Shiwei Tang

Microwave Absorption Properties of Carbon Nanocoils Coated with Highly Controlled Magnetic Materials by Atomic Layer Deposition

In this work, atomic layer deposition is applied to coat carbon nanocoils with magnetic Fe(3)O(4) or Ni. The coatings have a uniform and highly controlled thickness. The coated nanocoils with coaxial multilayer nanostructures exhibit remarkably improved microwave absorption properties compared to the pristine carbon nanocoils. The enhanced absorption ability arises from the efficient complementarity between complex permittivity and permeability, chiral morphology, and multilayer structure of the products. This method can be extended to exploit other composite materials benefiting from its convenient control of the impedance matching and combination of dielectric-magnetic multiple loss mechanisms for microwave absorption applications.

Dynamical control on helicity of electromagnetic waves by tunable metasurfaces

Manipulating the polarization states of electromagnetic (EM) waves, a fundamental issue in optics, attracted intensive attention recently. However, most of the devices realized so far are either too bulky in size, and/or are passive with only specific functionalities. Here we combine theory and experiment to demonstrate that, a tunable metasurface incorporating diodes as active elements can dynamically control the reflection phase of EM waves, and thus exhibits unprecedented capabilities to manipulate the helicity of incident circular-polarized (CP) EM wave. By controlling the bias voltages imparted on the embedded diodes, we demonstrate that the device can work in two distinct states. Whereas in the “On” state, the metasurface functions as a helicity convertor and a helicity hybridizer within two separate frequency bands, it behaves as a helicity keeper within an ultra-wide frequency band in the “Off” state. Our findings pave the way to realize functionality-switchable devices related to phase control, such as frequency-tunable subwavelength cavities, anomalous reflectors and even holograms.

Tunable microwave metasurfaces for high-performance operations: dispersion compensation and dynamical switch

Controlling the phase distributions on metasurfaces leads to fascinating effects such as anomalous light refraction/reflection, flat-lens focusing, and optics-vortex generation. However, metasurfaces realized so far largely reply on passive resonant meta-atoms, whose intrinsic dispersions limit such passive meta-devices’ performances at frequencies other than the target one. Here, based on tunable meta-atoms with varactor diodes involved, we establish a scheme to resolve these issues for microwave metasurfaces, in which the dispersive response of each meta-atom is precisely controlled by an external voltage imparted on the diode. We experimentally demonstrate two effects utilizing our scheme. First, we show that a tunable gradient metasurface exhibits single-mode high-efficiency operation within a wide frequency band, while its passive counterpart only works at a single frequency but exhibits deteriorated performances at other frequencies. Second, we demonstrate that the functionality of our metasurface can be dynamically switched from a specular reflector to a surface-wave convertor. Our approach paves the road to achieve dispersion-corrected and switchable manipulations of electromagnetic waves.

Multifunctional Microstrip Array Combining a Linear Polarizer and Focusing Metasurface

Although microstrip reflectarrays/transmitarrays have been extensively studied in the past decades, most previous designs were confined to monofunctional operations based on either transmission or reflection. In this communication, we propose a scheme to design multifunctional arrays that can simultaneously exhibit the functionalities of a reflectarray and a transmitarray on the basis of the appealing feature of a polarizer we discovered (i.e., constant phase difference between its cross-polarization transmission and copolarization reflection within a broadband). To demonstrate the proposed scheme, we designed and fabricated a multifunctional device comprising a 15 × 15 array of twisted complementary dual-split ring resonators, each carefully designed to exhibit the desired transmission phase satisfying a parabolic distribution. Feeding the device by a Vivaldi antenna at its focus, we numerically and experimentally demonstrated that our system functioned as a directive emitter working in a transmission/reflection mode for cross-polarization/copolarization radiation at low/high frequencies, and it can radiate directively in both directions with different polarizations at intermediate frequencies. The half-power beamwidth of the array antenna was ~15°, which is 40° narrower than that of a bare Vivaldi antenna. Moreover, the gain was higher than 13 dB in all cases studied, which is at least 7 dB higher than that of the Vivaldi antenna.

Polypyrrole Composite Nanoparticles with Morphology-Dependent Photothermal Effect and Immunological Responses.

Polypyrrole composite nanoparticles with controlled shape are synthesized, which exhibit a morphology-dependent photothermal effect: the raspberry-like composite nanoparticles have a much better photothermal effect than the spherical ones, and the immune responses to the nanocomposites are also dependent on their morphology. The outstanding performance of the nanocomposites promises their potential application in photothermal therapy and immunotherapy of cancer.

