Flexible microcameras with tunable-focus lenses
Prior work :
Jiang’s group has developed tunable liquid microlenses using different approaches including stimuli-responsive hydrogel-driven lenses as well as electrowetting-based lenses. Jiang’s group has also developed a flexible fabrication technology for microelectromechanical systems (MEMS).
We will further develop these technologies to realize batch fabrication and integration of the proposed camera array.
- L. Dong, A.K. Agarwal, D.J. Beebe and H. Jiang, “Adaptive liquid microlenses activated by stimuli-responsive hydrogels,” Nature, 442, pp.551-554, 2006.
- L. Dong, A.K. Agarwal, D. J. Beebe, and H. Jiang, “Variable-focus liquid microlenses and microlens arrays actuated by thermoresponsive hydrogels,” Advanced Materials, 19(3), pp. 401-405, 2007.
- L. Dong and H. Jiang, “pH-adaptive microlenses using pinned liquid-liquid interfaces actuated by pH-responsive hydrogel,” Applied Physics Letters, 89(21), art. no. 211120, 2006.
- X. Zeng and H. Jiang, “Tunable liquid microlenses actuated by infrared light-responsive hydrogel,” Applied Physics Letters, 93(15), art. no. 151101, 2008.
- C. Li, and H. Jiang, “Electrowetting-driven variable-focus microlens on flexible surfaces,” Applied Physics Letters, 100, art. no. 231105, 2012.
- X. Zeng, and H. Jiang, “Fabrication of complex structures on non-planar surfaces through a transfer method,” IEEE/ASME Journal of Microelectromechanical Systems, 20(1), pp. 6-8, 2011.
- C.-C. Huang, X. Zeng, and H. Jiang, “Fabrication of large-area three-dimensional microstructures on flexible substrates by micro-transfer printing methods,” IEEE/ASME Journal of Microelectromechanical Systems, 21(3), pp. 749-755, 2011.
Smart, micro-scale actuators
Prior work :
Jiang’s group recently reported a novel type of LCE actuator and used it to realize artificial heliotropism. The LCE actuators can contract along their pre-defined alignment direction when heated up. The actuators were applied to realize heliotropism, or light tracking: the actuators facing the light source (sunlight or white light) in temporal sequence would absorb the heat and contract, pulling the solar cells that they support towards the light source, thus the light tracking and a resultant large increase in photocurrent output.
Future work :
In this project, we will further develop LCE actuators to be implemented in our camera sheet to re-orientate individual micro-cameras.
Relevant publications :
- C. Li, C.-W. Lo, C. Li, D. Zhu, Y. Liu, and H. Jiang, “A synthesis process of photoresponsive liquid-crystalline polymer containing azobenzene,” Macromolecular Rapid Communications, 30(22), pp. 1928-1935, 2009.
- C. Li, Y. Liu, C.-W. Lo, and H. Jiang, “Reversible white-light actuation of carbon nanotube incorporated liquid crystalline elastomer nanocomposites”, Soft Matter, 7(16), pp. 7511-7516, 2011.
- C. Li, Y. Liu, X. Huang, H. Jiang, “Direct sun-driven artificial heliotropism for solar energy harvesting based on photo-thermo-mechanical liquid crystal elastomer nanocomposite,” Advanced Functional Materials , 22(24), pp. 5166–5174, 2012.
Preliminary Testing of Multicamera Array
We have also begun testing with an array of single millimeter-scale fixed cameras. Here, we create a 3×3 array of these small cameras embedded in a flexible sheet of PDMS. This was achieved by first utilizing stereolithography to fabricate a rigid array of camera holders configured in a 10mm grid. The resulting flexible camera sheet can acquire images while adhered to a planer surface, or the camera sheet can be wrapped around a convex shape, such as a cylinder. The following figure shows the set up and configuration of the camera sheet.
a) Setup for acquiring images from the nine camera planer array, highlighted by the blue box.
b) A close up of the camera array on a flat surface.
c) Setup for acquiring images from the camera array wrapped on an aluminum cylinder.
d) A close up of the camera array wrapped on the convex surface to increase field of view.
Compiled images of the camera array in planar (a-b) and convex (c-d) configurations.
a) Nine individual images acquired from 9 cameras of the array on a flat, planer surface, as show in Fig 2b.
b) The nine images in (a) stitched together into a single image.
c) Nine individual images acquired from cameras on convex array as shown in Fig. 2d.
d) Six of these images in (c) stitch into a single image.
Note that the borders corresponding to individual images are shown here for presentation only; they can be chosen not shown.
Flexible, Tunable Microlens Array
We have previously demonstrated individual liquid lenses actuated through electrowetting by utilizing area density modulated electrodes on rigid substrates. This design has been translated into an array, fabricated of entirely flexible materials. The following figure shows this array which has a PDMS substrate fabricated on a carrier wafer. Each lens in the 5×5 array can be independently turned by applying different voltages to the pad which corresponds with each lens via EWOD (electrowetting on dielectric) actuation. All lenses share a common ground.
5×5 array of lenses on flexible (PDMS) substrate. (a) full array wrapped on a cylinder of radius=30mm. (b) close of of four lenses showing details of electrode design
Schematic cross section of an individual lens for EWOD actuation.
Demonstration of lens actuation. Dark central region in the oil droplet surrounded by water.
As voltage is applied to the underlying copper electrodes the oil droplet is squeezed,
increasing it’s contact angle and shorting the focal length of the lens.
Relevant publications :
- A. O. Ashtiani, and H. Jiang, “Design and fabrication of an electrohydrodynamically actuated microlens with areal density modulated electrodes” in Journal of Micromechanics and Microengineering, 26(1), 015004, 2015.