kirigami/origami‐based soft deployable reflector for optical...

FULL P

APER

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com (1 of 9) 1604214

the light wave.[1–3] In macroscale applica-tions, mechanical beam-steering devices such as polygonal mirror scanners have been widely used due to the wide range of possible deflection angles while having a high resolution. However, such mechan-ical structures are bulky, expensive to build and maintain, and present signifi-cant challenges for scaling up due to the positioning of the mechanical trackers that rotate the entire module to maintain normal light incidence and other required apparatus.[4] A novel dynamic nonme-chanical beam steering approach for mac-roscale applications that is low cost and that can be easily scaled in size would be useful for various applications where the beam direction can change continuously and for an environment where larger beams need to be redirected to create microenvironments.[5,6]

Macroscale beam steering systems have been developed for applications such as heliostat mirrors to reflect sunlight into villages nestled in steep-sided valleys;[7] light pipe systems have been developed to transport daylight from the outside to interiors with poor light access;[5] and giant deployable reflectors have been proposed in aerospace to reflect solar energy into shadowed extreme environments where robots operate.[8] Solar tracking systems, considered as another kind of application for beam steering, aim to maximize electrical power generation over the course of a day.[4,9,10] Kirigami or origami structures have also been used for beam steering and diffrac-tion grating applications.[11,12] This type of kirigami or origami structures represent a promising alternative for the dynamic modulation of beam directionality due to being lightweight, low cost, compact, tunable periodicity, and simple operation from having the feature angle depending on the linear strain of the structure.[9,11,13] However, whether used for beam steering or for diffraction grating, this type of structure requires a large linear strain to produce the change in angle of the features, and most implementations have so far used external mechanical systems to realize this strain. To take advantage of the bene-fits of kirigami or origami-based reflectors, this study aims to develop a system with integrated kirigami or origami features that can self-actuate to control the feature angle for dynamic optical beam steering.

A potential approach to develop a structure capable of self-adjusting its strain to control the feature angle of

Kirigami/Origami-Based Soft Deployable Reflector for Optical Beam Steering

Wei Wang, Chenzhe Li, Hugo Rodrigue, Fengpei Yuan, Min-Woo Han, Maenghyo Cho, and Sung-Hoon Ahn*

The beam steering mechanism has been a key element for various applica-tions ranging from sensing and imaging to solar tracking systems. However, conventional beam steering systems are bulky and complex and present significant challenges for scaling up. This work introduces the use of soft deployable reflectors combining a soft deployable structure with simple kirigami/origami reflective films. This structure can be used as a macroscale beam steering mechanism that is both simple and compact. This work first develops a soft deployable structure that is easily scalable by patterning of soft linear actuators. This soft deployable structure is capable of increasing its height several folds by expanding in a continuous and controllable manner, which can be used as a frame to deform the linearly stretchable kirigami/origami structures integrated into the structure. Experiments on the reflective capability of the reflectors are conducted and show a good fit to the modeling results. The proposed principles for deployment and for beam steering can be used to realize novel active beam steering devices, highlighting the use of soft robotic principles to produce scalable morphing structures.

Dr. W. Wang, C. Li, Prof. H. Rodrigue, F. Yuan, M.-W. Han, Prof. M. Cho, Prof. S.-H. AhnDepartment of Mechanical and Aerospace EngineeringSeoul National UniversityGwanak-ro 1, Seoul 151-742, Republic of KoreaE-mail: [email protected]. W. Wang, Prof. S.-H. AhnInstitute of Advanced Machines and DesignSeoul National UniversityGwanak-ro 1, Seoul 151-742, Republic of KoreaProf. H. RodrigueSchool of Mechanical EngineeringSungkyunkwan UniversitySuwon 16419, Republic of Korea

