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Response to environmental thermomechanical inputs in applications that range from wearable electronics to aerospace structures necessitates agile communication systems driven by reconfigurable electromagnetic structures. Antennas in these systems must dynamically preserve acceptable radiation characteristics while enabling on-demand performance reconfiguration. However, existing reconfiguration mechanisms through stretchable conductors rely on high-strain behavior in soft substrates, which limits their applicability. Herein, this work demonstrates the use of mechanical metamaterials for stretchable conductors and dielectrics in antennas. Metamaterials allow conductor stretching up to 30% with substrate base material tensile moduli ranging from 26 MPa to 44 GPa. It is shown, through several antenna designs, that mechanical metamaterials enable similar frequency reduction upon stretching as monolithic conductors, while simultaneously providing a miniaturization effect. The conductor patterning, furthermore, provides control over coupling between mechanical stretching and electromagnetic reconfiguration. This approach enables designing reconfigurable antenna functionality through metamaterial geometry in response to arising needs in applications ranging from body-adapted electronics to space vehicles., Advanced Science, 10 (6), ISSN:2198-3844

Shape transformation offers the possibility of realizing devices whose 3D shape can be altered to adapt to different environments. Many applications would profit from reversible and actively controllable shape transformation together with a self-locking capability. Solutions that combine such properties are rare. Here, a novel class of meta-structures that can tackle this challenge is presented thanks to multi-stability. Results demonstrate that the multi-stability of the meta-structure is strictly tied to the use of highly anisotropic materials. The design rules that enable large-shape transformation, programmability, and self-locking are derived, and it is proven that the shapes can be actively controlled and harnessed to realize inchworm-inspired locomotion by strategically actuating the meta-structure. This study provides routes toward novel shape adaptive lightweight structures where a metamaterial-inspired assembly of anisotropic components leads to an unforeseen combination of properties, with potential applications in reconfigurable space structures, building facades, antennas, lenses, and soft robots.

In many applications, structures need to reversibly change between different 3D shapes to adapt to different environmental conditions or operational requirements. To date, the majority of reconfigurable structures require continuous actuation to hold a selected configuration. Multi-stable elements could potentially be used for shape reconfiguration because they can maintain different 3D shapes without needing a continuous power supply. However, when integrating multi-stable elements with other components, boundary conditions are negatively affecting the multi-stability. A new concept that combines flat fiber-reinforced polymer (FRP) composite shells with bi-axially pre-stretched membranes to realize highly multi-stable structures was recently presented by the authors. In this study, the concept of FRP metamaterials is adapted to realize a hinge that possesses five stable angular configurations. Thanks to the low influence of the boundary conditions on the multi-stability and the large shape change that the structure undergoes, the proposed hinge design demonstrates that FRP metamaterials enable the realization of highly reconfigurable structures. The hinge can achieve angular positions larger than 180° in both directions. Two parametric studies show that the angular positions of the hinge can be tailored by changing either the bending stiffness of the FRP composite shells or the pre-stretch of the membrane. A reconfigurable array of stiff panels connected by adaptive hinges is presented, showing potentials for the realization of a solar array that can change its shape to track the sun or be reversibly stowed and deployed.

Physical reconfiguration of spacecraft antennas promises to achieve on-demand performance while staying within the power constraints of space systems. Demonstrations thus far, however, have not resulted in structures compatible with the space environment as concepts have been either heavy, had low mechanical vibration frequencies, or could not be realized from space-qualified materials. This study proposes a novel physical reconfiguration concept based on stretchable mechanical metamaterials. The approach is validated through application to a frequency reconfigurable patch antenna. The antenna is realized from thin fiber reinforced polymer composites providing a dielectric support layer for a thin conductive film. Finite element simulations are used to select the metamaterial geometry and FRP layup to meet antenna requirements, in particular to maintain a Poisson's ratio of -1 over a large range of applied strains. Measurements of the prototype demonstrate a 19% frequency drop in response to a unixial tensile strain of 27.6%, comparable to theoretical predictions and competitive with the state-of-the-art. In addition, the antenna prototype is extremely lightweight, with an average density of only 0.15 g/cm3, shows stiff behaviour with a fundamental mechanical vibration frequency of 45.9 Hz, and is manufactured from space-appropriate materials.

