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![Quasi-optical setup utilizing a Rexolite lens to focus the Gaussian beam pattern of a horn antenna on to the metasurface under test to achieve planar wave illumination, which is used for characterization of the metasurface specular reflections.
Obtained from Ref. [60].](publication/324578495/figure/fig10/AS:11431281120785805@1676641115180/Quasi-optical-setup-utilizing-a-Rexolite-lens-to-focus-the-Gaussian-beam-pattern-of-a.jpg)
Quasi-optical setup utilizing a Rexolite lens to focus the Gaussian beam pattern of a horn antenna on to the metasurface under test to achieve planar wave illumination, which is used for characterization of the metasurface specular reflections. Obtained from Ref. [60].
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In this article, the basic principles and the main applications of Huygens’ metasurfaces (HMSs) are reviewed from microwaves to optics. In general, HMSs comprise a thin layer of orthogonal electric and magnetic dipoles, which form an array of Huygens’ sources. In a refraction setting, these sources radiate mostly in the forward direction and can be...
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We studied the effect of dielectric heating on the enhancement of freeze-drying by electromagnetic waves (EMWs) under different frequencies: 2.45 GHz microwaves (MWs), and 27 and 200 MHz radio frequencies (RFs). The irradiation with RFs, particularly at 27 MHz, reduced the duration of freeze-drying by 67%. We further analysed the water structure by...
Citations
... Active metasurfaces, which integrate components like varactors, and Huygens' metasurfaces-a novel concept employed to reshape EM radiation into a desired form while maintaining an extremely thin profile-may also serve as promising candidates for biomedical applications. [91,92]. Additionally, the inverse design approaches are emerging as the way forward both in metamaterial design and implementation, where physically unintuitive designs can deliver enhanced functionalities. ...
This mini-review examines the most prominent features and usages of metamaterials, such as metamaterial-based and metamaterial-inspired RF components used for biomedical applications. Emphasis is given to applications on sensing and imaging systems, wearable and implantable antennas for telemetry, and metamaterials used as flexible absorbers for protection against extreme electromagnetic (EM) radiation. A short discussion and trends on the metamaterial composition, implementation, and phantom preparation are presented. This review seeks to compile the state-of-the-art biomedical systems that utilize metamaterial concepts for enhancing their performance in some form or another. The goal is to highlight the diverse applications of metamaterials and demonstrate how different metamaterial techniques impact EM biomedical applications from RF to THz frequency range. Insights and open problems are discussed, illuminating the prototyping process.
... The unidirectional property of the Huygens source has been extensively studied, and passive and active Huygens sources find applications in various fields. Passive Huygens sources are used to attain flexible control of coupling direction to achieve directionality modulation 5-7 ; Huygens metasurfaces are proposed to achieve flexible modulation of electromagnetic waves with high efficiency [8][9][10][11] . In the field of antennas, the magnetoelectric (ME) dipole 12,13 and the electrically small Huygens source antennas 14,15 use a combination of electric and magnetic dipoles to construct high gain antennas leveraging the far-field directionality of Huygens source. ...
Electric dipoles and magnetic dipoles are the most fundamental particles in electromagnetic theory. Huygens and Janus sources, formed by the orthogonal combination of electric and magnetic dipoles, both show good directionality in the near field. Although the Huygens source has been widely used in antennas and metasurfaces, the applications of Janus source are heretofore limited. In this paper we report the physical construction of an active Janus source. Through full-wave simulations within the parallel plate waveguide (PPW) environment, we show that our source achieves the directional electromagnetic near-field and quasi-isotropic far-field requisite of the Janus source. Using this fact, we demonstrate that two active Janus and Huygens sources in close proximity (about 0.10 to 0.25 wavelengths) achieve a near 1000-fold reduced mutual coupling compared to electric dipole sources. Particularly, the simultaneous achievement of strong mutual coupling suppression and quasi-isotropic radiation make the Janus source an ideal candidate for consideration in future compact multi-input multi-output (MIMO) communication systems.