DOI: 10.1002/adfm.201604214

1. Introduction

Beam steering in optical systems is the dynamic redirection of collimated light to maintain the illumination of a static target. Beam steering has been a key function for various sensing and imaging applications and can be accomplished either by changing the refractive index of the medium through which the beam is transmitted or by redirecting the beam using mir-rors, prisms, or lenses. Most of the mechanisms for microscale applications are based on Fermat’s principle that the wavefront of a light beam can be modified by controlling the phase of

www.afm-journal.de

Adv. Funct. Mater. 2017, 1604214

www.advancedsciencenews.com

http://doi.wiley.com/10.1002/adfm.201604214

FULL

PAPER

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheimwileyonlinelibrary.com1604214 (2 of 9)

kirigami/origami reflectors is to use a self-deployable soft struc-ture capable of controlling the linear strain of the kirigami/origami reflectors. Recent advances in soft and smart materials have shown that soft morphing technologies can potentially reduce the mechanical complexity and implementation require-ments involved in producing and implementing morphing robots or structures.[14–18] Soft deployable structures made from smart materials for actuation and compliant materials for the surrounding structure are capable of changing signifi-cantly their configuration through applied stimuli without any external mechanical parts. Such structures have been developed for aerospace applications, soft robotics, and reprogrammable metamaterials.[19–21] Compared with mechanical traditional structures, these structures are capable of smooth and con-tinuous deformation for an adaptable morphology and capable of various complex deformations while being compact, light-weight, self-sensing, and inexpensive. Based on these proper-ties, soft deployable structures present significant potential to be applied for the control of a kirigami/origami macroscale beam steering mechanism. Pneumatically actuated twisting structures for tilting mirrors have been developed but require multiple pneumatic inputs and outputs for control.[22] Stimuli responsive hydrogels have been used to control folding struc-tures that can reflect beams at the sub-millimeter scale, but they are controlled by controlling both the pH and the temperature of the environment, such that they require heating and cooling systems to actively control the system.[12] Also, both structures rely on tilting or folding and could not be used for the imple-mentation of a kirigami concept such as the one introduced in this work.

In this research, a new type of shape-memory alloy (SMA)-based linear actuator is developed that can contract in one direc-tion and extend in the other; this concept is then extended to produce a scalable planar soft deployable structure. This planar soft deployable structure is then used as the frame in which the kirigami or origami films made from a reflective surface are inserted to produce a macroscale beam steering mechanism. The proposed concept could also be used to implement and control microsized kirigami features for diffracting grating.[11] Two different types of soft deployable reflectors are described based on simple kirigami and origami reflective films and the reflective angle of the kirigami or origami films depends on the deformation of the planar soft deployable structure. The design and manufacturing methods of both the planar soft deployable structure and of the kirigami and origami films are presented, a model and a control method for the structure are introduced, and after assembly of the structure, the beam steering capa-bility of the integrated soft deployable reflectors were evaluated using a single-longitudinal mode (SLM) green laser.

2. Results and Discussion

2.1. Design Principle for Soft Deployable Reflectors

The target structure is one where the actuation of a planar soft deployable structure controls the linear strain of a kirigami or origami reflective film integrated with the soft deployable struc-ture that is used for macroscale beam steering. To do so, the

proposed planar soft deployable structure is composed of uni-form hollow pockets in which the kirigami or origami reflective films are inlaid, and the deformation of the edges of each hollow pockets linearly stretches the contained kirigami or origami reflective films to change their feature angles (θk and θo), which corresponds to the angle between the reflective surface and that of the plane of the soft deployable structure. The design of the soft deployable kirigami reflector with a deployed con-figuration is described where the inlaid kirigami reflective film is stretched, changing from a flat state to a state with uni-form inclined reflective surfaces with a uniform θk (Figure 1a and Figure S1 in the Supporting Information). The kirigami structure consists of a flat, flexible, and continuous reflec-tive film with slit patterning, as shown in Figure 1b. During the deployable process, the cut film is pulled perpendicularly to the notches, resulting in a change in θk that corresponds to change in perpendicular height of the pocket in which the kiri-gami reflective film is positioned, as shown in Figure 1c. The design of the soft deployable origami reflector with a deployed configuration is described where the inlaid origami reflective film changes from the folded state to the deployed state by the deployment of the planar soft deployable structure (Figure 1d and Figure S1 in the Supporting Information). The origami structure consists of a similar reflective material as the kiri-gami structure with sets of creases as shown in Figure 1e. Its deployment process resulting in a change in θo is similar to the kirigami reflector, as shown in Figure 1f. One of the main dif-ferences between the designs of these two different reflectors is that, with an increasing axial strain, the kirigami reflector’s surfaces are all parallel while the origami reflector’s surfaces are oriented in alternating directions. Through this change in feature angle, the structure’s reflection angle can be controlled and can thus be used as a novel and simple method for beam steering.

