Foldable Structure Research Articles

Origami Morphing Surfaces with Arrayed Quasi-Rigid-Foldable Polyhedrons.

Artificial morphing surfaces, inspired by the high adaptability of biological tissues, have emerged as a significant area of research in recent years. However, the practical applications of these surfaces, constructed from soft materials, are considerably limited due to their low shear stiffness. Rigid-foldable cylinders are anisotropic structures that exhibit high adaptability and shear stiffness. Thus, they have the potential to address this issue. However, changes in shape and area at both ends during folding can lead to collisions or gaps on the morphing surface. Here, a quasi-rigid-foldable (QRF)rate is first introduced to quantify the rigid-foldability of a foldable structure and validate it through experiments. More importantly, a QRF polyhedron is then proposed, which is not only notably anisotropic, similar to a rigid-foldable cylinder, but also exhibits a zero-Poisson's ratio property, making it suitable for arraying as morphing surfaces without any collisions or gaps. Such surfaces have a myriad of applications, including modulating electromagnetic waves, gripping fragile objects, and serving as soles for climbing robots.

Foldable chain-based transformation method of 3D models

A 3D transformable model can be transformed into different shapes through folding operations to suit different needs, such as a table or a chair in daily life. Furthermore, the features of foldable structure and flat components allow it to be folded into a smaller stack for compact storage when not in use. To this end, this study applies a new foldable modular chain structure and proposes a novel method of constructing 3D models into 3D shapes based on this structure and guiding the transformation between shapes. For the construction of the model, that is, to find a module chain path that constructs the model shape, the divide-and-conquer method is adopted. The model is first divided into multiple units, and then the search for the linearly connected module sub-path is executed for each unit. This involves three major steps: unit-based segmentation of the model, search for the unit tree structure that can form the target 3D shape, and search for the modular chain path based on the unit tree. The experimental cases demonstrate the application of the square modular chain in the fields of furniture and toys and prove the effectiveness of the method in constructing and transforming the foldable chain-type modular configurations of the input 3D models.

Novel polyaryl isatin polyelectrolytes with flexible monomers for anion exchange membrane fuel cells

The stability of the anion exchange polyelectrolytes is closely tied to the durability of anion exchange membrane fuel cells. Given their excellent alkali resistance, ether-free polymer backbones have attracted considerable attention for use in anion-exchange polyelectrolytes. Herein, a series of side-chain-type poly(terphenylene-co-dibenzyl N-(6-bromohexyl)-isatin) copolymers (QAPTDBHI-n) were synthesized via superacid-catalyzed polymerization and a subsequent quaternization reaction. The cyclic cardo groups in the backbones enabled the formation of nanovoids, which facilitated ionic clusters’ self-aggregation. The introduction of flexible bibenzyl monomers provided the polymers with a spatially foldable structure, promoting the aggregation of ion clusters and strengthening interchain interactions. Compared with the membrane without flexible monomers, QAPTDBHI-n membranes exhibited higher hydroxide conductivity (>115 mS cm−1 at 80 °C), outstanding mechanical stability (tensile strength: 50.91–60.76 MPa, elongation at break: 14.27%–26.06%), and superior alkali resistance (1 M NaOH at 80°C for >1500 h and <9.5% OH− conductivity loss). Regarding fuel cell performance, the AEMFC based on QAPTDBHI-40 ionomer achieved a peak power density of 1.14 W cm−2 (H2–O2) and 0.86 W cm−2 (H2-Air, CO2 free) at 80 °C due to its higher water uptake, OH− conductivity, and lower phenyl concentration.

Micro-CT driven characterization and validation of constituents’ properties used in origami-inspired foldable composites fabricated via different manufacturing processes

High packaging efficient lightweight jointless deployable folding structures are nowadays fabricated from combination of rigid and thin flexible elastic hinges using fiber reinforced polymers composites (FRPCs) for various applications such as space, robotics, flexible electronics, etc. It is of high importance to optimize these structures in the design phase using computer aided analysis tools for which the structural-level elastic constants are challenging to find experimentally. In this work, a generic X-ray computed tomography (micro-CT) driven framework based on voxel modeling approach was developed to virtually characterize the smallest building block of a typical large-scale foldable structure that consists of a rigid region and elastic hinge needed for folding operation. The voxel-based description of a real representative volume element (RVE) was generated using the images obtained from the micro-CT. The homogenized mechanical properties for each of the material systems was then obtained by multi-parameter component segmentation and subsequent directional averaging of the corresponding voxels. Three-dimensional void analyses were also shown using the micro-CT based voxel modeling. The accuracy of the non-destructive framework was demonstrated for four materials systems, based on different combinations of the matrix and fabric architectures in comparison with the mechanical tests. The homogenized mechanical properties obtained using the present framework based on the real RVE showed good agreement with the experimental results providing a foundation for a structural-level computer aided analysis.

