Array Of Compound Eye Research Articles

An acoustic compound eye for omnidirectional broadband signal enhancement

We propose an acoustic compound eye based on a three-dimensional meta-sphere, which can achieve omnidirectional broadband acoustic signal enhancement. Imitating the insect compound eye system, a meta-spherical array of subwavelength planar metasurfaces with multiple gradient refractive indices is formed in space. The meta-spherical compound eye has multi-direction focusing and free-field anti-interference capabilities, which can focus and "inhale" the acoustic signals from different incident directions into the space surrounded by the lens array. The compound eye array size can control the frequency band of interference reduction. At the same time, the parameters of each "sub-eye lens" are consistent, and there is no obvious phase difference between the signals in each direction. In this way, the incoming and focused signals from different "sub-eye lenses" can be further converged and enhanced over a broadband frequency. The bionic structure of the compound eye extends the previous metalens design from two-dimensional unidirectional planar-lens focusing to three-dimensional omnidirectional meta-sphere focusing. While maintaining the subwavelength thickness of the metasurface, the structure can get rid of the dependence of the metasurface on the space and incident direction, which has a wide range of engineering applications.

Structure optimization of heterogeneous compound eye camera for improving the detection performance

To achieve fast location, precise tracking and accurate identification over a large field of view (FOV), we have proposed a heterogeneous compound eye camera (HeCECam), which consists of a heterogeneous compound eye array, an optical relay system and a CMOS detector. However, the current HeCECam can hardly acquire high-precision 3D information of the targets to realize these applications. To solve this challenge, we propose a scheme on optimizing the structure of the HeCECam to improving the detection performance, including the optimization of the distribution uniformity of the sub-eyes with the proposed “Three-direction center-of-gravity subdivision (TGS)” and the enhancement of the compatibility between heterogeneous compound eyes and the optical relay system with the proposed compensation method for tilt. The TGS significantly reduces the distribution unevenness of sub-eyes down to 117% from the previous 152%, and provides symmetry to the heterogeneous compound eye array. The tilt compensation effectively addresses previous imaging defects, such as distortion of sub-images, increased stray light, and support structures being imaged, and it improves the imaging clarity of the system, especially in external FOV. Based on two proposed methods, we re-design and fabricate the heterogeneous compound eye array to obtain a high-performance prototype. To verify the imaging capacities of the optimized HeCECam, a series of comparison experiments are performed, including blank scene imaging, FOV tests, resolution verification and real-world scene imaging. The results show that the previous imaging defects have been well eliminated, and the optimized prototype has stronger resolving power and wider FOV. This allow the HeCECam to perform better in subsequent practical applications, such as wide-area surveillance, forewarning, and navigation.

Heterogeneous compound eye camera for dual-scale imaging in a large field of view.

Multi-scale imaging with large field of view is pivotal for fast motion detection and target identification. However, existing single camera systems are difficult to achieve snapshot multi-scale imaging with large field of view. To solve this problem, we propose a design method for heterogeneous compound eye, and fabricate a prototype of heterogeneous compound eye camera (HeCECam). This prototype which consists of a heterogeneous compound eye array, an optical relay system and a CMOS sensor, is capable of dual-scale imaging in large field of view (360°×141°). The heterogeneous compound eye array is composed of 31 wide-angle (WA) subeyes and 226 high-definition (HD) subeyes. An optical relay system is introduced to re-image the curved focal surface formed by the heterogeneous compound eye array on a CMOS sensor, resulting in a heterogeneous compound eye image containing dual-scale subimages. To verify the imaging characteristics of this prototype, a series of experiments, such as large field of view imaging, imaging performance, and real-world scene imaging, were conducted. The experiment results show that this prototype can achieve dual-scale imaging in large field of view and has excellent imaging performance. This makes the HeCECam has great potential for UAV navigation, wide-area surveillance, and location tracking, and paves the way for the practical use of bio-inspired compound eye cameras.

A Biomimetic Model of Adaptive Contrast Vision Enhancement from Mantis Shrimp.

Mantis shrimp have complex visual sensors, and thus, they have both color vision and polarization vision, and are adept at using polarization information for visual tasks, such as finding prey. In addition, mantis shrimp, almost unique among animals, can perform three-axis eye movements, such as pitch, yaw, and roll. With this behavior, polarization contrast in their field of view can be adjusted in real time. Inspired by this, we propose a bionic model that can adaptively enhance contrast vision. In this model, a pixel array is used to simulate a compound eye array, and the angle of polarization (AoP) is used as an adjustment mechanism. The polarization information is pre-processed by adjusting the direction of the photosensitive axis point-to-point. Experiments were performed around scenes where the color of the target and the background were similar, or the visibility of the target was low. The influence of the pre-processing model on traditional feature components of polarized light was analyzed. The results show that the model can effectively improve the contrast between the object and the background in the AoP image, enhance the significance of the object, and have important research significance for applications, such as contrast-based object detection.