2.2. Design Principle for Soft Deployable Frame

The key part of the proposed concept is the planar soft deploy-able structure, which serves as the frame for the soft deploy-able reflectors, whose deformation needs to be both continuous and controllable throughout the deploying process. The struc-ture proposed in this work consists of repeating base elements where the number of base elements allows for easy scaling of the dimensions of the structure. The base element used in this work consists of a novel SMA-based soft linear actuator design whose configuration is similar to that of a bending actuator, but with multiple segments with alternating direction. This ele-ment can be active by applying an electric current to the pre-strained SMA wire, which increases its temperature through Joule heating until it reaches its austenite phase transition tem-perature, causing the SMA wire to contract within the matrix and thus deforming the structure. This design is essentially a multisegment linear actuator that contracts longitudinally and expands transversally as shown in Figure 2a, where the initial length L contracts to a length of L′ and the height H expands to a height of H′. The configuration of such an actuator with a single-segment SMA-based soft actuator corresponds to that of a basic bending actuator, whose deformation and relevant


www.afm-journal.de www.advancedsciencenews.com

FULL P

APER


dimensions are illustrated in Figure 2b. Due to the alternating eccentricity of the SMA wire, the deformation of the proposed actuator alternates between one direction and then the other, creating a wave-like shape. This actuator is made of smart soft composites consisting of embedded thin SMA wires in a poly-meric matrix with a 3D printed reinforcement. This reinforce-ment allows the use of a thinner matrix while obtaining larger deformations and a faster recovery speed.[23,24] After the SMA wire cools down below the austenite phase transition tempera-ture, the structure begins to recover to its original flat shape due to the elastic recovery force of the bended structure.

These base soft linear actuators are then assembled in an alternate direction to form the planar soft deployable struc-ture shown in Figure 2c, where the structure is shown in the deployed configuration. The configuration shown in Figure 2c consists of four soft actuators with three segments each that are connected using soft joints. Generally, this type of actuator is fabricated by polymer molding method, as shown in Figure 2d (see the Supporting Information). It would be possible to fab-ricate the target structure by manufacturing the individual soft linear actuators and then assembling them together using mechanical joints at specific positions; however, this method necessitates additional efforts and could lead to geometrical errors. To overcome these shortcomings, the proposed strategy

is to design and fabricate the whole structure through a one-stage molding process where the soft joints are also made from polymer. Through this method, the fabrication schematic of a planar soft deployable structure is shown in Figure 2e with the inner walls of the mold highlighted in yellow. The connecting grooves between the spaces for each individual actuator will allow the formation of soft joints. In this figure, all the other components such as the reinforcements and each SMA wires are also illustrated to show the assembly of the structure in the mold before pouring in the polymer. After curing of the polymer, the mold can be removed to obtain the planar soft deployable structure. Larger structures can be made by scaling up the design of the mold with more actuator or using actua-tors with more segments.

2.3. Performance of Soft Linear Actuator

Numerical models have previously been used in order to pre-dict the bending deformation of pure-bending actuators using the 1D constitutive model[25,26] and has been extended in this work to predict the deformation of the proposed linear actuator (see the Supporting Information). Experiments were conducted to understand the actuation performance with different applied


www.afm-journal.dewww.advancedsciencenews.com

Figure 1. Schematic of soft deployable reflectors and their function of optical beam steering. a) The deployed profile of the soft deployable kirigami reflector where the subareas of the reflective film incline in the same direction. b) General slit patterning for the kirigami reflective film. c) Schematic of the cross-section of the kirigami film showing the difference in reflection angle for two different axial strains. d) The deployed profile of the soft deploy-able origami reflector where the reflective subareas incline symmetrically in both directions. e) The general crease patterning for the origami reflective film. f) Schematic of the cross-section of the origami film showing the difference in reflection angle for two different axial strains.