Paper-folding-based terahertz anti-resonant cavity.

Recently, the concept of core-anti-resonant reflection (CARR) has been proposed, greatly expanding the options of cladding materials and morphologies for Fabry-Perot-type (F-P) cavities. For instance, a single-layer tube made of A4 paper can be a precision resonator in the terahertz (THz) band, which seemed counterintuitive before. More importantly, thanks to the involvement of paper-like materials as the cavity plates, it is possible to equip the CARR cavity with the currently popular origami functionality. Following this clue, in this work we combined a simple octagonal paper tube with different origami patterns and realized the programmable adjustment for the distance between two parallel surfaces of the tubular cavity. Accordingly, the combination of the CARR cavity and the origami property offers a new degree of freedom and flexibility to vary the cavity distance, tune the resonant frequency, and explore related applications. For applied examples, we carried out pressure sensing with this foldable structure and achieved a high sensitivity (S = 57.9 kPa-1). Meanwhile, the origami cavity could also act as a THz polarization converter, and the output polarization state of the cavity mode was easily modulated from the original linear to circular polarizations with different chiralities. In future works, besides the pressure-driven method used here, heat and magnetism, etc., can further be employed to tune the CARR cavity, benefiting from four dimensional (4D) or soft-magneto origami materials as the cavity wall.

A Zigzag-Based Thickness-Accommodating Foldable Prismatic Structure With a Single-Degree-of-Freedom

Abstract Origami inspires various designs of foldable prismatic structures with zero-thickness facets. However, there is a difficulty in directly applying them to thick materials. This paper presents a novel design of the foldable prismatic structure inspired by the zigzag pattern, which can accommodate the thickness of materials easily by placing hinges on the top or bottom surfaces of panels. The foldable prismatic structures are constructed by connecting multiple zigzag strips, in which each strip is made up of uniform-thickness hexagonal panels. By identifying the relationship between the foldable structure and spatial linkages, we analyze the mobility of the assembly based on the matrix method with DH notations. The result reveals that the foldable prismatic structure is equivalent to a network of spherical 4R linkages and Bennett linkages, and its motion has a single-degree-of-freedom. Based on the proposed foldable prismatic structure, a foldable manipulator is developed to demonstrate its potential engineering applications. The actuation strategy is designed by employing a motor-cable-driven system and torsional spring hinges. The physical prototype of the foldable manipulator is fabricated, and experimental results prove that our designs are feasible and effective.

A Rapid and Simple Method for Purification of Nucleic Acids on Porous Membranes: Simulation vs. Experiment.

Paper-based microfluidic systems have emerged as one of the most promising technologies for developing point-of-care diagnostic platforms (POCT) for detecting and monitoring various diseases. Saliva is a non-invasive biofluid easily collected, transported, and stored. Due to its accessibility and connection to systemic diseases, saliva is one of the best candidates for medical advancement at the point of care, where people can easily monitor their health. However, saliva is a complex mixture of DNA, RNA, proteins, exosomes, and electrolytes. Thus, nucleic acid separation from the salivary components is essential for PCR applications. Paper membranes are a highly porous and foldable structure capable of transporting fluids without pumps and sophisticated systems. The current work presents an insight into simulations for nucleic acid extraction on three types of porous paper membranes for use in point-of-care devices. The flow fluid model is solved on a COMSOL Multiphysics 5.3 free version platform, and the results are compared with experimental assays. The results show that pore uniformity, wet strength, porosity, and functional groups of MF1™ and Fusion 5™ paper membranes are vital parameters affecting nucleic acid extraction and PCR amplification efficiency.

