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The natural compound eye system has many outstanding properties, such as a more compact size, wider-angle view, better capacity to detect moving objects, and higher sensitivity to light intensity, compared to that of a single-aperture vision system. Thanks to the development of micro- and nano-fabrication techniques, many artificial compound eye imaging systems have been studied and fabricated to inherit fascinating optical features of the natural compound eye. This paper provides a review of artificial compound eye imaging systems. This review begins by introducing the principle of the natural compound eye, and then, the analysis of two types of artificial compound eye systems. We equally present the applications of the artificial compound eye imaging systems. Finally, we suggest our outlooks about the artificial compound eye imaging system.

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Augmented reality (AR)-based rehabilitation shows potential to improve upper and lower limb function after stroke. This study aims to review the effect of AR technology in the recovery of the upper and lower limb function in stroke patients. Published randomized controlled trials and observational investigations with adult stroke patients were retrieved from five electronic databases to analyze the effect of the AR systems in improving motor function and balance and gait function for stroke patients. The treatment effect was estimated by standardized mean difference (SMD) and 95% confidence interval (CI) using a random effect model for motor function outcomes at the body structure and function, body activity and participation level of the International Classification of Functioning, and balance and gait outcomes. In total, 13 investigations (9 for the upper limb and 4 for the lower limb) were identified. AR demonstrated a significant influence on the upper limb function (SMD = 0.657; 95% CI, 0.287 to 1.026; p = 0.000) and the lower limb function (SMD = 0.52; 95% CI, 0.039 to 1.001; p = 0.034). The present analysis suggests that AR applications could offer options for increasing treatment intensity and promoting motor recovery after a stroke. This approach can be used with the conventional rehabilitation methods as a new intervention for recovering upper and lower limb function.

Neurons communicate with other neurons in response to environmental changes. Their goal is to transmit information to their targets reliably. A burst, which consists of multiple spikes within a short time interval, plays an essential role in enhancing the reliability of information transmission through synapses. In the visual system, retinal ganglion cells (RGCs), the output neurons of the retina, show bursting activity and transmit retinal information to the lateral geniculate neuron of the thalamus. In this study, to extend our interest to the population level, the burstings of multiple RGCs were simultaneously recorded using a multi-channel recording system. As the first step in network analysis, we focused on investigating the pairwise burst correlation between two RGCs. Furthermore, to assess if the population bursting is preserved across species, we compared the synchronized bursting of RGCs between marmoset monkey (callithrix jacchus), one species of the new world monkeys and mouse (C57BL/6J strain). First, monkey RGCs showed a larger number of spikes within a burst, while the inter-spike interval, burst duration, and inter-burst interval were smaller compared with mouse RGCs. Monkey RGCs showed a strong burst synchronization between RGCs, whereas mouse RGCs showed no correlated burst firing. Monkey RGC pairs showed significantly higher burst synchrony and mutual information than mouse RGC pairs did. Comprehensively, through this study, we emphasize that two species have a different bursting activity of RGCs and different burst synchronization suggesting two species have distinctive retinal processing.

Objective: Our objective was to investigate the effect of the rehabilitation system using augmented reality (AR) on upper extremity motor performance of patients with stroke. Methods: The system using AR applying mirror therapy mechanism provides the intervention protocol for the patient with hemiplegia after stroke. The system consists of a patient positioning tool (a chair), a white surface table, an image acquisition unit, an image processing unit, an image displaying unit, an arm holder, a Velcro-strap, and two blue circle stickers. To assess the feasibility of our system in motor function recovery, a stroke patient was recruited to receive the AR intervention. The treatment was performed two times a day for ten minutes over two weeks (ten days of treating weeks), except for the time of installation, calibration, and three minute breaks. Jebsen Taylor hand function test and Arm Motor Fugl-Meyer assessment were used as primary and secondary outcome measures, respectively, to evaluate the effect of motor function recovery. Additionally, stroke impact scale, Korean version-Modified Barthel Index (K-MBI), active range of motion of wrist joint (ROM), and the grasp force in Newtons were measured. Participants’ feedback and adverse effects were recorded as well. Results: Motor function improvements were exhibited in wrist and hand subtest of Arm Motor Fugl-Meyer (baseline: 19; post-intervention: 23), proximal arm subtest of Fugl-Meyer (baseline: 31; post-intervention: 34), ROM (extending ROM: 10° and 3° for flexion and extension, repeatedly), stroke impact scale (baseline: 46; post-intervention: 54), K-MBI (baseline: 92; post-intervention: 95), nine-hole pegboard (baseline: 30 s; post-intervention: 25 s), and grasp force in Newtons (baseline: 12.7; post-intervention: 17.7). However, the adverse effects were reported after the intervention. Conclusion: The system using AR applying mirror therapy mechanism demonstrated the feasibility in motor function recovery for the stroke patient.

Polarization converters play an important role in practical applications to manipulate the electromagnetic wave. However, the development of a polarization converter that possesses both high conversion efficiency and a wide frequency band is very challenging due to the trade-off between them. Here, we present an ultra-wideband and high-efficiency cross-polarization converter based on a double split ring shaped metasurface. The performance of the proposed converter is simulated and verified by experiments, showing a good agreement. The proposed polarization converter shows the cross-polarization conversion with a conversion efficiency above 93% in a wide frequency range from 4.0 to 14.0 GHz covering the entire C- and X-bands and a part of the Ku-band due to the combination of multi-modes of magnetic and electric resonances. Compared with other ultra-wideband polarization converters, the proposed converter shows excellent characteristics in terms of high efficiency, wide frequency band, and lightweight design, demonstrating a great potential application in C-, X-, and Ku-bands.

Developing a millimeter-wave (mm-wave) antenna that enables wide bandwidth with its operating band covering the entire global 5G spectrum is highly desirable but very challenging for achieving both compact size and high-performance antenna. Herein, the mm-wave microstrip patch antenna (MPA) and its multiple-input multiple-output (MIMO) configuration based on the metasurfaces for 5G system applications are proposed and investigated by the simulation method. To improve performance and keep the low-profile and low-cost MPA antenna, square ring resonator (SQRR) metasurface and radiating patch are printed on a single dielectric layer. With the presence of the metasurfaces that acting as a secondary radiator, the performance of the designed antenna is significantly improved with a wide operating band in the range of 23.9-30.7 GHz, high peak gain of 9.4 dBic, and radiation efficiency of above 87%. Based on this design, four-port MIMO antenna configuration is performed for evaluating a MIMO system that realizes the advantage features such as compact size, wide bandwidth covering the entire global mm-wave 5G spectrum band of 24.25-29.5 GHz, and excellent diversity performance characterized by good isolation between the adjacent elements and low envelope correlation coefficient. Thus, the MIMO antenna design is a very promising candidate for 5G MIMO mm-wave applications, specifically in cellular systems.