FULL

PAPER


end conditions. The overall dimensions of the soft actuator are fixed at 3 mm in height, 10 mm in width, and 120 mm in total length. The height of each segment is 2 mm, the height of the actuator at the overlap between segments is 3 mm, and the overlapped length of two adjacent segments is 2.5 mm (Figure S2, Supporting Information). The distance between the SMA wire and the reinforcement is fixed at 1 mm. Experiments were conducted by positioning the actuator vertically and fixing one end. Then, the actuator was fully actuated by applying an electric current of 0.65 A for 10 s such that no further deforma-tion can be detected, as shown in Figure 3a (see the Supporting Information). This value of the current was obtained through trial-and-error to allow for full and sustained actuation of the SMA wire. Then, the length L′ and height H′ of the actuator in the fully deformed configuration are measured visually through recorded images.

In the first experiment, the effect of the number of segments on the performance of the actuator is analyzed by keeping con-stant the total length of the actuator at 120 mm and by varying the number of segments without any additional loads. Three samples were fabricated for each configuration, with a number of segments ranging from two to six. The results are shown in Figure 3b for the contracted length and transverse expansion. The results show that having fewer segments leads to both a larger linear contraction and a larger expanded transverse deformation for this actuator length.

In the second experiment, the number of segments is kept constant at two, and by varying the weight of a load attached to the tip of the actuator. Three samples with a total length of 120 mm were built with attached weights ranging from 0 to 60 g in increments of 10 g. The results are shown in Figure 3c for the percentage of length contraction depending on the sus-pended weight and compared to a model for predicting its defor-mation (see the Supporting Information). The results show that the length contraction changes from 22.6% to 11.3% when the attached weight is increased from 0 to 60 g (Figure S3, Sup-porting Information). Results show some deviation between the experimental data and the modeling data, which could be due to the distance between the SMA wire and the neutral sur-face not being constant, and to the inhomogeneous deforma-tion along the length of the actuator while the deformation is modeled as an arc of constant radius in the model.

The third experiment is to test the reliability of the actuator with the effect of repeated sequential actuation on both the max-imum contraction length and the cooled length of the actuator. Since the SMA wire is embedded in the flexible matrix, the heat generated by the SMA wire has to first transfer to the matrix and then to the environment. Therefore, repeated sequential actuation will result in residual heat in the matrix that cannot dissipate entirely if the actuator is not allowed sufficient time to cool entirely. To test the capability to repeatedly actuate the actuator, the repeatability actuation test was conducted with 5 s



Figure 2. Design and fabrication of the soft deployable structure. a) The profile of a soft linear actuator composed of three segments before and during actuation. b) Schematic of force analysis of an SMA-based soft actuator with a single segment of the actuator showing its working principle for a bending deformation. c) The profile of the assembly composed of four basic actuators connected using soft joints. d) The fabrication process for one soft actuator by positioning the SMA wires and the reinforcement in the mold, pouring polymer into the mold and, after curing of the polymer, by removing the actuator from the mold. e) Mold design and components for fabricating the planar soft deployable structure with connecting grooves for forming the soft joints.

FULL P

APER


of actuation, 10 s of cooling, and with a suspended weight of 40 g. It can be seen from the results shown in Figure 3d that both the length after actuation and after recovery behave in an asymptotic manner until an equilibrium state. With regards to the linear contraction, this asymptote is at a contraction of 15%.

2.4. Performance of Soft Deployable Structure

A planar soft deployable structure consisting of eight soft linear actuators with five segments each was fabricated using the man-ufacturing method outlined previously. The dimension of each soft actuator is 190 × 3.75 × 10 (mm, length × height × width), and the dimension of the fabricated planar soft deployable struc-ture is 190 × 37 × 10 (mm, length × height × width) including the height of the soft joints. However, because of the prestrain of the SMA wires undergoing a slight recovery after demolding, the structure deforms slightly, resulting in an initial height of 54 mm. The structure can still be compressed manually to its minimum height of 37 mm, as shown in Figure 4a. The eight SMA wires of the planar soft deployable structure can be simul-taneously actuated to obtain a homogeneous deformation of the assembly with an overall height of 172 mm as shown in Figure 4b (Movie S1, Supporting Information), which is an increase of around 465% compared to its original minimum compressed height. Additionally, the eight SMA wires can be actuated independently to obtain different deformed configu-rations. In a second test, the upper four SMA wires and the bottom four SMA wires of the structure are actuated individu-ally, and the configurations after actuation of each case are

shown in Figure 4c. Under these two configurations, the height of the structure is expanded to around 320% of its original com-pressed height (Movie S2, Supporting Information). The resist-ance of this type of SMA wire is around 0.055 Ω mm−1, thus the total resistance of the SMA wires embedded in whole structure is ≈83.6 Ω. With an applied current of 0.65 A, the total power consumption to actuate the entire structure is around 35.3 W.

