Experimental demonstration of broadband impedance matching using coupled electromagnetic resonators.

Impedance matching is an important factor for the electromagnetic resonators used to construct metasurfaces with perfect absorption and transmission properties. However, these resonators usually exhibit narrowband characteristics, thus greatly restricting their potential for application to metasurfaces to obtain excellent absorption and transmission performances. Therefore, realization of impedance matching over a wider range is of major importance. In this work, we demonstrate broadband impedance matching both theoretically and experimentally through use of coupled inductor-capacitor (LC) resonant coils, which are typical electromagnetic resonators. By adding a third resonant coil into the conventional system composed of two completely mismatched resonant coils, the new system realizes broadband impedance matching when the reflected impedances of the first two coils with respect to the third resonant coil are equal. The results in this work can provide useful guidance for realization of metasurfaces with broadband perfect absorption and transmission constructed using any type of electromagnetic resonator.

Broadband Perfect Optical Absorption by Coupled Semiconductor Resonator-Based All-Dielectric Metasurface.

Resonance absorption mechanism-based metasurface absorbers can realize perfect optical absorption. Further, all-dielectric metasurface absorbers have more extensive applicability than metasurface absorbers that contain metal components. However, the absorption peaks of the all-dielectric metasurface absorbers reported to date are very sharp. In this work, we propose a broadband optical absorption all-dielectric metasurface, where a unit cell of this metasurface is composed of two coupled subwavelength semiconductor resonators arrayed in the direction of the wave vector and embedded in a low-index material. The results indicate that the peak absorption for more than 99% is achieved across a 60 nm bandwidth in the short-wavelength infrared region. This absorption bandwidth is three times that of a metasurface based on the conventional design scheme that consists of only a single layer of semiconductor resonators. Additionally, the coupled semiconductor resonator-based all-dielectric metasurface shows robust perfect absorption properties when the geometrical and material parameters-including the diameter, height, permittivity, and loss tangent of the resonator and the vertical and horizontal distances between the two centers of the coupled resonators-are varied over a wide range. With the convenience of use of existing semiconductor technologies in micro/nano-processing of the surface, this proposed broadband absorption all-dielectric metasurface offers a path toward realizing potential applications in numerous optical devices.

Tunable artificial microwave blackbodies based on metasurfaces.

Inspired by the classic hole-cavity blackbody model, we propose an open metasurface blackbody operating at microwave frequencies, whose unit cell is a dielectric resonator lying on an opaque metal plate. The resonator has a high temperature coefficient of dielectric constant, thus the blackbody can be thermally tunable. Furthermore, when the resonator is combined with ferrite, a magnetically tunable blackbody is also obtained. Absorption spectra of these two tunable blackbody unit cells are measured, and they agree very well with the simulated results. The proposed blackbodies offer a new opportunity for practical tunable microwave absorbers in applications.

Poynting vector analysis for wireless power transfer between magnetically coupled coils with different loads.

Wireless power transfer is a nonradiative type of transmission that is performed in the near-field region. In this region, the electromagnetic fields that are produced by both the transmitting and receiving coils are evanescent fields, which should not transmit energy. This then raises the question of how the energy can be transferred. Here we describe a theoretical study of the two evanescent field distributions at different terminal loads. It is shown that the essential principle of wireless energy transfer is the superposition of the two evanescent fields, and the resulting superimposed field is mediated through the terminal load. If the terminal load is either capacitive or inductive, then the superimposed field cannot transfer the energy because its Poynting vector is zero; in contrast, if the load is resistive, energy can then be conveyed from the transmitting coil to the receiving coil. The simulation results for the magnetic field distributions and the time-domain current waveforms agree very well with the results of the theoretical analysis. This work thus provides a comprehensive understanding of the energy transfer mechanism involved in the magnetic resonant coupling system.

MicroRNA-137 chemosensitizes colon cancer cells to the chemotherapeutic drug oxaliplatin (OXA) by targeting YBX1.

