flexible electronics have demonstrated extreme bendability. [21,22] Even so, wrinkles and folds are inevitable when wrapping flexible sheets on 3D surfaces with two nonzero principal curvatures. A recently developed curved image array demonstrated that selectively cutting the flexible sheet can effectively reduce folding and wrinkling when conforming it to a 3D surface. [23] On the other hand, stretchable electronics enabled by stretchable serpentine interconnects, [24,25] liquid metal, [26] nanomeshes [27] and nanoscrolls, [28] or intrinsically stretchable conductive and semiconducting polymers [29][30][31][32] are able to not only bend but also expand inplane, hence capable of conforming to 3D surfaces such as spherical domes. But so far, there are limited studies on the conforming process, especially when the target object has a complex 3D surface. Except for conforming planar electronics to 3D surfaces, direct printing of electrical components on 3D surfaces has been demonstrated. [33] However, only limited materials such as conductive inks and devices such as 3D antenna can be printed so far. As a result, simple but versatile transferring techniques are in need for conformable electronics.Water transfer printing (WTP) technology, also known as hydrographic printing, is commonly used to transfer planar graphics to 3D surfaces. [34] The process begins by printing graphics on a water-soluble substrate, which is then placed on water surface. As the substrate gets dissolved by water, the ultrathin graphics layer stays floating on water. A solid Perfectly wrapping planar electronics to complex 3D surfaces represents a major challenge in the manufacture of conformable electronics. Intuitively, thinner electronics are easier to conform to curved surfaces but they usually require a supporting substrate for handling. The water transfer printing (WTP) technology utilizes water surface tension to keep ultrathin electronics floating flat without supporting substrate, enabling their conformal transfer on 3D surfaces through a dipping process. In many cases, however, the size of the microfabricated electronics is much smaller than the target 3D surface. This work proposes that such mismatch in size can be overcome by leveraging stretchable electronics in WTP. Stretchable electronics are compliant to inplane stretch induced by water surface tension, hence can first self-expand in water and then be transferred onto 3D objects. Uniaxial and biaxial expansion ranging from 41% to 166% has been achieved without any externally applied tension. The results demonstrate that expansion-enhanced WTP is a promising fabrication process for conformable electronics on large 3D surfaces.
Shaped continuous parallel plate waveguide delay lenses are proposed in this paper. The previous configurations introduced by the authors displayed a residual side lobe imbalance, showing the limitations of elliptical delay lens profiles, derived from a starting bifocal constrained lens. Polynomial profiles are proposed here as a way to enhance the scanning performance and the pattern shape. Optimized configurations demonstrate a reduction of the phase aberration levels over a large scanning range ([-30°, 30°]). The associated radiation patterns demonstrate lower and more balanced first side lobe levels (≅-18 dB), as compared to the previous elliptical approach (≅-13.2 dB). A validation has been proposed through the manufacturing and test of a prototype over the down-link Ka band ([27.5-31] GHz). Excellent radiation performance (HPBW, SLL) has been obtained experimentally over a wide angular range ([-31.5°, 31.5°]), including low scanning loss and high radiation stability over the entire frequency range. High radiation efficiencies are demonstrated with this fully metallic design, particularly suitable for space applications. The mechanical simplicity offered by the concept is also quite attractive for low-cost multi-beam platforms.
Modulated metasurfaces (MTSs) have sprung up in the last decade as an attractive solution for wave guidance and radiation. More precisely, modulated MTS antennas stand out for providing an unprecedented control of the aperture fields with low-profile and lightweight structures. In this class of antennas, a surface-wave (SW) is gradually radiated, owing to its interaction with a modulated impedance boundary condition (IBC). This IBC is typically implemented in the microwave regime by several thousands of sub-wavelength patches printed on a grounded slab. However, dielectric losses may hinder the use of standard printed circuit board (PCB) technology at higher frequencies. In this paper, we will address this issue by introducing a new class of metal-only modulated MTS, which can be easily fabricated by additive manufacturing or micro-machining for millimeter-wave and sub-THz applications.
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