Biological visual systems have inspired the development of various artificial visual systems including those based on human eyes (terrestrial environment), insect eyes (terrestrial environment) and fish eyes (aquatic environment). However, attempts to develop systems for both terrestrial and aquatic environments remain limited, and bioinspired electronic eyes are restricted in their maximum field of view to a hemispherical field of view (around 180°). Here we report the development of an amphibious artificial vision system with a panoramic visual field inspired by the functional and anatomical structure of the compound eyes of a fiddler crab. We integrate a microlens array with a graded refractive index and a flexible comb-shaped silicon photodiode array on a spherical structure. The microlenses have a flat surface and maintain their focal length regardless of changes in the external refractive index between air and water. The comb-shaped image sensor arrays on the spherical substrate exhibit an extremely wide field of view covering almost the entire spherical geometry. We illustrate the capabilities of our system via optical simulations and imaging demonstrations in both air and water.
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The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.
The source codes for MATLAB are available from the corresponding authors upon request.
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This research was supported by IBS-R006-A1. This research was also supported by the National Research Foundation (NRF) of Korea (2017M3D1A1039288 and 2021R1A6A3A01087961) and the GIST-MIT Research Collaboration grant funded by the GIST in 2022.
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Extended Data Fig. 1 Hemispherical (convex type) cornea facet lenses in the eyes of terrestrial arthropods.
(a) Optical microscope images of a dragonfly eye (Epophthalmia elegans, left) and its SEM image (right). Its cornea facet lens has a convex-type hemispherical surface. (b) SEM images of a fly eye (Calliphora vomitori, left) and its magnified view (right), which show the convex-type hemispherical surface of the cornea facet lens.
(a–c), Each layer of each g-ML array is scanned by confocal microscopy to reconstruct the 3D surface profile of each layer. The diameters (D) of the g-MLs are 17 μm (a), 80 μm (b), and 400 μm (c). (d–f) Colorized cross-sectional SEM images of the g-MLs (top) and deviations of the RoCs from the average RoCs in the g-ML layers (bottom) for three different micro-lens diameters, that is, 17 µm (d), 80 µm (e), and 400 µm (f). (g) 2D cross-sectional profiles of g-MLs with three different diameters (17 µm, 80 µm, and 400 µm in the top, middle, and bottom frames, respectively).
Extended Data Fig. 3 Custom-made experimental setup for lens characterization in air and water, and measurement results.
(a) Optical camera image of the custom-made experimental setup. The setup consists of a white light source or laser sources with wavelengths of 450, 532, and 635 nm; an objective lens (10×); and a CMOS image sensor. (b–d) Optical camera images showing the components, including the water container, for amphibious imaging. (e) Measured light intensity distribution of the h-ML (micro-lens size of 400 μm) for three wavelengths (left: 450 nm, centre: 532 nm, and right: 635 nm). (f) Cross-sectional light intensity profile of the g-ML with a micro-lens size of 400 μm at the focal length in air (solid line) and water (dotted line). These results show that the g-ML obtains identical profiles in both media at the same focal length. (g) Imaging results of a letter ‘E’ obtained by the g-ML (top) and h-ML (bottom) for various micro-lens sizes (that is 17, 80, and 400 μm) under white light. (h) Measured focal lengths of g-MLs and h-MLs with three sizes in air and water. For all sizes, the g-MLs show consistent focal lengths in air and water, whereas the h-MLs show large changes of their focal lengths between air and water.
Extended Data Fig. 4 Schematic illustrations of multiple soft moulding processes for the fabrication of the g-ML array.
(a–c) Fabrication steps for a spacer layer and a base micro-lens array. (a) An anti-adhesive (Teflon AFTM) is coated on a quartz mould. (b) The prepolymer (clear flexTM 50) for the spacer and base micro-lenses is poured onto the quartz mould and thermally cured for 20 h. (c) The spacer and base micro-lens layer is detached from the quartz mould. (d–g) Fabrication steps for intermediate lens layers of the g-ML. For intermediate g-ML layers, silicone (EcoflexTM) moulds of plano-concave shapes with different curvatures are prepared. These steps are repeated for two intermediate NOA layers. (d) NOA is poured onto the silicone mould, and air bubbles are removed. (e) The silicone mould and base micro-lenses are aligned using a microscope. (f) The silicone mould and base micro-lenses are brought into contact. NOA is cured by UV illumination. (g) The silicone mould is removed, and unnecessary NOA is removed using tweezers. (h) The multi-layered NOA structure is formed on the base micro-lens. (i–l) Fabrication steps for a flat g-ML surface. (i) The silicone mould for the flat surface lens is prepared. NOA for the flat surface lens is poured onto the silicone mould. The multi-layered lens and silicone mould are aligned using a microscope. (j) The silicone mould and the multi-layered lens are brought into contact. NOA is cured using UV radiation. (k) Unnecessary NOA is removed using tweezers. (l) A g-ML with a flat surface is fabricated. (m, n) The screening pigment (SP) is spray-printed onto the g-ML and dried. (o, p) For light transmission, the SP on the g-ML surface is removed by bringing it into contact with solvent-coated (propylene glycol methyl ether acetate) glass.
Extended Data Fig. 5 Design of the panoramic artificial vision using the spherical 3D structure and finite element analysis (FEA) of the induced strain in the image sensor array.
(a) Schematic illustration of the panoramic artificial vision. The comb-shaped image sensor array and the g-ML array are integrated on the spherical 3D structure. (b) Schematic illustration defining the acceptance angle (∆θ) and inter-ommatidial angles in the vertical and horizontal directions (∆φv and ∆φh). Considering the acceptance angle, the inter-ommatidial angles are determined to avoid overlapping between the visual fields of neighbouring pixels. (c) Geometry of the g-ML used for FEA. (d) Elastic modulus (e) of each layer in the g-ML. (e) Strain distributions induced in the image sensor and g-ML arrays. Because the outermost lens has the highest elastic modulus, the entire g-ML experiences only a nominal strain under the bending deformation.
(a) Imaging simulation results of a cubic pattern with eight different acceptance angles (∆θ) from 5.7° to 18°. The inset shows an original image of the cubic pattern. (b) Imaging simulation results of a cubic pattern with eight different inter-ommatidial angles (∆φ) from 1° to 15°. The dashed boxes indicate the used conditions in the measurement.
(a) Schematic for the distance-relative visual field of the ommatidia with an acceptance angle of ∆θ and an inter-ommatidial angle of ∆φ. (b) Illustration for the visual field variation by changing the acceptance and inter-ommatidial angles. An undetectable region, the area which cannot be captured by ommatidia, can be compensated by changing the angles. (c) Schematic illustration for describing the number of ommatidia capturing the object. (d) Calculated number of related ommatidia in (c) as a function of the acceptance angle and inter-ommatidial angle at an object distance of 5 mm, 40 mm, and 80 mm. (e) Original crab image for the image simulation. (f) Results of the imaging simulation with an object distance of 5 mm and an inter-ommatidial angle of 1°. (g) Results of the imaging simulation at an object distance of 40 mm with various acceptance angles and inter-ommatidial angles for the enhanced imaging resolution.
Extended Data Fig. 8 Simulation and experimental results of the panoramic imaging by the artificial vision.
(a) Schematic illustration of the artificial vision from the top view. (b) Simulation results of the panoramic imaging. (c) Experimental results of the panoramic imaging by the artificial vision.
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Lee, M., Lee, G.J., Jang, H.J. et al. An amphibious artificial vision system with a panoramic visual field. Nat Electron 5, 452–459 (2022). https://doi.org/10.1038/s41928-022-00789-9