaterials results in cross-coupling between electric and magnetic fields.Prominent chiral metamaterials with circularly polarized eigenmodes 12-25 include twisted U-shape split ring resonators and twisted complementary split ring resonators. However, the working bandwidth of the polarization rotator based on these metamaterials is relatively narrow. To broaden bandwidth, an infrared broadband circular polarizer with periodic gold helix structure has been proposed 12 . It is later scaled down to microwave 13 and terahertz 14 region. Unfortunately, the thickness of the polarizers studied in 12-14 is of the order of the resonant wavelength so that it is hard to integrate them. Some approaches [15][16][17][18] to miniaturize the structure to subwavelength thickness have been proposed.In this paper, metamaterial of dual-square array is proposed to design a dual-band circular polarizer. Compared with previous designs [25][26][27] , the proposed structure is simpler. It transforms incident linearly polarized wave into left/right-handed circularly polarized wave at two resonant frequencies. The differences of transformation between left-handed circular polarization (LCP) and right-handed circular polarization (RCP) waves are more than 15 dB at both resonant frequencies. Design PrincipleInspired by the original multiband chiral metamaterial of twisted arc structure 24 , a dual-band circular polarizer with two aligned identical square arrays of periodicity p separated by a dielectric slab of thickness h is proposed in this paper. Two aligned unit cells of the arrays are shown in Fig. 1 while the configuration of arrays is shown in Fig. 2. In each unit cell, a centered PEC circle of radius R and width w is broken into two arcs at angle φ 1 with an angle g...

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