As described in Figure 1 and Figure S1 (Supporting Informa-tion), the kirigami reflective film cannot be completely folded, and thus a thin rope is used to connect the ends of each pocket, as shown in Figure 4d, that allows control over the initial posi-tion of the actuator by using a rope shorter than the folded length of the pocket. However, this is not necessary for the ori-gami structure. Proportional-integral-derivative (PID) control is used to control the deformation of the structure between this initial position and the deployed position of the structure. The PID controller is applied using the resistance of the SMA wire as the process variable such that the SMA wires can be used as a type of self-sensing sensor within the actuator. This is due to the change in resistance of the SMA wire corresponding to a change in its phase. When the temperature of the embedded SMA is increased by applying an electrical current, the mar-tensite fraction of the SMA wire will be reduced gradually, resulting in a decrease of the current resistance of the SMA wire. This is due to the martensite phase having a higher resist-ance than the austenite phase. As such, PID control can be used to achieve a specific resistance corresponding to a proportional martensite fraction. This martensite fraction then corresponds to a certain strain of the SMA wire and thus of the overall struc-ture (see Figure S4 in the Supporting Information). From the



Figure 3. The performance of soft linear actuators. a) Experimental setup and the configuration of the soft linear actuator with two segments before and after actuation. b) Linear contraction and transverse expansion of the actuator with two to six segments. c) Length contraction of the two-segment linear actuator with different suspended weight from 0 to 60 g. d) Results for the repeatability test of a linear actuator with two segments.

FULL

PAPER


results in Figure 4e, it can be seen that the deformation of one hollow pocket in the vertical and horizontal directions almost changes linearly from 18 to 35 mm and from 94 to 84 mm, respectively, with a linear change in resistance from around 0.055 to 0.048 Ω mm−1 for any of the embedded SMA wires.

2.5. Soft Deployable Reflectors

A flat piece of reflective film is cut using a laser cutter to obtain the kirigami reflective films whose shape and relevant parameters are shown in Figure 5a (Figure S5, Supporting Information). In order to avoid interference between the kiri-gami reflective film and the frame structure during the deploy-ment process, the initial shape of the kirigami reflective film before stretching is based on the shape of the hollow pocket of the planar soft deployable structure before actuation. Since the kirigami reflective film is symmetric, one of the attachment flaps of the kirigami is attached to the inner wall of the frame structure and the other one is attached to the external wall of the opposite wall to guide the deformation of the feature angle in the desired direction (see the Supporting Information). In Figure 5b, the feature angle of the kirigami reflector changes from 0° (defined under initial configuration) to 75° during the deployment of the assembly composed of two soft actua-tors, which takes 4 s. In the case of the kirigami reflector, the planar soft deployable structure is predeformed using ropes, which causes the actuator to not deform in the first 3 s when a current is applied. After 3 s, the structure starts undergoing

a deformation for the next 4 s. The deployment of a planar soft deployable structure with eleven kirigami reflective films is shown in Figure 5c (Movie S3, Supporting Information).

The origami reflector is made, similarly, by cutting a piece of reflective film using a laser cutter to obtain the origami reflec-tive film whose shape and relevant parameters are shown in Figure 5d (Figure S6, Supporting Information). The shape of the origami reflective film is determined by the fully deployed shape of the hollow pocket of the soft deployable structure. In the case of the origami reflector, both of the attachment flaps of the origami reflective film are attached to the inner walls of the frame structure since this reflector is symmetric, and the feature angle of the reflector changes from a large angle to a small angle. The sequence in Figure 5e shows the deployment process of the assembly composed of two soft actuators, which takes 7 s, with the reflective feature angle changing from ≈80° (folded state) to 0° (flat state). The deployment process of a planar soft deployable structure with eleven origami reflective films is shown in Figure 5f (see Movie S4 in the Supporting Information).