Easy snap-folding of hexagonal ring origami by geometric modifications

Hexagonal ring origami is a type of foldable structure that has impressive packing abilities and can be tessellated into two-dimensional or three-dimensional surfaces without any gap or overlap. It can be folded under bending or twisting loads into a peach core-shaped configuration with only 10.6% of its initial area. However, in applications of large-scale foldable structures, folding by bending or twisting is usually technically difficult. Here, we propose strategies to facilitate easy snap-folding of the hexagonal ring by a simple point load or localized twist or squeeze. This is enabled by two geometric modifications made to the hexagonal ring: introducing residual strain and creating pre-twisted edges. By combining theoretical modeling, finite element simulations, and experiments, we systematically investigate the snap-folding behaviors of modified hexagonal rings with residual strain and pre-twisted edges. It is found that the geometric modifications promote easy snap-folding of the hexagonal ring by different mechanisms: introducing residual strain can significantly decrease the energy barrier and thus reduce the required moment to snap-fold the ring, while creating pre-twisted edges allows for easy out-of-plane deformation which is a necessary condition for a ring to fold. Combining the two methods further enables the snap-folding of the hexagonal ring by a point load or localized twist or squeeze. To demonstrate the easy folding of large assemblies of the modified rings, we construct various structures that can be snap-folded from their initial three-dimensional states to significantly lower-volume final states by a simple compression at the corners of the rings. We envision that the proposed geometric modification strategies can provide a new perspective on the rational design of easy-to-fold ring origami-based foldable functional structures with extremely high packing ratios.

Air-Stable Dy(III)-Macrocycle Enantiomers: From Chiral to Polar Space Group

Air-Stable Dy(III)-Macrocycle Enantiomers: From Chiral to Polar Space Group

Development of an Offsite Construction Typology: A Delphi Study

Offsite construction (OSC) delivers multiple products that vary in design and building complexity. Considering the growing prevalence of OSC, a systematic categorization of OSC types can offer operational and macroeconomic benefits to the construction industry. The purpose of this study is to develop an OSC typology through a systematic process, as existing studies do not present a rigorously evaluated typology that suits the modern OSC context. The research addresses the following research question: what are the distinct characteristics of unique OSC types that have emerged through the adoption of Industry 4.0-based technological advancements? Due to the rapid advancement of production and construction technologies, the existing OSC classifications are becoming outdated. As such, a detailed review of OSC technologies was conducted which enabled the identification of OSC categories: components, panels, pods, modules, complete buildings, and flat-pack (foldable structure). A series of case studies was then reviewed to explore and analyze the relevance of these OSC types in practice. It was then subjected to a Delphi-based multi-level expert forum to develop a modern and future-proof OSC typology. The rigorous process validated, defined, and delineated the boundaries between the OSC types. The research confirmed that OSC types can be broadly categorized as volumetric (pods, modules, complete buildings) and non-volumetric (components, panels, foldable structure). The results indicated that OSC skills vary with the complexity of OSC types, and that lightweight steel and timber are the most common materials.

Reinterpretation of Dalí's »Vidriera Hipercubica« designed by Pérez Piñero in 1971

In 1971, the Spanish architect Emilio Pérez Piñero designed a foldable system of glass panels to separate the stage from the inner courtyard of the Dalí'Theatre‐Museum in Figueras. It is one of his last projects, before his early death by a car accident, ended abruptly this very creative period of the extraordinary constructor. The project is directly appointed by the artist Salvador Dalí himself, who was enthusiastic about Piñero's filigree constructions and called the foldable structure »Vidriera Hipercubica«, making a reference to the 4th dimension as a constant theme in the art of the 20th century. Analogous to the 4th dimension in physics – time, movement stands for the 4th dimension in architecture. The invention of the last system is patented in 1976, four years after the death of the architect under the description »System of Articulated Planes«. It can be read like a construction manual for the hypercubic glass. In the seminar »Movable Structures«, which takes place every summer semester since 2015 at the Institute of Structural Design at Universität Siegen, the realisation of a reinterpretation of the »Vidriera Hipercúbica« is the content of the current course. Following the assembly instructions of different patents by Pérez Piñero, it is possible to use the movement as a design tool, which allows to interpret the 4th dimension in architecture. One of the objectives is to pass the technical limits of that time and to integrate new possibilities in manufacturing. In particular, new types of glazing material will be used as well as digital production processes for connecting details. The reinterpretation focuses not only in its architectural interest, but also in the further development of the research work started by Piñero 50 years ago as well as to achieve innovative options of application. Hence, the imaginable use of foldable structures for the mobile installation of solar collectors could be one of them.

