No Arabic abstract
Antenna technology is at the basis of ubiquitous wireless communication systems and sensors. Radiation is typically sustained by conduction currents flowing around resonant metallic objects that are optimized to enhance efficiency and bandwidth. However, resonant conductors are prone to large scattering of impinging waves, leading to challenges in crowded antenna environments due to blockage and distortion. Metasurface cloaks have been explored in the quest of addressing this challenge by reducing antenna scattering, but with limited performance in terms of bandwidth, footprint and overall scattering reduction. Here we introduce a different route towards radio-transparent antennas, in which the cloak itself acts as the radiating element, drastically reducing the overall footprint while enhancing scattering suppression and bandwidth, without sacrificing other relevant radiation metrics compared to conventional antennas. This technique offers a new application of cloaking technology, with promising features for crowded wireless communication platforms and noninvasive sensing.
In this paper, a novel concept of a leaky-wave antenna is proposed, based on the use of Huygens metasurfaces. It consists of a parallel-plate waveguide in which the top plate is replaced by a bianisotropic metasurface of the Omega type. It is shown that there is an exact solution to transform the guided mode into a leaky-mode with arbitrary control of the constant leakage factor and the pointing direction. Although the solution turns out to be periodic, only one Floquet mode is excited and radiates, even for electrically long periods. Thanks to the intrinsic spurious Floquet mode suppression, broadside radiation can be achieved without any degradation. Simulations with idealized reactance sheets verify the concept. Moreover, physical structures compatible with PCB fabrication have been proposed and designed, considering aspects such as the effect of losses. Finally, experimental results of two prototypes are presented and discussed.
We propose the design and measurement of an acoustic metasurface retroreflector that works at three discrete incident angles. An impedance model is developed such that for acoustic waves impinging at -60 degrees, the reflected wave is defined by the surface impedance of the metasurface, which is realized by a periodic grating. At 0 and 60 degrees, the retroreflection condition can be fulfilled by the diffraction of the surface. The thickness of the metasurface is about half of the operating wavelength and the retroreflector functions without parasitic diffraction associated with conventional gradient-index metasurfaces. Such highly efficient and compact retroreflectors open up possibilities in metamaterial-based acoustic sensing and communications.
The model of ideal fluid flow around a cylindrical obstacle exhibits a long-established physical picture where originally straight streamlines will be deflected over the whole space by the obstacle. As inspired by transformation optics and metamaterials, recent theories have proposed the concept of fluid cloaking able to recover the straight streamlines as if the obstacle does not exist. However, such a cloak, similar to all previous transformation-optics-based devices, relies on complex metamaterials, being difficult to implement. Here we deploy the theory of scattering cancellation and report on the experimental realization of a fluid-flow cloak without metamaterials. This cloak is realized by engineering the geometry of the fluid channel, which effectively cancels the dipole-like scattering of the obstacle. The cloaking effect is demonstrated via direct observation of the recovered straight streamlines in the fluid flow with injected dyes. Our work sheds new light on conventional fluid control and may find applications in microfluidic devices.
Smartwatch is a potential candidate for the Internet of Things (IoT) hub. However, the performance of smartwatch antennas is severely restricted by the smartwatch structure, especially when the antennas are designed by traditional methods. For adapting smartwatches to the role of IoT hub, a novel method of designing multi-band smartwatch antenna is presented in this paper, aiming at increasing the number of frequency bands, omni-directivity, and structural suitability. Firstly, the fundamental structure (including the full screen and the system PCB) of the smartwatch is analyzed as a whole by characteristic mode analysis (CMA). Thus, abundant resources of characteristic modes are introduced. The fundamental structure is then modified as the radiator of a multi-band antenna. Then, a non-radiating capacitive coupling element (CCE) excites the desired four 0.5-wavelength modes from this structure. This method could fully utilize the intrinsic modes of the smartwatch structure itself, thus exhibits multiple advantages: significantly small size, smaller ground, omni-directional radiation, and fitting to the full-screen smartwatch structure.
Total internal reflection fluorescence microscopy (TIRF) has enabled low-background, live-cell friendly imaging of cell surfaces and other thin samples thanks to the shallow penetration of the evanescent light field into the sample. The implementation of TIRF on optical waveguide chips (c-TIRF) has overcome historical limitations on the magnification and field of view (FOV) compared to lens-based TIRF, and further allows the light to be guided in complicated patterns that can be used for advanced imaging techniques or selective stimulation of the sample. However, the opacity of the chips themselves has thus far precluded their use on inverted microscopes and complicated sample preparation and handling. In this work, we introduce a new platform for c-TIRF imaging based on a transparent substrate, which is fully compatible with sample handling and imaging procedures commonly used with a standard #1.5 glass coverslip, and is fabricated using standard complementary metal-oxide-semiconductor (CMOS) techniques, which can easily be scaled up for mass production. We demonstrate its performance on synthetic and biological samples using both upright and inverted microscopes, and show how it can be extended to super-resolution applications, achieving a resolution of 116 nm using super resolution radial fluctuations (SRRF). These new chips retain the scalable FOV of opaque chip-based TIRF and the high axial resolution of TIRF, and have the versatility to be used with many different objective lenses, microscopy methods, and handling techniques. We thus see c-TIRF as a technology primed for widespread adoption, increasing both TIRFs accessibility to users and the range of applications that can benefit from it.