2.6. Evaluation of Reflective Performance

The goal of this type of soft deployable reflector is to change the reflection angle of the incident light at any angle within a certain range. Experiments are conducted to test the perfor-mance of each type of soft deployable reflector using the exper-imental setup shown in Figure 6a,b. Each reflector composed



Figure 4. Configurations of the soft deployable structure. a) Minimum compressed height of the planar soft deployable structure under a weight of 100 g. b) Homogeneous deformation of the planar soft deployable structure under actuation. c) Nonhomogeneous deformation of the planar soft deployable structure by actuating only the top four SMA wires and the bottom four SMA wires. d) The structure where the top four actuators are constrained using ropes to fix the initial deformation. e) The relation between the deformation of one hollow pocket in the vertical and horizontal directions and the resistance change of the embedded SMA wire. Scale bars, 50 mm.

FULL P

APER


of two actuators is fixed vertically through a predesigned jig to the center of a circular platform that has a radius of 600 mm. An SLM green laser with a wavelength of 375 nm and a laser beam expander is fixed in a line perpendicularly with the soft deployable reflector. The laser goes through the expander and hits the soft deployable reflector and is then reflected in a dif-ferent direction based on the feature angle of the soft deploy-able reflector detected by a sliding laser power sensor, and the light intensity is read by a laser power meter. The laser is pointed toward the center of the kirigami or origami reflector, as shown in Figure 6a. The reflection angle of the incident light, defined here as the angle between incident light and the reflected light, is measured and read directly using the angle pointer.

When testing the kirigami reflector, the kirigami reflective film is stretched by the soft deployable structure from an initial deformation of 20 mm to the maximum measured deformation of 26 mm in increments of 1 mm. Then, the corresponding axial strain for the kirigami film ranges from 0 to 0.3 in incre-ments of 0.05. Simultaneously, the feature angle of the reflector increases gradually. For each feature angle of the reflector, the measured reflection angle is where the strongest reflective light intensity is recorded (see Figure S7 in the Supporting Information). For the kirigami reflector, the reflective light is

unidirectional and the results are shown in Figure 6c. It can be seen from the results that the reflection angle increases as the axial strain increases in an asymptotic manner, and that the performance using the proposed soft deployable structure for actuation is comparable to kirigami structures using a mechan-ical system for actuation and larger than micromirror tilting systems.[9,22,27,28]

However, in the case of the origami reflector, the beam is reflected in two opposite directions due to its symmetric con-figuration. Another point of interest of the origami structure is that if the feature angle is large then the beam will hit the reflector two or more times between opposing reflective sur-faces before being reflected away from the structure. In this work, we only will consider one of the directions of reflection and only the cases where the beam hits the reflector once or twice (see Figure S8 in the Supporting Information). The results show that the reflection angle decreases as the axial strain increases, but also that there are two distinct regions on the graph that exhibit this trend. The beam is reflected twice by the reflector at lower axial strains and only once at higher axial strains. Thus, this design is capable of bidirectional beam reflection from the symmetric reflective surfaces and has two distinct phases that could be useful to quickly jump from one reflective angle to another.



Figure 5. Soft deployable reflectors. a) The cut shape and pattern of the kirigami reflective films. b) The deployment process of the assembly composed of two soft actuators and one kirigami reflective film. c) The deployment process of the extended kirigami reflector. d) The cut shape and folding pat-tern of the origami reflective films. e) The deployment process of the assembly composed of two soft actuators and one origami reflective film. f) The deployment process of the extended origami reflector. Scale bars, 30 mm.

FULL

PAPER

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheimwileyonlinelibrary.com1604214 (8 of 9) Adv. Funct. Mater. 2017, 1604214


3. Conclusion

This work has demonstrated the feasibility of making dynamic reflectors by integrating soft deployable structures with kiri-gami/origami reflective films by pairing their motion such that the soft deployable structure is used to control the feature angle of the reflector. This work first introduced the design and fab-rication of a novel soft linear actuator capable of longitudinal contraction and transversal expansion. A new type of planar soft deployable structure that is easily scalable was then developed by patterning of the developed soft linear actuators. These soft deployable structures show a significant deployment deforma-tion that is both continuous and controllable. The structure was then used to control a beam steering kirigami/origami struc-ture, forming a structure capable of large angular variations that can be controlled using only an applied current without the use of any external mechanical structures. The proposed struc-ture can be adapted to control either the beam steering kiri-gami/origami structure proposed in this work or the diffraction grating kirigami structures presented in other works.

