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 while still on carrier wafer. (b) close-up on carrier wafer. (c) full array wrapped on a cylinder of radius=30mm. (d) close-up on flexible array.
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.
Preliminary testing of multi-camera 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 (b) of the previous figure.
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 (b) of the previous figure.
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.
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 :
- K. L. Van Grinsven, A. O. Ashtiani, and H. Jiang, “Fabrication and Actuation of an Electrowetting Droplet Array on a Flexible Substrate” in Micromachines, 8(11), p. 334 (11 pages), 2017.
- 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.