... The management of this superposition creates the required dephasing in the scattered light. 15,16 High-contrast metasurfaces use engineered high-refractive index materials that act as truncated waveguides that induce a dephasing dependent on their geometry. 17,18 Independently on the approach chosen, these methods typically necessitate the incorporation of multiple materials, to create the required response of the meta-atoms, e.g., to make high dielectric nanopillars on a low refractive substrate, or to create plasmonic effects on metallic layers deposited on dielectric features. ...
Photonic metasurfaces are typically realized by the periodic distribution of meta-atoms, which incorporate two or more different materials. This requirement introduces constraints in the design and fabrication that are particularly significant for flexible and conformable metasurfaces. Here, we report on the design and fabrication of efficient, polarization-independent, all-polymeric metasurface membranes for holographic applications in the visible range. These results will facilitate the large-scale production of holographic metasurfaces, advancing their adoption in practical, real-life scenarios.
... Due to the exotic EM response of the metasurfaces, many promising applications have been developed, including polarization control [6], manipulation of beam shift [7,8], analog computing [9], to mention a few. In recent years, Huygens' metasurfaces (HMSs) have offered a promising approach for exquisitely controlling the EM waves in a reflectionless manner [10][11][12][13]. In general, HMSs are made up of co-located orthogonal electric and magnetic dipoles known as Huygens' sources, which manipulate wavefronts utilizing Schelkunoff's equivalence principle [14]-a rigorous formulation of the classical Huygens' principle. ...
Huygens’ metasurfaces – fundamentally based on Schelkunoff ’s equivalence principle, Huygens’ metasurfaces consist of a two-dimensional array of Huygens’ sources formed by co-located orthogonal electric and magnetic dipoles. Such metasurfaces provide electric and magnetic responses to an incoming electromagnetic (EM) wave, leading to unidirectional scattering and 2π phase coverage. We herein report a near-reflectionless coarsely discretized dielectric Huygens’ metasurface that performs anomalous refraction, offering a low-loss platform for wave manipulation at high frequencies as compared to their lossy metallic analogue. The coarse discretization dramatically simplifies the design, resulting in a metasurface that is highly efficient, cost-effective and robust. In this paper, the proposed metasurface comprises two metaatoms per period, and is hence named the bipartite dielectric Huygens’ metasurface. Through full-wave simulations at 28 GHz, we show that the proposed metasurface can reroute an incident EM wave from θ i = 15 o to θ t = −44.5 o with a very high efficiency: 87% of the scattered power is anomalously transmitted to θ t . Based on our observations, a coarsely discretized dielectric Huygens’ metasurface platform can be efficacious to design meta-devices with multifaceted functionalities in different frequency regimes.
... Metamaterials and their two-dimensional (2D) analogue, metasurfaces, provide access to exotic EM properties, not found in natural materials, which is achieved by properly engineering their subwavelength elementary building blocks, i.e., the so-called meta-atoms. Due to the meta-atoms' architecture the local currents excited by an impinging EM wave are engineered, thus offering the possibility of unconventional EM wave control, which leads to a variety of applications in the vast EM spectrum, from sensing, shielding, energy harvesting, to wave-front shaping and beam steering [1][2][3]. The integration of tunable and active materials enables even more advanced EM functionalities and external control. ...
We present a CMOS-compatible silicon-based patch antenna providing a tunable dual-band behavior in the 8–12 GHz frequency range. The dual-band operation is induced by an asymmetrically aligned complementary split-ring resonator (CSRR) meta-atom, etched in the metallic, back-reflector part of the antenna. By rotating and moving the CSSR we can force a multimode response in the antenna cavity, which leads to the excitation of two highly radiating modes at 8 and at 10.35 GHz. The tunability is provided by the inclusion of a planar phase shifter based on an ultrathin hafnium oxide ferroelectric layer interposed between the silicon substrate and the top metallization, thus allowing us to electrically modify the radiation characteristics of the antenna in terms of resonant frequency, amplitude of the reflection coefficient, and gain, with sub-μs values of the polarization switching time. The results are supported by theoretical modeling, full-wave electromagnetic simulations, fabrication, and experimental validation and represent a stimulus for the integration of metamaterials and two-dimensional ferroelectrics into high-frequency electronics.