A Hybrid Structure of Piezoelectric Fibers and Soft Materials as a Smart Floatable Open-Water Wave Energy Converter.

An open-water wave energy converter (OWEC) made of a new soft platform has been developed by combining piezoelectric macro-fiber composites (MFCs) and a low-cost elastomer. In the past decades, numerous types of water wave energy conversion platform have been developed and investigated, from buoys to overtopping devices. These harvesters mainly use electromagnetic-based generators, and they have faced challenges such as their enormous size, high deployment and maintenance costs, and negative effects on the environment. These problems hinder their practicality and competitiveness. In this paper, a soft open-water wave energy converter is introduced which integrates piezoelectric MFCs and bubble wrap into an elastomer sheet. The performance of the OWEC was investigated in a wave flume as a floatable structure. The maximum 29.7 µW energy harvested from the small OWEC represents a promising energy conversion performance at low frequencies (<2 Hz). The elastomer was able to protect the MFCs and internal electrical connections without any degradation during the experiment. In addition, the OWEC is a foldable structure, which can reduce the deployment costs in real-world applications. The combination of no maintenance, low fabrication cost, low deployment cost, and moderate energy harvesting capability may advance the OWEC platform to its real-world applications.

Origami-based auxetic tunable Helmholtz resonator for noise control

In this paper, we propose an origami-based auxetic tunable Helmholtz resonator by controlling the volume of the cavity to allow a real-time tunability of the resonance frequency. The design is inspired by the waterbomb origami base, which expands when stretched and contracts when compressed. Such a foldable structure offers a wide range of volume variation, which corresponds to a larger frequency shift in the bandwidth of interest. Based on the design of the origami resonator, multi-physical models are established to understand and predict the parameters’ effect on the device’s behavior. After fabrication, experimental tests are conducted on physical prototypes to validate the models and illustrate the effectiveness of the concept.

A Crawling Soft Robot Driven by Pneumatic Foldable Actuators Based on Miura-Ori

Origami structures are highly demanded for engineering applications. Using origami folding to design and actuate mechanisms and machines offers attractive opportunities. In this paper, we design a crawling robot driven by pneumatic foldable actuators (PFAs) based on Miura-ori, according to the parallel foldable structure and different control patterns, which can perform different movements. The PFA inspired from Miura-ori is composed of a folding part, transition part, and sealing part, made by flexible materials and a paper skeleton. This actuator can obtain a large deformation by folding under negative pressure due to its own characteristics, and the relationship between deformation and pressure is analyzed. According to the different folding and unfolding times of left and right actuators, the crawling robot can perform both linear and turning movements. The speed of the robot is about 5 mm/s and it can turn at a speed of about 15°/s. The crawling robot uses the ability of the foldable structure to cope with the challenges of different environments and tasks.

A micro monolithic integrated force-torque sensor with piezoelectric tuning mechanism

A novel micro force-torque sensor with tuning mechanism is presented in this paper. The sensor is designed and fabricated based on monolithic integrated method, including planar graphic manufacturing and lamination process. The sensing element is composed of cross-shaped double cantilever beams which will deform when loading force and Torque. The process of sensor is divided into two parts. The structure-circuit integration process is proposed to realize the planar structure of sensor, which integrates flexible printed circuit (FPC) in the graphic multi-layer materials. The assembly of force-torque sensor is realized by the design of foldable mirror structure with each component connected by flexible limited hinges, which can form and lock at 90°. By bring in piezoelectric (PZT) composite cantilever beams as tuning mechanism, the position of the sensor can be further tuned, so that the system precision can be significant improved. According to the result of calibration and experiments, the sensor prototype has a force sensitivity of 0.29 μm/mN, a torque sensitivity of 0.33 μm/μNm and a bandwidth of 481.44 Hz, the range of force and torque measurement is – 7~7 mN and – 14~14 μNm respectively. And the linear-adjustment sensitivity of PZT composite cantilever beam is 24.69 nm/V.