A simple process optimization route to fabricate curved bionic compound eye array

In this paper, a complete and simple process optimization route for the curved bionic compound eye (BCE) array fabrication is presented based on digital micromirror device (DMD) maskless lithography. Firstly, based on the study of edge bulge effect in the thermal reflow process, a proper curved BCE structure is designed. Then, through the optimization of multilayer coating process it can obtain a better uniformity of different photoresist layer and accurate thickness. Next, combined the DMD maskless lithography technology with the Poor Man’s dissolution rate monitor (DRM) approach, well-preformed hierarchical cylindrical structure can be simply fabricated. Lastly, the curved BCE structure can be obtained precisely by choosing the reasonable process control parameters, which depended on the study of two-step thermal reflow processes. This process optimization route makes it very easy to realize the curved BCE array structures with different ommatidium shapes. Experimental results showed the effectiveness of our process optimization method. The presented method is expected to provide a fast, economic and simple strategy for curved BCE array fabrication.

Fabrication and Characterization of Inhomogeneous Curved Artificial Compound Eye.

Compared with the conventional compound eye processing method, a new fabrication method—namely, a mold casting method—was presented. This method is simple, low-cost, easy to implement, and can be reused. A bionic compound eye array model with 61 ommatidia arranged inhomogeneously onto a curved surface was fabricated. The curved surface had a radius of 9 mm and a thickness of 0.5 mm. The margin imaging quality was improved significantly by the analysis of light beam focus and the optical imaging properties of the fabricated compound eye. The sub-image of each ommatidium had a high resolution. There was 5% error between the collecting spot brightness and simulation analysis results, which proved that the production method is feasible.

Flexible fabrication of biomimetic compound eye array via two-step thermal reflow of simply pre-modeled hierarchic microstructures

A flexible fabrication method for the biomimetic compound eye (BCE) array is proposed. In this method, a triple-layer sandwich-like coating configuration was introduced, and the required hierarchic microstructures are formed with a simple single-scan exposure in maskless digital lithography. Taking advantage of the difference of glass transition point (Tg) between photoresists of each layer, the pre-formed hierarchic microstructures are in turn reflowed to the curved substrate and the BCE ommatidia in a two-step thermal reflow process. To avoid affecting the spherical substrate formed in the first thermal reflow, a non-contact strategy was proposed in the second reflow process. The measurement results were in good agreement with the designed BCE profiles. Results also showed that the fabricated BCE had good performances in optical test. The presented method is flexible, convenient, low-cost and can easily adapt to the fabrications of other optical elements with hierarchic microstructures.

Computational efficiency circuitry for detecting shadows in hexagonal array of compound eye

Compound eyes in invertebrates are mostly arranged in hexagonal array for computational efficiency. Hexagonal arrangement provides geometric symmetry for efficient local computation of light-intensity level between adjacent ommatidia (photodetecting elements). Shadow motion detection circuitry for detecting critical velocity of light shadows for flight escape reflex is explored using a set of light-intensity comparers and time-delay circuitry. Motion of shadows is detected by comparing the light-intensity level between adjacent cells (ommatidia) using light-intensity difference comparers. Predation escape reflex is triggered by a critical velocity detector for shadow movements. We show that a time-delay local circuitry can be used in a hexagonal array to process local differences of light intensity efficiently for flight escape reflex in flying insects.

Computational efficiency circuitry for detecting shadows in hexagonal array of compound eye

Compound eyes in invertebrates are mostly arranged in hexagonal array for computational efficiency. Hexagonal arrangement provides geometric symmetry for efficient local computation of light-intensity level between adjacent ommatidia (photodetecting elements). Shadow motion detection circuitry for detecting critical velocity of light shadows for flight escape reflex is explored using a set of light-intensity comparers and time-delay circuitry. Motion of shadows is detected by comparing the light-intensity level between adjacent cells (ommatidia) using light-intensity difference comparers. Predation escape reflex is triggered by a critical velocity detector for shadow movements. We show that a time-delay local circuitry can be used in a hexagonal array to process local differences of light intensity efficiently for flight escape reflex in flying insects.