The mechanisms underlying oxaliplatin (OXA) resistance in colon cancer cells are not fully understood. MicroRNAs (miRNAs) play important roles in tumorigenesis and drug resistance. However, the relationship between miRNA and OXA resistance in colon cancer cells has not been previously explored. In this study, we utilized microRNA microarray analysis and real-time PCR to verify that miR-93, miR-191, miR-137, miR-181 and miR-491-3p were significantly down-regulated and that miR-96, miR-21, miR-22, miR-15b and miR-92 were up-regulated in both HCT-15/OXA and SW480/OXA cell lines. Blocking miR-137 caused a significant inhibition of OXA-induced cytotoxicity, therefore, miR-137 was chosen for further research. An in vitro cell viability assay showed that knockdown of miR-137 in HCT-15 and SW480 cells caused a marked inhibition of OXA-induced cytotoxicity. Moreover, we found that miR-137 was involved in repression of YBX1 expression through targeting its 3'-untranslated region. Furthermore, down-regulation of miR-137 conferred OXA resistance in parental cells, while over-expression of miR-137 sensitized resistant cells to OXA, which was partly rescued by YBX1 siRNA. The results of this study may aid the development of therapeutic strategies to overcome colon cancer cell resistance to OXA.

Microwave Bandpass Filter Based on Mie-Resonance Extraordinary Transmission.

Microwave bandpass filter structure has been designed and fabricated by filling the periodically metallic apertures with dielectric particles. The microwave cannot transmit through the metallic subwavelength apertures. By filling the metallic apertures with dielectric particles, a transmission passband with insertion loss 2 dB appears at the frequency of 10-12 GHz. Both simulated and experimental results show that the passband is induced by the Mie resonance of the dielectric particles. In addition, the passband frequency can be tuned by the size and the permittivity of the dielectric particles. This approach is suitable to fabricate the microwave bandpass filters.

Essential role of Na+/Ca2+ exchanger 1 in smoking-induced growth and migration of esophageal squamous cell carcinoma.

Tobacco-derived carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a major environmental risk factor for the pathogenesis of human esophageal squamous cell carcinoma (ESCC). However, the molecular mechanisms by which tobacco induces ESCC are not well understood. Na+/Ca2+ exchanger 1 (NCX1) is a plasma membrane transporter protein that plays an essential role in maintaining cytosolic Ca2+ ([Ca2+]cyt) homeostasis under physiological conditions and is implicated in tumorigenesis as well. In this study, we found that NCX1 expression was significantly higher in ESCC primary tissues compared to the noncancerous tissues and was overexpressed in tumor samples from the smoking patients. The expression of NCX1 proteins was also significantly higher in human ESCC cell lines compared to normal esophageal epithelial cell line. Moreover, NNK potentiated the [Ca2+]cyt signaling induced by removal of extracellular Na+, which was abolished by KB-R7943 or SN-6. NNK dose-dependently promoted proliferation and migration of human ESCC cells induced by NCX1 activation. Therefore, NCX1 expression correlates with the smoking status of ESCC patients, and NNK activates the Ca2+ entry mode of NCX1 in ESCC cells, leading to cell proliferation and migration. Our findings suggest NCX1 protein is a novel potential target for ESCC therapy.

Mode jumping of split-ring resonator metamaterials controlled by high-permittivity BST and incident electric fields.

We investigate the resonant modes of split-ring resonator (SRR) metamaterials that contain high-permittivity BST block numerically and experimentally. We observe interesting mode-jumping phenomena from the BST-included SRR absorber structure as the excitation wave is incident perpendicularly to the SRR plane. Specifically, when the electric field is parallel to the SRR gap, the BST block in the gap will induce a mode jumping from the LC resonance to plasmonic resonance (horizontal electric-dipole mode), because the displacement current excited by the Mie resonance in the dielectric block acts as a current channel in the gap. When the electric field is perpendicular to the gap side, the plasmonic resonance mode (vertical electric-dipole mode) in SRR changes to two joint modes contributed simultaneously by the back layer, SRR and BST block, as a result of connected back layer and SRR layer by the displacement current in the BST dielectric block. Based on the mode jumping effect as well as temperature and electric-field dependent dielectric constant, the BST-included SRR metamaterials may have great potentials for the applications in electromagnetic switches and widely tunable metamaterial devices.

Magnetically tunable broadband transmission through a single small aperture.