... In order for the transmittance to approach unity and to have a large enough phase span, we tune the radii of the holes (r hole : 1.113 mm) and the patches (r patch : 1.094 mm), respectively. Consequently, one pair of TE-like degenerate resonances overlap with another pair of TM-like resonances in the spectrum, leading to a high copolarized transmittance [48][49][50]. Detailed discussions about enhancing the transmittance by overlapping degenerate resonances can be found in Appendixes B and C. As shown in the left panel of Fig. 2(b), the measured transmittance is high near k k ¼ 0 (in about the 10 degrees range) over a moderate spectral range. ...
Imaging is of great importance in everyday life and various fields of science and technology. Conventional imaging is achieved by bending light rays originating from an object with a lens. Such ray bending requires space-variant structures, inevitably introducing a geometric center to the lens. To overcome the limitations arising from the conventional imaging mechanism, we consider imaging elements that employ a different mechanism, which we call reciprocal lenses. This type of imaging element relies on lateral ray shifting, enabled by momentum-space-variant phase modulations in periodic structures. As such, it has the distinct advantage of not requiring alignment with a geometric center. Moreover, upright real images can be produced directly with a single reciprocal lens as the directions of rays are not changed. We realize an ultrathin reciprocal lens based on a photonic crystal slab. We characterize the lateral ray shifting behavior of the reciprocal lens and demonstrate imaging. Our work gives an alternative mechanism for imaging and provides a new way to modulate electromagnetic waves.
... The rapid development of metasurfaces [17], [18], [19], [20], [21] has enabled unprecedented manipulations on coefficient [22], [23], phase [24], [25], [26], and the polarization of reflected and transmitted EM waves [27], [28], [29], [30]. Among them, metasurfaces based on the equivalent circuit model [31], Huygens' principle [32], [33], interference cancellation mechanism [34], [35], universal impedance matching [36], and anisotropic metasurfaces [37], [38] were proposed to enhance transmission. Nevertheless, these metasurfaces also suffer from complex structures, narrow bandwidth, or narrow angular range. ...
... The rapid development of metasurfaces [17], [18], [19], [20], [21] has enabled unprecedented manipulations on coefficient [22], [23], phase [24], [25], [26], and the polarization of reflected and transmitted EM waves [27], [28], [29], [30]. Among them, metasurfaces based on the equivalent circuit model [31], Huygens' principle [32], [33], interference cancellation mechanism [34], [35], universal impedance matching [36], and anisotropic metasurfaces [37], [38] were proposed to enhance transmission. Nevertheless, these metasurfaces also suffer from complex structures, narrow bandwidth, or narrow angular range. ...
As protective apparatus, electromagnetic windows (EMWs) are usually realized utilizing dielectric materials with higher permittivity or larger thickness to perform good mechanical properties. However, due to impedance mismatch, higher insertion loss is inevitably created, especially at large incident angles. It is now still a great challenge to engineer EMWs with stable operating bands and a wide range of incident angles for both transverse electric (TE)-and transverse magnetic (TM)-polarizations. In this article, we propose a method to achieve such EMWs by the synergy of multimechanism resonances, which enables broadband transmissions of both TM-and TE-polarized waves in an ultrawide range of incident angles. Fano resonance is first introduced to expand the bandwidth for TE-polarization on the basis of thickness resonance. Drude resonances are then introduced to suppress adverse influences of the parasitic Lorentz resonance for TM-polarization, to maximize the shared transmission band for TM-and TE-polarizations. The ultrawide-angle broadband functionalities of this EMW are validated by experiments, which agree well with numerical simulations. This work provides an efficient route to realize practical high-performance EMWs, under sufficient consideration of available materials, structures, and fabrication techniques, which may find wide applications in radar, communication, and imaging systems.
... The metasurface is an artificial planar structure composed of meta-atoms with unique electromagnetic properties and works effectively in manipulating wavefronts. Therefore, metasurface finds broad applications from microwaves to the optics [1][2][3][4][5][6][7], including anomalous reflection and refraction [1][2][3], beam generation [4,5] and multifunctional optical devices [6,7]. Among various kinds of metasurfaces, the metalenses specifically are designed for focusing and imaging systems, as they can flexibly control the amplitude, phase, and polarization of the incident light beams [8][9][10]. ...