Multi-stability in lightweight structures has been the subject of intensive research. This property is advantageous for the realization of shape adaptable structures because it allows, for example, maintaining different configurations of the structure without the presence of a continuous power supply. However, the integration of multi-stable components into complex structures is not widely implemented yet due to high coupling between the stable modes, suppression of stable modes due to the influence of boundary conditions, and complex fabrication techniques. In this work, a novel class of highly multi-stable periodic structures is presented. The investigation is first conducted on a single cell structure that possesses eight stable modes and, second, expanded to grid structures with periodicity. The multi-stability of the unit cell is preserved in the periodic structures and, in fact, the grid possesses further stable configurations not observed in the unit cell. Prototypes are fabricated by combining flat thin fiber-reinforced polymer (FRP) composite frames with bi-axially pre-stretched membranes. Therefore, the proposed approach enables the fabrication of highly multi-stable FRP grids without the need of a mold. Finite element analysis and experimental results show that the multi-stability property depends on the level of anisotropy of the laminate employed. Highly anisotropic laminates strengthen the multi-stability while isotropic ones suppress it. The realization of such highly anisotropic components with additive manufacturing techniques such as 3D-printing has been proved to be feasible, enlarging the range of materials suitable for the proposed concept. The presented technique is expected to be advantageous for the realization of highly reconfigurable, yet foldable, space habitats and antennas.

Dual-matrix composite structures with localized elastomer composite hinges have been proposed to enable packaging with much smaller fold radii than allowed by traditional resin-based fiber reinforced composites. Previous studies have been limited to proof-of-concept of folding capabilities and constitutive modeling of elastomer composites. A novel closed cross-section dual-matrix deployable hinge is studied here to develop the tools for studying the deployment of general dual-matrix structures. A set of tools for the analysis of deployment of this simple structure is developed: an analytic model that minimizes the strain energy in the folded configuration, experimental characterization, and finite element techniques using the LS-Dyna commercial software. The three models are used to predict the packaged shape and deployment moments, and are shown to be in good agreement amongst themselves. The analytic model is used to demonstrate control of the folded shape of the hinge using the stiffness of the elastomer composite. This behavior is verified using finite element models developed in the LS-Dyna commercial code. The simulations are used to predict the localized fold radius of the hinge within 3% and deployment moments within 5% by accounting for the microbuckled stiffness of the elastomer composite.

A novel methodology for the rapid preliminary design of deployable antennas for CubeSats is proposed in this article. It uses a graphical representation of antenna performance, consisting of a set of plots of different performance metrics against antenna geometry parameters. Coupled electromagnetic and structural design problems are addressed easily, enabling the rapid and direct comparison of different antenna concepts. This approach is demonstrated for a case study at ultrahigh frequency (UHF), comparing the performance of a dipole, a helix, a conical horn, and a conical log spiral (CLS), all based on dual-matrix composite deployable structures. The initial design space of antenna geometries is reduced by two orders of magnitude to a set of constraintsatisfying designs. A graphical user interface implementing the approach is presented, and the accuracy of the method is briefly addressed.

Thin fiber reinforced polymer (FRP) composites are widely implemented in adaptive and morphing structures. However, realization of the necessary complex 3‐dimensional FRP structures requires the use of expensive molds thereby limiting the design space and flexibility. Using the elastic strain energy of pre‐stretched membranes holds potential for addressing this challenge. In this work, a novel manufacturing technique for fabricating 3‐dimensional FRP structures moldlessly is presented where pre‐stretched membranes are used to drive out‐of‐plane buckling instabilities of FRP composite shells. To explore the potential of this approach, a simple square frame design is investigated. An analytical model based on high deformation beam buckling theory is developed for understanding the parameters driving the out‐of‐plane behavior of these structures. Experimental and finite element results are used for model validation and reveal excellent agreement, with errors less than 10% over a large portion of the design space. Analytical and finite element models demonstrate that the out‐of‐plane deformation can be tailored by varying the structure’s geometric and material parameters. A new design space for FRP composite laminates is characterized, enabling highly flexible design. The manufacturing and modeling techniques can be extended to other geometries for the realization and analysis of arbitrarily complex surfaces., Composite Structures, 268, ISSN:0263-8223, ISSN:1879-1085

