Edited by Wilson S. Geisler, The University of Texas at Austin, Austin, TX, and approved April 23, 2013 (received for review November 7, 2012)
Artificial and natural curved compound eyes. (A) Image of the CurvACE prototype. The entire device occupies a volume of 2.2 cm3, weighs 1.75 g, and consumes 0.9 W at maximum power. (B) Illustration of the panoramic FOV of the fabricated prototype. The dots and circles represent the angular orientation and acceptance angle Δρ of every ommatidium, respectively. Compound eye of the extinct trilobite Erbenochile erbeni (22) (C) and of the fruit fly Drosophila melanogaster (D). [(C) Reprinted from ref. 22 with permission from AAAS; (D) Reprinted from ref. 44 with permission from AAAS.]
CurvACE design and assembly. (A) Scheme of the three layers that compose the CurvACE artificial ommatidia: optical (microlenses and apertures), photodetector (CMOS chip), and interconnection (PCB). (B) Accurate alignment and assembly process of the artificial ommatidia layers in planar configuration. (C) Dicing of the assembled array in columns down to the flexible interconnection layer, which remains intact. (D) Curving of the ommatidial array along the bendable direction and attachment to a rigid semicylindrical substrate with a radius of curvature of 6.4 mm to build the CurvACE prototype. Two rigid circuit boards containing two microcontrollers, one three-axis accelerometer, and one three-axis rate gyroscope are inserted into the rigid substrate concavity and soldered to the sides of the ommatidia through dedicated pads (Figs. S3D and S4).
Characterization of CurvACE angular sensitivity. (A) Measured ASF along the middle (equatorial) row (black curves), with the corresponding interommatidial angles Δφh eq (red triangles) and mean acceptance angles Δρh (blue circles) of the CurvACE ommatidia averaged along every column. Error bars display SDs. (B) Mean horizontal interommatidial and acceptance angles averaged along every row of artificial ommatidia as a function of the elevation angle α. The black curve shows the theoretical Δφh values obtained using Eq. S10 with a constant Δφh max of 4.2°. (C) Schematic representation of the acceptance angle Δρ of an ommatidium and the interommatidial angle Δφ calculated from the peak ASFs of two neighboring ommatidia. (D) Measured ASFs along a single column of artificial ommatidia (black curves), mean vertical interommatidial (red triangles), and acceptance angles (blue circles) averaged along every row of artificial ommatidia. a.u., arbitrary units; deg., degree.
CurvACE autoadaptation to ambient light at the single ommatidium level. Steady-state (red dots) and transient (green dots) responses of the adaptive analog VLSI photodetectors [design based on a circuit proposed by Delbrück and Mead (27)]. Each of the four dynamic operating curves (in green) shows the V(log I) response, averaged over 11 ommatidia (photodetectors with optics) of one column, to step increments and decrements of irradiance (Fig. S6) about four steady levels (red circles).
Optic flow fields from the CurvACE prototype. Cylindrical equidistant projections of the optic flow field calculated with a modified version of the Lucas–Kanade method (29, 30) from the visual signals obtained by the CurvACE prototype subjected to roll motion (Fig. S8B) at 32° per second and at a distance of about 1 m to a wall displaying random black and white patterns (A) or to linear translation (Fig. S8C) at 3 cm/s toward the patterned wall at a distance of 1 cm (B). The red spot displays the center of rotation (A) or the focus of expansion (B).
Characterization of CurvACE motion detection capabilities. (A–C) Angular speed characteristics of CurvACE calculated with a method based on the time-of-travel scheme (32) (Fig. S9) assessed by applying steps of yaw rotational speed Ωyaw to the sensor at 10° per second, lasting 10 s each, with the prototype placed at the center of a 105-cm diameter arena lined with prints of a natural image. The dashed line displays the theoretical trend.
Specifications of CurvACE prototype compared with the characteristics of the Drosophila melanogaster compound eye
| CurvACE | Drosophila eye [Ref(s).] | |
| Number of ommatidia | 630 | 600–700 |
| Facet diameter, μm | 172 | 16 (42) |
| Eye diameter, mm | 12.8 | 0.36 (42) |
| Facet diameter/eye diameter, % | 1.3 | 4.4 |
| Interommatidial angle, Δφ; deg. | ∼4.2 | ∼4.7–5.5 (42) |
| Acceptance angle, Δρ; deg. | 4.2 | ∼4.5 (24) |
| FOV, deg. | 180 × 60 | 160 × 180 (43) |
| Signal acquisition bandwidth, Hz | 300 | <100 (28) |
| Adaptability to illuminance | Yes | Yes (4) |
| Crosstalk prevention | Yes | Yes (24) |
deg., degree.
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