Compact UHF/VHF Monopole Antennas for CubeSats Applications

In this paper, two compact monopole antennas working at 149 MHz (VHF) and 398 MHz (UHF) are proposed for CubeSats applications. Two monopole antennas are integrated on a double layer ceramic substrate. The overall dimensions of the folded antenna are 101 mm × 40 mm × 8.9 mm which is very small. Meander-line technique and foldable structure are proposed to achieve a compact design. The introduction of decoupling structure solves the problem of high coupling caused by small size. Computer simulations and measurements are conducted. The results demonstrate that the proposed design is a very promising candidate for CubeSats applications.

STRUCTURAL ANALYSIS OF CARBON COMPOSITE FRAME FOR FOLDABLE ELECTRIC WHEELCHAIR DEVELOPMENT

Electric wheelchairs developed so far have difficulties for elderly people to use, because of their bulkiness and heavy weight. To address this problem, this study presents a design for the construction of an electric wheelchair with an application of light duty materials at frame and a foldable structure that can be easily loaded in a narrow space. A structural analysis was performed to evaluate the structural safety of the foldable wheelchair. For the purpose of analysis, a carbon composite was used as the material for the frame; Structure Mechanics Module of COMSOL Multiphysics was used as the analysis software; and for the boundary condition, the lower part of the body frame was fixed, and a load of 150[Formula: see text]kg was applied to the upper part of the wheelchair. According to the results of the structural analysis, a maximum displacement of 2.869[Formula: see text]mm occurred at the handle where the carbon composite was applied, and tensile and compressive stress of 103[Formula: see text]MPa and 107.3[Formula: see text]MPa, respectively, were measured at the seat part of the wheelchair where the load was applied. The safety factors were 7.5 and 5.5 for tensile stress and compressive stress, respectively. A maximum variation of 0.0872[Formula: see text]mm occurred at the aluminum wheel shaft, and a maximum variation of 0.2046[Formula: see text]mm occurred at the joint. The maximum stress was 116.3[Formula: see text]MPa that corresponded to a safety factor of 2.66; this indicates that the wheelchair can be considered to be structurally safe as the safety factor exceeds the initial target of 2.

Programming the deformation of a temperature-driven bilayer structure in 4D printing

4D printing deforms a 2D foldable structure to another shape evolve over time by using heterogeneous material. The deformation of the 2D foldable structure is stimulated by actuators that are fabricated by shape memory materials or bilayer structures. Therefore, the deformation programming method of actuators is a critical technology in 4D printing. This paper proposes a method for programming the deformation of a temperature-driven bilayer structure actuator in 4D printing. The thermo-mechanical mechanism of the bilayer structure actuator is analyzed and three kinds of deformation behavior are modeled. Then a constitutive model with five main deformation programming parameters including the line width, the print height, the print temperature, the filled form, and the stimulation temperature is fitted by the orthogonal experiment and response surface method. The permanent deformation of the bilayer structure actuator results from the programmed parameters and time evolution of the 3D printed structure upon heating. A typical temperature shape memory material polylactic acid is used as a case study to illustrate the methodology and a desired programmed deformation is achieved.

Design and fabrication of novel auxetic weft-knitted fabrics with Kevlar yarns

For the purpose of fabricating three kinds of auxetic weft knitted fabrics, three different geometrical structures namely rotational structure, foldable structure and double-headed arrow topological structures with three different knit loop lengths were produced using computerized flat knitting machine. Experimental results show that all three different weft knitted fabrics have auxetic effect. The Poisson’s ratio values of the three fabrics are inversely proportional to knit loop lengths. However, differences exist between the curves of Poisson’s ratio relative to strain. With regards to the rotational and double-headed arrow topological structures, the curves tend to be monotonic, whilst that of the foldable structure takes the form of a parabola. This research thus confirms the possibility of producing auxetic fabrics based on several geometrical structures using flat knitting technology

Smartphone-based low-cost microscope with monolithic focusing mechanism

Abstract Microscopy enables fast and effective diagnostics. However, its functionality is not accessible to everyone. Smartphone-based low-cost microscopes could be a powerful tool for diagnostics and educational purposes. Current smartphone-based microscopy approaches struggle with high cost, poor image quality and/or insufficient smartphone compatibility. In this paper, a very feasible and effective lowcost microscope is presented which addresses these issues. To minimize cost, a monolithic foldable structure is designed for production by injection molding. The design has a high order of functional integration, minimizing the number of components, while still enabling a micrometer focusing accuracy.