The structure presented in this work was manufactured manually due to the impracticality of developing an integrated manufacturing system for a small number of parts, but could be automated using auxiliary devices to place the different components such as the SMA wires during construction. Flex-ibility could be added into the process to automate resizing of components. The design of the proposed work is described at the macroscale, however, by exploiting the scale-free geometric characteristics of the soft deployable reflectors and by means of recent developments in microscale fabrication and actuation, the approach for beam steering in this study can be extended

to the micro- and nanoscale structures as well as to the meter-scale structures resulting in a simplified route for the design of active beam steering devices over a wide range of dimensions.

Compared with conventional heavy and bulky mechanisms, the proposed active reflectors have no cumbersome mechanical components and it is possible to accurately control the reflec-tion angle as predicted by the modeling results. The designed kirigami reflector is a unidirectional reflector with an increasing reflective angle range from 0° to 75° while the origami reflector is a bidirectional reflector with two reflective angle ranges that decreases from 60° to 12.8°, then jumps to 82.8° and decreases to 0°. This is due to the beam hitting two reflective surfaces at high feature angles, and then hitting only one reflective sur-face at lower feature angles. This origami reflector could be also designed as a unidirectional reflector for feature angles smaller than 45° by cutting off the subareas in the opposite orientation to keep only parallel reflective.

These two kinds of active reflector show a range of contin-uous and controllable deflection angles while being simple, compact, lightweight, and low cost. In addition, the soft planar deployable frame structures containing these reflector struc-tures are a polymeric structure where other functional com-ponents such as flexible electronics and stiffness modulation mechanism could easily be embedded. The work described the deployable mechanism fabricated using SMA-based smart soft composites; however, other actuation mechanisms such as ionic polymer–metal composites, shape memory polymers, and pneumatic actuators could also be used. In particular, the integration of a stiffness modulation mechanism will enable the capability to morph at low stiffness and then to retain the deformed shape at high stiffness without continuous energy

Figure 6. Performance evaluation of soft deployable reflectors. a) Schematic of the experimental setup. b) Experimental setup where a soft deployable reflector is under evaluation. Scale bar, 70 mm. c) Relation between the axial strain of the soft deployable structure and the reflection angle for the kirigami reflector. d) The relation between the axial strain of the soft deployable structure and the reflection angle for the origami reflector.

FULL P

APER

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com (9 of 9) 1604214Adv. Funct. Mater. 2017, 1604214


consumptions. Moreover, with further research, the proposed active reflector concept has the potential to be applied to a wide range of applications in many fields such as sensing and imaging applications, solar tracking systems, and dynamic building skins.

4. Experimental SectionSee the Supporting Information for details of the experiments.

Supporting InformationSupporting Information is available from the Wiley Online Library or from the author.

AcknowledgementsThis work was supported by the Industrial Strategic Technology Development Program (10049258) funded by the Ministry of Knowledge Economy (MKE), Korea, the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (NRF-2015R1A2A1A13027910), the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (2012R1A3A2048841), and a grant to Bio-Mimetic Robot Research Center funded by the Defense Acquisition Program Administration and by the Agency for Defense Development (UD130070ID).

Received: August 15, 2016Revised: November 6, 2016

Published online:

[1] M. Khorasaninejad, W. T. Chen, R. C. Devlin, J. Oh, A. Y. Zhu, F. Capassoet, Science 2016, 352, 1190.

[2] Z. Wei, Y. Cao, X. Su, Z. Gong, Y. Long, H. Li, Opt. Express 2013, 21, 10739.

[3] B. W. Yoo, M. Megens, T. Chan, T. Sun, W. Yang, C. J. Chang-Hasnain, D. A. Horsley, M. C. Wu, Opt. Express 2013, 21, 12238.

[4] H. Apostoleris, M. Stefancich, M. Chiesa, Nat. Energy 2016, 1, 16018.

