This work describes the design, manufacturing and testing of a deployable antenna for deep-space missions based on a hybrid honeycomb truss made of shape memory alloy (SMA). The deployable characteristics are enhanced by the equivalent auxetic (negative Poisson’s ratio) behaviour of the cellular configuration. Specific emphasis is placed on the modal analysis techniques used to test the lightweight SMA structure.

Abstract. We describe the production development and experimental tests related to an hybrid honeycomb-truss made of shape memory alloy (Ni48Ti46Cu6), and used as a demonstrator for a deployable antenna in deep-space missions. Specific emphasis is placed on the modal analysis techniques used to test the lightweight SMA structure.. Background on SMA cellular structuresShape memory alloy (SMA) can be considered amongst the most successful smart materials to date in terms of spread of applications, and relative maturity of the technology. We do not aim in this work to provide an extensive review on the SMA field, however the interested reader can look for reference [1] for a detailed introduction on the subject. However, SMA honeycombs constitute a more recent development, being proposed by some of the Authors for the first time in 2004 at the SPIE Smart Materials and Structure Conference in San Diego, CA. Hassan, Scarpa and Mohammed [2] developed a OX (overexpanded) hexagonal honeycomb cold moulding some 1-way SMA ribbons, and gluing the hexagonal shapes obtained with a high temperature epoxy-based polymer. Almost at the same time, Shaw et al at the University of Michigan developed a patented assembling technique based on welding niobium rods, which allows producing small cellular samples with high manufacturing fidelity (i.e., low dimensional and precision tolerances) [3]. Prototypes of SMA honeycombs made with a similar welding techniques have been also manufactured and sandwich within composite face skins at the University of Tokyo. The sandwich panels subjected to low kinetic energy impacts and subsequent heating from martensite to austenite phase showed one of the main features for which SMA cellular structures have been developed -the capability of absorbing energy, and restoring (in a significant percentage) the original shape after impact [4]. Another interesting feature of SMA based honeycombs is also their intrinsic high hysteretic damping, 2-3 orders of magnitude higher than the commercial aluminium or steel-based honeycombs used in high end aerospace applications subjected to high cyclic fatigue loading or broadband vibration input [5].The cellular structures considered so far have a centresymmetric topology -I.e., two perpendicular axis of symmetry. However, it is possible also to adopt a rotational-type of symmetry, which provides a combined in-plane rotation and translational deformation when subjected to inplane uniaxial loading, and feature also a negative Poisson's ratio behaviour. This structure, called hexagonal chiral topology, has been proposed as load-bearing concept by Prall and Lakes in 1996 [6], although the idea of negative Poisson's ratio in chiral-related structures was first devised by Wojciechowski for molecular assemblies [7]. The Poisson's ratio of this cellular structure is close to

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