The design process and the deployment mechanism of a quadrifilar helix antenna (QHA) and a conical log spiral antenna (CLSA) are presented. The two antennas are proposed to operate in the UHF frequency band. They are composed of conductors that are embedded and supported by innovative structural techniques. This allows efficient folding, packaging, and deployment once in space. The conductors in the QHA are composed of beryllium copper and are supported by helical arms of $S_{2}$ glass fiber reinforced epoxy. The CLSA, on the other hand, has conductors that are made out of a mesh of phosphor bronze and incorporated inside thin insulators composed of continuous fiber composites. The new aspects of these designs lie in their structures and deployment mechanisms. The deployment mechanisms for both antennas include helical pantograph and origami patterns such as Z-folding configurations. Both antennas are fabricated and tested for both deployment and radiation performance. A comparison is executed between both designs, and their potential deployment possibilities from CubeSats are also investigated.

Despite major advances in morphing wing technology, morphing skins as a structural part of an adaptive aerospace system are still in their early development phase due to heavily contradicting requirements, such as highly anisotropic mechanical behaviour, air-tightness and lightness. Usually, airtightness in structural morphing skins is achieved with elastomeric covers which show poor mechanical performance and high weight. A novel design for an elastomer-free morphing skin unit cell is introduced and analysed in this work. A foldable unit cell is manufactured fully from lightweight engineering materials, based on hinge-like carbon fibre reinforced polymer ligaments. The latter reversibly fold a supported mid-section in order to generate large in-plane displacements with low actuation forces, while preserving a smooth surface in both states. The geometric parameters of the unit and the ligament design itself determine the mechanical response of the system. Within the design space of the unit cell, extreme global strains up to 100% and highly anisotropic mechanical behaviour is achieved, where resistance against aerodynamic loads exceeds the in-plane actuation force by a factor of 3.64. When used periodically, the novel unit cell is a promising base for a functional morphing skin system involving large displacements., Composite Structures, 254, ISSN:0263-8223, ISSN:1879-1085

Mechanical metamaterials undergoing extreme deformations span an ever-increasing design space of mechanical performance. However, achieving selective deformability in load-carrying metamaterials remains unexplored. Anisotropic thin fiber-reinforced composite shells, which are soft in bending and stiff axially, present an attractive option for addressing this challenge but are difficult to realize in practice due to fabrication complexity. In this work, an integrated fabrication technique enabling single-step curing of complex composite mechanical metamaterials is proposed. By using 3D-printed tooling and silicone spacers, composite assemblies can be cured in an autoclave without the need for post-cure bonding of individual shells. The technique reduces manufacturing times and eliminates adhesive bonds, which add mass to the structure and can be points of failure. The proposed technique is demonstrated on a modified rotating square auxetic metamaterial geometry, with fabricated prototypes withstanding up to 60% global tensile strains elastically. The composite anisotropy is, moreover, used to control the deformation mechanism in the metamaterial, thereby delaying failure of the structure and allowing tunability of elastic properties. This work sets the stage for the use of composites as a means of expanding the design space achieved by mechanical metamaterials for shape adaptation in lightweight, load-carrying applications., Composite Structures, 246, ISSN:0263-8223, ISSN:1879-1085

The advent of CubeSats has revolutionized the space research industry. The small physical size and constraints owing to outer space applications present significant challenges for antenna engineers to come up with innovative solutions. This paper presents a novel wide band antenna high gain antenna which is capable of deploying from a CubeSat platform.

This paper discusses the design of a new conical log spiral antenna that can operate at UHF frequencies. The antenna constitutes a suitable candidate for deployment on top of a 6U CubeSat system. The conical log spiral is designed to operate between 300 MHz and 600 MHz and exhibit circular polarization as well as an acceptable gain. The antenna is also required to satisfy size constraints by being compactly folded during launch and deployed successfully once in orbit.

A dual-matrix composite boom is proposed as a way of realizing a deployable closed cross-section boom that is stiff, lightweight, and can be packaged in small volumes. Little work exists studying the folding and deployment behavior of closed cross-section boom made of composite shells and this paper addresses this by investigating the behavior for two closed cross-section designs. Experimental techniques for measuring the folded shape of curved shells undergoing large deformations is presented. Furthermore, experimental measurements of the moment-rotation response of the two booms are discussed. A study using commercially available finite element software yields simulation techniques for successfully predicting the folded shape of closed-cross section booms. The drawbacks of the software when predicting the moment-rotation response are addressed. The application of these techniques for the chosen designs demonstrate that dual-matrix booms are a promising alternative to existing composite deployable booms.