Deterministic Self-Rolling of Ultrathin Nanocrystalline Diamond Nanomembranes for 3D Tubular/Helical Architecture

Nanocrystalline diamond nanomembranes with thinning-reduced flexural rigidities can be shaped into various 3D mesostructures, such as tubes, jagged ribbons, nested tubes, helices, and nested rings. Microscale helical diamond architectures are formed by controlled debonding in agreement with finite-element simulation results. Rolled-up diamond tubular microcavities exhibit pronounced defect-related photoluminescence with whispering-gallery-mode resonance.

Nonlinear responses in optical metamaterials: theory and experiment

We employed both theoretical calculations and experiments to study the nonlinear responses in optical metamaterials. The spectra of second-harmonic generations measured on a fishnet metamaterial are in quantitative agreements with calculations based on full-wave numerical simulations combined with field integrations, both exhibiting ~80 times enhancements at the magnetic resonance frequency. Our calculations explained several interesting features observed experimentally, and suggested an optimal metamaterial structure to yield the strongest nonlinear signals.

High-Efficiency and Full-Space Manipulation of Electromagnetic Wave Fronts with Metasurfaces

Metasurfaces offered great opportunities to control electromagnetic (EM) waves, but currently available meta-devices typically work either in pure reflection or pure transmission mode, leaving half of EM space completely unexplored. Here, we propose a new type of metasurface, composed by specifically designed meta-atoms with polarization-dependent transmission and reflection properties, to efficiently manipulate EM waves in the full space. As a proof of concept, three microwave meta-devices are designed, fabricated and experimentally characterized. The first two can bend or focus EM waves at different sides (i.e., transmission/reflection sides) of the metasurfaces depending on the incident polarization, while the third one changes from a wave bender for reflected wave to a focusing lens for transmitted wave as the excitation polarization is rotated, with all these functionalities exhibiting very high efficiencies (in the range of 85%-91%). Our findings significantly expand the capabilities of metasurfaces in controlling EM waves, and can stimulate high-performance multi-functional meta-devices facing more challenging and diversified application demands.

Effects of different doses of remifentanil on the end-tidal concentration of sevoflurane required for tracheal intubation in children.

We investigated the effects of different doses of remifentanil on the end‐tidal concentration of sevoflurane required for tracheal intubation in children without the use of neuromuscular blocking drugs. One hundred and thirty paediatric patients, aged 3–8 years, were randomly allocated to receive no remifentanil (group control) or remifentanil 0.1 μg.kg−1.min−1 (group remi0.1), 0.2 μg.kg−1.min−1 (group remi0.2), 0.3 μg.kg−1.min−1 (group remi0.3). All patients were anaesthetised using 5% sevoflurane. After loss of eyelash reflex, remifentanil 1 μg.kg−1 was injected over 1 min followed by an appropriate group‐dependent infusion and the end‐tidal sevoflurane concentration was changed. Predetermined end‐tidal sevoflurane concentrations for each group were determined using the Dixon up‐and‐down method. After the target concentration of sevoflurane was maintained for 5 min, the child’s trachea was intubated. Successful intubation was defined as excellent or good intubating conditions. The end‐tidal concentration (SD) of sevoflurane for successful tracheal intubation in 50% of children (ED50) were 5.16 (0.22)% in control, 3.27 (0.18)%, 1.81 (0.20)% and 1.01 (0.11)%, in remi0.1, remi0.2, and remi0.3 groups, respectively. Using probit analysis, the 95% effective dose (ED95) of sevoflurane were 5.60% (95% CI 5.35–7.66), 3.77% (95% CI 3.45–7.74), 2.18% (95% CI 1.96–3.86), 1.19% (95% CI 1.06–1.82) in control, remi0.1, remi0.2, and remi0.3 groups, respectively.

Integrative optofluidic microcavity with tubular channels and coupled waveguides via two-photon polymerization

Miniaturization of functional devices and systems demands new design and fabrication approaches for lab-on-a-chip application and optical integrative systems. By using a direct laser writing (DLW) technique based on two-photon polymerization (TPP), a highly integrative optofluidic refractometer is fabricated and demonstrated based on tubular optical microcavities coupled with waveguides. Such tubular devices can support high quality factor (Q-factor) up to 3600 via fiber taper coupling. Microtubes with various diameters and wall thicknesses are constructed with optimized writing direction and conditions. Under a liquid-in-tube sensing configuration, a maximal sensitivity of 390 nm per refractive index unit (RIU) is achieved with subwavelength wall thickness (0.5 μm), which offers a detection limit of the devices in the order of 10-5 RIU. Such tubular microcavities with coupled waveguides underneath present excellent optofluidic sensing performance, which proves that TPP technology can integrate more functions or devices on a chip in one-step formation.