Multifunctional composite structures (MFCS) have become an increasingly important field of research with the large-scale adoption of composite materials in many industrial sectors such as aerospace, automotive, sport and recreation equipment (bikes, scooters, etc.) and maritime. It is a diverse field which includes scientific areas in electromagnetics, electronics, material sciences, structures and structural augmentation, sensors, and thermal management. The paper investigates Conformal Load-bearing Smart Skins (CLSS) as a part of multifunctional composite structures specifically related to aerospace applications and focuses on the seamless incorporation and synergistic coexistence between electronic devices and composite materials. Current trends in materials and manufacturing processes, as well as measurement techniques used to validate both the electromagnetic and structural responses have been explored and discussed. Furthermore, it identifies some of the challenges and complexities associated with CLSS and explores future areas of research which still need to be addressed.

A conformal metasurface antenna exhibiting a pencil beam radiation pattern at 10.0 GHz has been designed using the Voronoi partition approach, and fabricated on the Kahu Uninhabited Aerial System (UAS) fuselage. Two manufacturing methods are presented and compared. The first approach utilized a 3-axis Trotec fiber laser to etch the flattened metasurface geometry in copper foil. The etched pattern was then ‘stretched’ over the UAS geometry. The second approach utilized a 6-axis nScrypt (retrofitted with an IDS aerosol jetting tool) to conformally print the metasurface pattern directly on the UAS fuselage. An electroless copper plating step was then utilized to improve the radiofrequency (RF) conductivity of the printed silver. Both manufacturing methods yielded functional metasurface antennas with equivalent performance at the operating frequency. However, the first method is limited to geometries that can be ‘flattened’ with acceptable tolerances, whereas the second approach is amenable to all practical geometries. This demonstration of two manufacturing techniques is a critical step forward in the cost-effective deployment of truly conformal metasurface antennas on realistic geometries.

This work presents a comparison between two metasurface antennas operating at 10.0 GHz utilizing either a conventional hexagonal grid (with a continuous distribution of gap dimensions) or a Voronoi partition (utilizing a constant gap dimension). The Voronoi partition was generated using the point-shifting method (proposed by Lee and Sievenpiper) and is (to the authors’ knowledge) the first demonstration of this approach in the design of a radiating metasurface antenna. The traditional Hexagonal Artificial Impedance Surface (H-AIS) and Voronoi Artificial Impedance Surface (V-AIS) antennas are shown to exhibit near identical surface impedance profiles, insertion loss, radiation efficiency and realized gain. However, the Voronoi partition can be adapted to follow an arbitrary conformal surface, whereas the hexagonal grid is restricted to a two-dimensional plane. To reinforce this advantage, a third metasurface antenna on an arbitrary conformal geometry is designed utilizing numerically generated ‘reference’ and ‘objective’ fields. Lastly, the fabrication of all three antennas utilized a unique process that is compatible with conventional aerospace glass fiber reinforced composite manufacturing. Hence, this work represents a significant step forward in the deployment of truly conformal multifunctional composite structures.

Vanadium dioxide (VO₂) has been identified as a material capable of transitioning from an insulator to a metal close to room temperature. Previous works have demonstrated potential applications of this material in various microwave components or devices. However, the complex permittivity and permeability characterization of the VO₂ over X-band has not been previously reported. Knowledge of these properties is essential for accurate modeling of the components and devices utilizing VO₂. This paper characterizes a VO₂ film deposited on a quartz substrate in a WR90 waveguide using a vector network analyzer. The S-parameters, conductivity, relative complex permittivity, and permeability of the VO₂ film are determined across the transition temperature.

This article presents a fabrication method for a $C$ -band, low-power, frequency-modulated continuous wave (FMCW) radar front–end technology demonstrator that is fully embedded in a representative aerospace composite structure. This demonstrator uses a structural glass-fiber-reinforced polymer laminate as both the mechanical load-bearing element and the multilayer substrate for the integrated microwave circuitry. The system design and optimization have been described in detail. The electromagnetic simulation of the technology demonstrator was shown to be in excellent agreement with the measurement results. Finally, the FMCW radar front-end was tested as a complete system and shown to yield correct distance-to-target estimations. The demonstrated integration technique will lead to smart skins where electronic circuits and complete systems are embedded in load-bearing composite structures to yield truly multifunctional capabilities.