... The metasurface is an artificial planar structure composed of meta-atoms with unique electromagnetic properties and works effectively in manipulating wavefronts. Therefore, metasurface finds broad applications from microwaves to the optics [1][2][3][4][5][6][7], including anomalous reflection and refraction [1][2][3], beam generation [4,5] and multifunctional optical devices [6,7]. Among various kinds of metasurfaces, the metalenses specifically are designed for focusing and imaging systems, as they can flexibly control the amplitude, phase, and polarization of the incident light beams [8][9][10]. ...
... where 0 is the wave impedance of free space. When Re{Y} = Re{Z} = 0 and Im{Y} = Im{Z}, Eq. (2) requires that the surface is reflectionless (r = 0) and a broad transmission phase variation with respect to frequency can be realized [3,30]. Based on the reflectionless property of the HMS, many interesting and efficient metadevices have been demonstrated for beam steering [36][37][38], beam generating [39], and beam focusing [22,23]. ...
Achromatic lenses, which have the same focal length regardless of the illumination frequency, find strong applications in imaging, sensing, and communication systems. Making achromatic lenses with metasurfaces is highly desirable because they are flat, ultrathin, relatively light, and easily fabricable. However, existing metalenses experience combinations of limitations which include single polarization operation, narrow bandwidth, and small numerical aperture (NA). In this work, we propose a dual polarized, broadband and high NA achromatic metalens based on the Huygens’ metasurface. We use Huygens’ metasurface unit cells with three tunable resonances to realize a stable group delay over a large bandwidth, while also achieving high transparency and large phase tunability. With these cells, we construct a dual-polarized achromatic Huygens’ metalens with an NA of 0.64 that works from 22 to 26 GHz. Our achromatic metalens achieves diffraction-limited focusing with 2 % maximum focal length deviation and 70 % average focusing efficiency over a bandwidth of 16.7 %. Most key performance metrics for this lens surpass or are comparable with the best of previous metalenses. An achromatic metalens simultaneously achieving broad bandwidth, large NA, and polarization-independent operation will open wide-ranging opportunities for microwave and mm-wave imaging and communication applications.
... The other is based on multilayer surface unit structures [143], where the relationship between the discontinuous fields on the two sides of the MTS is often decomposed into a cascaded form, as discussed in [144], [145], and [146]. Recently, the design, transmitted wave manipulation, and radiated wave control of Huygens ′ MTSs have been widely investigated and reported [147], [148], [149], [150], [151], [152], [153], [154], [155]. When applied to lens design, Huygens ′ metalens is used to enhance the radiation performance [156], mechanically reconfigure the beam direction and polarization [157], [158], and electrically reconfigure lenses on the order of µs [159]. ...
Recently, there has been growing interest in the use of metamaterial (MTM)-based lenses, also known as metalenses, as innovative antenna technology. Increasingly widespread applications of metalenses in modern microwave communication and sensing systems have been found, following the development of the first microwave artificial lens in the 1940s based on the concept of an artificial dielectric, which was later broadly termed an “MTM.” This article examines the evolution of metalens antennas over the past 80 years and introduces the principles and technologies underlying their design. It then focuses on the latest progress in the research on and applications of MTMs and metasurface (MTS)-based metalens antennas. The principles and basic structures of transmissive focusing metalens antennas in the microwave band are elaborated. Selected metalens antennas are introduced chronologically, starting with metallic waveguide lens antennas, followed by metallic or metal–dielectric Fresnel zone plate lens antennas, transmitarray lens antennas, MTS lens antennas, and flat transformation-optics-based MTM Luneburg lens antennas. The technical merits, challenges, applications, trends, and future research of each type of metalens antenna are also addressed. The information presented in this article will benefit the research, development, and application of metalens antennas in fifth-and beyond-generation communications, Wi-Fi 6 short-range connections, and next-generation microwave sensing and imaging systems.
