Jingxuan Tian

Direct observation of valley-polarized topological edge states in designer surface plasmon crystals

The extensive research of two-dimensional layered materials has revealed that valleys, as energy extrema in momentum space, could offer a new degree of freedom for carrying information. Based on this concept, researchers have predicted valley-Hall topological insulators that could support valley-polarized edge states at non-trivial domain walls. Recently, several kinds of photonic and sonic crystals have been proposed as classical counterparts of valley-Hall topological insulators. However, direct experimental observation of valley-polarized edge states in photonic crystals has remained difficult until now. Here, we demonstrate a designer surface plasmon crystal comprising metallic patterns deposited on a dielectric substrate, which can become a valley-Hall photonic topological insulator by exploiting the mirror-symmetry-breaking mechanism. Topological edge states with valley-dependent transport are directly visualized in the microwave regime. The observed edge states are confirmed to be fully valley-polarized through spatial Fourier transforms. Topological protection of the edge states at sharp corners is also experimentally demonstrated.The photonic valley-Hall effect can enable the unidirectional propagation of edge states, but often require covers which shield the states from direct measurement. Here, Wu et al. realize photonic valley-Hall effect using designer surface plasmons, enabling the direct observation of topological states.

Low-frequency tunable acoustic absorber based on split tube resonators

We demonstrate a high-efficiency tunable acoustic absorber for low frequencies (<500 Hz) with subwavelength thickness. The acoustic absorber is based on split tube resonators and could reach high-efficiency absorption at tunable resonance frequency with wavelength in air at least 30 times larger than its total thickness in simulations and experiments. The resonance frequency and high-efficiency absorption of the absorber are robust under oblique incidence even at large angles. The absorber could have potential applications for acoustic engineering due to its high structural stability, ease of fabrication, subwavelength thickness, and robust high-efficiency.

Broadband reflective metasurface for focusing underwater ultrasonic waves with linearly tunable focal length

We report a metasurface for focusing reflected ultrasonic waves over a wide frequency band of 0.45–0.55 MHz. The broadband focusing effect of the reflective metasurface is studied numerically and then confirmed experimentally using near-field scanning techniques. The focusing mechanism can be attributed to the hyperboloidal reflection phase profile imposed by different depths of concentric grooves on the metasurface. In particular, the focal lengths of the reflective metasurface are extracted from simulations and experiments, and both exhibit good linear dependence on frequency over the considered frequency band. The proposed broadband reflective metasurface with tunable focal length has potential applications in the broad field of ultrasonics, such as ultrasonic tomographic imaging, high intensity focused ultrasound treatment, etc.

Digital microfluidic programmable stencil (dMPS) for protein and cell patterning

Patterning biomolecules and cells on substrates is usually a prerequisite for biological analysis and cell studies. A stencil is a versatile tool for sample patterning owing to its reusability and easy operation but it lacks addressable fluid control and programmable change of pattern. Here, we combined the advantages of a microfluidic chip and stencil to design a digitally controlled microfluidic programmable stencil. The key design is automatic passive matrix addressing based on combined application of two types of elastomeric valves. These two valves have distinct actuation thresholds, typically 13.4 psi for a round valve and much higher than 13.4 psi for a rectangle valve. Different types of protein and cell pattern on a 2D substrate could be obtained by controlling the fluid addressing code based on the passive matrix addressing method. An automatic microsampler was also applied to facilitate fast sample selection and introduction in the patterning process. A successful protein and cell pattern was obtained which could be used for downstream analysis and study.

High-efficiency ventilated metamaterial absorber at low frequency

We demonstrate a ventilated metamaterial absorber operating at low frequency ( 90%) has been achieved in both simulations and experiments. This high-efficiency absorption under the ventilation condition originates from the weak coupling of two identical split tube resonators constituting the absorber, which leads to the hybridization of the degenerate eigenmodes and breaks the absorption upper limit of 50% for conventional transmissive symmetric acoustic absorbers. The absorber can also be extended to an array and work in free space. The absorber should have potential applications in acoustic engineering where both noise reduction and ventilation are required.

A valve-free 2D concentration gradient generator

We report a concentration gradient generator featuring valve-free and simultaneous two-dimensional (2D) concentration generation. Each analyte is first diluted by a 1D gradient generator to five different concentrations and then directed into different chambers to generate combinations of different concentrations. The chip consists of three layers, which realizes a 3D fluid path, forming a skywalk structure that allows two perpendicular channels to cross each other in different layers. In this way, this chip could get rid of the pneumatic actuated valves (PAVs) or complicated channel designs that are conventionally adopted in controlling the infusion of multi-analytes. We believe that this design, which makes the chip independent of cumbersome external apparatus in controlling multi-analytes infusion, may potentially benefit the process of making microfluidic chips a portable and cost-effective product.

Synergistic Effect of Sunlight Induced Photothermal Conversion and H 2 O 2 Release Based on Hybridized Tungsten Oxide Gel for Cancer Inhibition

A highly efficient photochromic hydrogel was successfully fabricated via casting precursor, which is based on amorphous tungsten oxide and poly (ethylene oxide)-block-poly (propylene oxide)-block-poly (ethylene oxide). Under simulated solar illumination, the hydrogel has a rapid and controlled temperature increasing ratio as its coloration degree. Localized electrons in the amorphous tungsten oxide play a vital role in absorption over a broad range of wavelengths from 400 nm to 1100 nm, encompassing the entire visible light and infrared regions in the solar spectrum. More importantly, the material exhibits sustainable released H2O2 induced by localized electrons, which has a synergistic effect with the rapid surface temperature increase. The amount of H2O2 released by each film can be tuned by the light irradiation, and the film coloration can indicate the degree of oxidative stress. The ability of the H2O2-releasing gels in vitro study was investigated to induce apoptosis in melanoma tumor cells and NIH 3T3 fibroblasts. The in vivo experimental results indicate that these gels have a greater healing effect than the control in the early stages of tumor formation.