Extraordinary transmission through a small aperture is of great interest. However, it faces a limitation that most of approaches can not realize the tunable transmission property, which is not benefit for the miniaturization of the microwave system. Here, we demonstrate a magnetically tunable broadband transmission through a small aperture. By placing two ferrite rods symmetrically on both sides of a single small aperture, the strongly localized electromagnetic fields are effectively coupled to the two ferrite rods. Both the simulated and experimental results indicate that such structure not only realizes a nearly total transmission through a small aperture, but also obtains a magnetically tunable property. This work offers new opportunities for the miniaturization of the microwave system.

Dual-band-enhanced transmission through a subwavelength aperture by coupled metamaterial resonators.

In classical mechanics, it is well known that a system consisting of two identical pendulums connected by a spring will steadily oscillate with two modes: one at the fundamental frequency of a single pendulum and one in which the frequency increases with the stiffness of the spring. Inspired by this physical concept, we present an analogous approach that uses two metamaterial resonators to realize dual-band-enhanced transmission of microwaves through a subwavelength aperture. The metamaterial resonators are formed by the periodically varying and strongly localized fields that occur in the two metal split-ring resonators, which are placed gap-to-gap on either side of the aperture. The dual-band frequency separation is determined by the coupling strength between the two resonators. Measured transmission spectra, simulated field distributions, and theoretical analyses verify our approach.

Magnetically tunable Mie resonance-based dielectric metamaterials.

Electromagnetic materials with tunable permeability and permittivity are highly desirable for wireless communication and radar technology. However, the tunability of electromagnetic parameters is an immense challenge for conventional materials and metamaterials. Here, we demonstrate a magnetically tunable Mie resonance-based dielectric metamaterials. The magnetically tunable property is derived from the coupling of the Mie resonance of dielectric cube and ferromagnetic precession of ferrite cuboid. Both the simulated and experimental results indicate that the effective permeability and permittivity of the metamaterial can be tuned by modifying the applied magnetic field. This mechanism offers a promising means of constructing microwave devices with large tunable ranges and considerable potential for tailoring via a metamaterial route.

Total broadband transmission of microwaves through a subwavelength aperture by localized E-field coupling of split-ring resonators.

Resonance coupling of two resonators with the same resonant frequency is a highly efficient energy transfer approach in physics. Here we report total broadband transmission of microwaves through a metallic subwavelength aperture using the coupled resonances of the strongly localized electric fields at the gaps of two split-ring resonators (SRRs) placed on either side of the aperture. At the center frequency of the broad band, the phase difference between the two localized time-varying electric fields is 90°, which is consistent with the critical coupling state that is a sufficient condition for the two-resonator system to realize total transmission if the resonators are assumed to be lossless.

Microwave memristive-like nonlinearity in a dielectric metamaterial.

Memristor exhibit interesting and valuable circuit properties and have thus become the subject of increasing scientific interest. Scientists wonder if they can conceive a microwave memristor that behaves as a memristor operating with electromagnetic fields. Here, we report a microwave memristive-like nonlinear phenomenon at room temperature in dielectric metamaterials consisting of CaTiO3-ZrO2 ceramic dielectric cubes. Hysteretic transmission-incident field power loops (similar to the hysteretic I-V loop of memristor which is the fingerprint of memristor) with various characteristics were systematically observed in the metamaterials, which exhibited designable microwave memristive-like behavior. The effect is attributed to the decreasing permittivity of the dielectric cubes with the increasing temperature generated by the interaction between the electromagnetic waves and the dielectric cubes. This work demonstrates the feasibility of fabrication transient photonic memristor at microwave frequencies with metamaterials.

Negative and near zero refraction metamaterials based on permanent magnetic ferrites.

Ferrite metamaterials based on the negative permeability of ferromagnetic resonance in ferrites are of great interest. However, such metamaterials face a limitation that the ferromagnetic resonance can only take place while an external magnetic field applied. Here, we demonstrate a metamaterial based on permanent magnetic ferrite which exhibits not only negative refraction but also near zero refraction without applied magnetic field. The wedge-shaped and slab-shaped structures of permanent magnetic ferrite-based metamaterials were prepared and the refraction properties were measured in a near-field scanning system. The negative and near zero refractive behaviors are confirmed by the measured spatial electric field maps. This work offers new opportunities for the development of ferrite-based metamaterials.