[5] J. T. Kim, G. Kim, Build. Environ. 2010, 45, 256.

[6] E. J. Gago, T. Muneerb, M. Knezc, H. Kösterd, Renewable Sustain-able Energy Rev. 2015, 41, 1.

[7] P. H. Deshayes, Phys.org Technology, http://phys.org/news/2013-10-giant-mirrors-winter-sun-norwegian.html (accessed: October 2013).

[8] M. B. Quadrelli, A. Stoica, M. Ingham, A. Thakur, Proc. AIAA SPACE, Pasadena, CA 2015.

[9] A. Lamoureux, K. Lee, M. Shlian, S. R. Forrest, M. Shtein, Nat. Commun. 2015, 6, 8092.

[10] B. Svetozarevic, Z. Nagy, J. Hofer, D. Jacob, M. Begle, E. Chatzi, A. Schlueter, IEEE Int. Conf. Robotics and Automation (ICRA), Stockholm 2016, p. 4945.

[11] N. A. Kotov, L. Xu, X. Wang, Y. Kim, T. C. Shyu, J. Lyu, ACS Nano 2016, 10, 6156.

[12] C. K. Yoon, R. Xiao, J. H. Park, J. Cha, T. D. Nguyen, D. H. Gracias, Smart Mater. Struct. 2014, 23, 094008.

[13] R. V. Martinez, C. R. Fish, X. Chen, G. M. Whitesides, Adv. Funct. Mater. 2012, 22, 1376.

[14] S. W. Kwok, S. A. Morin, B. Mosadegh, J.-H. So, R. F. Shepherd, R. V. Martinez, B. Smith, F. C. Simeone, A. A. Stokes, G. M. Whitesides, Adv. Funct. Mater. 2014, 24, 2180.

[15] S. Felton, M. Tolley, E. Demaine, D. Rus, R. Wood, Science 2014, 345, 644.

[16] A. S. Gladman, E. A. Matsumoto, R. G. Nuzzo, L. Mahadevan, J. A. Lewis, Nat. Mater. 2016, 15, 413.

[17] B. Mosadegh, P. Polygerinos, C. Keplinger, S. Wennstedt, R. F. Shepherd, U. Gupta, J. Shim, K. Bertoldi, C. J. Walsh, G. M. Whitesides, Adv. Funct. Mater. 2014, 24, 2163.

[18] W. Wang, H. Rodrigue, H. I. Kim, M. W. Han, S. H. Ahn, Composites, Part B 2016, 98, 397.

[19] W. Wang, H. Rodrigue, S. H. Ahn, Sci. Rep. 2016, 6, 20869.[20] S. A. Morin, S. W. Kwok, J. Lessing, J. Ting, R. F. Shepherd,

A. A. Stokes, G. M. Whitesides, Adv. Funct. Mater. 2014, 24, 5541.[21] J. T. B. Overvelde, T. A. de Jong, Y. Shevchenko, S. A. Becerra,

G. M. Whitesides, J. C. Weaver, C. Hoberman, K. Bertoldi, Nat. Commun. 2016, 7, 10929.

[22] B. Gorissen, T Chishiro, S. Shimomura, D. Reynaerts, M. D. Volder, S. Konishi, Sens. Actuators, A 2014, 216, 426.

[23] W. Wang, J. Y. Lee, H. Rodrigue, S. H. Song, W. S. Chu, S. H. Ahn, Bioinspiration Biomimetics 2014, 9, 046006.

[24] A. A. Villanueva, K. B. Joshi, J. B. Blottman, S. Priya, Smart Mater. Struct. 2010, 19, 025013.

[25] C. Liang, C. A. Rogers, J. Intell. Mater. Syst. Struct. 1990, 1, 207.[26] H. Rodrigue, W. Wang, B. Bhandari, S. H. Ahn, Smart Mater. Struct.

2015, 24, 125003.[27] P. F. Van Kessel, L. J. Hornbeck, R. E. Meier, M. R. Douglass, Proc.

IEEE 1998, 86, 1687.[28] M. F. L. De Volder, J. De Coster, D. Reynaerts, C. Van Hoof,

S. G. Kim, Small 2012, 8, 2006.

kirigami/origami‐based soft deployable reflector for optical...

Documents